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

[karls59tr]

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?

 

[DavidApp]

I did not have an issue getting them back in. Just lubricated the piston seal with brake fluid and applied some pressure with a flat board so I could push equally on the piston. Had more trouble getting the dust seal to stay in the grove in the cylinder.

David

 

[DavidApp]

I had more trouble getting one of the pistons out. One side came apart no problem with a careful puff of air in the brake line port. The other side one piston came out but the other one was stuck.
I ended up attaching a grease fitting to the brake line port, blanking off the other side and pumping grease in till it moved. Did not think the grease gun was going to get it done at first. At last it moved. It seems there was a blockage in the passageway in the caliper which took some time to get clear.
That may have been why the brakes were sticking on that side.

David

 

[karls59tr]

I had more trouble getting one of the pistons out. One side came apart no problem with a careful puff of air in the brake line port. The other side one piston came out but the other one was stuck.
I ended up attaching a grease fitting to the brake line port, blanking off the other side and pumping grease in till it moved. Did not think the grease gun was going to get it done at first. At last it moved. It seems there was a blockage in the passageway in the caliper which took some time to get clear.
That may have been why the brakes were sticking on that side.

David

Sounds like plan. How did you get the grease out of the caliper?

 

[Sarastro]

Pressing them into place with a vise is a time-honored method. Just be careful, and if they don't go in with modest force, take it all apart and see what's wrong.

Brakes

 

[DavidApp]

Lots of brake cleaner.

David

 

[DougME]

When I do brakes I always coat any exterior rubber seals with silicone grease, especially where they contacts the caliper and the piston. This helps prevent any water from working its way under the boot and starting the corrosion process. Brake fluid in these areas will only attract moisture. Been working well for me for many years

 

[karls59tr]

When I do brakes I always coat any exterior rubber seals with silicone grease, especially where they contacts the caliper and the piston. This helps prevent any water from working its way under the boot and starting the corrosion process. Brake fluid in these areas will only attract moisture. Been working well for me for many years

Would the silicone grease not get onto the rotor?

 

[DougME]

No reason it would, I'm not putting a lot of grease on the seals just a skim coat and working it down into the rubber/steel joint. No reason it should migrate all the way to the rotors.

 

[karls59tr]

No reason it would, I'm not putting a lot of grease on the seals just a skim coat and working it down into the rubber/steel joint. No reason it should migrate all the way to the rotors.

I see your point. I looked at that rubber steel joint on the piston that you mentioned and did see rust build up there. I will be ordering new pistons soon and will make sure to lubricate that area. I see that Moss does not have the standard rubber seal kit for the pistons. I found an unused original Girling set in a parts bin I had. The TRW outer seal that Moss shows look quite different than stock ones? Did you use those on your last rebuild?

 

[DougME]

Ummmm, haven't finished my TR-3 calipers but I've done this on eight vehicles in the last 10 yrs.

 

[karls59tr]

Ummmm, haven't finished my TR-3 calipers but I've done this on eight vehicles in the last 10 yrs.

Did you use the "TRW seal kit" from Moss on any of your rebuilds and did you notice any difference between that kit and the original "Girling seal kit" ?

 

[DougME]

Kind of stalled at this point on the TR-3, I've never used the TRW brand on any of my rebuilds just Girling or FLAPS.

 

[charleyf]

If you are using a vise to press in the pistons in place you must be separating the two halves of the caliper. This operation does not require you to do that. I have done quite a few now and have never separated the calipers.
Also I use a 1" by 3" by 12" board to push the pistons into the calipers. Very little force is needed. The key is getting them in straight.
Charley

 

[karls59tr]

If you are using a vise to press in the pistons in place you must be separating the two halves of the caliper. This operation does not require you to do that. I have done quite a few now and have never separated the calipers.
Also I use a 1" by 3" by 12" board to push the pistons into the calipers. Very little force is needed. The key is getting them in straight.
Charley

Thanks. That's why I did not understand Sarastros post. Normally TR3 calipers are never separated as there is no known torque value to reinstall the halves.

 

[Hamish Racing]

Thanks. That's why I did not understand Sarastros post. Normally TR3 calipers are never separated as there is no known torque value to reinstall the halves.

i did this on my sp250 the brakes are the same and the workshop manual gives figures.
but there is a small rubber "o" ring that seals the 2 faces that you would need to find and ensure they are brake fluid compatible
see the attached as there are differing numbers for the inner and outer bolts and it shows which is which.

H

 

[karls59tr]

i did this on my sp250 the brakes are the same and the workshop manual gives figures.
but there is a small rubber "o" ring that seals the 2 faces that you would need to find and ensure they are brake fluid compatible
see the attached as there are differing numbers for the inner and outer bolts and it shows which is which.

H

Were you able to find a torque value for those bolt? What torque did you go with? I've always heard that it is not necessary to or advisable to separate the caliper halves but I see how it would be easier to compress the pistons. Some say the new pistons go in quite easily?

 

[Hamish Racing]

Were you able to find a torque value for those bolt? What torque did you go with? I've always heard that it is not necessary to or advisable to separate the caliper halves but I see how it would be easier to compress the pistons. Some say the new pistons go in quite easily?

All the info is in the pictures I posted of the Daimler workshop manual

 

[karls59tr]

I've never seen that in any TR3 workshop manual. Thanks. This is excellent info to know.

 

[Hamish Racing]

I would add that the sp250 calipers are the same type as the later TR4 etc as they have the pad retaining pins. Unlike the earlier spring metal plate of the 3a.
But having done the sp250 brakes there is nothing scary in splitting the caliper (if you really have to)