Last week I noticed a problem with the air brake system on my 1988 Ford F800. I had been using the truck by itself daily during the week and all systems were working as designed. When I connected my trailer to move my dozer is when the problem became apparent. Problem; Setting the parking brakes (pulling the yellow dash mounted knob out), results in what sounds like a large volume of air either passing through the dash mounted control valve or exhausting from it. At the same time air exhausts from one of the two quick release valves at the rear of the truck. In addition, the same sound of a large amount of air passing through the tank mounted relay on the trailer can be heard. This air flow slows and eventually stops. During this time, the dash mounted air pressure gauge does not show any change in pressure. If I release the parking brakes, once again, I hear a large amount of air flowing through the control valve, the pressure gauge shows a drop in pressure till the governor reaches the cut in pressure, system pressure builds till the trailer tank is full and then all returns to normal.
System specifics; As you can see, this truck does not have a trailer supply control valve in the cab.
It appears to me that there are two relays at the back of the truck. And each is connected to a quick release valve. One relay provides air to the service brakes and one relay provides air to the spring/parking/emergency brakes. It appears to me that the two relays are connected to each other.
The blue air line on the trailer is connected to the service brake relay (which is relatively new) on the truck and to the “service” port on the tank mounted relay on the trailer. The quick release valve, between the truck service brake relay and the truck service brake air chambers, is where the air exhausts from during this senario. I believe the blue line is the “signal” or “control” line to the trailer relay. The red air line on the trailer is connected to the spring/parking/emergency brake relay on the truck and to the “emergency” port on the tank mounted relay on the trailer. I believe this is the “supply” line to the trailer relay/tank assembly. This truck has quick connects at the rear of the vehicle. No glad hands.
Diagnosis; Based on my very limited experience, what I believe is happening is the trailer air tank is dumping its contents through the dash valve and the quick release valve when I set the parking brakes. The trailer has service brakes only. No spring brakes. It was my understanding that the relay on the trailer tank was suppose to hold the trailer service brakes “on” when disconnected from the truck, at least until tank pressure is lost. But, considering the problem as described above, it appears that the tank mounted relay may be malfunctioning. This relay and tank are one year old; Liddell-Birmingham Any thoughts would be greatly appreciated.
Its probably normal. I have never seen a trailer spring brake Siamesed to the tractor park brake valve. Usually there is a second valve with a red knob. That being said the extra volume of the lines to the trailer being Siamesed in that way would definatly make it sound like its exsausting more air. Well because it is! If it had its own valve and circuit like normal the volume in the trailer circuit would not be so large as it would be combined trailer/ tractor.
Need to abort that Mickey Mouse system and get a tractor protection valve plumbed ASAP. I'm not even sure the way you are set up is legal.....
I was thinking the same thing
I don't think you can even have a vehicle to pull an air brake trailer without a red valve in the tractor. And a tractor protection valve is another necessary component. However, if the trailer reservoir is exhausting through the yellow valve when you set it, then that also indicates a problem in the trailer. The trailer should not release much air through the red line when it is relieved, but rather there is an inversion valve off the trailer air tank that should apply tank air to the trailer cans as you already know, until it leaks away. So the problem is two fold. The trailer is releasing its air through the red line, and the truck is kind of a cobbled up mess. Curious that it apparently has no proper trailer towing air, except for the hand valve on the dash there. How well do you understand this diagram? How many of these components are missing?
Thanks guys, I really appreciate the input. A little background; I believe that this truck is a former municipal truck and it looks to be all factory to me but who knows. I have owned it and the trailer for 10 years and never had this problem before. I bought the trailer from a local trailer dealer who replaced all of the brake chambers, a couple of the slack adjusters and the rubber air lines. The truck has been into the local heavy truck service center for inspections and repairs several times and no one has ever suggested there was any problems. I also pass State Commercial Vehicle Inspection every year. I have been studying my Ford air brake manual that contains similar information to that diagram posted by Birken Vogt. Agreed about adding the trailer air supply valve and tractor protection valve (if there is none). I wont be back to work till Monday to make additional review of the existing and or missing components. Thanks again.
Not even going to touch this one.
I suppose it is possible that the truck was that way from the factory. Maybe the requirements were different for a 2 axle bobtail and tag trailer back in 1988. Ford did some strange things back then like the vertical park brake flipper valve in C-series, I always thought they had to be a yellow diamond by then but they still made them that way. I'd like to see the page in that book that deals with the F-series system. At first glance it looks like somebody just grabbed the easy connections at the back for trailer brakes but then where does the hand valve in the cab tie in? There has to be another double check somewhere for it. Quick connects don't quite add up either. I would expect everyone was using glad hands back then but they could have been replaced. The ball valves are also suspicious but one of them has possibly original paint on it.
Oh well, this the system chart you need to use. Using a MV3 modular valve not the old PP1's. Don't worry about the stop light switch air supply at Pressure protection valve, you already have that.
The trailer may be plumbed legally, and the truck may be plumbed legally for itself, but definitely not as far as pulling a trailer on air, so each could technically pass an inspection on their own. Also just because it passed inspection doesn't mean it's legal, here anyway the inspection guidelines are so loose it's not even funny, it's basically up to each shop to decide what it includes and what it doesn't. I've seen so much shotty stuff passed/missed I still inspect my stuff after it's back from the shop to check any work done and to look over the truck/trailer myself because I just don't trust them. I had a truck plumbed for air lines for trailer at a dealership, and they didn't put in a tractor protection valve and just teed a line off the rear axle of the truck for trailer. It's pretty sad but right now there is not a single shop I totally trust. Be a different story getting pulled over and checked, I cannot imagine those quick connects being legal, the way those safety chains are hooked up also not legal here.
No F series specific page. All information is general to all trucks. I'm curious about that... Do any of you guys see trucks with quick connects? I'm not around a lot of trucks but have seen one other. A very sharp, customized tractor run by a heavy wrecker outfit from Attleboro, MA area.
Glad hands are the industry standard for years, I don't believe there is a rule against quick connects. But it is very impractical from the stand point you would have to carry glad hands with male ends to hook up to other trailers. But the real problem is volume of air through a quick connect like used on your truck. Brake system recovery is all about volume as well as psi.
Very dangerous, but creative. Good call, Gents. That's an accident waiting to happen.
Ford used a lot of morphodite air systems, that aluminum valve in the picture where the trailer air has a shutoff with a yellow handle may actually be a tractor protection setup. Some of the Louisvilles had it built into the nightmare of a foot valve sandwiched on both sides of the firewall. Don't ask. Just believe that Ford liked to roll their own when everybody else pretty much bought off the shelf. Politely suggest that unless you can find an exact air schematic for your exact truck, don't change anything without a lot of head scratching. Quick connects are common around here on dump trucks and lowboy (detachable gooseneck) setups at the back of the gooseneck. Sounds to me like you just have a gummed up check in the trailer relay valve, Just push in the parking brake, to be safe probably with the engine off and in gear so it doesn't try to roll away, then while it's all pressurized just pop the red trailer line off the quick disconnect, see if you actually are emptying the trailer tank there. If you look at the trailer brakes you may see them apply until the pressure drops too low to keep the cans extended. Relay valve failures are very common especially on a setup like this where it's really hard to keep dirt out of the open ends on the lines. YMMV
The aluminum valve in that picture appears to be an R-7 spring brake inversion modulating valve. It releases air from the spring brake cans and refills from the front reservoir to apply rear brakes proportionally if you lose air in the rear brake tanks. Feature on straight trucks only, otherwise you would have only the tiny front axle brakes to stop you if you lost rear air. Agreed on the failed trailer valve being the primary cause of failure and the OP has the correct diagnosis I believe. Agreed not to change anything until you draw a schematic of the air system with part numbers if you can find them on all the control valves.
What you have is a Moron that had no clue set up a Trailer brake system on a truck not set up for it. Needs a TP Valve at the Rear, with GLAD Hand connections and a SECOND control Just for the Trailer. If DOT ever catches this on the road and inspects it, expect to be towed and not able to drive it until corrected.
Truck and Trailer under DOT HAVE to be Separate systems capable of securing either machine if air pressure fails. YOURS will NOT.
https://www.sgi.sk.ca/air-brake/-/knowledge_base/air-brake/simple-tractor-trailer-system
If you had the work done at a shop and it wasn't plumbed legally because no tractor protection valve and the truck with air trailer cannot pass the air test, and you got stopped and ticketed, do you think the shop is liable? Even if they claimed the customer said to plumb it like that, they should refuse to do it if it's not correct right?
View attachment 227494 Yes. According to this, " R-7 modulating valve. Not inverted. I had it replaced 2 years ago June.
So when I got to work this morning I decided to see if maybe the shituation had fixed itself all on it's lonesome. But alass, the relay was still stuck and pissin' air. I did what you said and sure enough, air bleadin' out the red line. So, just to be a smart ass I disconnected the red air line at the valve and sprayed some WD into the valve, reconnected and charged the air system. After several applications of the trailer brakes that dang valve freed right up! Guess I'll be ordering a new valve, at least to have on hand if the gremlins come back.
I guess they might be... What about the state inspection station. I've gone to two different places over the last 10 years. Maybe one of them might have noticed? I'm not passing the buck. I just thought it was some old system that I just didn't understand. Ignorant you know.
Ha! Imagine the look on that DOT cops face when he came out from under that truck! Prolly bang his head on the way out to get me! I actually went to the State Police Barracks in town here last fall to see if I could get an inspection as the DOT cop used to live right up the road from me. Guy had just retired though so I dropped it.
Maybe, but I'm still not convinced that that moron was not Ford. It all appears to be too original to me. The pintle plate, trailer hand valve. If you read the operation section of that Bendix R - 7 Modulating valve it sounds like it may be there to provide tractor protection. Any other guys with similar vintage Ford trucks?
NO manufacturer builds anything like this. Taking your life and the Legal way to build these as a joke now.. I am done
The R7 valve does the same basic job of a SR1 valve, and neither one do the job of a tractor protection valve. that hand brake valve was generic some years back.
No need to get all bent there Mr Miller. I made an appointment this morning to take the truck in on Thursday. Nothing wrong with a little comic relief.
That is DANGEROUS, nothing comedy there but trying to fix it to work longer.
I was able to identify the relay valve that controls the rear axle service brakes. A search for E6HT-2A449-AA comes up with Bendix 103009X R-12 Relay Valve with Horizontal Delivery Ports https://www.anythingtruck.com/product/061-103009X.html
The foot valve... not too much luck with E0E0HT-2A270-AA.
Standard E-7 Treadle valve. The Ball valve on the R12 is not a factory install and DOT will not be happy it is on there.
Yes sir. That will be going away promptly.
So here's a thing. I've always thought that my trailer had great brakes. There are several small hills along my usual route and if I pick the right gear and tap the trailer hand valve I can just roll on down the hill nice and easy. So I woke up about 3 this morning thinking, how does that trailer hand valve control the trailer brakes with this setup? So when I got in to work I started getting into the dash. Based on the configuration of the valve body and the mounting brackets this valve sure looks to be factory. Then I actuated the valve. Now I know why my trailer brakes work so good....
Because it also actuates the truck brakes. In all actuality it was installed for Just the truck brakes.
You got it.
Many of the Old World dump trucks I worked around YEARS ago never set up for trailers or pups and had hand valves, Driver could work the clutch & throttle, be dropping the load and using his hand to manage the brakes. Makes spreading much cleaner and precise.
E7 valve.
From my manual;
I will have to trace down the air lines coming into and out of the trailer control valve but, if I can trust the colors and considering that the valve is actuating the service brakes on the rear axle, I'm assuming that the trailer hand valve is currently plumbed into the primary air system and that it will need to be re plumbed into the secondary system. Notice the third smaller line at the back of the valve.
One of the things I have thought about experimenting with on the spreader truck is two hand valves and two check valves plumbed into the rear wheel brakes so as to give me individual control, like a tractor.
http://www.vannattabros.com/truck6.html
I haven't looked at that link yet, but I already know I love that Vannatta Brothers site, that was one of the very first things I found on the internet, back in the dial-up days.
Will want to reroute the out line to that 2way check valve to the trailer glad hand side of TP valve off a secondary port. The small third line most likely exhaust thru firewall into engine compartment.
Yes. From the manual ;
Yes. Exhaust through the firewall.
That is done that way to provide habitat for mud daubers and employment for mechanics.
More on the trailer hand valve. With the air lines on the valve labeled and 'C' is exhaust, 'A' goes to the engine side of the Foot valve. It is connected to what I might guess is a double check valve with a stop light switch (also guess). 'B' goes to the left side of the cab side of the foot valve.
My foot valve does not look exactly like the ones that I've seen from the Bendix website and the one that Truckshop posted above. It looks like 'B' is Primary supply which would make 'A' the Delivery side....
What's that check valve in the last photo plumbed into?
This one? Could this be a way of balancing the primary and secondary systems? From Bendix; "BALANCED: PRIMARY CIRCUIT PORTION When air pressure delivered to the brake actuators and air pressure in the cavity on the delivery side of the primary piston equals the mechanical force of the brake pedal application, the primary piston will move and the primary inlet valve will close, stopping the further flow of air from the primary supply line through the valve. The exhaust valve remains closed preventing any escape of air through the exhaust port. BALANCED: SECONDARY CIRCUIT PORTION When the air pressure on the secondary side of the relay piston approaches that being delivered on the primary side of the relay piston, the relay piston moves closing the secondary inlet valve and stopping further flow of air pressure from the supply line through the valve. The exhaust remains closed as the pressures balance."
This is the right side of the valve 'in cab'. I still have to chase down where this goes.
Question; Are the Primary Delivery ports 'common' ports? Meaning, The 1/2" green air line provides Primary air to the foot valve through the Primary Supply port on the engine side of the foot valve. Primary air is then available through any primary supply port on the valve without actuating the valve . If this is the case then primary air is being pulled off the primary air supply port inside the cab, plumbed through the supply port on the trailer hand valve, out of the delivery port on the trailer hand valve and into the double check valve on the engine side where it can supply air to the relay at the rear axle.
Nothing is common to air brake systems Will have two supplies both will feed a balance check for spring brakes then one feeds drive side service the other steer side. Trailer will come off steer side for service.
Notice the double check valve in photo, one hose comes from hand valve on one end of check, the check is screwed into secondary/trailer/steer axle delivery port, then a hose runs from center of double check valve back to tractor protection valve. This valve is a E6 but same basic principle. click to enlarge.
I am beginning to REALLY like the new service connectors that Push Fit as replacements to the old Nut Sleeve and Ferrule style. Thoughts TS?
Thank You very much guys for your help with this. Thank You to everyone that has commented. I may never have realized the problem till it was too late. I was chatting with a local guy last night while fueling up at the service station and he just got nabbed by the DOT cop right up the road from here. He said it was painful.
Sorry to say the DOT will get Worse not Better as to nailing who they can as they can. Rules keep changing up not back.
The push lock fittings are good when new as long as installed correctly. I say correctly because if the nylon/plastic air line is too long or too short it will put stress on the inter lock part of the fitting. The air line especially 3/4" 5/8" and 1/2" are prone to pulling hard on the lock if not a real straight shot entering the fitting. The vehicle vibration will go to work on the tubing at the lock in fitting and over time start leaking plus it can wear a groove on the tubing making it tough to un-couple, and the dirt collected that gets down in the release collar. Which needs to be flushed with WD40 before trying to disconnect. We had a series of new trucks three years ago that had a problem area of leaking push lock fittings, The hoses were tied too tight and when the truck flexed it pulled on the fittings. And naturally those air lines were located in a spot inside the left frame rail just in front of rear engine mount and were a real pain to repair. Plus push lock fittings are not cheap, I use them in suitable areas-low stress, other wise I take out a mortgage on the company and buy the Weather Head Brass DOT fittings. And by the way the brass push lock fitting below {ain't Cheap and has the same problems}.
Will remember that.
So here's my plan. Currently my trailer hand valve is piped into the Primary air system. I will remove the Primary air line that is currently feeding it from the Foot Valve and plugging the port on the foot valve. I will then run a new air line directly off the Secondary air tank to feed the trailer hand valve (TC) and run another new air line from the TC to the new Bendix TP-5 Tractor Protection Valve.
The TP-5 Valve requires input from not only the TC valve but also the front and rear service lines.
Front Service brakes. Notice the T on the top of the quick release valve? The 3/8" line that comes off the T heads back to the R-12 relay at the back of the truck. I plan on T-ing into that line just behind the cab and running a new line over to the TP-5 Valve.
Only need a PP-3 most trucks stopped using the Three Valve assembly twenty years ago. a Bracket to mount under the dash and pipe as accorded in most Air Line Diagrams. PP1to PP3 to Trailer, that auto sets the trailer if the Truck valve is set,
I will T into the rear axle "Primary Delivery" service line in the same manner. There is an existing bracket at the back of the cab on a frame crossmember that has 3 bulkhead fittings through which both of these service lines go. It will be simple, and a secure way to add two T's to feed 'signal' air to the TP-5 valve.
I will be using a Bendix PP-7 trailer Supply Valve. It will fit neatly into the existing opening without modifying or deleting any of the other existing valves/gauges.
The way it is interconnected to the existing PP-1 valve, it will work just like the MV-3 unit.
Very similar function PP3 and 7 RED Knob https://www.sgi.sk.ca/air-brake/-/knowledge_base/air-brake/simple-tractor-trailer-system Essential lay out two valve set up.
You will have a DOT qualified and less likely to do you in system when completed.
My manual shows 3/8" air line for the TC valve which seems fine, But you'd think the PP-7 valve would need a larger line. The air supply for the trailer has to come all the way from the tank, up into the cab through the valve and then back out to the TP valve and then to the trailer?
I ordered a bunch of DOT air line and fittings from Mcmaster Carr. I forgot to order 1/4" stuff of the exhaust vents for the in cab stuff. Anybody know of any fancy vent fittings to keep the mud daubers out?
3/8 line to the trailer red line is fine. When the trailer tank is filled with air then the red line just has to replenish trailer air tank after you step on the brakes. If you had spring brakes then it would release them quickly from the trailer air tank and then refill the tank from the red line after you are on your way. A larger red line might help the trailer air tank fill faster from dead empty, but it would still be constrained by the ports in the valves and might not help a whole lot, and only help you on the first move of the day.
BV said it well. So long as in use daubers should not be a problem, just when sits and know of nothing worth putting over the ends.
I know on my boat I stick a piece of weedeater string in the pee tube on my outboard to help with the daubers
I made a little progress this morning. I slid my new air lines through an 8 foot length of 1 inch heater hose and then snaked it under the cab and into the engine compartment.
I added two new brass bulkhead fittings and then I connected my trailer hand valve delivery and supply lines. I also connected the PP -7 delivery line.
In the cab I tied in the trailer hand valve.
At the rear of the cab is a frame mounted bracket with 3 bulkhead fittings. I added 2 t’s here so I could supply the tractor protection valve with primary and secondary service brake signal air.
I tied the trailer hand valve supply line into the secondary air tank.
Waiting on more parts now.
References and resources; Bendix provides a tremendous amount of online resources for learning about and servicing air brake systems. From their online airbrake training school; https://www.bendix.com/en/servicessupport/brakeschool/on_linetraining/onsitetraining_1.jsp
Bendix Youtube videos;
And;
And;
And this one, in particular at about the 7:40 minute mark; The narrator is describing what happens during a trailer breakaway or trailer supply line failure. He states that the Trailer Air Supply Valve will shut off trailer supply air because the air is escaping faster than it can be replaced. So this goes back to my question in post #75 ; Based on the video, it appears that the 3/8” supply line is undersized intentionally to create this imbalance in the valve that results in the airflow being shut off and therefore retaining air in the truck system.
From Haldex; https://www.haldex.com/globalassets/north-america/documents/misc/l90396.pdf
More; https://www.govinfo.gov/content/pkg/CFR-2010-title49-vol6/pdf/CFR-2010-title49-vol6-sec571-121.pdf
Couldn't figure how to link to this one;
That's correct plus on long trailer set ups there is a thing called a speeder valve slang term. To speed up service brake delivery. Sealco is the main maker of that valve right along with most trailer valves.
The other day when I was adding the T’s I noticed that a couple of the original air lines had chafed against the frame and worn through the outside color and were showing the white under layer.
So this morning I headed in a little early and replaced all the air lies to the back of the truck.
I also finished up in the engine compartment. I removed the double check valve, the brake light switch and the bushing and short nipple. Before;
I installed a new 1/2 inch npt brass nipple, 1/2 x 3/8 adaptor and tied the drive axle service brake signal line into the primary delivery port on the foot valve. After;
It is so refreshing when someone comes on here and then listens to advice and then does the work in a professional manner. And quickly too!
Glad to see you are fixing that correctly. Not many people are able to do what you are doing. Looks good.
Agree with Birken, nice to see someone ask for assistance then use it, properly.
I am so grateful to this site and it’s members for the knowledge, instruction and encouragement . Online forums are a valuable part of the future of education but can only work if there are good people, willing to share, able to communicate clearly and probably most important, site staff that continuously work behind the scene to assure that everything works smoothly. Happy Thanksgiving and God bless.
Back to ya
A little project between turkey and punkin’ pie.
Just like my brothers black dane years ago---A lop eared galoot he was, what a knot head, could eat a 3lb roast in three bites.
So happy to see my valves came in today!
Yup daddy'o.
A few updates; Tractor protection valve bracket.
Installed.
The PP 1 and the PP 7 share supply air from the crossover between the primary and secondary air tanks. I accomplished this by adding a T to the supply side of the PP 1 ( black with orange). The PP 1 has 2 delivery ports. The yellow loop connects one of these ports to the control port on the PP 7.
I also tied the two exhausts together to be vented outside the cab.
All tied in and system pressurized.
Time for soap test...
Dang! :headbangin’:
Valid message
Trailer control valve works.
So, I have a little riddle. I think I know the answer but would like to hear what others have to say. Prior to all of this I had noticed that one or more air leaks was draining both primary and secondary air tanks , generally overnight. After several extensive searches, the only leak that I could find was a small leak from the drain valve at the rear axle air tank. This tank is T’ed into the primary air system only. Why would this one leak drain both systems?
Next clue. When I soap tested the dash valves I discovered two leaks (see post #114). In order to remove the valve assembly to repair the leaks I drained the wet tank first and was getting ready to drain the rest of the system but before I did I noticed this;
You are doing an awesome job there! Things with these systems get confusing. Ford also did some things different than the rest of the pack. If you are trying to combine the different set ups could be causing you issues. Regardless of the system a check valve should be present that prevents primary or secondary air from leaking to another tank.
Check valve bad from wet tank to the next tank?
Check valve. That was my guess. If the check valve at the secondary tank is malfunctioning, air can leak back to the wet tank and then out through the leak at the rear axle primary tank.
Still waiting on parts...
That looks like she's cold and lonely....
Bingo! New check valve solved the problem.
So, despite having installed a new seal kit in the PP-1 valve I continued to have excessive air loss out the exhaust port. What good are new seals while reusing the old spring? I think that was an exercise in futility. I ordered a new valve. That's what has taken so long to come in.
I don't know your exact situation here, but as a general rule, if air leaks out the exhaust port, often it is coming from some other source upstream, leaking by, and the valve is just doing its job. Is it possible the air being released from the PP-1 itself, or is it coming back from a leak in a relay valve, for example? You would disconnect the delivery port line from the PP-1 to check for this, not under pressure, of course. As a general rule I don't rebuild components of this type, just buy new or rebuilt ones.
Yes, I did think of that;
I did investigate whether air was leaking back from the R-7 valve. I cannot guarantee that is not the case but I decided to make a corporate decision and replace the PP-1. Now I have a new PP-1, PP-7, new TP-5, at least half of the air lines are new and the R-7 is only a year and a half old. I can now be fairly certain that I won't have to get back into the dash portion of the project. After connecting the valve assembly today I no longer have air leaking from the exhaust valve. Air loss was 25 psi over an hour and a half with the PP-1 pushed in, spring brakes in the hold off position, engine off. I'll check it tomorrow with parking brakes applied.
Yes, what that guy did was exactly what I was thinking.
Time to pay some attention to the service brake chambers.
According to my measurements these are type 16 service brake chambers.
Confirmed. Midland T - 16.
Midland N-20151 T -16. https://mpparts.com/part/midland-n20151-type-16-air-brake-diaphragm-n20151 or https://www.finditparts.com/product...0 X2lkeCI6MH0= &ga_list=Search Autosuggest v2
These are shot.
It looks like the band clamp style has changed to a two bolt style. Can anyone tell me if they are universal and if these would be a suitable replacement? https://www.finditparts.com/products/364920/haldex-cb16
Yes. Sometimes easier to replace whole air chamber. IMO
The 2 bolt style I linked to above is a suitable replacement. OK, thanks Truck Shop, I appreciate that. I just may do that. I will pull the other side chamber and evaluate it's condition. If poor, I will replace both with new. Thanks again.
Picked these up locally.
https://cbsparts.ca/admin/bulletins/PUSH ROD CUTTING PROCEDURE.pdf
Figure Base to Clevis on Old Chambers, set up New ones for Same Length, Stroke distance from Not Applied position off the S-Cam can support mount has to remain the same. Major point is at Full apply after base Adjustment, the S-Cam and Slack Adjuster cannot pass 90 Degrees when applied for maximum applied pressure(Best Braking Force). There was a reason the old units had that Oval Stagger section of Can off the Cam Support Mount.
Thanks Mr Miller. I appreciate that.