Brakes Drag when Engine Warms

[StevenPH]

I'm having trouble diagnosing my sporadically dragging brakes on my 89 Jetta 1.6.

When the engine warms up, usually after about ten miles on the highway, the front brakes start to drag. I've always noticed increased pressure on the front passenger brakes (I went through my last set of pads in about 6 months), but only after replacing the pads this last time two weeks ago did this new occurrence begin.

When cold the brakes act normally; there is normal give and return on the pedal, and the car accelerates fine. But after about ten minutes (whether or not i'm even using the brakes, i.e.. on the highway) they start to grab and drag, and pretty soon i'm stuck at 55 on the highway with black smoke pouring out the tailpipe and the engine running as hot as it does on a mountain pass. When this happens the pedal tightens up - it still depresses and returns, but it is very noticeably tighter.

I've raised the wheels while the engine is hot, and can't budge the PS wheel. It's burning hot. The DS is hot and doesn't spin freely, but i can move it.

I let the engine sit a few hours or overnight, and the brakes are fine again in the morning.

A couple other notes:
- I replaced both front calipers, rotors and pads, greased all moving parts, and flushed and refilled the brake fluid two days ago and nothing has changed.
- While bleeding the brakes I confirmed that all hoses are unobstructed. Though the PS hose is older but has no visible wear. I replaced the DS hose last winter due to visible wear.
- I don't know the age of the master cylinder, but it looks new (was very clean when i purchased the car)

My next step is to replace the master cylinder and the PS hose - but what i can't figure out it what the driving time/engine temperature has to do with it....

Thanks in advance for any ideas!
Steve

[82vdub]

I'd be willing to bet that the problem is within the transmission, CV's or wheel bearing. Since it's eating brake pads, I'd look at the wheel bearing first. If it's brakes and they are grabbing the rotor, the car would be very heavily pulling to one side (PS) as that seems to have more drag, but you don't mention this. Plus, a couple times of this happening, and the brake rotor would be so warped that the pedal would pulse. I can't think of any reason why the master cylinder would be effected this way with heat. I would think that the brake fluid would boil, and you would lose brakes if it was a heat issue. That's why I'm suspecting it's something at the wheel generating heat and causing the symptom to translate into the brakes??

Do you have an infrared thermometer? See if you can measure brake temps at the rotor, caliper, wheel bearing (spindle area), axle shaft (both ends) and the transmission. Your probably only have to go up the road a mile and stop to measure temps. I'd do this with using as little brakes as possible to try not to "influence" your temp readings. This should give an indication on where the heat is starting from first.

[StevenPH]

Interesting. Thanks for writing. All of these could make sense - i have a fresh tear in the PS outer CV boot, and have suspected the PS wheel bearing may be going. The DS axle is only a year old, but has had grease leaking out from under the boot on the outer CV joint (i've wondered about this because it's the second remanufactured axle i've put on it and it keeps leaking grease after only a few months). I have some weeping gear oil out of the DS tranny seal, but have kept a close eye on the levels and replaced the oil about 10,000 miles ago.

I was planning on replacing both axles and wheel bearings anyway, so i'll just do that ahead of schedule and see if it helps the brake issue.

I'm curious though - how would a bad CV joint or wheel bearing wear out the brake pads so fast? And how would that affect the pedal play?

[82vdub]

I can't explain how any of these would cause the premature break wear. I would still try to diagnose where the heat is coming from first to do your best at finding where the problem is.

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You said "when the engine warms up"... a simple test would be to start a cold engine, and let it come up to full temp without driving it and without touching the brakes. I would bet that its not the engine producing the heat, but the heat is from friction either in the brakes or wheel bearings. Sticky caliper is my first thought but you covered that.
The only way engine temp can effect braking is if a brake line is too close to the exhaust or something like that.
....although I just had another thought: Vacuum? Is it possible that engine vacuum is not releasing and so each tap of the brake causes the pads to get tighter and lock. Same symptoms of sticking caliper, but a different cause. Ive never heard of this happening, but I was just brainstorming how the engine and brakes are connected.

[TylerDurden]

Ja, I would disconnect and plug the vacuum line going to the booster, and see if the problem occurs.

Be safe... the brakes will have no assist.

[StevenPH]

Thanks for the ideas - this one has me baffled.

Did a couple tests today that point to a bad wheel bearing.

I drove until the problem occurred, then stopped and took the wheels off. The PS wheel/rotor/caliper/hub was too hot to even touch, and the rotor wouldn't budge. The wheel well reeked of burning brakes. The axle shaft was warm but not abnormally hot. Tranny and DS wheel assembly were hot but not anywhere close to the PS. The master cylinder and fluid reservoir were not abnormally hot.

I took off the DS calipers and the rotor turned again, no noises or grinding. I disconnected the brake hose and the brake fluid was smoking hot. Not much, if any, fluid came out when i disconnected the hose from the caliper, so suspecting a plugged hose replaced it (and the brake line - it was old enough that the union between the two was inseparable). Went for another drive and after ten minutes on the highway still the same problem.

My only thought here is that the bad bearing is heating up the wheel assembly so much that it is causing the brakes to bind somehow - maybe inhibiting the caliper return? Expanding the brake pads? This is the part that doesn't make any sense to me. That and the fact that the car does not pull at all when the problem is happening. The lack of pulling is so odd because when hot and the DS wheel is bound up, the other wheels move just fine.

I will check the vacuum possibility - but my wonder is if the problem was located in the master cylinder/vacuum assembly, wouldn't it affect all the brakes at least somewhat?

One more mystery - if it IS the wheel bearing, it has produced no other symptoms at all. No looseness or wobbling, no hum, rumble, grinding, nothing. There has been a very intermittent squealing, not too loud, most often at low speeds, but until now i've always attributed it to the brakes, since it goes away immediately when brake pressure is applied.

I've heard of bearings going bad without making their classic sound, but it seems odd it would get this bad without any symptoms other than the heat.

Thanks again for the help.

[Dakotakid]

Take the master cylinder off and shorten the rod going into it.

[StevenPH]

I've read about this - a couple questions on it:
if i trim some off and it isn't necessary would i be risking having to replace my master cylinder?
Would you have a suggestion for how much to cut off?
Would it be possible to put in a couple washers on the mounting bolts to test the theory? I've never pulled the master cylinder off so i'm not sure if this would even be possible.

thanks

[bscutt]

I'm not sure on the VW but some master cylinder rods are adjustable - they have threaded portions. This actually reminds me of a problem I had on my old 1951 Chevy pickup where the master cylinder bore was apparently worn to the point that the rebuild kits would not seal when the brake pedal was fully released so I would lose pedal pressure. I "fixed" it by adjusting the rod slightly to push the piston a little more into the bore. What then happened was that after driving for a while the brakes would start to lock up and I would have to stop and just stand on the pedal for a minute to force the master cylinder to compress a little and then the brakes would stop dragging. I believe the brakes were heating up and causing them to engage. I got the problem to go away by essentially shortening the rod on the master cylinder back down to just the right point. So it is possible the there could be a problem with the master cylinder rod. It's worth checking. If you shimmed out the master cylinder it might cause a vacuum leak on the booster but it's worth a try

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Dont cut the Master cylinder rod, Even if it does fix the problem, you would be treating the symptom, not the disease.
The rod did not grow longer, why would you cut it? Something else is worn out.
They are fixed length and not adjustable on late models.
If you cut it, be prepared to replace it in the future.

Another thought, have you checked the pedal return spring?

[StevenPH]

Checked the pedal return spring - functioning normally as far i as i can see.

I unplugged the vacuum hose, drove ten miles and the brakes seemed to do much better. No smells, no sluggishness. The vacuum pump is the post 84 kind, that isn't supposed to need replacing, but it's obviously been there a while - it has a fair amount of rusting on it.

Does this point to a new vacuum pump? New booster?

Are there any do-it-yourself tests i can perform on the pump before replacing it? The new ones aren't cheap.

On a side note - after the the 10 mile test drive i was inspecting the area and there was a substantial oil leak - it looked as if oil was coming up out of the dipstick, running down the dipstick sheath and all over below it. Probably a couple tablespoons of oil in ten miles. It definitely wasn't there when i left.
Could that have been related to pulling out the vacuum hose? I detached it up were it connects to the vacuum booster, and there was no oil around the pump itself. I've never had a leak there before, so it seems far too coincidental to be unrelated to the vacuum hose.

I'm headed to a car wash now to hose down the area and see if can't pinpoint the source.

If that weren't enough - i've also noticed a slight shimmy in the steering wheel above 65 mph. Anyone have thoughts on how that might be related?

Thanks

[82vdub]

If you pulled the vacuum hose from the brake booster, then the vacuum pump was pulling as much air as it can from atmosphere, and pushing that into the block. That's probably where the oil from the dipstick tube is originating from. Do you have a lot of blowby pressure inside the engine block from combustion blowing past rings normally?

The shimmy may be from lots of things, one of them being a warped brake rotor. Do the brakes pulse when you use them?

I still think that running the car for a short distance and using an infrared temperature sensor is the best way to determine where the source of the heat is coming from - or getting a professional opinion on the issue and you fix it yourself.

[StevenPH]

I dont know what blowby pressure in the engine is - but I do often find the dipstick pushed up out of the tube an inch or so. And I get a good amount of black smoke in my exhaust when accelerating hard - more than Ive had with any other diesel jetta of this age. My head gasket has started to weep oil consistently, but no coolant mixing with oil at all yet.

No pulsing in the brakes at all.

I'll pick up a heat sensor and try that method. I think a professional opinion might be a good way to go - most of my remaining options are pricey ones and I'd hate to fix what isn't broken.

[82vdub]

I would think that your brake rotors would warp pretty quickly, if the brakes were dragging so much that they got hot enough to severly slow down the vehicle. I still think it's something else.

The pushed up dipstick indicates that there's blowby and pressure in the block. This, coupled with a weak vacuum pump (or low oil pressure) could possibly contribute to a brake issue. However, I'm still not sure it's brakes though.