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Über Genius
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I figure this could use it's own thread. I looked and couldn't find one that was straight to the point in the first couple of posts..


Rebuilding brake calipers is not a huge undertaking. The hardest part is getting the pistons out.

First off, DON NOT split the calipers. There's no need to and it will only cause problems later.

When rebuilding the pistons on my first GT I used a really bad method to remove the pistons. I utilized a pair of screwdrivers and, using the groove for the seal, I walked the pistons out a little at a time.

The preferred method is to use pressure. You "can" do it by using the brake pedal and a friend but that's tricky and messy.

The best method is to use air. Just put a rubber nozzle on an air spray nozzle, attached to an air compressor, and you can push them out with the compressed air.

TIP: When using air on stubborn pistons it's going to be a LOT easier if you remove the seal, spray the piston with WD40, and then compress the piston in with a clamp. It makes piston removal take a lot less pressure.

The difficult thing is to pull both pistons at the same time. Once one piston is removed, the leaking air from the empty chamber makes it more difficult to remove the second piston with air.

TIP: After removing one piston, remove the rubber seal inside the piston bore. Then put the piston back in and clamp it in place. It will seal enough to allow pressure to push the second piston out.

It's important that the pistons are protected from smacking into metal when they are expelled from their bore. Sometimes the air pressure can be very violent and could damage the piston if it smacks the other side. Use a rag or a piece of wood to protect the piston face as it is expelled.

TIP: Do NOT use your finger to slow the expulsion of the piston when using air pressure. The piston can come out very fast and your finger can be smashed (Yes, I smashed mine which is why I'm adding this caveat).

You might be able to reuse the seals and the O-rings if the piston isn't damaged and the caliper wasn't leaking. It's always best, however, to use new rubber parts.

Most of the time the pistons will be reusable. You should clean them with soap, acetone, brake cleaner or any other solvent and using a green scotch brite pad is safe.

If there is ANY pitting on the sealing surface of the piston then it should be discarded. The outer piston walls should be perfectly smooth or the caliper may leak.

Check for rust in the piston bore. A light bit of rust is to be expected and can be smoothed out with 400 grit sand paper. When using sandpaper, follow the curve of the caliper bore. These are guide surfaces and aren't extremely critical to be perfect but you do not want to change the dimensions. The rubber seal is the most important and critical part.

TIP: Instead of using sandpaper to remove rust in the caliper bore you can soak the entire caliper in Evaporust® which will remove the rust but not the metal. Make sure to remove ALL of the evaporust with warm water, running it through the passages as well. Dry the caliper in your oven at 200°F for 20-30 minutes so new rust won't form.

CLEAN everything really well. Use a toothbrush to clean the groove where the inner seal sits. Then a final cleaning with a spray of Brake cleaner before assembly.

When installing, lubricate the parts with brake fluid as you assemble them. Brake fluid isn't an amazing lubricant but it's better than nothing and won't contaminate the system.

The outer seal is installed by pushing the piston past the inner seal but leaving 1/4 of the piston showing. Then put the seal over the piston so it just sits in the piston groove. Then push the piston in all the way and push the outer edges of the seal into their groove.

TIP: Using brake fluid as a lubricant on this stage helps as well. Don't saturate things, just use a light coating.

Before installing the pads, use brake cleaner to remove any and all excess brake fluid that went on as assembly lubrication.

If you are going to paint your calipers, use a HIGH heat paint. Brake calipers can get very hot so the hotter the better. Powdercoating holds up better than paint.

I hope this helps someone out there.
 
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When rebuilding calipers in a brake shop we used to use a special assembly lube on the piston seals and any other rubber parts. It was supposed to have stuff in it that was good for rubber seals. Unfortunately I don't remember the brand. Raybestos maybe? It may or may not be better than brake fluid but we were told to use it on every rebuild. Probably a reason for that since it cost them extra money to use it.
 

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Bikini Inspector
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For real stubborn stuck pistons where air pressure doesnt work....

hook up a grease gun to bleeder.

6-800 grit after the big stuff is knocked down. take your time and make sure ot your pistons will stick again, and you wasted all that effort.
 

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When rebuilding calipers in a brake shop we used to use a special assembly lube on the piston seals and any other rubber parts. It was supposed to have stuff in it that was good for rubber seals.
From SIL-GLYDE's website:
The material is formulated for optimal performance for all braking systems. Protects and seals out moisture, where other types of lubricants may deteriorate the rubber parts causing failure. SIL-GLYDE Brake Lubricant is recommended for stopping pad squeal, caliper slides, back-side of disc pads, for ease of rebuilding & assembly, backing plate contacts, for lubricating caliper piston bores, anchor & slider bolts, adjusters, and parking brakes.
I use a different brand than SIL-GLYDE because I didn't know about it at the time I purchased the piston lube I currently use. I'll probably switch IF I ever run out of what I've been using.

Harold

P.S. SIL-GLYDE is also good to lube your door weatherstripping to prevent seal damage from sticking doors due to freezing.
 

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I figure this could use it's own thread. I looked and couldn't find one that was straight to the point in the first couple of posts..


Rebuilding brake calipers is not a huge undertaking. The hardest part is getting the pistons out.

First off, DON NOT split the calipers. There's no need to and it will only cause problems later.

When rebuilding the pistons on my first GT I used a really bad method to remove the pistons. I utilized a pair of screwdrivers and, using the groove for the seal, I walked the pistons out a little at a time.

The preferred method is to use pressure. You "can" do it by using the brake pedal and a friend but that's tricky and messy.

The best method is to use air. Just put a rubber nozzle on an air spray nozzle, attached to an air compressor, and you can push them out with the compressed air.

TIP: When using air on stubborn pistons it's going to be a LOT easier if you remove the seal, spray the piston with WD40, and then compress the piston in with a clamp. It makes piston removal take a lot less pressure.

The difficult thing is to pull both pistons at the same time. Once one piston is removed, the leaking air from the empty chamber makes it more difficult to remove the second piston with air.

TIP: After removing one piston, remove the rubber seal inside the piston bore. Then put the piston back in and clamp it in place. It will seal enough to allow pressure to push the second piston out.

It's important that the pistons are protected from smacking into metal when they are expelled from their bore. Sometimes the air pressure can be very violent and could damage the piston if it smacks the other side. Use a rag or a piece of wood to protect the piston face as it is expelled.

TIP: Do NOT use your finger to slow the expulsion of the piston when using air pressure. The piston can come out very fast and your finger can be smashed (Yes, I smashed mine which is why I'm adding this caveat).

You might be able to reuse the seals and the O-rings if the piston isn't damaged and the caliper wasn't leaking. It's always best, however, to use new rubber parts.

Most of the time the pistons will be reusable. You should clean them with soap, acetone, brake cleaner or any other solvent and using a green scotch brite pad is safe.

If there is ANY pitting on the sealing surface of the piston then it should be discarded. The outer piston walls should be perfectly smooth or the caliper may leak.

Check for rust in the piston bore. A light bit of rust is to be expected and can be smoothed out with 400 grit sand paper. When using sandpaper, follow the curve of the caliper bore. These are guide surfaces and aren't extremely critical to be perfect but you do not want to change the dimensions. The rubber seal is the most important and critical part.

TIP: Instead of using sandpaper to remove rust in the caliper bore you can soak the entire caliper in Evaporust® which will remove the rust but not the metal. Make sure to remove ALL of the evaporust with warm water, running it through the passages as well. Dry the caliper in your oven at 200°F for 20-30 minutes so new rust won't form.

CLEAN everything really well. Use a toothbrush to clean the groove where the inner seal sits. Then a final cleaning with a spray of Brake cleaner before assembly.

When installing, lubricate the parts with brake fluid as you assemble them. Brake fluid isn't an amazing lubricant but it's better than nothing and won't contaminate the system.

The outer seal is installed by pushing the piston past the inner seal but leaving 1/4 of the piston showing. Then put the seal over the piston so it just sits in the piston groove. Then push the piston in all the way and push the outer edges of the seal into their groove.

TIP: Using brake fluid as a lubricant on this stage helps as well. Don't saturate things, just use a light coating.

Before installing the pads, use brake cleaner to remove any and all excess brake fluid that went on as assembly lubrication.

If you are going to paint your calipers, use a HIGH heat paint. Brake calipers can get very hot so the hotter the better. Powdercoating holds up better than paint.

I hope this helps someone out there.
Just wanted to thank you for all of the great information in your above post. You make it sound pretty easy and with your detailed instructions I think it just may be. However like all Opel projects, at least for me, they always seem to take longer than I think they should, but that's OK I have the time now to take my time. I have the rebuild kits, came in last week so I am ready to go. I also am replacing the rubber hoses with the stainless steel ones and the j lines and clips. I am going to use aircraft print remover, a first for me, and strip them and then a wire wheel to remove anything left for a good smooth finish and after rebuilt paint them gloss black with engine paint, Hi temp at your recommendation and then clear coat which is rated at 300 degrees. They should last another 50 years and with the addition last year of a new mastercylinder and brake booster the brakes can come off of my project list. I will also replace the lines and the fittings - all new stopping power. Thanks again, not just educated now but motivated as well, and that really helps....
 

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Thanks First Opel, I put your tips to use today and started my brake caliper rebuild project. Your directions/instructions were right on. I was amazed how easily the pistons popped out and your advice to use something to stop the piston was well taken as the pistons really come out easily and fast. I used a rag as a soft stop and bingo no problems.
Was happy to see that my pistons were in perfect shape, still a mirror finish with no pitting and I saw no signs of any leaking - the seals were also in great shape. I had replaced the outer seals 20 odd years ago but not the inter seal. I cleaned up the caliper using paint remover and a wire wheel and will paint it over the weekend. Only did one so a before and after shot, will finish them both tomorrow. Again thanks for taking the time to make it simple. Still a lot of work involved but no surprises....Except one. I notice that the rebuild kit, from OGTS, comes with 2 small rubber seals, about the size of the a pencil eraser but there were no seals like that in my calipers??? They do however fit the brake line hole ?

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Opeler
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Thanks First Opel, I put your tips to use today and started my brake caliper rebuild project. Your directions/instructions were right on. I was amazed how easily the pistons popped out and your advice to use something to stop the piston was well taken as the pistons really come out easily and fast. I used a rag as a soft stop and bingo no problems.
Was happy to see that my pistons were in perfect shape, still a mirror finish with no pitting and I saw no signs of any leaking - the seals were also in great shape. I had replaced the outer seals 20 odd years ago but not the inter seal. I cleaned up the caliper using paint remover and a wire wheel and will paint it over the weekend. Only did one so a before and after shot, will finish them both tomorrow. Again thanks for taking the time to make it simple. Still a lot of work involved but no surprises....Except one. I notice that the rebuild kit, from OGTS, comes with 2 small rubber seals, about the size of the a pencil eraser but there were no seals like that in my calipers??? They do however fit the brake line hole ?

View attachment 434088


View attachment 434087
Are the two round rubber "seals" perhaps rubber protective caps for the bleed ports on the calipers? Didn't see a picture of them..
 

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First off, DO NOT split the calipers. There's no need to and it will only cause problems later.
..Except one. I notice that the rebuild kit, from OGTS, comes with 2 small rubber seals, about the size of the a pencil eraser but there were no seals like that in my calipers??? They do however fit the brake line hole ?
For many, many years, and until quite recently, it was verboten to split the calipers, as the inner square-sided O-rings were not available. Splitting the calipers and re-using the original O-rings often resulted in a leaking caliper. Not good.

A few folks found reasonable replacement O-rings, but they seemed to be a bit of a secret.

But for at least a year or three, OGTS now includes the special O-rings in their rebuild kits. It isn't always necessary to split the calipers, but it is no longer forbidden. And in fact, a proper rebuild where the cylinders need to be honed is impossible without splitting the calipers.

Oddly, the OGTS instructions that come with the caliper rebuild kits do not mention that the special O-rings are included. But trust me, I have spoken to Gil on this matter. Oh, and their kit for the 1975 Manta/Ascona Big Brake calipers also has the special O-rings.

HTH
 

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Just to add to what Keith has said, I rebuilt a set of calipers years back, before I even heard about not splitting them. I just took the caliper piece to a hardware store and just kept test fitting till I found the best fit. I would suggest that you try and find an older more established hardware store that carries a lot of stuff.
These calipers are still sealed perfectly to this day.
 

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Greetings Gene, I have decided not to split the calipers so no need for the small seals and I am basing that on the condition of the internal rubber seals and the fact that I had no leakage. I am assuming that the large internal replacement seals provided by OGTS are the correct size and material as I have not read anything to the contrary. Frankly I am tempted to reuse the old ones as they look and feel pristine and again did not leak. I too have found a lot of things that I needed for the GT at the hardware store. Just curious, did you know when you bought the seals from the hardware store that they would work with brake fluid. I understand some rubber does not hold up well to brake fluid.
Thanks, Carl
 

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Greetings Gene, I will not be splitting the calipers so no need for the small seals and I am basing that on the condition of the internal rubber seals and the fact that I had no leakage. I am assuming that the large internal replacement seals provided by OGTS are the correct size and material as I have not read anything to the contrary. Frankly I am tempted to reuse the old ones as they look and feel pristine and again did not leak.
 

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Can someone tell me the OGTS part number for the stock 72 GT caliper rebuild kit? The only ones I found on the website were the 75’ big brake kits 4039. I ended up buying a centric 143.36001 kit to do one caliper off evilbay. I’d like to tack on the other kit to my OGTS next order. I’ve got 2 1970 GT calipers on my shelf
 

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Cub, part number 4029 caliper rebuild kit, 68-74 front brakes 48mm. $19.00 each. 2 outer seals/dust covers 2 inside seals 2 clips to hold outside dust covers in place and 2 small seals, I learned today, for the interior of the caliper in the event you split the caliper. My calipers are in great shape, no rust and a mirror finish on the pistons so I chose not to split it. Carl
 

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Just a couple of final notes to add to First Opel 1981's well done instructions/tips on rebuilding front brake calipers.
  • The more I thought about your comment about walking the pistions out with screw drivers, pretty sure I did the same thing as it was back before the forum and I had no idea so pretty sure I replace the outer and inner seals using that method as there was evidence of that taking place, in the late 90's
  • Don't know if it is important but I marked not only the right and left calipers but also marked the pistons to be sure I put them back in the same bore they came out of
  • My pistons were in perfect condition however there was a little light rust/discoloration, in a couple areas on the bore, mostly on the outer ring, that is outside of the inner seal, which I removed with 1000 grit sand paper - 400 grit seemed a little aggressive - but that is just my opinion and being cautious
  • Replacing the outer dust covers/outer seals and retainer rings worked really well for me if I closed the piston to almost closed - they seemed to fit most naturally at this position - I reused the retailing clips from my last rebuilt in the late 90's as I liked them more than the newer ones. The newer ones were round where the old ones were flat
Again your directions were spot on and a simple, a straight forward process to follow. My calipers are now reassembled as per your directions and I used airplane paint remover and them wire wheels to completely clean the exterior of the calipers so that the next warm day I can paint them so they will not only be close to new operationally but will also look the part, but who cares about the paint as I will be the only one that see them - but I think there are a lot of those of us inflicted with opelitious that take the same kind of steps. Wait till you see what I do with my new copper brake lines!!!!
 

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Using aircraft paint remover for stripping the calipers and using a wire brush to finish the job was a process but the results turned out pretty good. Once I get started on something like this I am all in so I had to clean the parts that hold the brake pads in place as well - I painted the cross shaped part and put the pins in my drill holding them against sand paper, made pretty quick work of the rust, couple minutes tops. Wish I could have done that on my wheels. I plan to put a light coat of grease on the pins to prevent them from rusting again, hopefully. I am also adding the stainless steel brake tubes as pictured. I will have this all reassembled tomorrow, after the paint has cured for 24 hours and then I start on the back brakes to be sure the cylinders are at 100%. One of the problems I am running into is remembering everything I did 25 years ago which is when I did the majority of the work and at that time thought I was finished, LOL. Pretty sure that I replaced the pistons and seals but don't recall the condition of the cylinders so I am going to check that out and move forward from there. Next I will get the additional tools needed for the installation of new brake line starting from the back of the car, yea that's right, the easy part. Everything there is right out in the open and easy to get at. I will be using the copper/nickel combination 3/16 brake line as it is much easier to bend and I can do that no problem all the way to the master cylinder. Then I will remover the alternator the coil and voltage regulator so that I can tackle the driver side brake line, I hope/think I can pull that off - that leaves the passenger side and I just do not see a way to do that with out removing the engine, not going to do that just to install some brake line. Have been practicing my inverted flairs and getting pretty good at it - again thanks to YouTube. See below for the fruits of my labor leading to installation tomorrow. Hope First Opel does not mind me adding to his thread - I hope the additional information will help current and future Opel owners and as I have always said pictures make it seem so much more real, make it easier to understand. And considering the next generation of Opel owners will not have grown up working on their car for decades, like most of us did, This kind of information and pictures/videos will go a long way in helping them to figure it out. At this point and I have said it before, I am just a caretaker with my purpose," to pass on the best example of an Opel GT that I am capable of. Everyone understands that really means what all of you have taught me as I could not pass on this car without all of the knowledge and expertise of the members that contribute to the cause daily. Thanks all, Carl

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