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Discussion Starter · #1 ·
Truck was in the shop last thursday to replace horn. After I picked it up and drove away, the brake pedal felt like there was nothing there the first 20% of push. I also noted that when I let off the throttle, the truck would slow quicker than before. I took it back in to the dealer and explained it to the service writer and he looked and questioned me like he has never heard of it ever happening before. It feels like something is sticking or binding in the brake system. I don't want them to give me that can't duplicate or nothing is wrong stuff. I know my truck, and something is wrong with the brakes. Any ideas from the pros? Much appreciated.


LA DMAX
 

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The first thing you need to do is jack it up and try to turn the wheels. See if they truly are sticking. If you determine that you do have a problem, it is time to start your inspection. I have seen rock stuck in calipers. The calipers could not retract and the breaks were on all the time. One of the strangest things I have ever seen is having the inner wall of a brake HOSE collapse and act like a check valve. You could apply the brakes but they would not release because the pressure was trapped in the caliper. It took me a while to isolate that one. This problem USUALLY only happens on older vehicles, not one as new as yours, but you never know.
 

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Discussion Starter · #3 ·
ag4gt,


Thanks for the help. The dealer already has my truck so I can't do anything now. My main concern is if they tell me nothing is wrong. But if they do tell me that now, I'll tell them to jack up the truck and see if the wheels spin. Thanks again.


LA DMAX
 

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Discussion Starter · #4 ·
Well, just as I feared. In 2 days all the dealer did was test drive my truck, tell me they could not duplicate problem, and say that it's probably the Allison and the way it shifts. I called BS on that and asked to talk to the tech. I spoke to the tech and told him all the symptoms and that I thought it was the brakes and if he had done anything to check that. He bluntly said, it's not your brakes, your truck is too new and those symptoms don't sound like a brake problem. I thought to myself, maybe I'm stupid here, but I wouldn't even have this guy change my oil if this is how he does his analysis. I asked if he could put the truck up on his jack and spin the wheels to see if they stick. He was reluctant to do it but finally got them up there. Now he left it in park and it took alot of effort for me to spin the rears compared to the front. I would expect some resistance due to the trans and drivetrain, but I'm not sure how much. He just passed the buck and said that was normal and if I was so concerned about brakes I should pay for an inspection.


I told them I would gladly pay for one but it was 5:00 and all were leaving, come back another day. I'm going to schedule one next week when I have more time but I wanted to ask the experts: what can I look for when they pull apart my brakes to see if anything is sticking or possibly causing this drag or stuck brake feeling? I fear this same guy will be pulling them apart and feel he may not be truthful or do just a 1/2 a$$ job. I might just go to my buddy's this Sunday and jack the rear up, turn the truck on and put it in neutral, then spin the rears; and possible compare that to his 2003 2500 Yukon XL. What would the techs look for? Help me out here fellas, please. Thanks


LA DMAX
 

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Pull the wheels of and spin the axel.

Look for anything that should not be in the brake system, dirt, rocks, sticks…

Have someone step on the brakes and see that they grab the rotor. Then check that the rotor is free again when they let off on the brake peddle. You should have “some” drag, as the pads are designed to run “just touching” the rotors.

Pull the calipers off. Take note of how difficult it is to get the calipers off. They should be snug but you should not need a 3 foot pipe to get them off. As a mater of fact, I always have to compress my calipers with a C-clamp to get them back on. Which brings up another thing to look for. When you use a C-clamp you should be able to compress the pistons but it does take some effort. I have found that the pistons will compress about a quarter turn on the c-clamp then I stop for about 10 seconds and make another quarter turn. If you try and go more then a quarter turn you run into A LOT of resistance. This is normal and has to do with valving in the break system.

While you have the wheels and calipers off, spin the hubs and axels. The fronts should free wheel very easily. The rears have more drag. You are turning a bunch of parts in the rear. You should be able to turn them by hand however.

It may be a good idea to check the Yukon XL just for grins. It should give you some feel for how things “should be”.

After all is said and done, it may be the Allison. I have a VERY steep hill on part of my driveway. I almost have to give my Dmax gas to get it to go DOWN the hill.

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Discussion Starter · #6 ·
ag4gt,


You have mail, check your pm. Thanks for the advice.


LA DMAX
 

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Discussion Starter · #7 ·
I put my truck and my buddy's truck up on jack stands this weekend to see if there was any difference. My wheels were definatly more difficult to spin than his. His wheels felt more free and spun longer with the same or actually similar amount of push. I had my buddy try it and he felt the same thing I did.


Next I took off my wheels and inspected the pads and rotors. I didn't find any rocks or debris caught up anywhere, just a little caked brake dust ot the top edge of pads. I had my buddy press/release the brakes to see if they disengaged, but to be honest I couldn't make a good call if they were or were not. Either my lighting or my eyes were bad, especially the inner pad was difficult to see if it would release. Then I spun the axles, and that was hard to do, even with gloves on.


Finally I put the wheels back on, started my truck, released the parking brake and put it in drive. I couldn't hear any real grinding but when the brakes were applied then released there was a thunk that came from what I felt was the pads releasing from the rotor. I don't know if that thunk is suppose to be that loud or not.


I'm sorry if this post is getting old, I just need to find out what's happening. I can feel it every time I drive my truck, and I'm getting tired of it. My next step is to take it back to the dealer and get a brake inspection. Anyone else having similar problems. Thanks ag4gt for helping me out on this so far.


LA DMAX
 

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You might try going down the road at about 20 mph and slipping it into nutral and let it coast down. Then try it in drive from about 20 mph and see what the diferance is. I am willing to bet it is the braking action of the Allison. I think if things were not releasing, you would not have been able to turn the wheels at all.
 

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Discussion Starter · #9 ·
ag,


Funny thing happened this morning on the way to work. Driving down the road, which was still damp from rain, and a guy pulls out of nowhere right in front of me. I slam on my brakes, as hard as I ever have, and the back end locks up just for a second and then I feel the ABS kick in. There was also construction repavement going on and the street was really bumpy. Unfortunatly I was braking hard as I was going over the bumps and it felt like the truck was being pulled over rail road tracks. Well I slowed from 40 to zero before I hit that guy and after a few kind gestures I drove away. As I drove away the pedal feel was better and it didn't feel like the brakes were dragging anymore. Actually felt really close to normal.


After work I went back to my buddy's house and put the truck up, spun the wheels and although they didn't spin as easy as my buddy's Yukon, they did spin easier than yesterday.


We've been having alot of rain the past 2 weeks(alot for around here) and I was wondering if that might get things a bit rusted and more prone to stick. Are there parts on the calipers that should be greased regularly? I know you might feel that it's the Alli, but I've driven this truck over 2 years and it didn't feel like anything the Alli has done before. I can best describe it as maybe not releasing the parking brake all the way and driving off. Thats the feeling I get.


Even though it's better, I'm still going to have the dealer inspect the brakes pretty soon. I don't feel like spending $200 on new brake pads. What I really need to know is if there are areas where the caliper may stick or the parking brake shoes may get caught up. Thanks for all your help, I greatly appreciate it.


LA DMAX
 

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The only thing in the calipers that need to need greased is the “pins” that hold the calipers to the mounting bracket. That area is usually quite well sealed however. It is possible they are sticking, heck anything is possible.

I have see brake rotors completely rust over in just one day of sitting in damp weather. This is just surface rust however and is wiped of the first time you hit the brakes.

I think you need to pull the pads and clean everything up. I take some course sand paper and go over the pads AND rotors every time I have the wheels off. The hard breaking you did may have loosened some crud up and allowed thing to work more normally. I sand the face of the pads until they look gray and have a new surface exposed. I sand the rotors until the surface is well scratch and doesn’t have the smooth shinny appearance. Do all this by hand and you can’t remove enough material to damage anything. If you have an air compressor, blow everything out real well, if not, use a brush.

One thing you might consider is changing the brake fluid also. From what I understand, the ABS system is VERY sensitive to contamination of the brake fluid. It should be changed every 2-3 years. I just got done changing mine on both my ’01 and my ’84. One thing, ABSOLUTLY, POSITIVELY DO NOT let the master cylinder go dry. If you do you are in for huge problems getting the air out. You almost need a pressure bleeder to do this. You can find several homemade versions on the web.
Please continue to keep me informed, I want to know what you find.
 
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