HELP... rear brake issues

[Haggar]

Sorry missed the word bypass in your first post.....  (doh)

 

If we take out any problems with the physical mechanical parts in the rear brakes there are only two other choices:

 

1) The factory setup proportioning valve is applying too much balance to the rear system.  (this seems like it would be all the time, not just worse when hotter.  and like you said most people don't have this problem)

2) The master cylinder or proportioning valve (or tubing/hoses) to the rear axle are leaving too much residual pressure in the rear system. 

 

When you remove your foot from the brake pedal, a molecule of brake fluid (should it wish) could move un-hindered from the rear wheel cylinder to the reservoir of the master cylinder. (all lines should be open, and all valves should be too.)(this is how the brake springs compress the wheel cylinders so the brakes will not be engaged.)  

 

The next time your truck starts acting up, quickly release the bleeder on one of the rear wheel cylinders.  you should only get a tiny dribble, if any flow at all.  If it squirts you have some residual pressure that should not be there, and you just let the wheel cylinders relax.  See if you have some pressure when the problem gets pretty bad.

 

HTH

Hag

 

 

Edited April 28, 2016 by Haggar
added bleeder to quickly release

[dodgedieselnewbie]

Thanks a million for the info Hag.! see what happens after I swap cylinders again and flush the fluid.  Will try what you suggest if it happens again. YTB

 

Edit.. oops.. forgot my question.. so if #2.. too much residual pressure.. how do you determine how that's happening? Do I start replacing a component at a time? First being hoses.. then proportion valve.. next master cylinder? 

 

Edit #2... also.. how would the tubing or hoses affect or bring too much residual pressure? Would that mean they may be collapsing or swelling? 

Edited April 28, 2016 by dodgedieselnewbie

[dodgedieselnewbie]

Today... inspected all mechanical parts (everything new) and all seemed okay.. Nothing was sticking/binding. Removed 1 ton cylinders and installed new 2500 wheel cylinders. Took it for a drive.. 15-20 minutes working the brakes... they started out fine and slowly developed a shudder.. not as terrible but a noticeable shudder. They are not super grabby and no lock up or ABS kicking in. So.. there is improvement. My mechanic seems to think the drums just need turning again. We jacked the truck up as soon as we returned to see if there was too much pressure.. but the wheels turned freely and when the bleeders were broken loose.... just a dribble came out. I hope to goodness... it's just in the drums!

[Haggar]

DD,

wow.   If you found pressure, we were going to work through what it could be (MC not returning properly, internal hose failure etc.)

 

Since it is not retaining residual pressure....  I can think of 2 things (I thought of one last night....)

 

First thing  since you have turned the drums, are you reshaping the shoes to the drums?  Assuming the brake manufacturer got the radius right (missed more often than you might think) it is the new drum radius.  as you turn the drum that radius gets larger.  the smaller radius of the shoes only contacts the drum in one spot (the middle), possibly making the shoe very hot.  (reshaping shoes is not hard)

 

The other possibility I don't think we have considered... could the front system not be performing properly putting more of the stopping load on the rears?  I realize that sounds stupid, but usually our fronts do so much of the braking, if the rears were not used we would hardly notice it.  (until we had a load etc)  So for yours to act up during normal driving, seems odd.

 

Hag

[dodgedieselnewbie]

HI Hag.. Makes sense about the drums being cut and the shoes maybe not meeting the same now.  By reshaping... are you referring to the "bedding" procedure? 

 

Front brakes are definitely working.. as there is more brake dust than I care see and clean off the rims. :-)

 

I drove around town today with light braking and all seems well.. no shudder. 

 

Getting ready to head out with the camper... see how it goes. Will keep you posted.. Thanks and have a great weekend (everyone)!!!!

[dodgedieselnewbie]

HI Hag.. Makes sense about the drums being cut and the shoes maybe not meeting the same now.  By reshaping... are you referring to the "bedding" procedure? 

 

Front brakes are definitely working.. as there is more brake dust than I care see and clean off the rims. :-)

 

I drove around town today with light braking and all seems well.. no shudder. 

 

Getting ready to head out with the camper... see how it goes. Will keep you posted.. Thanks and have a great weekend (everyone)!!!!

[dodgedieselnewbie]

No issues braking with the camper.. miles there and back 80 miles ... and just did a 40 mile round trip without the camper. Everything seems okay.. Thanks for everyone's help! `

[Buzzinhalfdozen]

So what fixed it? Installing stock sized wheel cylinders and turning the drums?

[dodgedieselnewbie]

Don't know exactly what the problem was.. Everything is new back there.. so not sure what fixed it. Appears the larger cylinders were just too much for my application. 

[Mopar1973Man]

On 4/27/2016 at 8:57 PM, TFaoro said:

Hmm... just doesn't seem like a smart thing to do. Proportioning valves are in everything for a reason. I can see the larger cylinders, but at least put in an adjustable valve.

 

It's a Mopar video but for the older vehicles but does explain the valve quite well...

 

 

[Haggar]

lol,  he is right and immediately wrong!   He makes fun of an engineer calling it a "proportioning" valve, then he himself calls it a pressure reducing valve!  W-R-O-N-G.   It may be a pressure limiting valve, but it has no circuitry to reduce a downstream pressure once it is already there....  omg... then he goes on and says 500psi line pressure on 6 square inches is 3000 psi!!!!  3000lbs force yes, 3000 psi... ummm maybe he shouldn't be pointing fingers at enginerds. 

 

Sorry,  his explanation is decent, just don't get hung on the details....  The engineers used the valve to set the proportions of brake bias.  So I can see how they came to calling it a proportioning valve.  At least they didn't call it a "pressure reducing valve". 

 

Bluto: "What? Over? ....  Was it over when the Germans bombed Pearl Harbor! Heck No!"  (Otter: Germans?  Boon: Forget it he's rolling)

Edited May 3, 2016 by Haggar
put regulating when I meant reducing

[dodgedieselnewbie]

Well... the problem is not resolved. Again.. no problems when I first start out each day. The more driving/braking the worse it gets.. and I try to go as easy as I can on the brakes. Shudder is there and they become more grabby. Pulling into my development just rolling 5-10mph.. the rears will lock up when I hit the pedal firmly but not stomping on it at all. I pulled into my driveway and immediately got out to loosen the fitting like Hag suggested.. again just a trickle. The drums are not hot either.. warm enough that I can keep my hand on them. I'm so disgusted and don't know what to do. :-(

 

 

[CSM]

Have you fully bled the system?  What did the fluid look like?  Any solids?

[Buzzinhalfdozen]

One more experiment for you. Before driving it, trans in neutral, jack up the rear end and rotate both rear tires by hand to get a feeling for how much drag is on the brakes. Then go drive it until it's acting up and do the same thing. If they feel tighter this will point to a mechanical problem, if they don't it's probably a hydraulic problem. 

Obvoiusly something is heating up and making your brakes grabby. If it was mine (assuming parts are still under warranty) get a new set of drums and have them machined. I've seen A LOT of brand new warped drums. Get a high quality set of shoes and make sure they make even contact with the drums before installing. 

If none of this works sorry to say but you'll probably have to put the proportioning valve back in. I know others have had success bypassing it but like I said before mine will lock up hard if I adjust the valve to far. 

[dodgedieselnewbie]

5 minutes ago, Buzzinhalfdozen said:

One more experiment for you. Before driving it, trans in neutral, jack up the rear end and rotate both rear tires by hand to get a feeling for how much drag is on the brakes. Then go drive it until it's acting up and do the same thing. If they feel tighter this will point to a mechanical problem, if they don't it's probably a hydraulic problem. 

Obvoiusly something is heating up and making your brakes grabby. If it was mine (assuming parts are still under warranty) get a new set of drums and have them machined. I've seen A LOT of brand new warped drums. Get a high quality set of shoes and make sure they make even contact with the drums before installing. 

If none of this works sorry to say but you'll probably have to put the proportioning valve back in. I know others have had success bypassing it but like I said before mine will lock up hard if I adjust the valve to far. 

 

Did what you said the time before this and the wheels did move freely.. and cracked the lines open.. no pressure. The system is going to be flushed (again.. I think) and new drums and shoes. I'm thinking.. Adaptive One from Napa. And like you said.. If this doesn't work... the weight sensing valve will go back in... but I have to find one as all I can find of my old one is the rod. 

[Buzzinhalfdozen]

 

1 hour ago, dodgedieselnewbie said:

 

Did what you said the time before this and the wheels did move freely.. and cracked the lines open.. no pressure. The system is going to be flushed (again.. I think) and new drums and shoes. I'm thinking.. Adaptive One from Napa. And like you said.. If this doesn't work... the weight sensing valve will go back in... but I have to find one as all I can find of my old one is the rod. 

I'm contradicting myself some, but I find it hard to believe the hydraulic side of the brake system is causing so many problems just based on fluid temperature. Unless there are extreme temp changes typically a hydraulic system won't change in pressure/flow that much.  

Keep doing what you're doing. Replace the shoe/drums and report back. 

[dodgedieselnewbie]

I'm finding this whole situation hard to believe.. it's becoming a nightmare to me. I'm hoping it's the shoes.. either just a crap set or maybe they are contaminated. Not sure if contamination is visible... never dealt with it before. 

 

 

edit: Can the master cylinder be a problem? I mean.. if it's not functioning properly.. it can cause drag in the braking system.. no? 

 

I have no idea what a brake booster does... can it be a problem?

Edited May 5, 2016 by dodgedieselnewbie

[Dieselfuture]

I had similar issue, ended up being bad caliper in rear, got them all rebuild for 40 bucks. Also I've seen rubber lines get rusty around metal clamps and pinching line shut, fluid will go one way but takes a while to let go. 

[Haggar]

DDn,

 

Yes the master cylinder could,  but you would see the residual pressure at the wheel cylinders.  Since you are not seeing this, it has to be something else!!!! (temperature rise can cause this too, but you would have residual pressure...)

Grrr this is frustrating!!!  If you can put your hands on the drums they are not hot at all.  So it seems like a dragging brake is not the problem either. (neither is a residual pressure problem)

 

Do you have the 4 wheel abs (3 channel?)?  I wonder if it could be actuating after temperature.  (mine performs differently in the cold than the hot.  need to get it fixed, but not totally broken yet)  For giggles, disconnect it.  Drive for a day and see what your braking results are.  You will lose the speedometer, but that is the only down side.  

 

HTH  Hag

[dodgedieselnewbie]

They got warm but not hot yesterday.. I could keep my hand on the drum.. I guess it would depend how hard I use them as to how hot they get though... because other times they've gotten pretty hot. I have two wheel abs.. wouldn't a light come on if abs was acting up? And how would it actuating cause my shuddering and locking up/grabby issue?

Edited May 5, 2016 by dodgedieselnewbie