Rear Brake Imbalance, Wrong Calipers? Help!

[keeperlit 4 1 Cars]

Okay, I've been having a lot of fun with my rear brakes after the beam rebuild. The short story is the car has just failed the THIRD MoT this evening, this time on rear brake imbalance which it squeezed through on last time. I've got until Monday to fix it, book and take a re-test. (The lovely Northern Irish govt run MoT centre rulez).

 

So, there's new discs, pads, pipes/flexis on both sides and both compensators are in the bin. Handbrake cable is nice and loose when down to let the adjusters work. Bled the brakes many times over, fluid runs clear with no bubbles now. At different stages BOTH CALIPERS have been replaced - Drivers side from a 206 XSi and Pass side from a Xsara. They look almost identical but could this be the problem?

 

On all 3 MoT tests, the pass side (Xsara caliper) has consistently pulled stronger than the drivers side (from 206) on handbrake and footbrake tests. The only difference between them I can see is the handbrake lever...

 

Tonight I also tried screwing both pistons into the caliper and testing the adjusters by pushing footbrake then tugging the handbrake. Immediately both calipers adjusted to where they were previously so I think they're both working.

 

Here's 2 pics of the passenger side caliper from a xsara:

 

And the drivers side caliper from a 206:

 

I really need help with this soon! I'm thinking of replacing the Xsara caliper with another 206 one to see if it fixes the problem...

[keeperlit 4 1 Cars]

I forgot to add - both caliper guide bolts appear to be nice and free, I can move both of them back and forth easily.

[welshpug 1,646]

Xsara will have a 32mm piston, 206 may well have 30mm as its a lighter much less powerful variant.

[Anthony 1,002]

How bad is the imbalance?

 

Given that it affects both foot and hand brake, and you've confirmed that the pistons and sliders move freely, I would be wondering if it's actually a friction issue - either contaiminated/glazed pads (unlikely if it's the same after replacement) or the pads not running true to the disk due to a bent carrier or stub axle - especially if you're saying that it's only happened since the beam replacement.

 

I've seen 306's with mismatched (32 vs 30mm piston) rear calipers sail through MOT's over here on the mainland (I don't know if yours are the same or different in Northern Ireland) so I would be surprised if it was that alone.

[keeperlit 4 1 Cars]

I really, really appreciate the help guys. :-)

 

Here are the results from tonight:

 

I *love* the way the front brake efficiency is at over 100%. That's my Xsara VTS front brakes with shiny new discs and pads :-)

 

Anyway, back to the problem! The 1.9 beam was rebuilt using a pair of Xsara rear arms so there is indeed the possibility one of the stub axles being bent. Both rear wheels look pretty similar though in terms of their alignment. I'm really hoping it's not the stub axle....

[keeperlit 4 1 Cars]

...so if it was an alignment issue on one side then as the pads wear in the issue should go away? I might see about getting a second 206 caliper or a second xsara caliper to make sure both are the same. The 206 XSi that the OS caliper came from (only a month ago) might still be sitting there in the breakers yard with the NS caliper attached...

[keeperlit 4 1 Cars]

Okay,I checked the part numbers on Peugeot/Citroen servicebox and the 206 caliper seems to match the 205 (4401 61/62) ones but the Xsara part is different (4401 A2/A3). I'm guessing that's not going to help...

[Miles 331 1 Cars]

I'd start by giving the carriers a good clean up, 99% of the time that does the job over hear

[Anthony 1,002]

That Bosch caliper on the nearside isn't an original Xsara caliper I don't believe, so it may well be a 30mm piston anyway.

 

The piston size I think should only affect the footbrake (ie hydraulic) and not the mechanical handbrake, although that is making the assumption that the handbrake mechanism is the same design between the two designs.

 

Certainly having matching calipers on both sides can only be a good thing, but I'm not convinced that this difference is purely down to that, particularly since it is affecting both service and hand brake by similar amounts.

 

Have a careful look at the rear pads and wear on the disks - is there anything that looks a bit odd, normally that the pad is beginning to wear wonky like a wedge or the disk only being clean on one side of the pad wiping area? Problem is that if you've only been running to and from the MOT station then there's likely not enough wear to tell anything yet, particularly given that you still have fairly good brake efficiency on both sides (to the point I think that would pass over here as rear balance isn't tested AFAIK and it's only overall hand brake efficiency)

 

My gut feeling is that it is not a nearside caliper issue if it's all free moving, as generally any problems would show as either low effort or as binding, but given that is the easiest item to change, it might be worth ruling it out with a matching one from the 206. If anything, I'd guess that the offside one is under-performing, but without any figures to compare against for a similar spec car, it's hard to say.

[keeperlit 4 1 Cars]

Miles, I'll give that a crack and let you know how I get on. I had cleaned up the calipers but I hadn't paid special attention to the (brake pad?) carriers and I hadn't greased them or anything.

[Miles 331 1 Cars]

Don;t forget to make sure if it's there of course to have the notch on the dimple on the pad

[Alastairh 47]

They are mismatched calipers, you can tell by the handbrake lever arm. But as said you normally can mismatch them and be ok. I would also clean everything up and start again.

 

Al

[Redtop 14 2 Cars]

Seen that problem before on a 206 where it failed on rear brakes with a mismatch of 30 and 32mm calipers. Haven't put it through the n.i test yet as I'm rebuilding the car at the moment, but I matched a pair up for it now. Another thing maybe worth checking is the 2 bias valves in line at the front of the petrol tank if they are still there?

 

Did the tester give it a couple of goes on the rollers or did he just do it once and say fail? I know the 106's are a nightmare to get through even with new shoe kits and adjusted up well over here and the testers know that.

[keeperlit 4 1 Cars]

Cheers Richard, the 2 inline brake compensators have been removed as I'm running GTi6 front brakes and 406 master cylinder.

 

The MoT tester did retry the test and gave it 2 or 3 goes on the rollers - the imbalance varied but never went below the 30% threshold unfortunately.

 

I'm going out at lunchtime to pick up a N/S caliper from the breakers that sold me the O/S one and the MoT retest is booked for Friday. I'm planning to strip, clean and copper grease both calipers on Thursday night and hopefully that'll do the job....

[welshpug 1,646]

Don't use copper grease on the moving parts, standard moly or brake grease, copper should only go on the on sliding surfaces, threads etc.

Edited October 3, 2012 by welshpug

[keeperlit 4 1 Cars]

Okay so I went to the same breakers and got the passenger side caliper off the same 206. Cleaned it up tonight and then tried to carefully loosen the bleed nipple and .. it... sheared! I also notice the piston seal is ripped in a couple of places. Oh dear.

 

So without a replacement caliper I turned my attention to the underperforming side. I took it apart, cleaned up the carrier and greased the pads. I cleaned the surface of the disc and the pads and re-assembled. Seems to have a bit better stopping power when I tested with the handbrake on, but still not as powerful as the passenger side (xsara caliper). So I had the genius idea of swapping out the new pads on the passenger side for the old pads which hopefully will reduce the performance and make them more equal. All assembed now, and both sides seem to be pretty similar on the handbrake. A road test shows very little pull to either side so hopefully tomorrow night it'll pass...

 

A mate happens to have a pair of xsara calipers in his shed. No time to get them tonight but the plan would be to fit them with new pads on both sides and ebay the collection of calipers I seem to have amassed! It'll all be over soon.....

[Emmy Seize 8]

As stated somewhere above, this looks very much like mixed calipers.

 

I've checked a couple of old TÜV bills I have from various cars and it seems that ~1.2 kN is as much as you can expect from brand new standard calipers, pads and discs without compensators.

[keeperlit 4 1 Cars]

Hi Emmy, thanks for the info!

 

The 1.2kN certainly matches what I'm getting from the 206 caliper with new discs and pads, good to know it's doing the job okay. The Xsara caliper was pulling almost 2kN which is a tad high. I'll maybe try and fix up the second 206 caliper tonight and replace the xsara one. Just need to replace the dust seal and get the wrung bleed nipple out...

[keeperlit 4 1 Cars]

Good news! Passed the MoT tonight, well chuffed. I've got a bolt remover tool to remove the wrung bleed screw from the 206 caliper and a replacement dust seal.

 

Thanks to all for the help!

[ablister 31]

you say that you have removed the rear compensator, does that not fail the MOT over there? It would here...

[Alastairh 47]

Never had a problem myself when removed for gti6 etc brakes.

 

Al

[ablister 31]

Never had a problem myself when removed for gti6 etc brakes.

 

Al

 

It actually is a fail if it is meant to have one but unless the tester knows it's meant to be there then i suppose it'll get overlooked, ignorance is bliss and all that...

[keeperlit 4 1 Cars]

As far as I know the compensators do nothing apart from limit the maximum force applied to the rear brakes. MoT are only interested in the effectiveness of the rear brake and the left/right balance. I'm not sure if they actually check these at MoT, however there was no issue with mine and the tester definitely knew they had been removed.