brake pull

99burb · March 6, 2005

need some help with a brake problem...

99 suburban k2500. pulls hard to the left when you hit the brakes. so far have replaced most all the brake components at the wheels (hoses, calipers, rotors, pads, shoes, wheel cyl, etc. it now has complete praise dyno stage 2 kit.) system has been bled/flushed many times. nothing so far has changed the pull.

any ideas?

thanks!

marshall

Ben · March 7, 2005

Mighty fine braking stuff, Praise Dyno Brakeing components, but even the best won't fix this, as the "problem" is elsewhere.

Mainly in two areas.

First the calipers are single piston, so floating type. Needs to center themselves in the rotor center line via the slide tubes on the mounting bolts. Slide tubes has "O-Rings" inside the caliper bore. The O-Rings need to be replaced each time the pads are and they need to be greased with high temp grease.

Two per caliper bolt, four for each caliper. About a buck each O-Ring. Tough to get out and tough to get the new one in. But doable.

New slide tubes might be in order, as the OEM has them pinched onto the bolts as a complete assembly.

Second is that the rear self adjusters don't. Usually will find a GM OBS truck with rear drum/shoes showing the shoes almost brand new. Even over 150K miles and they will look brand new.

Because they haven't been self adjusting and not in the ball game so to speak.

The fronts will be doing 99.99% of the braking and why so many pulling and wrapped rotors.

Best to manually adjust them "tight" and do so at each oil/filter change. I do mine about every two weeks or so. Takes more time to get out the jack & tools than to do the actual adjustment.

I've worked up a solution that has them self adjust, but they are working too good and over tightening. So not ready for prime time, yet.

Other is that the rear cylinders do wear out and need replacement. Not hard nor expensive.

Use DOT4 fluid. ATE better yet but $$$$.

I too have Praise Dyno and can initiate ABS on all four. Just about any time, even on dry pavement. Here's a picture of my LT265/75R16 "E" Michelin LTX-MS after some high speed braking. Notice that the tires have "feathered" and means I have way more brakes than tire. They are on Alcoa/Mickey Thompson Classic 16x10's.

99burb · March 7, 2005

thanks ben. i have been greasing the guide pins, but maybe the o-rings are toast.

my rear brakes had been doing their fair share. pm'd them when i bought the truck and adjust them regularly. i just did the complete (including rear wheel cyl's) praisedyno conversion, so of course, there are no original brake components in the back anymore...;)

i do use dot4, in fact i do use ate...have lots of it around for the race car.

i thought maybe a warped rotor might have been the case, but with everything replaced at once, pull was still there.

the pull is not a gentle one. hit the brakes and the steering wheel immediately jerks to the left. it gets scary when the enclosed car trailer is back there too.

if the pin o-rings aren't it, maybe a blockage in the right front channel of the abs is decreasing the pressure to that wheel?

marshall

Mighty fine braking stuff, Praise Dyno Brakeing components, but even the best won't fix this, as the "problem" is elsewhere.

Mainly in two areas.

First the calipers are single piston, so floating type. Needs to center themselves in the rotor center line via the slide tubes on the mounting bolts. Slide tubes has "O-Rings" inside the caliper bore. The O-Rings need to be replaced each time the pads are and they need to be greased with high temp grease.

Two per caliper bolt, four for each caliper. About a buck each O-Ring. Tough to get out and tough to get the new one in. But doable.

New slide tubes might be in order, as the OEM has them pinched onto the bolts as a complete assembly.

Second is that the rear self adjusters don't. Usually will find a GM OBS truck with rear drum/shoes showing the shoes almost brand new. Even over 150K miles and they will look brand new.

Because they haven't been self adjusting and not in the ball game so to speak.

The fronts will be doing 99.99% of the braking and why so many pulling and wrapped rotors.

Best to manually adjust them "tight" and do so at each oil/filter change. I do mine about every two weeks or so. Takes more time to get out the jack & tools than to do the actual adjustment.

I've worked up a solution that has them self adjust, but they are working too good and over tightening. So not ready for prime time, yet.

Other is that the rear cylinders do wear out and need replacement. Not hard nor expensive.

Use DOT4 fluid. ATE better yet but $$$$.

I too have Praise Dyno and can initiate ABS on all four. Just about any time, even on dry pavement. Here's a picture of my LT265/75R16 "E" Michelin LTX-MS after some high speed braking. Notice that the tires have "feathered" and means I have way more brakes than tire. They are on Alcoa/Mickey Thompson Classic 16x10's.

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Ben · March 7, 2005

Other potentials:

1) Front hose pinched from rust in the frame rail mounting tab that the rubber hose goes through. Holds or blocks pressure.

2) Bad piston and it's sticking (been there done that twice with my Burb).

3) Bleed your ABS system. Actually mine comes on a regular basis, both wet and dry weather. When it's slick, I purposely initiate ABS to get the old stuff out of the ABS system. I don't have a scan tool, otherwise I'd bleed them when doing the rest of the system. Mine actually has better pedal "feel" after an ABS initiated cycle.

4) Uneven bedding in of the rotors/pads. Smearing friction material over onto the rotors and "curing" the friction material (baking out the green resins, etc).

5) Your rears are not evenly adjusted and not "tight" enough. I really mean "tight" as in touching and dragging. Almost too much and if too much will smoke them. I've had vibration from them too tight and so much vibration thought the hood was going to pop open on the freeway. I MEAN TIGHT!!!! when manually adjusting the rears.

The other thing is that your front suspension might be worn and needs rebuild. If so, use Moog HD components. Not that much more and solves many problems. NAPA carries Moog HD as their store "gold" brand, best to ask though.

Ben · March 7, 2005

Forgot, yup if the old O-Rings still in there, they have gone dry and toast.

They will stick to the slide tube and pull like you mention.

Just add that to the list just posted.

99burb · March 8, 2005

i have done all 5 items on your list over the last year, no change in symptoms. at least i am checking/adjusting/replacing the right things!

gonna recheck those guide pins.

what suspension parts need overhaul? truck has 50k miles, fairly certain the previous owner did nothing to it. (classic soccer mom, what she was doing with a k2500 big block i don't know....) i have replaced all the shocks and made sure the zirk fittings got used. you refering to all the rubber bushings and such?

i agree on the abs exercise! the best "feel" i have had in the brake pedal was after using the abs constantly (on purpose) for the better part of an hour on the way home from the office in a snowstorm last month. didn't help the pulling, but felt better!

thanks,

marshall

GM-Tech · March 8, 2005

the pull is not a gentle one. hit the brakes and the steering wheel immediately jerks to the left.

We had a problem with brake hoses in those years. Generally, a hose or stuck caliper will cause a pretty violent jerk of the wheel. A friction type pull will be a more gradual pull. If I had to choose between a hose and a caliper, I'd say 99% are the hose and 1% are the caliper.

Couple of things that usually happen when it's a hose. First, when you step on the brake it can yank the wheel out of your hand. Then, if you don't release the brake, it will straighten out. Then, when you release the brake it will momentarily pull to the other side, though gently and sometimes you may not notice this if you have a death grip on the wheel.

Go into some big empty parking lot and take your hands off the wheel and brake. No need to slam 'em on, just enough to make 'em pull. Watch the steering wheel. Does it tend to straighten out after a few seconds and then go right when you release the brake?

What happens is that the inner liner of the hose starts to delaminate. It allows some fluid through, but slowly, hence the tendency of the wheel to straighten out after a few seconds when the pressure levels in that caliper finally catch up to the other side. Then, it tends to hold the fluid in and the caliper applied when you let off the brake, making it go the other way until the pressure finally escapes.

Ben · March 8, 2005

Forgot about those hoses deteriorating interanlly!!!

Changed mine to stainless hoses from Praise Dyno Brake.

Tough to find them. They will be found, but not in stock and/or delays in shipping.

Praise Dyno is almost always "out" of stock, as they supply the majority of the Hummer's over in Iraq. Since "defense" related, when an order comes in, takes priority over anything 'civilian'.

Stainless hoses makes a huge difference in pedal feel too.

For those who don't know, not stainless hoses, but braided stainless weaving over a higher spec hose. Less ballooning, so more pedal effort gets to the pads.

99burb · March 9, 2005

the symptoms gm-tech described are very close to what i have. pull hard left on initial brake, straightens out if i stay in the brakes. it seemed as if fluid pressure was slow coming to the right front due to a restriction, but built eventually.

based on what i had heard and read, brake hoses were the first thing i tried. replaced those last year. no change to pull. then replaced the calipers as i thought it might be a sticking piston. no change to pull.

quite literally, i have replaced every moving/soft part of the front and rear brake system at the wheels (except those o-rings on the caliper pins which i will try this weekend!). alldata talks about a "brake hardware kit" that should be replaced when doing calipers. is that the pins, orings and bolt seals?

suspension stuff maybe? abs pump a possible culprit? it seems to work ok.

marshall

Ben · March 9, 2005

Double check the hose clips. They rust and close down on the hose to pinch it off. Ruins the hose.

If suspension lifted, then did you go with longer hoses? What brand/kind/etc?

Other highly likely is stuck/sticking caliper piston. I've had them stick right out of the box (rebuilt). For this try the old "C" clamp bleeding cycle on both. Frees the piston "for now" and flushes. Careful to make sure and loosen the bleeder screw and not push back old fluid into the ABS valves, as they HATE that and go bad pretty soon after.

Finally, CHANGE OUT THOSE OLD CALIPER O-RINGS !!!!

Ben · March 9, 2005

PS...I fill the cavity between'm inside the caliper with mixture of mobil 1 synthetic and high temp disc brake grease.

Keeps them plyable longer.

GM-Tech · March 9, 2005

suspension stuff maybe? abs pump a possible culprit? it seems to work ok.

Boy, this sure sounds like a hose/caliper problem. In all my time, I have seen exactly one abs unit cause a pull, but it wasn't a pull like one gets with a restricted hose or stuck caliper. It was more of a gradual pull like one gets with braking friction that is not equal side to side. And that one would temporarily correct if you put it through an abs activated stop.

A really loose suspension component could cause a similar jerk to the left, but I wouldn't expect that to straighten out after the initial pull.

If I had the truck in the shop, I wouldn't be happy until I replaced the brake hoses, no matter how long ago you put them on. I'd want to see that not fix it for myself.

99burb · March 10, 2005

suspension stuff maybe? abs pump a possible culprit? it seems to work ok.

Boy, this sure sounds like a hose/caliper problem. In all my time, I have seen exactly one abs unit cause a pull, but it wasn't a pull like one gets with a restricted hose or stuck caliper. It was more of a gradual pull like one gets with braking friction that is not equal side to side. And that one would temporarily correct if you put it through an abs activated stop.

A really loose suspension component could cause a similar jerk to the left, but I wouldn't expect that to straighten out after the initial pull.

If I had the truck in the shop, I wouldn't be happy until I replaced the brake hoses, no matter how long ago you put them on. I'd want to see that not fix it for myself.

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so where is your shop in florida? i lived in south florida for a long time. coral gables and pembroke pines. now i am freezing up here in va.

based on your input, i went out today and purposely tried your test a few times. i must of been imagining the return to straight after initial pull. it just keeps drifting left under braking. i also excercised the abs fully a few times. the pull almost went away for several stops afterwards and the brake pedal felt firmer. i just got home and read your symptoms of the one abs pump failure you have seen. hmmm, this may be the second......

now having read your abs symptom descriptions, i am going to test again tomorrow.

really appreciate the continued help in the diagnosis! you guys are great!

marshall

GM-Tech · March 10, 2005

so where is your shop in florida? i lived in south florida for a long time. coral gables and pembroke pines. now i am freezing up here in va.

based on your input, i went out today and purposely tried your test a few times. i must of been imagining the return to straight after initial pull. it just keeps drifting left under braking. i also excercised the abs fully a few times. the pull almost went away for several stops afterwards and the brake pedal felt firmer. i just got home and read your symptoms of the one abs pump failure you have seen. hmmm, this may be the second......

now having read your abs symptom descriptions, i am going to test again tomorrow.

I'm a bit south of the Gables, but I'm freezing too! It plummeted into the 50's today when a cold front came through. Too late in the season for that! Been rainy all day too, but we really need the rain.

Ummmm... friction problems will sometimes clear up after several hard stops... such as ones you might make trying to activate the ABS.

In fact, I've fixed more than a few of these brake pulls by going out on the highway, getting up to 60 or so and then stopping just as fast as I could without locking up the brakes or kicking in the ABS. I'd do that a half-dozen times, allowing a couple miles of driving in-between to make sure the brakes cool off. This "burnishing" in sometimes works. But if you've had this problem for a year, it's probably beyond that.

Ben · March 10, 2005

........In fact, I've fixed more than a few of these brake pulls by going out on the highway, getting up to 60 or so and then stopping just as fast as I could without locking up the brakes or kicking in the ABS. I'd do that a half-dozen times, allowing a couple miles of driving in-between to make sure the brakes cool off. This "burnishing" in sometimes works. But if you've had this problem for a year, it's probably beyond that.

this is called "bedding in" the green rotor and green friction materials.

I'm not home right now and will post the bedding process later.

Racers used to be the only folks who knew/did, but with todays higher and higher performance materials, bedding in is becoming more critical to the general public.

Bedding in is the curing of the friction material (mainly the bonding agents) and the smearing of friction material onto the cast iron.

Why going out on the freeway and nailing the brakes ***HARD*** and *NOT* letting the vehicle stop rolling while the friction material is outgasing cures most bedding issues.