Rear wheel lock up while braking

[86M10086.2L]

So my M1009 has developed a nasty habit of locking the right real wheel up while braking. This can happen under hard or even light braking on a dry surfaces. If I try to panic stop or stop short it'll do it every time. If I ease the brakes I can avoid it. But it's not normal style of driving to do that. I've replaced both rear wheel cylinders. One was weeping the other was apparently fine but it was easy to change and a matched set adds peace of mind. Rear shoes are in excellent shape so is the hardware. Adjusted the brakes multiple times according to the TM procedures. No effect. Even loosened up the adjustment on the offending wheel also with no effect. Rear lines are clear of obstruction or kinks. Front calipers are working. One is in fact also brand new. Keep in mind this was happening before all these components were changed. Where do I go from here? Master cylinder? Proportioning valve? Every account I've heard so far in regards to proportioning valve failure results in the rear brakes not working or getting pressure at all. All my brakes are working. In my case the rears are working too much. At least one in particular. Any thoughts would be appreciated.

 

[cpf240]

Have the brake lines been replaced? A brake line can look great from the outside, but swell on the inside, trapping brake fluid, and leaving the brake(s) engaged.

 

[86M10086.2L]

The hard lines for the rear are clear. I removed both and blew them out. I can't imagine if the flex line which feeds both rear wheels, were swollen or colapsing would only effect one wheel.

 

[gringeltaube]

I suggest a few very simple next steps: 1) Return springs (only); switch sides, left wheel <-> right wheel; if nothing changed, -> step 2) brake pads (as a pair): also switch sides left <-> right; if it's still the same side wheel locking, -> step 3) Brake drums: also switch sides.
Then let us know what happened.



G.

 

[Recovry4x4]

Are the brake shoes oriented correctly. Shoe with longer lining in back? I've seen folks put both long shoes on one side and short on the other causing similar symptoms.

 

[MtnSnow]

Also double check to make sure the brake shoes are not oil soaked from a leaky axle seal.

 

[86M10086.2L]

Yes, the shoes are in the correct positions. No leaking oil seals. I'll try swapping the parts side to side and see what if anything happens. I'm working all weekend so it may be a few days before I can do more than just swapping drums.

 

[The HUlk]

I'm thinking use inline liquid flow and pressure guages on the brake line and take a reading on each side to see if the fluid energy is balanced. If not, then work your way toward the master cylinder to figure out where the imbalance is coming from. Full disclosure: I have never tryed this before, just an idea.

 

[The HUlk]

Have the brake lines been replaced? A brake line can look great from the outside, but swell on the inside, trapping brake fluid, and leaving the brake(s) engaged.

If there is buildup inside of a line or manifold reducing the inner diameter it would have a tendancy to decrease flow and cause an imbalance in brake force. That would seem to explain why there is flow on both sides yet stronger brakes on one side as compared to the other.

 

[infidel got me]

A prop. valve shouldn't cause a lock-up -- check your e-brake cable -- if your cable is frozen holding the arm forward it can cause a lock up. Also make sure backing plates are not worn where shoes contact hope this might help

 

[The HUlk]

A prop. valve shouldn't cause a lock-up

It shouldn't but if it is not functioning correctly due to contamination, wear, or damage then it may. If a valve or other component is changing the amount of flow or pressure to one or more lines then the amount of brake force will be different which would cause one or more brakes to lock the wheel before the others. Think hydrualic troubleshooting if all mechanical is well.

 

[infidel got me]

Make sure that the hard metal lines [that run on top side of axel] are not crushed or mashed--- I had a truck towed to me and had a similar problem. The wrecker driver pinched a metal brake line with his j hook while towing it. It came in not running and developed a brake pull while sitting in my bay lol. It took a little while to find-- take your time and never overlook the simple stupid stuff. That's where Mr.Murphy seems to hang out.

 

[The HUlk]

That's where Mr.Murphy seems to hang out.

Hiding around every corner just beyond view!

 

[infidel got me]

Seems like somedays we all roll thirteens

 

[german m1008]

It shouldn't but if it is not functioning correctly due to contamination, wear, or damage then it may. If a valve or other component is changing the amount of flow or pressure to one or more lines then the amount of brake force will be different which would cause one or more brakes to lock the wheel before the others. Think hydrualic troubleshooting if all mechanical is well.

From the prop. valve goes one brakeline to the rearaxle and then splits up, it would be unusual if only one side (always the same) blocked.

 

[The HUlk]

From the prop. valve goes one brakeline to the rearaxle and then splits up, it would be unusual if only one side (always the same) blocked.

That would seem to indicate the problem would be in the splitter or afterward if it is a hydualic issue.

 

[86M10086.2L]

Infidel, I'll have to double check the emergency brake cable. The side that's locking up is the only original cable left. The other was replaced. But while I had the brakes apart replacing the wheel cylinder I don't recall the lever/cable being frozen or stuck. But to be fair I wasn't paying strict attention to it.

 

[86M10086.2L]

Hulk I had both lines off and blew them out with compressed air. No obstruction in either line or the splitter.

 

[doghead]

Almost always, contaminated shoes cause this.

Pull the drums and look again.

Leaks are not always visible outside the drum(enough to cause this).

 

[The HUlk]

Hulk I had both lines off and blew them out with compressed air. No obstruction in either line or the splitter.

I gathered that there is flow on both sides, no leaks, and mechanical items & linings are okay. The point I was trying to make is that an imbalance in flow on one side caused from a partial obstruction may cause the brake force to be different on either side. Such as the pinched line scenario previously mentioned. I may be wrong but figured it could be something tricky to find such as this since you have already spent some time trying to figure it out.