Momentary Pull to the Left when Brakes Applied Quickly

[macinlover]

I have a 94 AWD Astro van that momentarily pulls to the left when the brakes are applied quickly. I’ve replaced the right front caliper and pad, flushed both front and rear brake lines, and bled air from the system, but there’s no apparent change in the symptoms. The van only pulls to the left momentarily (approximately: 0.5 sec) if the brakes are applied quickly. Increasing brake pedal pressure gradually, over a couple of seconds, results in no pull. Removing the ABS fuse, has no effect on the symptoms. The vehicle steers and handles normally, otherwise. This problem began after the van had sat idle for several months.

I suspect a restriction in the line to the right front caliper is causing the problem, but I’m not sure of the easiest way to locate just were this restriction lies, if this is in fact the case. Any thought on just what is going wrong or how to debug my brake system problem further, would be appreciated.

[spongebob218]

Could be the RF hose. If there is a restriction, it is most likely in the hose(partially collapsed), not in the metal lines. Bad suspension components like idler arms or shocks could cause a pull under braking sometimes also.

[WVKayaker]

Broken ball joint caused my pulling...have your front end looked at

[astro355]

Is there a reason why you replaced on the pads on the right side? Change the pads on the left side also and see if it still does it. My 'guess' would be that since the left pads are broken in, they grip better than the new right side ones.

If there was a restriction in any of the hoses, not only would the brakes be slower to grab the rotor, that caliper would also have a symptom of releasing the rotor slow also.

[Matrixx]

Hi macinlover

Welcome to the Forum

Some good pointers given so far to look at. This happens to me from time to time and it's "usually" a sticking caliper that has the momentary pull to that side when you apply the brakes. That caliper should be looked at as well. The usual cure is replacing the caliper (or it is with mine). If it does turn out be a stiff caliper, then I would suggest replacing it. I replace both front calipers at the same time, their cheap enough. Hope this helps.

[macinlover]

Is there a reason why you replaced on the pads on the right side? Change the pads on the left side also and see if it still does it. My 'guess' would be that since the left pads are broken in, they grip better than the new right side ones.

If there was a restriction in any of the hoses, not only would the brakes be slower to grab the rotor, that caliper would also have a symptom of releasing the rotor slow also.

The brake rotor on the right front side was scored, as though at sometime in the past the pads had wore out and there was metal to metal contact close to the outside diameter of the rotor. This rough part of the rotor had chewed up the pad area near the outer edge, reducing the amount of pad area in contact with the rotor during braking. I thought that might be what was causing my left pull during braking, and replaced both the rotor and the pads on the right front side, but that did not fix the problem. I replaced the right front caliper, thinking that perhaps it was sticking, and that's what was causing the pull. But there was no preceived difference between before replacement and afterward. I still had the brake pull problem.

I like your excellent comment regarding a restriction in one of the lines to a caliper causing that caliper to be slow to release, and hence cause a pull to the opposite side when the brakes are release abruptly. I ran a test tonight, to see if I could detect such a pull, but didn't feel any.

I think that puts my fluid restriction hypothesis to rest. I notice when I first ran the brake test, there was no noticeable pull to the left for abrupt braking. It's been raining here this evening, and the brake rotors where probably damp. Once they dried out, the pull was back for an abrupt application of the brakes. I took a hose, and wetted the left front rotor again, and my brake pull went away, until the rotor dried out.

That test seems to favor your hypothesis that the pads in use on the left side have a greater coefficient of friction, than those on the right. But I'm still wondering why the vehicle tracks perfectly straight ahead, when I release the steering wheel, and apply the brakes gradually, until I've got enough force on the brake pedal to energize the ABS. It seems to me a coefficient of friction difference ought to show up for the gradual application as well. Also, it's been more than six months, and 6,000 miles, since I replaced the right pads, so I would have expected those to have worn in by now.

I'll try changing the brake pads on the left, since that doesn't cost much in terms of time, and post how that turns out.

Mark

[Matrixx]

Hmmm, I'm blind in one eye and can't see out the other at times. I didn't see your mention of replacing the front right rotor and pad until now. The difference in shoes and rotor thickness between the 2 could cause the pull as well. There is less fluid in the caliper cylinder with the new rotor and shoes on it, and more fluid in the caliper cylinder with the old rotor and shoes.

This hydraulic imbalance can cause the slight pull you mentioned. That's why it's so important to replace things in pairs when it comes to brakes. Please keep us updated, Thanks.

[astro355]

Yes, that's why I asked. As Matrixx already mentioned, anytime you replace the pads and/or rotor on one side, you should do both sides. Differences in the manufacturer of the rotors, pads, thickness of pads, pad material, etc will cause this type of problem.

[maximus7001]

I have had the same problem but much worse. Changed both calipers, rotors and pads with no change. It got so bad that after stopping the right front caliper would not release for a few seconds while being honked at for not moving yet. Changed both front brake hoses and that fixed it for good.

You need to change both hoses. I changed just the right one first and the pull switched sides.

Lately the rear brakes have started doing something similar. I will have to change the rear hose as well.

[rich1902]

It's your brake hose, replace both of them.

Rich

[astro355]

It's your brake hose, replace both of them.

Rich

Honestly, lets keep this simple. The OP only replaced the pads and rotor on the right side. Replace the left side and then go from there.

[macinlover]

I wanted to thank all of you who sent suggestions for possible sources of my brake problem. It will be at least several weeks before I have time to get back on this problem, but when I do, I'll post an update.

Mark

[gwd]

Hi
I had the same problem with my 1993 AWD. It end being the brake hose that was causing the problem. I changed them both.
Later on I had a problem with the master cylinder that the rubber inside was rotting of old age and started to have braking problems again. Replaced it then problem went away.

[macinlover]

My momentary brake pull to the left, was caused by a restriction in the right front rubber brake hose, as many of you predicted. This was the first part I checked out after the recommendations made here. When I removed this hose, I tried blowing air through it, with almost no flow. I installed a new hose, which restored the brakes to perfect working order.

The hardest part of replacing this hose, is installing the metal retainer clip that holds the metal portion of the hose against the upper mount, where it interfaces with the metal pipe. I worked for over an hour trying to get the retainer clip back on, with no luck. There's very little room to maneuver the clip back in place, and I never could get it to go into the groove on the hose assembly. Perhaps the replacement hose was a bit different. I ended up fabricating a retainer to hold the metal part of the hose in place.

Replacing this hose would have been a farily easy job, if not for the problem of being unable to get this retainer clip back on. The second retainer clip, positioned near the mid point of the hose, was much easier to install.

Below are some pictures of my brake hose replacement project.

The retainer I fabricated to hold the hose end in place.


This pic shows the metal pipe which has threaded end fitting that screws into rubber brake hose metal end fitting.


New hose installed. There's a second retainer, which holds the rubber hose against the mount on the swing arm, at roughly the mid point of the hose.


Brake hose connection on caliper.

[Matrixx]

Those are great pictures macinlover, Thanks for posting them.

[eustisgoober]

All,
While I’m still in a learning phase on these vans (meaning you can’t know it all) There are some very good points made in this thread. Macinlover, the responses that were posted by Spongebob 218 Matrixx and Astro 355 were all very good advice. And before I babble on here let me say it was pointed out a few times about different thickness pads, same supplier etc… In my humble opinion you can only expect the brakes to react the same if the same material is installed on both sides. Example, the Rotors should have the same surface area, and both are about the same thickness (within reason). There is a minimum spec for this on the rotor itself. Brake pads should be the same thickness, supplier and lot number. This way the pad composite is the same on both corners. Wheel bearings also play a part in this with the amount of play / drag. This will only be felt in a dynamic state and not when testing statically. With the above being said I would approach this condition this way. Have someone apply the brakes and see if you can feel one of the front wheels lock up first. If you can it “could” be a hose. However before I would replace the hose I would flush the brake system and then re-evaluate ( I do this every 2 years along with my coolant regardless of miles traveled). My reason for this is simple; brake fluid collects moisture, which can be internally corrosive and damaging to the system. Remember the ABS system comes into play here and the internal proportioning valves can stick or hang up with in this non-serviceable unit. If the fluid makes no change then I would inspect the rear brakes for proper function. If ok I would then install both front hoses and at the same time “exercise” the calipers to ensure they are free. This should resolve the concern. If not by now you would have already completed a front-end check. I would start checking the suspension more closely because I only have brake hoses and brake fluid invested, not a big deal.
Please let us know what happens, sorry for the long rant. BTW, while I'm not GM / Chevy certified I do work on cars for a living. So preventative maintenance is very important to me. I don't like replacing expensive parts! Maintaining a good PM program is the best way to approach things from my point of view.

[visitor]

It's your brake hose, replace both of them.

Finally got around to replacing front brake hoses here and we're back to even braking after months of that slight pull ThaNX for all the help here

[rev_les]

common sense dictates on something like this, if you're going to change one, they're the same age... change them both, as the other one's surely not far behind.