Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[kgx]

so GM is retarded. we all knew that.

anyway, i'm using a set of rear calipers (need e-brake calipers) and for some reason GM put a hole in the face of the piston. it's supposed to be sealed off by the inner piston that ratchets on the e-brake screw, but usually that inner piston seal dies and it starts to weep fluid. the inner seal is not serviceable.

so is there any reliable way to seal that hole? i've considered a screw/EPDM o-ring, JB weld (it can handle 500F continuous/600F peak and is tolerant to brake fluid) and brazing it shut. i'm afraid brazing it would warp the piston.

should i just try the JB weld? worst that can happen is it fails and leaks a tiny bit of fluid. it won't leak enough pressure to cause the brake balance to change.

any other ideas? i picked these calipers because they're the right piston area to match the porsche front calipers, they're light, they're cheap and they don't need to come off to change pads (remove pin, slide pads out the top).

anyone have any temperature data from the piston face? i know the pad faces can see upwards of 1600F, but these are rear calipers, and the pistons are on the other side of the pad material. maybe a titanium insulator plate would help.

i know they can get hot enough to boil fluid, but usually when you boil the fluid it's because the fluid is old and wet and the boiling point is significantly lower under those conditions than the 500F JB weld can handle..

[snm95ls]

Do you have access to a lathe?

I would think that a press fit plug with a shoulder that sits inboard towards the fluid chamber would suffice and be easy to make.

I would also think that carefully TIG work would work just fine as well.  how small is the piston?

[jagojon3]

Thread the hole, install a set screw or any threaded type of plug you please with JB weld.

Used this on the dodge garage dsm bov mod, works great.

[79fairmont]

Tap it to pipe thread.

[stealthiskey]

buy reman calipers from autozone for $30?

[kgx]

these aren't very common calipers (only 2 cars ever used them), so the reman thing isn't as easy as it would be with another application. even the pistons for these things are discontinued/bought out across the country. i'm rebuilding it with a new piston seal and dust boot, but everything inside that is almost impossible to find.

i may end up tapping it. the hole is about 5mm in diameter, and the material is only about 1.5mm thick though, so there isn't much meat for tapping.



thanks for the suggestions. have some titties.

[snm95ls]

I wouldn't trust 1.5 mm to hold jack squat for pressure.  I still think a press fit slug would do the trick.

Just my $0.02.

[kgx]

the  side where the hole is doesn't see brake pressure.

the whole piston looks liek this:


inside is this fucker:


you can see the inner piston at the end of the shaft. there's a seal around it that seals brake pressure away from that hole. it's when that seal goes bad, or there's internal pitting in the piston bore (my problem) when it starts to weep fluid into the section that's supposed to be sealed off.

here's another diagram:


the small yellow area on the left is the small rubber plug GM put in the hole. light green areas are pressure seals.

you may be onto something with press-fit though. maybe i can hit the hardware store and see if there's anything close to a slight interference fit that i can coax in there.

[onlyflash944]

you doing the gm 14 bolt full floating disc conversion?

[kgx]

I'm using these to balance my front brakes.

My front calipers are monoblocks from a porsche 996c4, and the pistons are 2mm bigger than the stock MR2 36mm. I'm also using supra twin turbo directionally vented front rotors, which are 323mm diameter.

My rear rotors are front rotors from a RAV4 and these calipers are 88 fiero calipers with 48mm pistons. The stock MR2 rears are 43mm, but I need the extra rear area to offset the largers area up front, and give a little extra clamp force to make up for the rav4 rotor's shorter lever arm (302mm diameter) relative to the supra bits. The stock rear rotors are larger than the fronts on the MR2.

Brake bias moves about 2.5% rearward with this setup.

[snm95ls]

Hell, now that I think about it, if one had acess to a lathe, it would be pretty easy to just make a new piston.  I assume you don't have that luxury.

Are you planning on leaving the inner piston in there?  Seems like it could possibly cause issue if there is no way to keep it located.

[nock]

silbraze the bitch and hone the caliper till it fits again....

[PhilStubbs]

use different calipers that dont have a retarded design. its not hard to make a bracket to mount almost any rear caliper where ever you want

[ApexSilver06MR]

any other ideas? i picked these calipers because they're the right piston area to match the porsche front calipers, they're light, they're cheap

get some new ones

[Ravage70]

get some new ones

[kgx]

any other ideas? i picked these calipers because they're the right piston area to match the porsche front calipers, they're light, they're cheap

get some new ones

use different calipers that dont have a retarded design. its not hard to make a bracket to mount almost any rear caliper where ever you want

unfortunately, it's not that easy.

1. it has to have the e-brake mechanism. i wish toyota had designed the MR2 to use the exclusive (drum) parking brake like the camry/celica/supra, but they didn't. exclusive e-brakes make rear caliper selection much easier.

2. you'd be surprised how hard it is to find rear brake calipers that are big enough. mid-engined cars tend to have much more rear brake bias than front-engined cars, and need bigger pistons to generate the clamp force. EVO/STi/350z etc are too small. GM is the only manufacturer using rear calipers with big enough pistons.

3. with the exception of the damn hole in the piston, they're actually really good calipers. the sliders are huge- 1" diameter. the caliper body is aluminum, the crossover is steel, so they're about 3-4lbs lighter per corner than any other e-brake caliper. pads can be pulled out the top, and every pad maker that i'd consider using makes pads for them (carbotechs are listed under the AWD pontiac 6000).

[PhilStubbs]

porsche?

[kgx]

porsche?

two problems with the porsche rears:

1. still too small for the rotors i'm running.

2. no e-brake.

thanks for the ideas. i'm going to try to press fit something in there. i think as long as i can polish the inner surface well enough, the inner piston will seal just fine. i'm probably worrying about nothing. hopefully i can hit 60-0 in 95ft with this setup.

[snm95ls]

...hopefully i can hit 60-0 in 95ft with this setup.

I hope you have some sticky tires with a good sized contact patch.

Sounds like a neat setup.

[79fairmont]

I have a nice set of sn-95 rear calipers and brackets that you might be able to use.

[kgx]

...hopefully i can hit 60-0 in 95ft with this setup.

I hope you have some sticky tires with a good sized contact patch.

Sounds like a neat setup.

235/40/17 fronts with 255/40/17 rears. brad bedell did decimated the competition with 97 ft at the SCC USSC on stock 93t brakes with those tire sizes, but with tires that aren't as sticky as what's out now.

I have a nice set of sn-95 rear calipers and brackets that you might be able to use.

if the info i'm finding on those is correct, they're 38mm. that's way too small.




here they are bolted up with the brackets i made:


and the fronts:



if only my camera didn't suck ass.

[HiProfile]

Thread the hole, install a set screw or any threaded type of plug you please with JB weld.

Used this on the dodge garage dsm bov mod, works great.

Holy fucking apples, how did they get that rod to bend inside but still stay straight on the ends? Unpossible.







Tap, preheat, braze/solder a buttonhead bolt screwed in from the backside. Win. Brake fluid will boil around 450-550F, and most tough solders will take much more.

BTW if you're really badass I'd say go with 2 smaller calipers. Per wheel. I can't remember where I've seen it though.

[NoPistons!]

use different calipers that dont have a retarded design. its not hard to make a bracket to mount almost any rear caliper where ever you want

This.