fitting rubber seal rear caliper

Started by Mollydog, December 5, 2022, 20:06

0 Members and 1 Guest are viewing this topic.


This past weekend I replaced the rear pads on my MR2, apart from trying to take out the two Clevis Pins, which were both rust welded to the hand brake lever on the calipers, the process of removing the old pads was straight forward

Only snag I had was when rewinding the piston on the second caliper, I must have caught the rubber seal as it started to weep oil

I've ordered new seals and piston which will arrive tomorrow, I've looked at a few YouTube videos on the method of fitting the main seal to the piston and have seen two methods,

one with the seal first seated to the caliper then slide/screw in the piston in to the seal/caliper finally fitting the metal ring

then the other way with seal attached to the piston and screwing/sliding both in to the caliper together and finally fitting the metal ring

Any opinions on which is the better method/easier?


By 'main seal' do you mean the bellows style dust cover? 

The main seal is inside the bore of the caliper.  If it's leaking, the main seal is damaged.  When you take it out, you need to clean out the groove it sits in, before you put in a new seal.  Lubricate it with brake fluid before you wind the piston in.  I wind the piston in most of the way before installing the dust cover.
Perry Byrnes Memorial Award 2016, 2018.  Love this club.



In spring 2022 I dismantled front and rear calipers, cleaning the caliper bodies inside and out with the idea of renewing pistons and seals. But I found that to totally refurbish the rears required tools that I did not have and decided instead to replace the rears with new, with a 5 year warranty at £75 each.
Fronts were more straight forward and I renewed the internal components.
What I did find was that a 20 year old caliper is very dirty inside and the seal retaining grooves need some careful, but quite aggressive cleaning.
I removed the calipers to do the work.
Based upon what I did on the fronts:
The square section seal should be placed in the cleaned caliper groove, I greased this first with the supplied special grease.
Iirc I placed the dust cover into the groove of the piston, lubricating the edges of the cover.
Pulling the cover back to expose some of the piston and lubricating that,  I pushed/ rotated the piston past the caliper seal.
I did think that it would be awkward to place the dust cover into the caliper but that was not the case.
Once in carefully place the metal ring.

As said iirc as when I was thinking about it I thought that the difficult part would be fitting the dust cover and ring and so tried to do that first. I couldn't then see to get the piston in!
I tried both methods, the way I've described worked on the fronts for me.
With the rear you will be screwing the piston onto the handbrake mechanism. There may be a requirement to pre apply special grease but I did not research that.

@Carolyn suggests the opposite procedure, but she has done this on a rear caliper.
I have not.
As you have read elsewhere about alternatives it is likely that it can be done either way.
The major difference front to rear is the handbrake screw .
I have also amended my script to read dust cover to be correct as Carolyn.


Apologies, it's the bellows looking dust cover that I was referring to, when I was winding the piston back I grazed it and oil weeped out,

now you mention it, when I took out the actual rubber seal ring it came out with ease and it was already sapped and on closed inspection I noticed it had been what looked like chewed, Mr T replaced the pads back around 2010

Being my wife's car she used to take care of the servicing, if I remember correctly that was also the last time we took it to Mr T as while fitting the pads they phoned my wife saying the car needed all it's disks replaced (at an extra cost of £399 in 2010 money) as the disks were 95% rusty, it was at this point I drew the line and told them to just fit the pads and we never went back for its servicing, playing with un-knowledgeable peoples fear of non working brakes

Looks like the mechanic didn't take too much care when fitting the piston in to it or was already damaged before fitting

I noticed there were rubber particles in the barrel once I took out the piston but didn't cross my mind where this came from



It's things like that why we are generally not fans of main dealer type servicing.


My new seals and piston arrived this morning, one thing I noticed is the new piston is minus the screw innards as shown in the images below, any idea how to remove the innards from the old piston and in to the new one?

(New on the right)

May thanks


I had hoped you were aware of that.
To my knowledge I don't believe that can be done though maybe someone, somewhere knows why as they are offered by several suppliers!
I do know that a piston with the necessary is available at a higher cost than without.
Sorry, I can't recall which supplier.


Clean up the old piston with some 400grit wet and dry and use that.  It will be fine.  I've rebuilt a few of these and never used a new piston. 
Perry Byrnes Memorial Award 2016, 2018.  Love this club.

Call the midlife!

It's doable but you have to cut the original piston to get the plate out and then hold it in place in the new piston with the big circlip that should be in the kit.
But if it's anything like the one I used then the circlip will probably fail and render the handbrake useless.
Either swap it for a new one with the plate pressed in or as Carolyn says, clean up and reuse the original...
Oh and if you DO go down the route of cutting the original plate out you'll need a "special tool" to refit all the mechanism held in place by the pressed in plate.
60% of the time it works everytime...


If you can't save what you have-
I've had a look on the wwww and found this:
"The adjuster mechanism must be swapped from the old ..."
But I really don't know how that could be achieved.

My pistons were beyond redemption when I got them out as Imwas less than careful because I intended to replace the pistons.
But once out and looking at what was offered I realised there was a problem
I looked again at Brakeparts , they do not show the inside of the piston, but their piston is £23 or so and may be correct at that price.
I would ask the question of them.

As CTM advises
there is no way of doing it as OE !


I'll do as you say Carolyn, looks like the factory one is meant not not to come out

@Call the midlife!

Thanks for this info, another reason for using the old piston, I'll keep the new piston as a souvenir and polish up the old one,  shame they didn't explain this in their eBay add,

Shame really

Call the midlife!

You're not the first one to fall foul of it, won't be the last.
60% of the time it works everytime...


Glad i saw this before attempting to fit the bigredd o/h kit i have. Just checked and the piston is empty as above...


Quote from: Joesson on December  6, 2022, 10:38If you can't save what you have-
I've had a look on the wwww and found this:
"The adjuster mechanism must be swapped from the old ..."
But I really don't know how that could be achieved.

The above, I have now noticed referred to a MkII , not seen a similar warning for our mk111's.
Perhaps some companies are guilty of misrepresentation by omission!
I now note that there is indeed a circlip slot in the replacement piston, but as CTM mentioned his did not hold the supplied circlip,  so not a lot of use.
When I was looking for my replacements I noticed that the replacement pistons offered were generally without the hand brake mechanism.
At that time I did see pistons offered with the necessary so, hopefully still available somewhere.
As said though I decided on replacement calipers, as the parts and tools bill was too close to buying new.
Hope it works out for Mollydog but I do doubt the longevity of the new seals on the surface of those old pistons.


Yes those do look quite pitted.  Try Paul at TCB performance parts.  Best to phone.
Perry Byrnes Memorial Award 2016, 2018.  Love this club.


If these seals last me till summer then I'll have the car up on axle stand in the summer and buy proper pistons and seals and do it again (for the sake of a few more quid) I got out my small tin of Red Rubber Grease and after a dry run I went over the parts used with a good dollop of RRG

Made sure the seal ring was seated comfortable

I didn't spare the horses with the RRG

I wound in the piston before attempting fitting the dust boot in to it's slot

I've more or less lost the will to live trying to fit the metal ring round the dust cover boot, I just cat see me getting it on, is this  crucial part needed to be fitted? 

If it is then I'm taking the complete caliper to my local (Indi) garage and pay them to fit the ring



I use a dental pic to manipulate the ring.  Persevere - you'll get there.  Might be easier with a little less grease!!
Perry Byrnes Memorial Award 2016, 2018.  Love this club.



It keeps all the road grit and dirt out.  It's not unsafe per se, but your repair won't last long.
Perry Byrnes Memorial Award 2016, 2018.  Love this club.


Quote from: Mollydog on December  6, 2022, 15:34would it be safe not to fit it?

I believe you would be back to where you are now even quicker.
I would try backing off the piston to give you some more visibility.


in this case I'll have another try in the morning, then if I'm sucsefule I'll pop down the local garage to fit the metal ring for me


just had a thought... Have you got the dust cover the right way up?  it has a lop on the outer fold that takes the ring clip.
Perry Byrnes Memorial Award 2016, 2018.  Love this club.


I thought I fitted it the right way,  I fitted it this side up facing the top, the side you see when looking at the piston

And this side facing down, can't be seen when looking at the piston from the top

Fitted to the piston


That's ok.  Screw the piston out so the bellows are extended, then you can get at the lip the ring clip has to go in.  Then screw the piston back in.
Perry Byrnes Memorial Award 2016, 2018.  Love this club.


just to report back, I think I was doing it wrong,  it's firmly seated in now so will fit the calliper back on the car in the morning

I was going to give up but for the encouragement on here, it made me persevere, once I got one side firmly down the other side seemed with a little nudge to just slide in