I have a 1990 GMC Top KIck 10.4 liter Cat 3208. Allison trans. Case 580 Super N backhoe on the trailer. Route 11/30 from Peru is seven miles to where it meets Route 7. I came down the mountain in third gear allowing it to get up to 40 MPH before helping with brakes. Some hills are 8% grade, but others are gentle grade or flat. The onramp to route 7 North is very steep & at lowest point is joined by the onramp from 11/30 West. I came on the brakes hard entering the onramp & little or nothing happened. I realized my foot was to the floor! pulled it into second in desperation. The inevitable was about to happen! An Old Dominion tractor trailer was feet from entering the intersection & he piled on his brakes. By some miracle, I made the curve & he didn't enter the ramp. Ramp turned uphill, & I looked at air pressure, 100 LBS. Electric trailer brakes were working fine, but not set on highest setting. I got home, tried the brakes, as usual, at low speed they are too good, they'd put you through the windshield if you press too hard. All is new within 5000 miles. New tanks, lines, mysterious control devices, cans, shoes, rear drums this spring. My theories were too hot intermittently using them down the mountain, or I used up the air, but immediately there was 100 psi. I haven't figured out what went wrong!
Hot brakes fade terribly. Might help if you sandblast the drums clean and paint with a high heat resisting paint like VHT paint meant for exhaust manifolds. I know that may be hard to fathom but a rust buildup common on brake drums becomes an insulator to disallow rapid heat dissipation in comparison to a new brake drum.
Even if you used up all the air, the spring cans should have then been applying, but with 100 of air they wouldn't be on yet. I'm guessing fade. You should probably pull them and see if the drums are heat cracked and/or the shoes are damaged or glazed. Check the adjustment also, especially since they were all new, it takes a little adjusting after they first get run in. Say a little prayer and enjoy your thanksgiving, knowing you've got something to be especially thankful for. Could have been far worse.
Was it possible you had some ice in the system?
Rear drums, shoes cans are months old, no rust yet. One garage claimed the left front brake drum was out of round. I tried to replace front drums also, but couldn't find them. I've not been able to confirm any out of round.
Are the brakes full air, or air over hydraulic? Is your treadle valve in good shape? No sticking valves?
do you know the drum number? It will be cast onto the drum surface usually in a raised elongated oval shape. Do you know how much free play you have in the brake shoes? Hopefully they are adjusted correctly and not camming over.
A few weeks ago I couldn't get the spring brakes to work. Two friends with many years trucking & mechanic experience adjusted them, I've driven a few hundred miles since & all has been fine. I'll try again to adjust, & look for the number in question. Fleet Pride had front drums correct except 1/2" too wide. I'd have to remove the dust shields to fit them. I ponder if dust shields are useful. I once had a mouse nest in one rear brake assembly. kind of a mess, but I've no reason to think it caused failure. Open brake mechanism would be less tempting to mice.
Full air.
I have a couple of friends that are truck parts vendors and they find all kinds of obsolete stuff for my antique trucks. Usually the drum number is four, or five digits and if you can get that I'll see if any luck can be had. Won't matter where it's shipped to direct from the vendor. On your spring parking, or service brakes; if you had problems with them I'd replace the relay valves wholesale given the age. A Bendix type R-14 is an inexpensive valve mounting right on the tank usually and directly feeding the chambers. This valve has anti compounding built in and seems to be a very good valve; but there may be better. On air brake "S" cam brakes I block the truck from rolling, release the brakes, adjust the slack adjusters till the brakes are firmly set into the drum friction surface, then back the adjuster off two "flats" of the adjuster till the spring collar pops back out. Under no circumstances do you allow that slack adjuster to exceed 90 degrees to the actuator rod from the chamber. If if does, this is "camming over" and the brakes are releasing under a hard application. If the brake chambers are installed correctly this cannot happen, but I've seen stranger things..... Hopefully TruckShop will see this and input information also.
Lot of variables here, If brakes were hot enough to fade---you would still be smelling them. Don't know the roads, only a idea of how it was driven and haven't seen the brakes on this particular truck. So it's only guessing and when it comes to brakes I don't like to guess.
Brakes and brake balance. When I was learning to drive an old timer told me to always feel my hubs when I bounced the tires. I took that a bit further many years ago when I started running a lowbed. Once in a while after getting my brakes pretty warm (not too hot to touch) I would feel the drums and compare the temp with all the other drums and adjust them accordingly. When the infrared thermometer was developed, I got one and used it and documented the temp at each drum, then tightened or loosened as needed. Getting all the drum temperatures to be near the same after a long hill assured me I had the brakes balanced as close as possible. Another thing I did before descending a hill when "heavy" was stop at the top, shut engine off and hold around 60# application pressure & watch for air loss. Only took a few minutes and could save ones life. I always felt if I had to use more than 15# application going down a hill, I was going too fast or I had a brake issue. Just my 2cents.
Does that have automatic adjusters? I can't remember what year those became standard equipment. I took all the dust shields off my truck (what was left of them that hadn't rusted away).
No. adjusters were replaced when I first put it on the road summer of 2020. They are manual adjust, but adjusted a few hundred miles ago.
The owner of the garage I had it inspected at last year said right rear shoes were delaminating. He said I'd have to bring it back, he didn't have parts, or time to install them. After that, he had a stroke. Changed them out last fall, but didn't get to the left wheel until late summer. I found no evidence of delaminating on either, but a big mouse nest In right. A few weeks ago brakes were fine stopping, but spring brakes wouldn't prevent rolling on a hill. Sunday afternoon it's a good bet a couple guys will be around telling each other lies. Minutes, they were both under the truck adjusting. They did what 1693TA said. All was fine. Yesterday morning we were heading out on another job up, then down the mountain. My son Seth took it upon himself to repeat the process. He said they were loose on both rear adjusters. Used them & all was well, though I confess I was in next lower gear descending the mountain (Route 140 Wallingford).
You're saying the spring brakes would not preclude the truck for rolling on an incline? You may have a broken parking brake spring in a chamber and if so they, (chamber complete) should be replaced without delay. That truck should not even think about rolling if the spring brakes are applied. Glazed brake linings, hard spots in the drums, mouse nesting all can have effect on brake performance, but the truck in no shape, nor form should allow the wheel ends to rotate if the spring brakes are applied. Do you know the chamber size in service, and parking sides? Maybe someone has installed type 24/24 where a 30/30 size should be? Too small and the truck could roll from not enough brake force applied and this also could explain weak service brake performance when loaded.
Wrong s cams or installed on the wrong side? Strange you should have trouble adjusting the spring park brakes to hold.
Federal--single axle loaded to a GVW of 32,000 with correct components {30-30} brake cans {long or short stroke} has to be able to hold the truck on a 20% incline rolling back no more than 1'. That rule goes for any truck also. * Not degrading anyone but, someone who is a pro at air brakes needs to look at this truck.
You mean some black paint on the drums won't fix this?
Agree.
It's the reason I said what I said in #11.
I wonder what the cam rotation degrees are
Be interesting to know the outcome on this one and conditions of the parts evaluated. Slacks are recent but still have cams, bushings, rollers, and ancillary hardware that are all wear items which have probably not been addressed in a while. Just after brake adjustment I always have someone apply and release the service brakes several times while I look for shifting movement that shouldn't be, (such as cam to tube) and that the rollers ride the cams proper. Shoe retraction is another I watch for. Seen a lot of "Cowboys" out there and don't want to see anybody hurt because of something not repaired correctly on braking systems.
Someone could have used standard Q shoes on Q+ cams. That would skew the degrees of cam rotation. That could be possible, but Q+ shoes cannot be installed on standard Q cams-you would not be able to slide the drums on
Yes, a mismatch of parts is a distinct possibility. Spring brakes not holding a truck is a dead giveaway something isn't correct.
Perhaps a good inspection if the air lines is in order. Could someone have a steel or cast fitting in the system and it rusted and plugged up and blew out and started work. Pulling on a string here
Update: While I haven't personally been under it in a few months, #1 son reports the adjusters had been turned the wrong direction. He estimates 12 full revolutions to bring them to where they should be. How they worked at all is a mystery. Truck had a major overhaul summer 2020. All were replaced: air tanks (2), all lines, all controls mounted on frame, cans, wheels, tires, Tried to replace front drums then, but wasn't successful sourcing them. At one time I had a problem with ice in the air lines. Replaced the air dryer. Last inspection, garage owner said one rear shoe was delaminating. He didn't have time or parts. Later he had a stroke. We changed at home one, then months later, the other. Neither was delaminated. They were old, but in good condition. I'm not sure who is responsible for maladjustment. My 38 year old son has done many dozens of successful brake jobs. Brakes have worked well since I've owned it except the one time. We found a logical problem. I've used it on several trips since the problem all involving steep downhill grades, without issue. This truck has about 15,000 miles on it.
This is relieving to me personally as I knew a party involved in a fatality collision encompassing a large truck, it's maintenance practices, and the findings. The brakes were found to be deficient by "in house" maintenance practices.
I like to put these stroke indicators on makes checking easier With all the hills you have you will need to stay on top of those manual adjusters check the stroke very often to stay safe https://www.truckspring.com/product...MIxcmmmtDbggMVjf3ICh0NwxcoEAQYBCABEgJxdvD_BwE
My involvement in large trucks is limited to two medium duty trucks I've owned. First was a 1976 Chevy C65. It was a baptism of fire. Bought it two large states away. It had been prettied up. Dump body original was built of bent sheet metal was rusted severely & concealed behind Bondo & paint. Perfect wood floor disintegrated first load. Air compressor shook loose many times in the 13 hour drive home. The list goes on and on. I spent more time on that truck than I should have. Newly rebuilt 427, cab corners & rockers, paint, tires, etc. etc. Yes brakes. This one was another big project. Retired fire truck 10,000 miles, it needed a bunch of work to remove fire equipment & install dump body. Since early in the purchase I've searched for a garage to take care of the not simple stuff. I haven't had a complete success. All truck repair facilities have a HEAVY load of jobs to do. Each has several dozens of trucks waiting for attention, I'd have to do it myself. First major challenge was removing 128 rivets in the frame. I never did buy a MAG drill, I did use several other methods. Most successful was grinding the head off, drilling through length of the rivet, then using acetylene cutting torch to enlarge the hole until I could see a bit of the frame material. I'd let it cool & use hammer & punch to remove. These rivets must be pressed under extreme pressure, the shank of the rivet was expanded to fit very tight in the hole. While I expected grinding or burning the head off, & punching them out, that just didn't work, It only bent the frame. My best effort was an 8 hour day I removed 28 rivets. 2020 I found a guy working alone in a new venture. It was just the kind of project he was used to. Took him several months to shorten the frame, move all the cross members, build brackets etc. for carrier bearing, hydraulic tanks. Removing the fire pump meant a new driveshaft was needed. Local engine shop built that. The list of new parts was extensive. Everything suspension was new. Everything brake related was replaced. I got it home, he went on to a major project for Vermont Marble. It was then we put new cans, slack adjusters, wheels, tires, wiring, lights, The pintle hitch was mounted to the dump body & I felt too far behind the rear axle. I built the hitch plate & mounting, moved it forward about 30".