Brake Calipers - pistons rusted in

[Styria]

When reconditioning caliper pistons, especially on cars that have been laid up for some time, there are two problems that one will be confronted with immediately:

1) Brake pads that have virtually "rusted" themselves to the disc rotors - so how do you remove those especially if you have a pronounced ridge at the outer edge of the rotors.

2) Having removed the calipers from their mounting points on the hub, you find that the caliper pistons are again "rusted" to the bores and they seem to defy all attempts to be removed from the bores.

I have some ideas on these problems, and how to overcome them, but I would be interested to hear from the "knowledgeable" as to how they would arrive at satisfactory solutions so that the calipers can be resealed and reconditioned. Please help. Regards Styria

 

[s class]

I know it doesn't help much, but I've actually had a piston break during attempts to remove it from the caliper. And its still there.

What I've found is that its easiest to remove the pistons before splitting the caliper. Wedge a block of wood in the area normally occupied by the disc and pads - to limit the available travel of the pistons. I've used compressed air to drive them out. If you dont use the block of wood, you will find one piston pops right out, and then you're buggered trying to get the second one out.

My favourite, and most successful method, is to do it while the caliper is still attached to the car. Just remove the pads, press firmly on the brake, and out they come.

I don't have much experience trying to remove pads that have become attached to the disc.

 

[Styria]

Hi S-Class, well, to a greater extent you have saved my bacon - i.e. here's me thinking that this most interesting, yet perhaps infuriating jobs is not even going to attract a reply.

I am not yet quite ready to give away my secret procedure which would just about have a 100% success rate to get those pistons out - obviously the use of compressed air on the bench is the most ideal, but would not be successful with rusted in pistons.

Using the car's brake hydraulics is just about guaranteed to work each and every time, but what if you have internally swollen brake hoses - can be quite common on older Benzes ? Also, if your pads are still in situ, you're still up against it, aren't you ? Obviously, that block of wood is essential (or some other usable tool) as the two pistons virtually have to come out as a pair.

I'll give it another day or two before I'll divulge my just about foolproof method. Regards Styria

 

[s class]

I'm listening with anticipation - despite my methods, I stilll struggle sometimes. That would be struggle with a capital 'S'.

 

[s class]

Also, if your pads are still in situ, you're still up against it, aren't you ? Obviously, that block of wood is essential (or some other usable tool) as the two pistons virtually have to come out as a pair.

If I was really up against it, I would split the caliper while it was still mounted on the car, remove the outer half of the caliper, then remove the inner half from the hub carrier. Next I would reassemble the caliper on the bench to allow pressing the pistons out with compressed air or even hydraulics.

 

[Parks]

Hi S-Class, well, to a greater extent you have saved my bacon - i.e. here's me thinking that this most interesting, yet perhaps infuriating jobs is not even going to attract a reply.

I am not yet quite ready to give away my secret procedure which would just about have a 100% success rate to get those pistons out - obviously the use of compressed air on the bench is the most ideal, but would not be successful with rusted in pistons.

Using the car's brake hydraulics is just about guaranteed to work each and every time, but what if you have internally swollen brake hoses - can be quite common on older Benzes ? Also, if your pads are still in situ, you're still up against it, aren't you ? Obviously, that block of wood is essential (or some other usable tool) as the two pistons virtually have to come out as a pair.

I'll give it another day or two before I'll divulge my just about foolproof method. Regards Styria

just tell them

 

[Styria]

I wish I had taken some photos to illustrate some of the problems I encountered. As S-Class has alluded to, sometimes one may have to split the calipers whilst still on the car. Of course, if then you're going to attempt to remove the pistons from the caliper bores, one will need to bolt them back together.

I can tell you now that immersing the whole assembly in any of the penetrating solutions will help very little, if at all, to loosen the grip with which the internal seal has on the pistons. Trying to prise the piston out with two screwdrivers and/or slight tapping with a blunt chisel will usually result in the rubber seal retaining groove breaking off.

The answer lies in the use of grease. It is necessary to sweat a grease nipple to the brake fitting (without the piping) and screw it into place where you have the brake fluid intake. Connect up your grease gun, and start pumping. Remember, you have to fill up two cavities, so a fair amount of grease is required. However, once the pressure builds up, watch the two pistons coming out slowly but surely. That's all, other than having to remove a lot of grease from the calipers. Regards Styria

N.B. I'll also have a few more words to convey regarding Benz Calipers for your 109s.

 

[s class]

Ah that sounds like a stroke of genius. I will definately remember (and use) this trick. Thanks

 

[GreaseMonkey]

Great idea, the grease trick, if all else fails.
If the piston is stuck because of any corrosion on the surface then you should be throwing it in the bin and replacing it with a new one, so any damage done in removing it is irrelevant.
I used to rebuild a lot of brakes, (in a former life I was employed by Midas UK to train shop staff in all aspects of brake servicing) and found the best way, was to remove the brake pads, and replacing them with strips of wood of a suitable thickness, pump the pedal to free the pistons, and they will eventually pop out, and the wood is there to stop them coming too far out as once they get past a certain depth in the bore they can twist and get jammed at an angle.
If the pistons are now halfway out, the caliper can be removed from the car, and the pistons removed on the bench.
If any pitting visible on the surface is only on the outside of the seal area, you might get away with polishing them up, not recommended though.
Cleanliness is everything in reassembling and fitting new seals, which MUST be seated correctly in the groove.
At this point too, pushing the piston back in needs care to ensure it goes in square, lubricating the seal with a wipe of brake fluid helps.
A final point, I have found more brake caliper problems are caused by lack of use than anything else, so I guess we should all move our cars regualrly, if only a few metres, to ensure the brakes free off, and re-apply.
Chris M.

 

[Styria]

Hi Grease-Monkey, thanks for your input - I find it of great interest, and whilst obviously I am not nearly as qualified as you would be, there are one or two items that I would handle differently as compared with your procedure.

When using grease, and this is one of the real advantages, no damage is caused to the pistons, nor the bore of the caliper, and they also come out completely square as long as you feed in the grease with the pressure gun. I have also found that even if they're halfway out, they can still be very stubborn to come the rest of the way. Thus, grease it is all the way out.

Unlike British units, such as AP or Girling, the chrome plating on the German caliper pistons appears to be of quite superior chrome plating. With British units, one may have a success ration(re-usable) of 30%, whilst ATE units would work out to 90% at worst.

Last but not least, I do not use brake fluid to re-assemble the calipers, i. e. re-inserting the piston into the bore. Nowadays, and it may have been in your time as well, one can purchase a special caliper piston assembly oil - hellishly expensive, but ten times more slippery than oil or other such substance. It also acts as a lubricant on the internal caliper seal. Regards Styria

 

[GreaseMonkey]

Interesting.
You are right in the description of Girling, AP or Lockheed pistons re the plating, but I never knew ATE were that much better.
Having said that, I don't think I have ever needed to strip a caliper for a Benz.
C.M.

 

[Styria]

Hi Grease Monkey, you'd find that ATE Calipers are more "maintenance friendly" than Girling Calipers that were fitted to Rovers (the type I am familiar with).

ATE calipers have a much thicker 'shoulder' and one can actually put some leverage on that shoulder with screwdrivers to extract pistons from bores. On the Girling units, the shoulder referred to is very thin and breaks easily if you are anywhere near 'ham fisted'. Regards Styria

 

[AAB]

I have a 450SEL,,1974 vintage, & am giving my rear brakes a birthday.

The calipers that I have, came from an identical " wrecker ", so I am not without wheels.

I have split the calipers, Ate, & my spares supplier says that the small rubbers ( probably not rubber ) do not come with the repair kit !!

Any clues where I can source a kit for the Ate calipers with all of the rubbers, or where I can get these small rubbers ?

Regards from Melbourne,

AAB

 

[Styria]

Hi AAB, the kits that I buy from my source do not have those rubbers either. Perhaps if one bought genuine, those small rubbers might be included.

I have always re-used the old one (as long as you haven't lost them), and thus far have never experienced any problems with internal leakage of the calipers. BTW, any reason why you're reconditioning the rear calipers and how did you get on removing pistons from their caliper housing ?

Also, don't forget to check your brake hoses for flow restriction. Regards Styria

 

[Styria]

I have previously referred to rear calipers for the 6.3's and in view of the fact that the 109 models fall into the "Talking Torque" category, further details are posted in that section titled '6.3 brake caliper features'. Regards Styria

 

[s class]

No, the genuine MB kits also dont include the internal rubbers. They can be very problematic to get. ATE will not sell them to me here in South Africa. I use items made by LMB, who are a local after market caliper seal manufacturer.

You must only use seals specifically made for this purpose, because most types of rubber will dissolve in brake fluid.

 

[Styria]

No, the genuine MB kits also dont include the internal rubbers. They can be very problematic to get. ATE will not sell them to me here in South Africa. I use items made by LMB, who are a local after market caliper seal manufacturer.

You must only use seals specifically made for this purpose, because most types of rubber will dissolve in brake fluid.

That's interesting, S - Class. I had never tried to purchase 'genuine' on account of the cost factor - I wonder if perhaps suitably sized 'O' rings could be purchased that may be used as an alternative ? If I remember correctly, some years ago (many), I may have tried that but ran into trouble with the appropriate thickness. Regards Styria - and, of course, resistance to brake fluid is another very important factor.

 

[AAB]

Styria,

I bought this " wrecker " for $500 delivered,..the seat covers & the rear vision mirrors were worth the money, so I took off all of the electronic gear, rear brakes, & anything else that was easy to remove, hence the calipers.

Worrells quoted me a Benz MAP sensor ( 1 in Australia they said !! ) $3,600 plus GST.

I did my current calipers about 10 years ago & 3 of the 4 pistons on them were seized,.. probably because the car had been drive only 500 km in the previous 10 years,..husband died & wife did not use the car much in ten years.

I think that lack of use led me to some automatics problems,..( dried seals ? ) that I had initially.

All 4 pistons were seized in this one,..tried compressed air,..no good & eventually got them out using 2 screw drivers,...gently gently !!

My spares man said that a bearing service will probably be able to help with the small rubbers. I will let you know if I am successful, otherwise I will reuse the originals.

Regards,

Alex

 

[Styria]

You're dead right about the 'gently, gently' business - and don't forget your knuckles whatever they may hit if one of the screwdrivers happens to slip from the groove ! Better use that grease. Regards Styria

 

[s class]

and, of course, resistance to brake fluid is another very important factor.

Therein is the problem. Not something you want to take a chance with.