964RS brakes

[creaturecat]

Thanks Bill.
Much appreciated.

[95993CAB]

Good Evening Guys

I am hoping someone can help me understand the Used 993 Big Red Calipers I purchased. (I also purchased real 993rs rear calipers new).

I purchased 4 x 44 mm pistons and 4 x 36mm pistons per spec to rebuild the used units. The 44mm pistons fit perfectly; however, the 36mm items were swimming in the bores - way too small. I measured the pistons that came with the used calipers and they measured 40mm. My new 40 mm pistons arrived today and fit like a glove.

This leaves me a bit confused. Everything I have read about the Big Reds states piston sizes of 44 mm and 36mm. I have found no reference to 44/40mm pistons. I am unsure if the previous owner had these machined or ??? Does anyone have an answer or could point me in the right direction? Am I simply mistaken and these are correct or was I sold a different caliper altogether?

Any help is much appreciated?

Much Appreciated,
Michael

[Bill Verburg]

Originally Posted by 95993CAB

Good Evening Guys

I am hoping someone can help me understand the Used 993 Big Red Calipers I purchased. (I also purchased real 993rs rear calipers new).

I purchased 4 x 44 mm pistons and 4 x 36mm pistons per spec to rebuild the used units. The 44mm pistons fit perfectly; however, the 36mm items were swimming in the bores - way too small. I measured the pistons that came with the used calipers and they measured 40mm. My new 40 mm pistons arrived today and fit like a glove.

This leaves me a bit confused. Everything I have read about the Big Reds states piston sizes of 44 mm and 36mm. I have found no reference to 44/40mm pistons. I am unsure if the previous owner had these machined or ??? Does anyone have an answer or could point me in the right direction? Am I simply mistaken and these are correct or was I sold a different caliper altogether?

Any help is much appreciated?

Much Appreciated,
Michael

As I told you over on Rennlist, pictures would be necessary.

You either have misidentified or modified calipers

[95993CAB]

Bill

Sorry, I didn't see your note on Rennlist. Thank you for the help. Attached are photos.

Sincerely,
Michael

[perelet]

Looks like audi s8 44/40mm calipers - can see cotter pin holes on your pics. Porsche calipers use quick release wire clamps and no cotter pins - see pics in the beginning of this thread.

PS. "if" they fit you may try to experiment, they will increase front bias.
Oleg.

[Bill Verburg]

Originally Posted by 95993CAB

Bill

Sorry, I didn't see your note on Rennlist. Thank you for the help. Attached are photos.

Sincerely,
Michael

are they really axial mounts? W/ ears?

I believe that those are the fronts from a Brambo Kit, probably the GT2 kit, but they could be something else like that too(Possibly Audi S8 too). The GTP fronts were 40/44 the rears were either 28/30, 30/36 or 36/44 depending on the year, they had real issues w/ bias

Definitely not any Brembo that came oe on a Porsche

[95993CAB]

Thanks guys - easy to understand if you know where to look. I purchased these used represented as Porsche 993 Big Reds from a popular Dismantler on the West Coast. 2nd time I've had a bad experience with them. I appreciate the identification.

This upgrade has been an odyssey, but I'll press on. New calipers on order. I'll let you guys know how it turns out.

[Boydyrs]

Guys this thread is very informative but can someone suggest best way forward to upgrade rear brake assembly on '89/'90 964 C2 with small single piston rear caliper?
Also is it easier to replace the rear arms to later style?

[Bill Verburg]

Originally Posted by Boydyrs

Guys this thread is very informative but can someone suggest best way forward to upgrade rear brake assembly on '89/'90 964 C2 with small single piston rear caliper?
Also is it easier to replace the rear arms to later style?

Depends on what you mean by a brake upgrade.

The 2 piston rears actually develop more brake toque than the 4 pistons, the 4 pistons have a bigger pad, it's actually the same as the front pad.

If you want to use a 4 piston rear caliper then any 964 rear(not RS) bolts in. The 944 4 piston rears would also work but the bleeds and feed would need to be swapped on those.

you would be looking for 28/30 axial mount calipers

On left 2 piston on right 4 piston, both are 9634 rears

[Boydyrs]

Thanks Bill, what would be a really good set up/recomendation for fast road/track with KW Clubsport with top mounts, front and rear for '89/'90 C2?
Can I and is it worth changing the rear arms to later style in light of above?
Not trying to recreate the wheel but value the knowledge of experience

Raymond

[Bill Verburg]

Originally Posted by Boydyrs

Thanks Bill, what would be a really good set up/recomendation for fast road/track with KW Clubsport with top mounts, front and rear for '89/'90 C2?
Can I and is it worth changing the rear arms to later style in light of above?
Not trying to recreate the wheel but value the knowledge of experience

Raymond

Not sure what you mean by changing the rear arms on a 964.
AFAIK there were 3 types, normal, RS and turbo. Turbo owners often change to the RS because they can use wider wheels and the RS uses extra washers to stiffen the connection to the chassis. You could use RS arms on a normal car too.

Another option is to replace the rubber joints w/ spherical joints like this


Lots of people use the stock 964 brakes w/o any trouble, one reason to change to the 4 pistons would be to use the same pads f/r newer pads in front then cycle them to the back and for better pad selection. So from that point of view stock w/ race pads and relly good fresh brake fluid would be good,

What brake fluid you need depends on how hot the fronts get ATE200 is stock fill but there are some much better performing fluids available from Motul, Endless, Castrol, Prospeed etc.

Some people spend more and upgrade to a version of what was used on the 964RS, there are different ways to do it depending on how much you want to spend but at a minimum you will want 322x32 964RS/turbo/928GTS front rotors and either 964 RS/turbo or 993 or 993RS/tt calipers and 4 piston 993 rear calipers. It's best to swap in 993 brake boost and m/c too and even better to switch to 993RS wheel carriers/tierods. It all gets very expensive

[porterdog]

Originally Posted by Bill Verburg

It all gets very expensive

Ha. Think maybe I'll print that out and post it up in the garage

[cavlino]

Terrific information Bill, I am going to have to come over here more often

[BertoSpid]

Very, very interesting, Thank's !

[911jettat]

Thanks Bill for the two/four piston comparison pictures and technical information.
I hate having the dual piston calipers on my '90, not because of the performance...but because of the limited pad availability. Thanks again for the info.

[Rey Gunn]

Originally Posted by Bill Verburg

The last piece of the puzzle
the BMW 10mm to 12mm brake line adapter part #
34-32-6-752-405

Hi Bill,

Resurrecting this thread cuz I'm in the middle of upgrading my 964 to Big Reds. I bought this piece and dropped it off to my mechanic who is doing the installation. He doesn't know where it goes. Can you please tell me where this line is installed? I also need to know where the brake pressure regulator goes as well. Thanks for any help.

Rey

[paul284pt]

Some people spend more and upgrade to a version of what was used on the 964RS, there are different ways to do it depending on how much you want to spend but at a minimum you will want 322x32 964RS/turbo/928GTS front rotors and either 964 RS/turbo or 993 or 993RS/tt calipers and 4 piston 993 rear calipers. It's best to swap in 993 brake boost and m/c too and even better to switch to 993RS wheel carriers/tierods. It all gets very expensive

Hi,

With Bill's help this was what I finally opted for on my C2:

Fronts:
322 x 32 Rotors
964 Turbo callipers
Adapters

Rears:
968 MO30 Rotors
993 Callipers

993 Master cylinder
993 Brake booster

The 993 MC and booster are a tight fit and I believe even more difficult if you have an RS sway bar.

And yes, I'm afraid it was very expensive, even with refurbished callipers. Also brake lines needed to be flared to fit.

Good luck,
Paul

[paul284pt]

Hi,

I almost forgot and since this is the goto thread for brake upgrades, I'll post up the other parts I used if you are considering going the whole hog:

A 55 bar brake bias valve (the Turbo I believe is 60 bar).



993 master cylinder and brake booster:





You will also need one of these, the 993 Master Cylinder Support bracket. Please note this one is for a RHD car - (part no. 993.355164.03) for a LHD car use 993.355.163.03



And last but not least one of these:



Brake lines will need to be stepped up from 10mm to 12mm to fit.

Cheers,
Paul

[540964]

I followed Bills thread, fitted the RS big blacks, 993 rears and 993 m/c and booster. He suggested that I remove the bias valve, that's what I did. The new brakes along with all new suspension bushings (Elephant Racing RS spec), OE strut and shock mounts, drop links, sway bar bushings, H&R greens, Bilsteins and a fresh set of Conti DW tires...sublime. I contacted Bill several times, he was really helpful. And yes, fitting the m/c and 993 booster and brake line was a chore.

[Cobalt]

May I ask why you went with the greens? After all the upgrades you don't find the greens to be a bit soft?