Hi folks, It's been a minute since I've been around. Anyway I'm looking for a little help understanding trailer air brakes. I have a customer with a Kenworth T660 dump that usually pulls a tandem maybe 40T equipment trailer, with ABS on the front axles. The sensor is on the front, I should say. I'm replacing the brakes on the trailer. Liners, drums, slack adjusters, and oil seals. I did one side last week and I'm doing the other side today. So he calls yesterday and tells me that the left side is locking up on normal braking, unloaded. I told him that's quite possibly because that's the new side and the braking action is much stronger than the other (old) side. So he finally let me do the brakes on the other side. That's happening today. So my question is twofold. First, was I correct in my response to him about the effectiveness / braking force of new vs old brakes? If that's true, shouldn't the ABS system have kept the brakes from locking up, or is the "one side new, one side old" thing just too much to ask of the system? Thankye!
Would think it all depends on how you set the brakes.
Is the abs even operational? Does it have operation test light on side of trailer? Can you hear it going through self test mode as soon as key is turned on?
View attachment IMG_2372.jpeg Hah. I think I found the problem. Yikes.
Quite the picture. Wasn't going to be on the road for long. Simon C
View attachment IMG_2373.jpeg Just for giggles, old hub new hub. Wow.
Got yerself quite the lathe there. lol
For us uninitiated, what exactly are we looking at in the picture?
Not picking on anyone, but that is the direct example of or lack of regular maintenance. Stuff like that is rolling along as I type. Glad you found it.
Not pointing fingers either, but all that silver pixie dust from that hub spinning should have been picked up in a simple pretrip. Yikes indeed.
We're looking at a hub and drum for a Dexter 12K axle. The bigger round part is the drum. The smaller kind of spider looking thing is the hub. In the first pic, those shiny parts are supposed to be bolted together quite tightly. The bolts came out, and rubbed and wore it all to hell, so it all had to be repoaced.
I've been working on this guys stuff for 3 years now, and he's never asked me to even look at that trailer. Apparently he never did either. He's damn lucky CDOT never looked at it either.
Only thing I question here is why doing "one side" at a time? Then do the opposite side later. I would object, but if pressed by customer I would do one axle, left and right side, then a second axle at a later date, but one side at a time seems rather odd to me. But that's just my opinion.
Makes sense. It turned out the way it did because of timing. I did one side on a Friday afternoon, and I was supposed to do the other side first thing Monday morning. Well, you guessed it, that Monday took a few weeks to happen.
Yep, that's why I question that method, **** happens. Knowing that, I'm going to do one axle at a time and be just dang frustrated I couldn't wipe it all out in one sitting.
And removes liability.
Absolutely! I've said this for years, and the fact that one could sue McDonalds, and win the case, because, who knew coffee was hot? Whenever you do work for "customers" you have to CYA. Me, you want air brake work? You're getting drums, bearings, seals, pads, S cam rods removed, if worn, replace, new S cam rod bushings/bearing, slack adjusters, and that one more thing, I'm replacing the 30/30 chambers as well. When I'm done with that axle I expect zero call back on it.
The first three items DOT looks at in accident, {Brakes are are number 1, tires #2, lights #3, steering#4, if brakes are found defective number 2, 3 & 4 are all just addon violations.
On an episode of Highway thru Hell there was a trailer with the brakes so far out of adjustment they didn't hold even when the air lines were disconnected. The trailer just pushed backwards trying to get the fifth wheel hooked up. They hooked up the air lines and the driving brakes held enough to hook the trailer up. I thought when there's no air the wheels should be locked solid.
Air brake system is only as good as the components providing all are in working order and in proper adjustment. Shown is standard 3030 brake chamber, there is also long stroke versions all doing same job. A standard 3030 stroke is not to exceed 2" travel or go over center {90*} of s-cam, slack adjuster and pushrod. Force is lost once stroke goes over 90*. And all of that is depending on drums, shoes, s-cam bushings and rollers being in spec. Parking spring only has so much travel and requires all other components in working order. And diagram below even has error. *
I have seen several SR-5 valves that did not dump the air when the emergency air was released so the spring brakes did not apply. The drivers never caught this on the pre trip either.
Thanks TS. What is the error in the diagram? I should probably take an air brake course even though I don't drive on the road with my dump truck. It would be good to know in case I need to work on the brakes. I had a big air leak I plugged with a 5/8" fine thread bolt. Thread pitch was similar to the fitting. Upon further inspection the brass bulkhead fitting through the frame cross member somehow broke. Brakes still worked with the line plugged but once I realized the fitting broke it was an easy fix. The hoist doesn't creep at all but I put a big wood beam across the frame rails just in case. Actually the truck has a support to hold the box up but I didn't need it lifted very high.
There was/is a national recall of the SR-5 valve--The way to know if it was replaced is a {Green zip tie attached to it}. I had to replace several, plus new trailers were being sold with rebuilt SR-5's. I questioned Utility reps over it, which it all came about because of the way Utility didn't plumb air ride correctly causing dock walk when unhitched ruining landing gear. * https://www.bendix.com/media/services_and_support/product_action_center_pdfs/tch-003-054_us_001.pdf
Service brake diaphragm is not in returned/no pressure applied position in second diagram.
Good info for us that are still learning.
Correct but if the parking brake springs become weak more brake application can be applied by the service brake.