1999 GMC Suburban 1500 4WD brakes pull right

[chestervan]

Hi there,

I have an early 1999 (8th gen, '92-'99) GMC Suburban ½ ton that has had a pull to the right for years. I've had several shops try to fix it, including the dealership, to no avail. What I know is that the right rear brake is working too hard. It seems to engage when the pedal is first depressed, the front swings right, and then somewhat evens out as the pedal is depressed harder. The right brake actually locks up if the road is wet, and the ABS kicks in. It also gets hotter (quite hot with just a short drive) and wears the tire quickly. I've changed right shoes, drum, wheel cylinder. A shop recently replaced my master cylinder, and said it was fixed but after picking it up I left on an errand that was about 200 miles with the right rear grabbing and smelling hot. I've ground the grooves out of the right backing plate. Because I know the right rear is grabbing I've not paid much attention to the front but I just did a test on my driveway (concrete) braking hard until the ABS kicked in and was surprised to see not only skid marks from the right rear but also some marks from the front right.

I've read on the forum here about replacing proportioning valves. But I don't believe mine has one. From what I can tell there is one brake line going from the ABS module to the rear, where it splits on the rear axle. There are two lines coming from the ABS unit to the two front calipers. Am I missing something?

There is no sign of damage to the lines from the split on the rear axle to the master cylinders.

My main questions are: 1) Is there a proportioning valve I'm not finding? 2) In the absence of a proportioning valve, could the ABS unit be sending too much pressure to the rear or to one front caliper? 3) Are solid brake lines not showing any sign of compression or damage likely to get "clogged" up (yet still bleed as expected)?

My next steps are going to be (unless I'm guided otherwise):
1) Check front calipers. I've replaced them both not too long ago but I'll ensure neither are sticking.
2) Replace front brake hoses.
3) Replace left rear wheel cylinder and shoes and grind out grooves in that backing plate.
4) Try to find a shop that can test the brake fluid pressure side to side and front to rear.

I don't know what else to do and I don't seem to find a shop that can help me.

Thanks in advance.

 

[MrMarty51]

Hello Chestervan.
I dont have ideas on what could be the matter with them brakes.
Chiming in to say hello and welcome to the forum.

 

[ak diesel driver]

The proportioning valve is internal to the ABS. Possible different size wheel cylinders from side to side? Leading and trailing shoes reversed?

 

[MrMarty51]

The proportioning valve is internal to the ABS. Possible different size wheel cylinders from side to side? Leading and trailing shoes reversed?

Yeah, brake shoe with the short lining goes to the front.

 

[MrMarty51]

If there is any differential lube getting on those brake shoes, that can cause them to lock up.

 

[chestervan]

Hello Chestervan.
I dont have ideas on what could be the matter with them brakes.
Chiming in to say hello and welcome to the forum.

Thanks! I have an '83 K30 and '99 Suburban and this seems to be one of the best forums for discussing and learning. Glad to be here.

 

[chestervan]

If there is any differential lube getting on those brake shoes, that can cause them to lock up.

I did have that a couple years ago, but I've replaced the axle seal and shoes/drum so I don't think that's the current issue. Thanks!

 

[chestervan]

Yeah, brake shoe with the short lining goes to the front.

I'll double check that. I'm sure the right side was correct before it went to the shop, I've not paid as much attention to the left. Thanks!

 

[chestervan]

The proportioning valve is internal to the ABS. Possible different size wheel cylinders from side to side? Leading and trailing shoes reversed?

Thanks for the info about the proportioning valve. I'm going to replace the left wheel cylinder too so I'll know they're the same, and double check that the short shoe is on the front on both sides. Thank you!

 

[Rockabillyrat]

This sounds like a bad left front brake hose to me. It could be restricting fluid flow when initially pushing the pedal causing the pull to the right. We run into this issues alot at the shop. I would double check the adjustment on the rear too. 20 years as a mechanic I've only see one ABS unit cause a pull.

 

[Will L.]

I am not a fan of using the parts cannon (just throwing parts at a problem)
But a couple things to do here before that starts.
Check items listed above- all are plausible.

So getting a pressure gauge on there is a good idea at this point. Amazon and other places have kits for under $100. You remove one bleeder at a time and install the gauge. Have some apply the brakes while you read the gauge.
If you determine the size bleeders you have, sometimes you can buy just that adapter or have a hydraulic hose made with that size fitting- then just buy a 3,000 psi gauge.


This is an old truck so brake line deteriorating is a serious probability. So restrictions inside the lines is also.

You are already good with replacing the two rear wheel cylinders- I would say replace the Two hard lines and the Tee that connects them as well. That nickle copper line is a lot easier to work with than stainless. A restriction in one of those two lines or something plugging the T can cause this. If replacing the cylinders anyways- do this at same time.

While shooting the parts cannon- replace the two front rubber hoses. While tempting- don’t so it at exactly the same time. Do the front hoses first, flushing the front system of new fluid and get the system working. Then do the rears if the front hose does repair it.
The front hose damage is the most common, and rubber hose deterioration is the most likely. The idea behind the rear locking from a bad front hose is there is resistance in the hose building pressure but not applying brakes on the left front. So the right front is braking which pulls right, and as more brake is applied the abs acting as proportion valve sends more pressure to he rear, causing the lock up. The only part of this theory that throws a curve ball is both rears should lock- not just the right.

As mentioned the proportioning is done by the abs unit. I don’t think you have a problem with the abs because it is a single line going to the rear axle, which splits to the two tires. Then pressurized the front is maxing And your abs is activating like it should.

A ton of pictures posted would be a good thing here. We realize the frustration you must have- please be sure to post details when solved so someone else sees the results in th future to ease their chaos

 

[jrsavoie]

I did have that a couple years ago, but I've replaced the axle seal and shoes/drum so I don't think that's the current issue. Thanks!

Better check. I had a new bad axle seal out of the box on the 98 Suburban once

 

[dbrannon79]

Welcome to the forum @chestervan sounds like you've been pointed in the right direction. sometimes we have to think outside of the box on these rigs. if a wheel or two are breaking better than the other. check the opposite side for issues like mentioned above rubber brake hoses and blockages in the line.

one other thing I didn't see others mentions for the rear shoes is the shoe adjusters. make sure both sides are equally adjusted with the same resistance. if the right side is adjusted slightly too tight causing some drag while whoever installed your shoes forgot to adjust the left side and it's totally too loose. this can cause the same effect.

 

[MrMarty51]

Welcome to the forum @chestervan sounds like you've been pointed in the right direction. sometimes we have to think outside of the box on these rigs. if a wheel or two are breaking better than the other. check the opposite side for issues like mentioned above rubber brake hoses and blockages in the line.

one other thing I didn't see others mentions for the rear shoes is the shoe adjusters. make sure both sides are equally adjusted with the same resistance. if the right side is adjusted slightly too tight causing some drag while whoever installed your shoes forgot to adjust the left side and it's totally too loose. this can cause the same effect.

Some PO or mechanics shop left the slack adjuster springs out on My 2000 K3500. Springs that goes between the brake shoe self adjuster lever and whatever the other end sets against. The shoes would constantly back off. Pulled the drums/hubs and discovered that.
It could also be possible that there is the wrong slack adjuster on that side, a right side adjuster on the left side would continually tighten that set of shoes.

 

[chestervan]

This sounds like a bad left front brake hose to me. It could be restricting fluid flow when initially pushing the pedal causing the pull to the right. We run into this issues alot at the shop. I would double check the adjustment on the rear too. 20 years as a mechanic I've only see one ABS unit cause a pull.

Thanks, that's good to know.

 

[chestervan]

Better check. I had a new bad axle seal out of the box on the 98 Suburban once

I've had it apart many times since replacing the seal and it's always been dry. It does act about like that, though. I'll take a closer look for any evidence.

 

[chestervan]

I am not a fan of using the parts cannon (just throwing parts at a problem)
But a couple things to do here before that starts.
Check items listed above- all are plausible.

So getting a pressure gauge on there is a good idea at this point. Amazon and other places have kits for under $100. You remove one bleeder at a time and install the gauge. Have some apply the brakes while you read the gauge.
If you determine the size bleeders you have, sometimes you can buy just that adapter or have a hydraulic hose made with that size fitting- then just buy a 3,000 psi gauge.


This is an old truck so brake line deteriorating is a serious probability. So restrictions inside the lines is also.

You are already good with replacing the two rear wheel cylinders- I would say replace the Two hard lines and the Tee that connects them as well. That nickle copper line is a lot easier to work with than stainless. A restriction in one of those two lines or something plugging the T can cause this. If replacing the cylinders anyways- do this at same time.

While shooting the parts cannon- replace the two front rubber hoses. While tempting- don’t so it at exactly the same time. Do the front hoses first, flushing the front system of new fluid and get the system working. Then do the rears if the front hose does repair it.
The front hose damage is the most common, and rubber hose deterioration is the most likely. The idea behind the rear locking from a bad front hose is there is resistance in the hose building pressure but not applying brakes on the left front. So the right front is braking which pulls right, and as more brake is applied the abs acting as proportion valve sends more pressure to he rear, causing the lock up. The only part of this theory that throws a curve ball is both rears should lock- not just the right.

As mentioned the proportioning is done by the abs unit. I don’t think you have a problem with the abs because it is a single line going to the rear axle, which splits to the two tires. Then pressurized the front is maxing And your abs is activating like it should.

A ton of pictures posted would be a good thing here. We realize the frustration you must have- please be sure to post details when solved so someone else sees the results in th future to ease their chaos

Thanks, these are helpful ideas! I really appreciate your thorough input.

 

[chestervan]

Some PO or mechanics shop left the slack adjuster springs out on My 2000 K3500. Springs that goes between the brake shoe self adjuster lever and whatever the other end sets against. The shoes would constantly back off. Pulled the drums/hubs and discovered that.
It could also be possible that there is the wrong slack adjuster on that side, a right side adjuster on the left side would continually tighten that set of shoes.

Interesting. Hadn't thought about a wrong adjuster. Will check but just from my recollection putting it all together they seemed to be correct.

 

[chestervan]

Welcome to the forum @chestervan sounds like you've been pointed in the right direction. sometimes we have to think outside of the box on these rigs. if a wheel or two are breaking better than the other. check the opposite side for issues like mentioned above rubber brake hoses and blockages in the line.

one other thing I didn't see others mentions for the rear shoes is the shoe adjusters. make sure both sides are equally adjusted with the same resistance. if the right side is adjusted slightly too tight causing some drag while whoever installed your shoes forgot to adjust the left side and it's totally too loose. this can cause the same effect.

I've been thinking about that possibility - that the right rear is actually doing what it's supposed to and the others are the problem. I've adjusted both sides the same, though.... But if for some other reason it is doing most of the work, then getting hot, then grabbing more because it's hot....

 

[chestervan]

Thanks everyone, you guys are amazing. Here's my update:

I replaced the left wheel cylinder and both front flexible brake lines, and bled the system thoroughly. So both sides in the rear now have new shoes and wheel cylinders, and the right side a new drum as well. I believe I found evidence that the last shop (after replacing the master cylinder) hadn't bled thoroughly (left caliper had real old fluid in it). I do feel the pedal is better, but otherwise the brakes are unchanged.

I should add that the right rear grabbing is much more pronounced after driving for a few minutes, which is probably why the shops aren't picking up on it if they're not test driving far enough. A few minutes at 45 with stop lights and it's very obvious. Which does raise the possibility in my mind that the right rear (and front) is actually working properly and the left side is not doing it's part? When the drum gets hot enough it's grabbing more? It's hot enough that it smells of brake lining.

So I think my next step is indeed to get some measurements of brake fluid pressure at each position. The idea that the tee or hard lines in the back could be causing this is somewhat weakened by the fact that both sides bleed just fine. I'd think that if there were a restriction it would manifest then, not just when braking when the actual flow is minimal. But I could be wrong? I may go ahead and replace them just to eliminate that possibility. They are almost a quarter century old, after all.

Thanks again to all who've contributed ideas. I need to get better at taking pictures. I'll definitely keep you all updated.