Calliper leak problems

Alan Collins

CCCUK Member
Hi, I have a 1972 small block convertable which is giving me recurrent braking issues.

My front stainless steel sleeved callipers are starting to leak and have a history of repairs with lip seal service kits despite regular use, generally every two weeks:
First service kit fitted by previous owner in May 2017.
Second service kit by myself following sudden major leaks in May 2018, I found some seals twisted, some seal lips scored and white crystaline deposit around pistons inside the dust covers. I cleaned all parts meticulously, cleaned bores with 1200 wet and dry lubricated with brake fluid and replaced the fluid.
June 2019 brakes tested on a rolling road as part of general mechanical test, performing well, 273 and 288 kgf with wheels locking up.
February 2020, some pistons are leaking again! Looks like moisture has got past some dust seals, there is a greasy deposit containing soft crystals, and some seals have left a rubber lip deposit in the bore. Note I may have lightly lubricated the pistons with brake grease under the dust covers to prevent corrosion in May 2018. I now know this can cause a reaction with brake fluid.

Will fitting an O-ring seal and piston service kit rectify this? (I intend to split the callipers when fitting dustcaps this time to ensure they are perfectly pressed into place)
Should the bores be a dull matt finish as mine, or polished?
Or do I have a problem with my calliper bores and need remanufactured callipers?

Any help please
 

Attachments

  • BVR 141K Alan Collins piston.JPG
    BVR 141K Alan Collins piston.JPG
    102.8 KB · Views: 22
  • BVR 141K Alan Collins calliper.JPG
    BVR 141K Alan Collins calliper.JPG
    114.6 KB · Views: 23

kentvette

CCCUK Member
I confess I don't know if teh bores should be polished or dull and I've never been tempted to re-build a calliper.

But - O-Rings, O-Ring, O-Rings! My wife and I became able to swap callipers in our sleep some 20 years ago. Finally in about 2005 I got fed up with it and bought new Stainless Steel O-Ring callipers from Ecklers. (Actually the Ecklers items came from Dr Vette)

Quite simply, I haven't touched them since! Brake performance is spot on with no leaks and no air in the system.

On the face of it, new callipers might seem expensive. Generally, Corvettes are cheap to run and given how important the brakes are, callipers are not that pricey. Just get new ones and be done with it.
 

Oneball

CCCUK Member
That crud around the piston and seals would indicate to me there’s something else going on, have you been mixing brake fluids? Is water able to get into the system?

When you say brake grease what do you mean? There are seal greases that are formulated to work with brake fluid or do you just mean copperslip?
 

Roscobbc

Moderator
Alan the deposits are fairly typical. I've had my C3 twenty years and for the first 5 years had the same issues as you. There is a misconception that stainless steel sleeved calipers solve all issues.....they don't.....unless you remember that there is still ferrous metal in the braking system. \mineral Brake fluid is hygroscopic and absorbs moisture. If the car is stored in cold or damp conditions you will get condensation within the braking system. This will cause rust and deposits within the system unless you regularly replace the brake fluid. You should do this every couple of years if the car is stored in the above conditions. I replaced the original lip seals with 'O' ring pistons - this was 15 years ago and they are still OK.
You will need to thoroughly clean out the caliper with brake cleaner or petrol. You see the 'high spot' (the concentric line on the caliper bore?) you need to get rid of this.
I think the Americans call it Crocus cloth or paper (I can't recall what we call it here) - its a really, really ultra fine abrasive emery paper 1000 grade. Use this or initially a coarser grade CAREFULLY only on the high spot first if the 1000 grade won't shift it. 'Sand' a cross-hatch pattern all around the internal bore surface to remove any surface glaze (so both round and round and up and down) so that the surface has a nice even brushed pattern all over it. Much as you would when honing a cylinder bore. Clean the caliper thoroughly again with brake cleaner or petrol - job done - re-assemble.
Some people suggest the use of silicon brake fluid as it doesn't absorb moisture - true - BUT any moisture can still be present in the braking system - OK so it won't be diluting the mineral brake fluid and raising the boiling point but it will still be present and will boil under heavy braking causing potential brake fade........just saying!
 

Daytona Vette

Well-known user
To sum it up; Clean unworn parts - Stainless sleeved Calipers - "O" Ring Pistons and for me Anhydrous Brake Fluid to protect the system, especially the Master Cylinder as that is Cast Iron - not good when a failed Master Cylinder allows the Pedal to fall away when you need it - happened to me, that is why I use the Anhydrous / Silicon Fluid.
 

curious bystander

CCCUK Member
I re-rubbered all my calipers with new lip seals. All pistons were fine except ONE! So I whipped if off, cleaned and polished the bore with fine wet and dry, and the result? It leaked even worse! :mad:

So as Stephen says rebuilt calipers are probably the way to go. I replaced both my rears with AC Delco from Rock Auto. Not "O" ring as they don't seem to do them, but they weren't £250 a pop. And I sent the old ones back for a bit of a refund - and the original parts will get reused rather than going in the scrap.
 

Alan Collins

CCCUK Member
That crud around the piston and seals would indicate to me there’s something else going on, have you been mixing brake fluids? Is water able to get into the system?

When you say brake grease what do you mean? There are seal greases that are formulated to work with brake fluid or do you just mean copperslip?
Hi Oneball,

I have not mixed fluids and have none of the symptoms it would give such as swollen hoses.
I think water has got past some of the dust seals, I have only checked the worst ones, I shall prise out the well seated seals tomorrow and inspect for deposits and leaks.
If I did use grease it was only a little of the white grease that comes in the seal service kit. I have never done this in the past but may have done so here in an attempt to prevent oxidation of the aluminium alloy pistons. I used copper slip on the external piston faces, back of the pads, guide pins, and between pad edge and caliper as I have on many cars over the past 30 or 40 years with no previous problems.
 

Roscobbc

Moderator
Simply driving your car irregularly is enough to create condensation within the braking system. Garaging the car for extended periods (say over winter) in conditions at lower temperatures than ambient will have the same effect - the simple answer is to change the brake fluid regularly and it shouldn't be an issue .
 

DieselfitterDave

Regular user
Yes I agree if you have issues with foreign materials,change your brake fluid.
I may have been lucky with my 78 which I have had since2015 but having run around 18 months I had the same problem with leaking calliper and I decided to strip all the calipers off the car,split them push the pistons out and clean the original bores with a rotary emery tool,fit New “O” ring kit,which included pistons springs, rings,boots, bleed nipples etc and fitting them all back together I have not had a problem since.
7DA742E2-02AB-4B11-AB6B-034FD383F309.jpeg
 

Alan Collins

CCCUK Member
Alan the deposits are fairly typical. I've had my C3 twenty years and for the first 5 years had the same issues as you. There is a misconception that stainless steel sleeved calipers solve all issues.....they don't.....unless you remember that there is still ferrous metal in the braking system. \mineral Brake fluid is hygroscopic and absorbs moisture. If the car is stored in cold or damp conditions you will get condensation within the braking system. This will cause rust and deposits within the system unless you regularly replace the brake fluid. You should do this every couple of years if the car is stored in the above conditions. I replaced the original lip seals with 'O' ring pistons - this was 15 years ago and they are still OK.
You will need to thoroughly clean out the caliper with brake cleaner or petrol. You see the 'high spot' (the concentric line on the caliper bore?) you need to get rid of this.
I think the Americans call it Crocus cloth or paper (I can't recall what we call it here) - its a really, really ultra fine abrasive emery paper 1000 grade. Use this or initially a coarser grade CAREFULLY only on the high spot first if the 1000 grade won't shift it. 'Sand' a cross-hatch pattern all around the internal bore surface to remove any surface glaze (so both round and round and up and down) so that the surface has a nice even brushed pattern all over it. Much as you would when honing a cylinder bore. Clean the caliper thoroughly again with brake cleaner or petrol - job done - re-assemble.
Some people suggest the use of silicon brake fluid as it doesn't absorb moisture - true - BUT any moisture can still be present in the braking system - OK so it won't be diluting the mineral brake fluid and raising the boiling point but it will still be present and will boil under heavy braking causing potential brake fade........just saying!
Hi, The car is currently stored outdoors in the terrible weather we have been having. I am fighting a losing battle against these storms which came before I could finish building a lean to garage. Damp must have got to the brakes but I would not expect it to cause so much damage, my other cars are all parked outdoors and used in the rain with no ill effects. I will drain all fluid when I reassemble the system.
Only the the front callipers appear to have been affected. I have only inspected the two worst pistons on the worst caliper. One bore is totally clean whilst the bore in the photo has a black concentric line of rubber from the lip seal. I have just removed this with light rubbing by my finger nail. I do not think there is a high spot here, there is brake fluid in the chamber so the seal has not been dry. I cleaned all the bores carefully with 1200 wet n dry last time removing any glaze just like you suggest. They still feel perfectly smooth with an even matt, not ploished, surface. I have rebuilt dozens of callipers in the past and never had to replace one but I am stumped this time. I know the car was stood for a couple of years during the last ownership, maybe the fluid is contaminated or the bores worn, I am starting to think the best route forward is remanufactured AC Delco callipers with O-ring seals and a thorough strip down of the rest of the system followed by copious flushing.
 

Alan Collins

CCCUK Member
Yes I agree if you have issues with foreign materials,change your brake fluid.
I may have been lucky with my 78 which I have had since2015 but having run around 18 months I had the same problem with leaking calliper and I decided to strip all the calipers off the car,split them push the pistons out and clean the original bores with a rotary emery tool,fit New “O” ring kit,which included pistons springs, rings,boots, bleed nipples etc and fitting them all back together I have not had a problem since.
View attachment 4529
Following my reply to Roscobbc you give me hope that I might be able to service the calliper(s) myself if I follow through with the rest of my suggestions mirroring what you did on your vette. The bores look OK but the pistons look like they are original and the external surfaces past their best. I think they are made from gun metal with a protective plating, I don't fancy cleaning them too much as it will remove any remaining plating and they will corrode even faster. New O-ring pistons sound like the solution.
 

Daytona Vette

Well-known user
Calipers on C2, C3 Vettes that have been left standing for some time quite often weep fluid, "O" ring Seals prevent that
 

Alben78

Well-known user
Just seen you photos. That is the result or water contamination via the dust cap / outer seal and maybe brake fluid. Your rebuild with O ring seals new O ring pistons plus the use of silicone fluid should solve the problem. Earlier models of the C3 were recommended to seal the outer dust cap with silicon, not sure if this is applicable to the later models but maybe worth a try if water is somehow getting in via the dust cap/ outer seal. The only problem I had with the O rings is that they seal too well and it’s sometimes difficult to depress the piston back into the caliper on re assembly.
 

Alan Collins

CCCUK Member
Just seen you photos. That is the result or water contamination via the dust cap / outer seal and maybe brake fluid. Your rebuild with O ring seals new O ring pistons plus the use of silicone fluid should solve the problem. Earlier models of the C3 were recommended to seal the outer dust cap with silicon, not sure if this is applicable to the later models but maybe worth a try if water is somehow getting in via the dust cap/ outer seal. The only problem I had with the O rings is that they seal too well and it’s sometimes difficult to depress the piston back into the caliper on re assembly.
Hi, thanks for your advice. I agree with your observations and have got two front caliper O-Ring piston change over kits ready to fit. I shall split the calipers to gain better access for thoroughly cleaning out the dust cap grooves and pressing in the dust caps nicely. I like the idea of applying a shall bead of silicon in the grooves before pressing in.
 

Roscobbc

Moderator
Hi, thanks for your advice. I agree with your observations and have got two front caliper O-Ring piston change over kits ready to fit. I shall split the calipers to gain better access for thoroughly cleaning out the dust cap grooves and pressing in the dust caps nicely. I like the idea of applying a shall bead of silicon in the grooves before pressing in.
Perhaps don't 'split' the caliper halves unless you really need too - "if they ain't broke - don't fix 'em" - they will be challenging possibly to torque-up.........?
 

curious bystander

CCCUK Member
It's not the torquing up Ross. The mating surfaces aren't exactly perfectly machined so might not seal up without potential leaks. That said if you don't split them it's difficult to fit the dust seals properly. I've done it both ways. Pros and cons :unsure:
 

Alan Collins

CCCUK Member
It's not the torquing up Ross. The mating surfaces aren't exactly perfectly machined so might not seal up without potential leaks. That said if you don't split them it's difficult to fit the dust seals properly. I've done it both ways. Pros and cons :unsure:
Hi Guys, another can of worms opened. I didn't split last time as I agree with Rob, leave well alone if all is working however fitting the dustcaps was a real mission hence the water ingress. My O-Ring kits came with the O-Rings for joining the two calliper halves so I reckoned to try splitting this time. Upgrading the front brakes on my Capri based kit car to vented discs required fitting a sandwich plate between the two halves of the callipers, worked first time without any drama so far as I recall. Any other opinions on this one?
 
Top