TR2/3/3A Brake caliper piston install?

[karls59tr]

Has anyone made a video of installing new brake caliper pistons? I thought I saw a post where someone had a good method of doing this using a vice? Moss posted a method of heating the caliper and freezing the pistons.....has anyone tried this? What is the best method to do the install? I have the red rubber grease to coat the pistons. I was thinking I would not put any grease in the actual piston seal "groove" but just lubricate the "outer part of the seal that will contact the caliper bore" so as to better keep the seal in place when the piston is inserted. Not talking about the dust boot seal.
Karl

 

[Hamish Racing]

Karl they shouldn’t be that difficult. The tolerance should be compensated by the o ring seal.
they should be a push fit. I did this on a Daimler sp250 that have very similar brakes.
I haven’t watched this but may show the internals.

 

[karls59tr]

Has anyone made a video of installing new brake caliper pistons? I thought I saw a post where someone had a good method of doing this using a vice? Moss posted a method of heating the caliper and freezing the pistons.....has anyone tried this? What is the best method to do the install? I have the red rubber grease to coat the pistons. I was thinking I would not put any grease in the actual piston seal "groove" but just lubricate the "outer part of the seal that will contact the caliper bore" so as to better keep the seal in place when the piston is inserted. Not talking about the dust boot seal.
Karl

I just realized that I posted this question once before. Must be getting old.

 

[bobhustead]

Our late friend Randall Young would point out that heated metal expands in all directions. It would only make a hole bigger if the mass of metal surrounding the hole is noticeably smaller than the volume of the hole. Seems unlikely on a caliper.

Bob

 

[DrEntropy]

Shouldn't be necessary to use much force, and use the red grease on the piston, not the seal. Less chance for fluid contamination. An equal pressure with thumbs is all it should take to put the pistons in place, the boot is what usually becomes the challenge. That just requires patience! I've found a "popscicle stick" the best tool to use for getting the boots into the grooves. No metal objects.

 

[bobhustead]

Agree with doc on the problem being the boot.
Bob

 

[DavidApp]

I thought that separating caliper halves was frowned on as there is no Torque numbers on the bolts that hold them together.

I used one of the small picks that HF has to ease the dust seal over the piston. and a block of wood gives you enough leverage to push the piston in by hand.
If the fit is so close that you have to freeze the piston and heat the caliper something must be wrong. That sounds more like fitting a bearing on a shaft.

David

 

[DrEntropy]

I thought that separating caliper halves was frowned on as there is no Torque numbers on the bolts that hold them together.

Not an unheard of procedure, torque can be determined by bolt size and grade from torque charts. Done it many times when pistons refuse to be removed due to corrosion or gunk.

I used one of the small picks that HF has to ease the dust seal over the piston. and a block of wood gives you enough leverage to push the piston in by hand.
If the fit is so close that you have to freeze the piston and heat the caliper something must be wrong. That sounds more like fitting a bearing on a shaft.

As said above, no metal tools for seating boots here, too much chance for a slip and ruining a boot.

And yep, no brake piston should be an interference fit in the bore. Should move in and out smoothly with no seal or boot, as a check for fit.

 

[CJD]

+1 Only lubricate the seal with brake fluid...not the red grease. The grease is for the piston to the back of the pads.

 

[Sarastro]

You can use a vise to press the piston into the cylinder if necessary. It should not take much force; if not for the arthritis in my thumbs, I could have just pushed the motha into place by hand.

The risk, with a vise, is that it's easy to apply too much force and damage something if it gets hung up or misaligned. If it requires any effort at all, something is wrong.

When I did this, I split the calipers because I wanted to check the seal between them; I'm sure the seal had never been replaced. That should be done every 50 years or so, whether it needs it or not.

 

[Hamish Racing]

I thought that separating caliper halves was frowned on as there is no Torque numbers on the bolts that hold them together.

I used one of the small picks that HF has to ease the dust seal over the piston. and a block of wood gives you enough leverage to push the piston in by hand.
If the fit is so close that you have to freeze the piston and heat the caliper something must be wrong. That sounds more like fitting a bearing on a shaft.

David

I posted this info previously as the Daimler sp250 workshop manual has the torque figures and as the calipers are as good as the same they should be reliable.
With pics here

TR2/3/3A - Installing Brake Caliper pistons into the bore?

I've heard that after installing new seals on the brake caliper pistons that it is very difficult to get them to fit back in the caliper bore even if they are lubricated with brake fluid. Any advise on the best way to get the pistons back in?

www.britishcarforum.com

 

[Dave SW Pa.]

I don’t have any videos but I can tell you how I’ve done it in the past and recently on my gt6+ calipers. After sand blasting the disassembled body halves on the gt6 calipers and cleaning the boot and seal grooves with a 90 degree pick, thoroughly clean with hot soap and water and follow with brake clean. Don’t let the bare metal rust!!! I painted the halves prior to overhaul. Leaving the body halves o-ring recess and opposing seat area bare metal and the piston bores and boot grooves bare also. First install the piston o-ring properly into it’s groove and then fit the boot fully into its groove. Then lubricate the o-ring and boot throat with clear silicone brake parts assembly grease suitable for inside the caliper. On the half with the brake hose connection, take a air blow gun and while holding the piston centered over the boot opening nurse enough air in slowly enough to inflate the boot against the piston bottom. Wiggle the piston around enough to pick up the boot sides and fall inside the boot. Once the piston is inside the boot take the air away, and center the piston over its bore and started into it. If you have things lubed up enough and the piston square it should push straight down in and past the seal and bottom in the bore. The piston boot can the be final fitted on and into the boot to piston outer groove. Tuck the convolutes in the boot properly and square. In the case of the other half you blow your air in through the body hole where the body o-ring seals and brake fluid passes from one side to the other. On the hose half have the bleeder in and closed.
Occasionally getting a piston all the way in can be a pain. A board across the piston, or a pry bar or something you can bare down on like a press can be helpful to push it down all the way.
The big thing is making sure everything is CLEAN and RUST FREE. any rust or anything in the piston seal groove or boot seating groove makes the hole smaller and makes getting the boot seated and the piston in more difficult.
If you can’t find the proper assembly grease that is brake fluid compatible use new brake fluid for your lubricant but the grease works much better.
I’ve been blowing up the boots to get the piston past it for 50 years. Once you get it figured out and how to roll the piston around to pick up the boot enough to puff it out and let the piston in, it work like a charm.
Good luck
Sorry this sounded so long winded.

 

[DavidApp]

Thank you.
The air trick sounds like a winner. Have to try that next time I am doing the brakes.

David

 

[Dave SW Pa.]

Dave,
BTW, I don’t think separating the halves is a big issue, personally. If the planes were straight and CLEAN, then put in a new sealing o-ring and reassemble. I torqued my bolts to 55# with no problem. They are good sized and lightly hardened. My calipers work fine and are leak free.
Like anything else with a machined mating surface, straight and clean are the most important issues in reassembly. And torqued to spec or tight enough to not leak or come back apart. There are published charts that tell you what a safe torque is for different sizes and grades of bolts.
I’ve separated 4 and 6 piston calipers in the past and rebuilt them with no issue. The only bitch with doing the pistons in multiples in the same half is sealing the piston hole to hold air while your doing the other piston. A clean rag stuffed in the other hole and a helper makes the job easier.

 

[DrEntropy]

Dave,
BTW, I don’t think separating the halves is a big issue, personally. If the planes were straight and CLEAN, then put in a new sealing o-ring and reassemble. I torqued my bolts to 55# with no problem. They are good sized and lightly hardened. My calipers work fine and are leak free.
Like anything else with a machined mating surface, straight and clean are the most important issues in reassembly. And torqued to spec or tight enough to not leak or come back apart. There are published charts that tell you what a safe torque is for different sizes and grades of bolts.
I’ve separated 4 and 6 piston calipers in the past and rebuilt them with no issue. The only bitch with doing the pistons in multiples in the same half is sealing the piston hole to hold air while your doing the other piston. A clean rag stuffed in the other hole and a helper makes the job easier.

Can't guess at the number of calipers we've done, most were totally disassembled. The seals between halves are not to be trusted in 40+ year-old calipers. Especially after all else has been taken back to like-new spec's and pressures.

 

[DavidApp]

Where does one get the seals that go between the caliper halves? I have not done much looking because I was not thinking of separating them. The TR3B calipers almost got separated but I got the job done without taking that step.

David

 

[karls59tr]

Can't guess at the number of calipers we've done, most were totally disassembled. The seals between halves are not to be trusted in 40+ year-old calipers. Especially after all else has been taken back to like-new spec's and pressures.

If this seal fails there would be outer signs of leakage ,correct?

 

[Dave SW Pa.]

I got mine from TRF. They stock them. I got them with my kits and pistons. You have to ask for them separately. The only difference was they were round o-rings and the OE ones were square cut one. Mine were in good shape so I’ve saved them.
And yes if they leak they would leak externally along the parting line. If your running wires I’d assume it wouldn’t take long to get your attention. And your master fluid level would be dropping.

 

[Dave SW Pa.]

Before pistons inserted and once completed.