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-   -   W126 brake pull (http://www.peachparts.com/shopforum/showthread.php?t=67735)

Brian Carlton 06-16-2003 03:44 PM

W126 brake pull
 
I have a pull to the left on the W126. The pull is proportional to brake application. With light braking it is non-existant. With moderate braking it is slightly noticeable. With heavy braking it is quite apparent.

I have performed the following to diagnose:

1) Taken all the pads out, thoroughly cleaned and lightly lubricated all the caliper slides and pins.

2) Verified that all eight pistons will easily retract into their bores.

3) Replaced the rear pads (down to about .100).

4) Confirmed that none of the pads are "hanging" after the brake pressure is removed.


It would appear to me that neither the calipers nor the brake hoses are the culprit here. Any other ideas would be greatly appreciated.

Brian Carlton
1984 300 SD

psfred 06-16-2003 10:04 PM

Sure sounds like no brakes on one side, but these cars have zero or negative offset steering, so effects are usually minimal.

Things to look for:

Plugged or "Ballooning" brake line, so you only have brakes on one side.

Bad track rod bushings, or bearings, or maybe bad control arm bushing so control arm moves back on braking, changing the toe.

Rear brakes only working on one side.

Peter

Brian Carlton 06-16-2003 10:30 PM

Peter:

I sort have ruled out a plugged brake line because of the ease in which all eight pistons were able to be pushed back into the cylinders in order to remove the pads and clean the guides.

I do not see how a plugged brake line would allow me to retract the pistons. If I can retract the pistons using minimal leverage from a screwdriver, then the master cylinder certainly can drive the pistons forward with 1000 psi from my left foot.

If the rear brakes were not functional on one side, there would be abnormal pad wear. I would expect the side that is non-functional to have thicker pads than the side that is functional. However, this was not the case. All rear pads had worn evenly down to about .100 and I replaced them.

What could possibly cause one side of the rears to be non-functional, other than a bad brake hose or a sticking piston?(which I do not believe that I have).

I think that I am going to take your advice and look for something on the front end such as the track rod bushings. It makes sense that if one of these bushings is worn it would allow the wheel to shift rearward during heavy braking and thereby pull the car toward the side with the bad track rod bushing. Correct?

Thanks,

Brian Carlton

psfred 06-16-2003 11:47 PM

Brian:

Check upper ball joints and sway bar bushings, too -- if one is bad or the bushings out, the control arm can tilt on braking, changes the caster/camber on one side.

A brake hose with a loose lining can work like a one-way valve. I've had quite a few calipers hold pressure, refusing to release until the bleeder is opened. I see no reason why it wouldn't work in reverse -- allow fluid to move back up but not down when a peice of the lining is torn.

Check brake lines by flexing -- if you see crackes in the rubber on a rather sharp bend, replace them all. A bad liner will show up as bulges in the outer covering. Those will eventually leak.

However, if you have even pad wear (except for the normal condition of outer pads being slightly thinner), it's loose suspension parts.

Peter

vwbuge 06-16-2003 11:47 PM

check tire pressure

Brian Carlton 06-17-2003 12:37 AM

Peter:

Now that is quite interesting. You are saying that a hose could, potentially, allow fluid to move up toward the master but restrict flow downward when the brakes are applied. If this is the case, then all of my conclusions might be premature. With the brake hoses being rather low cost, I think that I'll just replace the two front hoses and be done with it. Then deal with the suspension issues if the problem does not go away.

I did already confirm that the tire pressures are all identical, 32psi, on all four, so that is not the problem.

I had a similar problem on a W123 before I sold it. I rebuilt the front calipers completely and the problem remained exactly the same as before the rebuild. Talk about frustration.

Thanks for your advise and assistance.

Brian Carlton

P.E.Haiges 06-17-2003 08:09 PM

Brian,

Do a hard stop and get out and feel the brake rotors to see if they are about the same temperature left to right both front and rear. Rear will not be as hot as the front.

If you find one side that is noticeably cooler than the other side, that is the the brake that is not working.

Be careful not to burn yourself. Go easy when checking.

P E H


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