Rear Caliper Internal Mechanism

[stuMR2lee]

As part of my brake refurbishments I've come across a few rear Pistons that come empty without the mechanisms.

Guides online show that the mechanism needs to be removed from the old piston. It doesn't just lever up though. The guides I found were pretty vague.

So, after a bit of practice I have it down to 3 angle grinder cuts (in a vice for safety with googles on).

First cut is horizontal and a few mm below the retainer. Second and third cuts are either side of the retainer plate. The aim being not to ruin the retainer plate or mechanism.

Once the cutting is done lever away the flap you created and the mechanism will come out. Be warned it's very hot.

[_Al_]

Interesting!

What does the mechanism actually do? Is it part of the handbrake (you mentioned rear only).

Wonder how they get it in there in the first place? And how do you get it in the new piston?

[stuMR2lee]

It is the handbrake self adjuster mechanism. Fronts are just straight Pistons that can be pushed in rather than requiring a rewind tool.

Good guide in the KY2 (for a MK1 but principle the same): http://www.mr2oc.co.uk/know-your-2-know ... kbartid=81

Short video of how it works: http://youtu.be/g12uwGnKwlY

Very useful post (MK3 but same principle): http://mr2.org.nz/phpbb3/viewtopic.php?t=8790

[_Al_]

Right, got it. So by slicing the old piston you're avoiding the need for the Adjusting nut SST and circlip pliers?

[stuMR2lee]

No mate. You're confusing the caliper internal mechanism (SST/Circlip pliers needed):

With the piston internal mechanism (angle grinder needed):

Toyota never designed the Pistons to be rebuildable. That's just a function of aftermarket Pistons being hollow and needing the old piston internals.

[_Al_]

O I C!

Glad you've got an eye for detail.. I'm forever missing / misinterpreting bits like that.

[richstany]

Did the new piston have a slot cut for the internal clip that you've used to retain the mechanism? Although I didn't need to replace my rear pistons I did wonder how you would go about fitting the mechanism into a new one as the factory ones look machine pressed in.

[stuMR2lee]

Replacement rear Pistons come with a cutout lip machined in for a Circlip . Actually easy to put back together once you have the mechanism out of the old Piston.

[MR2DI4]

The only reason you would need to pull the rear self adjuster out of the calliper itself is to replace the rear o-ring seal and personally I did not bother. If its not leaking then just clean the housings and pistons and reassemble, mine didn't even need new main seals but I got the rebuild set from Toyota. Its pretty hard to see why they cease up so badly even when apart but with everything cleaned up and the pistons inspected for any pitting they can be reassembled and with a new set of brake cables you can expect another 20 years of service.

The hassle is sometimes you do need another set of callipers to make a good set if the pistons are pitted as Toyota informed me the pistons themselves are no longer available.

[baileydom]

I disagree, its very very obvious why they seize up so badly. Usually, the brake fluid hasn't been changed often enough, the wrong type of grease has been used on the sliders by garages and owners, the seals perish and let in dirt which scores the pistons plus general wear and tear. Both myself and stu have pulled apart a lot of calipers from a lot of mr2s and 95% of the time if they haven't been regularly maintained then they at least need new dust and fluid seals and sometimes new pistons as well. The sliders are also usually far too stiff or seized and the pad springs are usually so caked in crud that the pads don't slide properly.

Also, I do not agree that brake calipers are a 'repair and forget for another 20 years' type job. They should be checked on a regular basis when pads etc are replaced.

UK roads, especially in the winter, are not kind to mr2 brakes. Please service them on a regular basis people, it makes a massive difference.

[stuMR2lee]

^this. Plus there are 2 seals on the handbrake mechanism.

The one under the handbrake lever arm fails and lets in dirt & water which causes rust. Pictures here: http://mr2.org.nz/phpbb3/viewtopic.php?t=8790. This is the cause of many a seized handbrake (there are small needle bearings inside which need to be kept clean). As is failing handbrake cables which is even more common.

This seal is included in Biggred's kit, along with the small o-ring that goes on the threaded pin.

A lot of people don't bother to replace these seals if the handbrake lever moves freely and that's your choice.

However if one caliper is starting to stick then I prefer to replace the seals and re-grease where needed.

Interestingly we have also had to strip down failed calipers that have previously been 'professionally' refurbished. The reason being that the needle bearings have been replaced by a nylon sleeve! Again if dirt gets in it becomes too tight and the lever doesn't move freely.

I've been DIY stripping and rebuilding brake systems since I was 16. Garage Mechanics won't do this as it is not cost effective for their time hence a new/re-manufactured caliper will be used.

Obviously if you are not confident to work on your own car then spend the extra £100 a pair (after cash back) and buy remanufactured ones. Brakes are a crucial safety feature.

As Dom says, they need regular cleaning & maintenance.

[SonicSW20]

All in favour of changing the 'Regional Rep' badge under Stu's name to 'MR2 Brake Guru'?

Top stuff as always. Plus, it's a great excuse to cut things with power tools, which is obviously the most important bit.

[stuMR2lee]

Yes, it's just an excuse to get the angle grinder out. It was disappointing on Saturday when Henry turned up with ones that had already had replacement Pistons previously. They were still seized up though and had an added complication I won't go into!

[SonicSW20]

Was Henry was the chap on Facebook where I tagged you in my reply to his post? I said on there about the pistons with and without internals after you did mine, so I think I owe you an apology for taking away an angle grinder opportunity... Sorry Stu!