w124 front brake imbalance MOT fail

[millo777]

Took the w124 for it's MOT yesterday and was failed on a front brake imbalance of 43%

I just had a really quick look at offending ns brake and nothing obvious like a bulge in a brake hose or similar so I'll have to remove the caliper clean it up and see if the problem becomes apparent. I'm guessing a seized piston.

The retaining pins for the pads look rysted to hell though so they'll need replacing.

So, to the questions. What is included with the Mb caliper rebuild kit part number A0004217186? it isn't clear on the russian online epc. Would this include the retaining pins, caliper bolts and anti rattle spring, or is just the seals for the pistons?

Are there any other causes I've missed? I read a thread with someone curing an imbalance of 27% with new pads only, but mine seems a bit high to be caused by pad glazing alone?

Any help greatly appreciated.

 

[grober]

By the look of it seals only Mercedes A 0004217186 Brake Caliper Repair Kit | Compare Prices I would seriously consider a pair of factory [ ATE] reconditioned calipers- as seizure is usually associated with scored caliper bores corroded pistons or bent/corroded pins if they are the sliding type although yours sound like the double piston fixed type?-- you could free them up and renew the seals just to have have them seize up again. The front brakes bear the brunt of stopping the car - new calipers would be a wise investment. Check the front flexibles haven't partially collapsed also

 

[millo777]

I think I will replace both calipers, it'll just mean having the car off the road for a week as mot expires on the 18th and I'm skint until payday on the 25th.

ECP don't have the front calipers listed, but gsf do at £96 plus £30 back on returning the old calipers, however they're "standard" quality whatever that means.

Where else could I try for rebuilt calipers?

I have checked the hoses, and they seem fine, but I'll replce them as a matter of course along with calipers, discs, pads and wear sensors.

 

[Dieselman]

Before doing anything, pry the pads back fully then apply the brakes to bring them back to the disk.
If necessary repeat a few times.

This will probably free off a sticky piston.

 

[grober]

I think I will replace both calipers, it'll just mean having the car off the road for a week as mot expires on the 18th and I'm skint until payday on the 25th.

ECP don't have the front calipers listed, but gsf do at £96 plus £30 back on returning the old calipers, however they're "standard" quality whatever that means.

Where else could I try for rebuilt calipers?

I have checked the hoses, and they seem fine, but I'll replce them as a matter of course along with calipers, discs, pads and wear sensors.

Are they the double piston or floating type? If they are the double piston fixed type these are the ATE part nos??

 

[millo777]

Thanks DM, will give it a go. I haven't had a proper investigation yet as I'm reluctant to take the caliper off the car until I have reaplcement mounting bolts. I also don't have a drift small enough to remove the pad retaining pins which are very rusty.

The strange thing is, I've noticed no issues when driving the car, and can't feel any imbalance such as the car pulling to the left under braking etc which with an imbalance of 43% I would have expected.

 

[millo777]

They're the double piston type. 4 pot, 2 each side of the pads.

 

[Dieselman]

The strange thing is, I've noticed no issues when driving the car, and can't feel any imbalance such as the car pulling to the left under braking etc which with an imbalance of 43% I would have expected.

So would I.

I once bought a Land-Rover that had significant front brake imbalance, which used to slew the thing sideways under heavy braking.

Stripping down the brakes and manipulating the slave cylinder a number of times fixed it totally.

Brake torque steer is more to do with steering geometry than the brake though.

 

[grober]

This a good reference for W124 brakes http://www.2phast.com/500e/techdocs/124_brakes.pdf

and this

http://www.ate.de/generator/www/com...taloge/download/ate_c1_classic_katalog_uv.pdf

these calipers are also fitted to W210 and some W202 models I believe.

Certainly worth trying DM's trick to free off the caliper pistons first. You can manufacture a drift to remove the pins by sawing off the end of a suitable 4 inch nail.

 

[millo777]

Good thinking re the nail. I tried the smallest pound threw screw driver I could find and still too big.

I will try Dms trick, but first I need to find which piston (s) are the problem otherwise I'll no idea if it's fixed or not! trial and error.

Either way, a good brake over haul is on the cards for pay day. If I can get it through the MOT I may just get some used original MB calipers and change all the seals and pins etc and paint them up.

 

[kth286]

they will be the 4 pot calipers like my 320 coupe, which have done 190,000
miles and no problems

I have changed the front hoses, as you cannot tell from just looking at them the condition inside which may have started collapsing causing a one way valve effect.

If the brake fluid changes have been missed, you need to undo the caliper
nozzles to get the crap out the fluid as a first step.

DM's idea looks good so do that also.

You could also take pads out for a good clean and grease the sliding points with copper.

Does it look like the pads discs are wearing unevenly - you can see this by
just turning the steering one way and looking, then other way and looking at other wheel.

 

[millo777]

Thought I'd update after a proper inspection at the weekend. The front offside caliper has one of the smaller pistons seized due to a missing metal protector plate on the end of the piston and crud getting behind the rubber boot. I managed to force the seized piston back in using a clamp, but it was obvious there is significant scoring and it's generally fubar.

The protector plate is £3.60 from the dealer, so had it been apparent earlier it would have been a quick and cheap fix. Such is life. I imagine these things get damaged when rewinding the calipers for pad changes or even get stuck to the back of the pads.

So, new calipers, hoses, discs, pads and wear sensors will be ordered on Friday ready for fitting over the bank holiday. It'll also need a fluid flush as the caliper was on the bench for hours and a lot drained out despite using a hose clamp.

All the above will be Pagid from ECP unless anyone knows of better options?

The next problem is the bleeding sequence for ASR. w124zone has a wis doc on this, but it's for ASR 2 and 3. Is that what I have on a '93 320TE?

 

[grober]

ABS/ASR bleeding is best done with a pressure bleeder. Are you sure you have ASR and not plain ol ABS?

 

[millo777]

Definitely ASR, I have the big triangle warning light with an exclamation mark in the middle of the speedo and the amazingly useful snow chain button. I have found the SP port on the ABS/ASR pump, there just seems to be conflicting info out there about when in the sequence to bleed the ASR unit and whether or not the engine needs to be on for this.

I was hoping to do the old fashioned two man method as I don't have a pressure bleeder, but they aren't expensive so will pick one up when I get all the brake parts.

 

[kth286]

Thought I'd update after a proper inspection at the weekend. The front offside caliper has one of the smaller pistons seized due to a missing metal protector plate on the end of the piston and crud getting behind the rubber boot. I managed to force the seized piston back in using a clamp, but it was obvious there is significant scoring and it's generally fubar.

The protector plate is £3.60 from the dealer, so had it been apparent earlier it would have been a quick and cheap fix. Such is life. I imagine these things get damaged when rewinding the calipers for pad changes or even get stuck to the back of the pads.

So, new calipers, hoses, discs, pads and wear sensors will be ordered on Friday ready for fitting over the bank holiday. It'll also need a fluid flush as the caliper was on the bench for hours and a lot drained out despite using a hose clamp.

All the above will be Pagid from ECP unless anyone knows of better options?

The next problem is the bleeding sequence for ASR. w124zone has a wis doc on this, but it's for ASR 2 and 3. Is that what I have on a '93 320TE?

I would see if merc will do front calipers on exchange basis.

Incidentaly, have you seen the price of those 4 pot calipers ?

 

[kth286]

Definitely ASR, I have the big triangle warning light with an exclamation mark in the middle of the speedo and the amazingly useful snow chain button. I have found the SP port on the ABS/ASR pump, there just seems to be conflicting info out there about when in the sequence to bleed the ASR unit and whether or not the engine needs to be on for this.

I was hoping to do the old fashioned two man method as I don't have a pressure bleeder, but they aren't expensive so will pick one up when I get all the brake parts.

As you are only working on the downstream side of the ASR unit, and it's not been drained, then you can bleed the brakes as normal, doing the longest run first and working back to shortest run.

It is the 124.036 model that is more complicated, with a special shop made wiring harness required to be used.

 

[millo777]

I would see if merc will do front calipers on exchange basis.

Incidentaly, have you seen the price of those 4 pot calipers ?

The main dealer wants £562.80 each for the calipers. GSF have rebuilt calipers for £96 and with another £30 refund when you return your old ones, so £66 net. I'd like to say I'll keep the old ones and attempt to rebuild them at some point, but they'd only clutter up the place and end up being binned in a year.

 

[kth286]

What do Merc want for exchange caliper ?

I would try and stay with Merc

The standard of their exchange will be to original standard with 2 year guarantee.

The quality of others will be unknown.

You will have Merc invoice when you sell the car, proving you use
original parts - it really does inspire confidence and you will be able to sell
car at premium price - everything else being equal.

 

[millo777]

I just checked with local dealer, and they don't do exchange calipers for the w124. They quoted £493.20 each for new ones. Previous quote was from Inchcape online.

I'm not too worried about the sale price, as I doubt I'll ever sell it. Realistically, the price of 2 new calipers from the dealer is about what the car is worth, so the affect on the sale price is not issue.

 

[trapperjohn]

Might be worth a call.

Brake Caliper Repair, Rebuild and Refurbishment

I had my 300D saloon ones done about 4 years ago. Sorry cant remember who did them, it might have been ECP -but they dont do them now. Car stopped on a tanner with 4d change after the refurb.