Brake calipers rebuild

[Deleted member 21878]

While waiting for my swivel pins I thought I might go ahead and start on the calipers. All cleaned up, clean groove in caliper...
but is there a trick to getting the new pistons in? I can't seem to get them past the dust shields without tearing them... let alone the seal.

thanks

 

[TimK]

Did you try putting brake fluid on the seals/shields and easing the pistons in slowly? It worked for me.

 

[Deleted member 21878]

Yes I did. But I still tore the dust seal going by the lower part. I am now trying putting the pistons in the freezer.
Of course I have to order another set of seals anyway since I tore one. So I figured I would experiment with the rest of them. And hope for some secret trick....
I just can't push them thru straight I guess. I rotate them a little so I know they are sitting straight but all my weight does not push them thru.

 

[bob hughes]

I have done both of mine and found it to be dead easy.

First of all I removed the pistons using compressed air and then split them, If memory serves me right I had a problem with piston removal, one side came out easily and I had to use two screw drivers to prize the other side out. Splitting the callipers makes all the difference to this process and the subsequent rebuild.

The seal kits that I acquired came from an hydraulic specialist and contained the small square section seals in the centre of the callipers. Everything was cleaned up and I used the red rubber grease on all components; the main seal was installed and the dust seal was inserted into the groove in the calliper, by twisting the piston, and if necessary teasing the dust seal over it you can push the piston down until it meets with the main seal, keep the piston square and gently apply pressure to push it past the main seal and then tease the top of the dust seal into the lip of the piston, I used a blunt angled piece of heavy wire with no sharp edges. Job done, then bolt the sections together again.



Bob

 

[Deleted member 21878]

actually i did not have much trouble getting them apart. i did have to turn up the pressure on the air compressor a little. but eventually i got all the pistons to pop out., i did split the calipers before cleaning them up. i hear what you are saying Bob and from what i read it should not be so tough to get those pistons in. i could put all my weight on them, 200 lbs, and they would not budge. actually i think most of the issue was getting thru the dust covers.
the rubbers i was using were with the car in one of the boxes. Maybe they were old and getting hard or maybe they were not the ones i should have been using. they were in an unmarked bag. it will be inetresting to see if the ones i have coming from Moss are the same. certainly they are newer so they should be as pliable as they are going to get. i also ordered some lube from them to see if that works better than the brake fluid.
we shall see when the new seals come. just wanted to make sure there was not something i missed... like the seals needed to be put in one way or some other trick.

Thanks

 

[steveg]

On my Jag rear disc girlings you insert the square o-rings into the grooves in the bores, then push the pistons in. Then you position the dust covers around the pistons and on a lip of the caliper. A wire ring holds the cover onto the lip of the caliper. I don't understand how you rip the dust cover. Doesn't it go on last?

 

[Deleted member 21878]

these do not have a ring. that sure would make it easier i think.
the dust cover has a lip on the bottom that fits in a groove on the caliper. you push the piston thru it and the piston holds the bottom in the groove. That is the way i read it. i just can't get mine to go thru the bottom part without ripping it.
again maybe my covers were old and had shrunk some or hardened up. they did not feel like it but really hard to tell. should have new ones from Moss tomorrow.

 

[steveg]

...you push the piston thru [the dust cover]...

That can't be correct. You install the piston first, push it all the way down until it's approximately flush with the top of the caliper opening, then install the dust cover in place. The rim of the piston protrudes above the dust cover and makes contact with the backing of the brake pad. You can use a c-clamp and piece of wood to compress the piston past the sealing ring.

I suppose alternatively you could install the dust cover on the piston, then install the piston in the bore.

 

[Deleted member 21878]

hmm, i will have to see if the piston will go that deep. i ws just going with what the bentley manual says. or i am reading it wrong which is possible.

 

[bob hughes]

Steveg
Some callipers have the dust seal fixed on the outside of the bore with a clip and some have the dust seal located in a groove just inside the bore. The BJ7 certainly has the second option, not sure about a BJ8, and as I said before, you need to tease the piston into the 'top' of the fitted dust seal with a right angled gismo, then you can ease it down to meet the main seal. Use plenty of rubber grease to assist. BTW a gismo is anything with a right angle in it and fairly thin, with no sharp points or edges.



Bob

 

[steveg]

Welp - sorry I was wrong and they're so much harder to deal with than the other type.

 

[glemon]

Believe these are the same as TR250/6 caliers. I had a **** of a time with mine, spent a whole Saturday and I think I got one or maybe two at the most on and tore the others. The first rebuild kit was cast a little crude and thick, and near impossible to get in, I got another set, it was still a challenge, but doable with the second set.

 

[Deleted member 21878]

put the new seals and dust covers in today. they went in without any issue. i guess the old ones were just old enough to get a little too hard.

 

[bob hughes]

Well done



Bob