2nd Gen Non-Engine/Transmission Rear Brake lock up

[HHhuntitall]

Texis,

You're telling us the tires have flat spots, and you wonder what the bouncing situation is? Now think about that, if the tire is not round, what is it doing? I'm not trying to be smart, I'm just asking you... ... . if it's not round, what does it do? Very likely to be intermittent because the sidewall flex takes a lot of the bounce out of the tire. Occasionally, the tires will have flat spots opposite each other, and they will "dribble" each other. One goes up, pushing down on the other one, which bounces up, pushing the other down; you've got a straight axle back there, and the shocks only take out sooo much play in the axle. Try airing down the tires and seeing if that helps. Also, if you have something to wiegh the truck down, say a bunch of feed sacks, wood, whatever; if you load it(not while aired down!) does it go away? That's gonna be the tires. And I'm betting you have Michelin's if you have that many miles on the tires, so watch for dry rot and cord separations, which look like balloon spots in the tread and sidewall. Oh, and you can try jacking up the truck and spinning the tire while watching it, watching for any vertical leap or humps.



jdrury,

Are they rear drum or rear disk brakes? While I'd suspect ABS, it could be the hydro-boost brake assembly behind the master cylinder. If it's overtraveling or bypassing, it could allow the steering pump to pressure up the chamber, and effectively "press the pedal for you. " Be sure to check your fluid levels in the power steering reservoir, and make sure there are not leaks in the brake master clyinder assembly. I've seen some that leak whenever the pedal is used hard for long periods of time(pulling a trailer), and then they'll start fading really bad a few hours later. When you pull them apart, the front of the assembly is full of steering fluid, showing where it's been leaking... .

 

[Joe Mc]

Guys - I can understand the confusion with "Are they drums or discs" because jdrury's signature shows a 96. However, in the first post he said
"It is a 01 2500 six speed four wheel drive with rear drum brakes. "

I'm guessing it could be 4W-ABS or RW-ABS only? I'm not sure if an 01, w/rear drums could have 4W-ABS? Anyway, I'm thinking if it is RW-ABS only then the rear brakes locking up could be related to the hydro valve mounted to the frame with the arm going to the diff that senses height of the bed/rear and proportions pressure to the rear wheel cylinders.

Is it "one" wheel that locks up, or "both"? If only one then there's the starting point - inspect everything mechanical on the side that's locking. If all is well the problem could be on the side that's not locking = because it may not be working at all and the other side is locking because its doing all the work. Always best to check both sides anyway. Man-I hate my rear drums=1999.

As far as the rear hose being the culprit. I'm on the fence because there is only one hose on a rear drum set-up coming from the valve on the frame to the diff housing, from there it turns to a block and has individual metal lines going to each wheel cylinder. I'm leaning more to this being related to the ride height sensor than anything else.

Typically if you disconnect the rod from the diff and tie-wrap it to the frame you can go for a drive and see if things lock up - more than likely they will. Then adjust the arm on the valve one way or the other, tie-wrap in place, and see if there's a difference. Once it is determined which way to move the arm (up or down) move it incrementally until the locking stops.

If nothing changes with the arm full one way and full the other way (assuming all other mechanical components in the rear brake system pass inspection) the valve itself could be bad. During a trouble shooting scenario on my truck I considered the valve could be a problem and priced it - WOW! it was well over $100 so I decided to continue looking elsewhere - all said and done with mine the valve was not bad.

Back to the locking up - tires and drums being out of round could potentially be an issue - obviously, but to cause the rears to lock up all the time? Do they lock up when you back up and hit the brakes?

Try the following - inspect the wheel cylinders for leakage, just pull an edge of the rubber cover on each side of the cylinder and look for moisture/wet - if wet replace. Let's not forget the ever popular bad axle seal which will soak the shoes meriting shoe replacement along with the new seal install. While you are there inspecting things - do the shoes easily move on the brake plate = are there groves in the perches on the plate where the metal edge of the shoe rides? If so, grind flat and smooth, then lube with brake grease. Also, since you're there, sand down the shoe material to remove any glazing and clean with a brake cleaner or rubbing alcohol. Turn to the drums - is the surface where the shoes ride nice and flat, not glazed or ribbed? If they are questionable get them trued up roughly $15-20 each drum - new ones will set you back around $100 each depending where you get them and the quality = buyer beware of off-shore junk. Assuming the drums are OK, scuff up the shoe to drum surface and clean as well. Make sure there isn't any rust on the axle face-inside drum to axle and outside drum to wheel - and the back of the wheel as well. Make sure (obvious) to torque the lugs. And finally adjust the shoes as others mentioned in earlier notes.

I know it was mentioned earlier as well, but I totally agree that it's pretty easy to get the front shoe and back one mixed up and installed backwards - this will totally screw things up.

Please keep us posted.

 

[Texis]

Certainly appreciate all the ideas, for me the puzzler is still the fact that it started the "INSTANT" the new wheels went on? The flat spots have been there for 50,000+ miles. I cannot get in my head how brake lines or the existing flat spots would not be a problem... . add new wheels and problem?



After another 400 miles in and out of weather, it is MUCH worse on wet roads, barely noticable on the dry, bounces all over the place when the road is wet?



Still pondering. Brakes have been fawless for 320K. The mystery continues, but I will figure it out.

Oh, and you can try jacking up the truck and spinning the tire while watching it, watching for any vertical leap or humps.

... . that check may be next, when I get the time! I'm getting into a situation that I actually need the truck lol. The tires still look really good, basically ALL highway miles. The Michelin dealer did the wheel mounts and inspected the tires, they felt like they should make another 20K.





Thanks for the ideas.

 

[RobertHiltz]

I would try adjusting the rear shoes and after that make a practice of doing a firm brake application while backing up. Two or three times per thousand miles should keep them adjusted.

 

[Bob Cochran]

I'm guessing it could be 4W-ABS or RW-ABS only? I'm not sure if an 01, w/rear drums could have 4W-ABS? Anyway,

Please keep us posted.

The answer to this is 4W-ABS was available on 2001 dually at least mine has it.



I have had problem sometimes with mine grabbing because of moister. It usually happens when first getting going but after a few applications of brakes goes away, Does not happen all the time.

 

[Hammer]

I know alot of guys who had this issue AFTER they did a brake job on their trucks. One thing I was told a very long time ago by Sam Peterson was our trucks needed to have the softest and cheapest set of shoes for the rear that we could get. I was told by him anytime you ran a expensive shoe/pad on the rear it always lead to premature rear brake lockup and could cause you problems. I run Carbomets up front and a cheap Wagner shoe out back and the truck will stop straight and not wheel hop at all... ... Andy

 

[SRath]

Have your new wheels checked for roundness. Lots of crap on the market these days and junk is junk no matter what name they carry. EDIT: It sounds too simple, but are you using the correct lugnuts for those particular wheels? Some wheels need shanked lugnuts to center them and some use the acorn shape or bell at the end of the lugnut. You cannot mix them up or the wheel could be off-center. You would be amazed how many guys have the wrong lugnuts on their mag wheels.

Once a tire starts wearing badly, and flatspotting is very bad, they will NEVER stop. If I can feel flatspots on 1 or 2 tires out of 18 that are 60+ behind me on a stiffly-suspended, bouncing, shaking, noisy semi trailer, I GUARANTEE you will feel flatspots on your pickup tires. And I'm not even a very 'sensitive' guy... :-laf

My '96 Dodge came from the factory with the short shoe in front on one side and on the rear on the other. Never saw such a thing before. I put the short shoe in front on both sides.

Another seldom-addressed issue with drums and shoes is the ASSUMPTION the curvature of the shoes and linings is correct and matches your "brand new and round" or freshly-turned drums. A truly good brake shop will check and match the shoes to the drums.

As already mentioned, though, the FIRST thing an experienced brake shop will say (if you have front brake sticking problems) is "Dodge, huh? Replace your brake hoses. " These mopars are justifiably infamous for bad brake hoses.

BTW: My '96 is rear wheel anti-lock only and it has no "sag sensor" to regulate rear braking.

 

[Texis]

Thanks for the inputs.

I really think this is an anti-lock problem. I believe if "anything" were out-round I would know it sitting on 80 mph for 5 hours. BTW, it is real smooth at 90 mph which I found out last weekend passing another vehicle, so the flat spots must not be that severe.



I think the difference in the weight of 2 aluminum wheels vs 2 steel wheels is screwing "something" up. It is unsprung weight. Also the problem is intermittent, which somewhat eleminates oval stuff.



So where is the rear ABS stuff? and how do I disconnect it?

 

[Joe Mc]

Thanks for the inputs.

I really think this is an anti-lock problem. So where is the rear ABS stuff? and how do I disconnect it?

I could probably try to tell you where and how, but I'm hoping someone can post a page from a CD Shop manual and save me an hour of trying to type something that probably wouldn't make sense even to me = a picture paints a thousand words.



Anyone out there that can post a CD Shop manual page of the rear load sensing system?

 

[DMcLeod]

Lots of info here. I've been experiencing a similar brake lockup problem and is gradually getting worse. I've got the same year 2001 2500 QC rear drums with rear only ABS. My ABS doesn't seem to be working anymore, and I suspect it is the culprit. By the way, rear ABS doesn't operate when in 4wd. I also need to flush pwr steering system, flush brake fluid, etc. All I need is a little time. Will keep watching this thread, and will post any results I find. Thanks.

 

[jdrury]

Guys - I can understand the confusion with "Are they drums or discs" because jdrury's signature shows a 96. However, in the first post he said

"It is a 01 2500 six speed four wheel drive with rear drum brakes. "

Actually, in the sig i have two trucks listed... But either way after the thread got hi-jacked by "texis" i did not respond.



However, i did gain some information that will help me track down the problem but unfortunatly i have picked up a slight engine misfire and am going to put that at the top of the priority list for now. .



Thanks for all your guys help

 

[fest3er]

Actually, in the sig i have two trucks listed... But either way after the thread got hi-jacked by "texis" i did not respond.



However, i did gain some information that will help me track down the problem but unfortunatly i have picked up a slight engine misfire and am going to put that at the top of the priority list for now. .



Thanks for all your guys help

I don't know if the ABS system can respond that quickly, but it sure sounds like the CAB (Controller, Antilock Brake) thinks the rear brakes are locking up (technically, they are slowing down faster than the CAB expects them to) and engages ABS. On my '98 (RWAL), this feels like a soft clunk and softening of the pedal and always resulted in the loss of most braking power; I don't know if the rear AL on a 4WAL system feels any different. Then when the CAB decides the rear wheels are turning as expected, it disengages ABS. But, by then, you've got the brake pedal to the floor and the rears obediently lock up.



Look for sudden speedometer changes when this happens. The PCM might hide short signal dropouts from you, so you might not see anything untoward there. But if you do see a sudden change that precedes the wheels locking up, you will know that the problem is in the VSS/ABS system.



If the proportioning valve is properly connected and functioning, the problem is then definitely somewhere between the tone ring in the rear differential and the CAB under the hood. Something is causing the A/C frequency from the rear sensor to change rapidly; the signal is probably dropping out for a few moments (or longer) under hard braking. If the sensor is clean inside the diff and solidly affixed to the housing, I would next look at wiring.



If it helps to visualize, never mind how fast the vehicle is moving or how fast the rear wheels are turning. Pretend you are a CAB on a RWAL-only truck. Your sole notion of the vehicle's speed is the sensor in the rear axle. You know the vehicle is moving when you see a nice, steady frequency from the sensor. When the frequency changes, you assume the vehicle speed is changing. If it's changing and the brake is on, you then look for sudden changes in frequency. If it changes too much in too short a time, you engage ABS. When the frequency seems to have stabilized or indicates a speed of less than about 3 MPH, you release ABS.



If you have 4WAL (I don't remember when Dodge changed over), then much of the above mayn't apply, as the 4WAL system has two extra sensors by which to gauge the vehicle's speed. [RANT] IMO, the RWAL system is just plain poorly designed and dangerous and should never have been shipped. At the least, the CAB should've had an accelerometer in it so the CAB could really know when the wheel speed doesn't match the vehicle speed. [/RANT]

 

[Texis]

I do need to apologize for the unintentional high jacking, I realized after it got going that I was... . well, a thread high jacker! I hate those guys.



Again, please accept my apologizes for the forum rudness.

 

[fest3er]

I do need to apologize for the unintentional high jacking, I realized after it got going that I was... . well, a thread high jacker! I hate those guys.



Again, please accept my apologizes for the forum rudness.

Well. ... . OK. We'll let it slide this time. Next time your atonement will be forty lashes with a wet noodle.



:-laf

 

[Rogan]

what ever came of this? My right-rear is locking up, randomly, when pedal pressure is applied.