Front brake issues - 320/6 Baur

[mendipdriver]

Hello all,

I have an issue with my front brakes where the nearside brake locks before the offside brake making the car pull to the left (badly), I was given the car 5years ago as a rolling resto - I have systematically replaced items on the brake system as the MOT required; I have replaced the following -

- offside f/calliper
- brake pads o/s & n/s
- all flexible hoses (F&R)
-o/s & n/s rear drums. shoes, cylinders and back plates
- n/s & o/s ARB bushes

I have checked both callipers for function and their pistons move smoothly in and out. I have checked the master cylinder and it is plumbed correctly - I'm really foxed.

I took it to my local garage, they popped it on the brake tester and confirmed that the n/s brake is locking out before the o/s brake - they then tested them individually and both the n/s and o/s brakes provided 300psi.

They bled the system and re-checked with no change. The discs were new when I received the vehicle (5yrs 20k miles) and appear to be good apart from some minor pitting.

I have checked the geometry and all appears to be ok; no wandering in the straight ahead position, and all suspension components have either been renewed (spax up-grade) or are in good condition.

The brakes pull up well but with the left pulling issue. Can anyone provide an answer to this mystery?

Thanks in advance.

Simon.

[Jeroen]

Tough cookie but something is causing a difference, nearside engaging/binding earlier than offside.

I'd go through a whole bunch of basis checks first, prolly most were performed already I guess. Thech for differences in for example:
caliper and hoses
disc thickness
pad/pad thickness
pad/disc clearance
in case of Até calipers, is the offset adjusted correctly (see image below)
check for damages/dents in brake lines
re bleed system again

After these checks, and I expect that here's the difference, remove both front calipers for a full rebuild with new seals. Check if the pistons are exactly the same.


Image taken from the bmwe21.net brakes FAQ

[E21-driver]

Hi Simon,

As Jeroen said, please check the 20 degrees assembly of the caliper pistons. You will find a template for drawing a little check tool for this purpose in the internet.
If the positions are not correct, they may cause a blockage. Were the calipers opened completely or did you just remove the pistons ? There are small channels in the caliper halfs, which are sometimes blocked by some rests of the rubber hoses. They also need to be cleaned when restoring the calipers. Also the master cylinder needs to be opened and cleaned. Some dirt and rubber rests may stick to the line outputs. We have identified same problem with a German e21 collegue here, he had the same problem though all components were new. After restoring the master cylinder, the problem was solved. There was a lot of dirt in the master cylinder (who wonders, the part is over 30 years old).
Murat

[Jeroen]

[mendipdriver]

Gents,

Thank you for your wise words - I recently took the shims out after I read that they more hassle than they are worth; I couldn't see the use of them as my new calliper didn't have the notched pistons - I can recall if the reconditioned calliper (n/s) had notched pistons, so I'm off in to the garage now to investigate.

I'm going to pop the shims back in the callipers to see if that assists - I'll let you know Jeroen.

If that doesn't work, the master cylinder is the next stop, although it was replaced in 2006 - but the car only covered 205miles between 2002 to 2010!

Ta, Simon.

[Jeroen]

Well I believe you better rebuild both calipers first

[Mihajlo]

if left caliper gives stronger braking force or applies force earlier than other, problem MUST be in the other caliper.

As Jeroen said, rebuild both calipers.
And inspect hard lines with some wire to be sure there is nothing blocking it...

[mendipdriver]

Thanks to all that have replied. Ok, I inspected both callipers (o/s that isn't applying as much braking force is a NOS item); I have the girling pattern callipers as they are solid discs. What I noticed is the n/s pads are snug on the disc, when the hub is rotated there is drag with slight resistance (this calliper was a reconditioned unit replaced 2yrs ago). However, the o/s inner pad was snug but outer pad could be moved side-to-side with my fingers when the retention spring was removed. The disc could rotated easily with little or no drag.

I reinstalled the shims to both callipers (BTW - both callipers didn't have notched pistons); I then popped the loose pad out and placed a narrower piece of wood in place and asked my able assistant (wife) to pump the brake pedal until the piston extended to the wood. I then bled the calliper, I believe air was released but couldn't be 100% sure due to my poor equipment.

I took the car up the road and apart from the very slight mushy feeling when the brakes are applied (I put this down to the shims) the brakes pulled up straight and the n/s didn't lock and skid.

I hope that this is a result, and the pulling doesn't return...

Many thanks to all of you for your help.

Ta, Simon.

[mendipdriver]

I spoke too soon; intermittently the left pulling issue reappears - back to the drawing board. I'll take Murat's advice and clean out the Master Cylinder and clean out the pipes as Mihajlo suggests - having not done this before is it a difficult job?

[mendipdriver]

Ok, cylinder came out and went back in last night with the symptoms continuing. So this evening I followed Jereons advice and serviced the calliper - I popped the calliper off and was stunned that the pistons were solid - after draining the fluid one piston could be moved with my fingers and the other was solid - hhhmmmm...
popped both pistons out with compressed air (warning - keep fingers away!) and inspected the pistons #1 was clean but #2 was slightly cacky with a small nick on the side - I can only conclude that this was always present and as my pads wore down the fault on the piston got closer to the seal until it made contact and eventually fouled the movement. The calliper was a recon unit, lesson I have learnt is to inspect the pistons before fitting - even if the unit is new!

BTW - she now stops beautifully in a straight line!!

[Peter V.]

Good to hear that the brakingproblem is over then.

[Jeroen]