Heavy brake vibration

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JohnM - 31 May 2005 21:15 GMT

While this is my first post to the group I'd like to start by saying a very
gracious thank you for all I've learned while lurking the past few years

I have a 1993 940 ABS/no turbo that is demonstrating some very powerful
vibrations while braking. This happens when the brakes heat up and it gets
worse the more I use them

I installed new calipers and rotors (4) last summer - They calipers were
rebuilt/loaded and have provided excellent service over the past year. The
rotors were of high quality and the wheels have always torqued on.

In the process of troubleshooting, I've checked bushings, shocks and
driveshaft center bearing-- I pulled the front wheels over the weekend and
found one seized caliper. At worst, that same problem with the rear brakes
would be great

I wonder if any of you have experienced anything similar or have an idea of
what else it might be -

Thanks

JM

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Michael Pardee - 01 Jun 2005 01:13 GMT

> While this is my first post to the group I'd like to start by saying a
> very gracious thank you for all I've learned while lurking the past few
[quoted text clipped - 19 lines]
>
> JM

I have had a similar problem with our '85 765T when a tie rod was failing.
The boot had torn and the lubrication was lost. The shaking was noticable
with light brake application but became violent with moderate braking. When
I changed the tie rod I was amazed to find the play was only a mm or so. It
was detectable by jacking the wheel up and trying to turn it side to side
(like steering). I could feel the play, and watching the tie rod and
steering column (alternately) I could see the tie rod was moving when the
steering column was not.

Mike

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Scott - 01 Jun 2005 04:05 GMT

Your problem is a seized caliper, which has probably warped the rotor due to
the excessive heat that it generates dragging against the rotor while you
drive. The caliper could have been rebuilt improperly or with poor quality
parts (new calipers aren't that expensive), or you could have a failing
master cylinder.

Recommend Volvo pads and ATE rotors for the front brakes. Aftermarket rotors
are known to warp. Your front calipers are most likely Girlings.

> While this is my first post to the group I'd like to start by saying a very
> gracious thank you for all I've learned while lurking the past few years
[quoted text clipped - 18 lines]
>
> JM

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athol - 01 Jun 2005 05:14 GMT

> I installed new calipers and rotors (4) last summer - They calipers were
> rebuilt/loaded and have provided excellent service over the past year. The
> rotors were of high quality and the wheels have always torqued on.

> In the process of troubleshooting, I've checked bushings, shocks and
> driveshaft center bearing-- I pulled the front wheels over the weekend and
> found one seized caliper. At worst, that same problem with the rear brakes
> would be great

> I wonder if any of you have experienced anything similar or have an idea of
> what else it might be -

I recently replaced all of the hoses on my 264 after experiencing a brake
that locked on. The caliper wasn't siezed at all - crack the bleed nipple
on the faulty circuit and the pads retracted. Pump the pedal a few times
and it would again drag! I think that it would also release over night.

Rubber brake hoses are rated for a life expectancy of 10 years. It is
entirely possible for the internal lining of the hose to come away from
the reinforcing and block the hose. The pressure of application is far
greater than the pressure of the fluid trying to release the caliper, so
the fluid will be forced in through the damaged hose but not be able to
get back out...

Mine now has a full set of (standards approved) stainless braided hoses.

Signature

Athol
<http://cust.idl.com.au/athol> Linux Registered User # 254000
The state of infrastructure in New South Wales is a disgrace.
I'm a Libran Engineer. I don't argue, I discuss.

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JohnM - 02 Jun 2005 02:46 GMT

I'd like to thank all of you that replied to my problem. Each reply brought
a different perspective that I had never considered

So now, buy some parts, do more work. We have 3 in all. Another 940 and a
1990 740 with only 56K on it (mine!) and all of them needy in one way or
another

Thanks again!

JM

Parts?? FCP Groton only!
Pads?? PBR® Deluxe Organic (no asbestos) And they are virtually dust free.
I no longer have dirty alloys

> While this is my first post to the group I'd like to start by saying a
> very gracious thank you for all I've learned while lurking the past few
[quoted text clipped - 19 lines]
>
> JM

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