Tiger03447

Guys..
I have just been through the 944 caliper grinder...again. In a prior post some time back, Michel Odonnell posted that he had replaced his early 944 calipers with the ones off of a 1993 Volvo 240 with ABS brakes. UPDATE: The 240 calipers are 4 piston calipers. The pad area is about the same as the original single piston calipers that come on the early 944. The only way AFAIK to change to the later 944 calipers is to change out most of the front suspension system. So, I opted for the Volvo calipers..since the frames on my original calipers were shot. UPDATE#2" The right hand calipers for the Volvo are in great supply..Not so much for the Left hand caliper. These calipers have disappeared from the remanufactured parts market...and can only be found in Volvo graveyards..or in wrecking yards if you are lucky enough to find one that still has a 91-93 Volvo that hasn't gone to the crusher. There are two models of the caliper. One has a single brake line... that's the ABS model..The other model has two brakelines. This is a redundency system that Volvo builds into the front brake system.(or used to) apparently they run 4 brake lines out of a double master cylinder that serves the front brakes only. If you have to use these calipers you might have to Tee into each front brake hard line and run double flex hoses to the caliper. Those type of calipers are in the remanufactured parts supply chains and are available. After talking to owners of several Volvo garages, they refuse to part with any of the L hand ABS calipers...otherwise they are considered out of unobtanium. Girling... the origianal manufacturer, has quit making them. The bugabear in this deal, is the lug spacing on the Porsche caliper. On the Early cars, it's 3" ..Later cars, it's 3.5 or so. Wilwood doesn't make a 3" spaced lug mounted caliper, and neither does almost anyone else that I have found. Not sure about Brembo. The 31/2 " calipers cost about 350 each. Rennspeed? makes an adapter for these early to late, But the package runs about 750+ for both calipers, using new Wilwood calipers. Just telling about what I have found out so far. I finally got a very used L hand one (needs to be kitted and cleaned) delivered today. Thanks for reading of my tale of quest.

tempest411

Why not just have your original early calipers properly rebuilt? I used these guys for my '84 944 and '87 924S: PMB Brakes

wildcat077

Nothing wrong with properly functioning early calipers ... i've been running my SP2 car for the last five years with early N/A calipers, i easily
rebuilt them two years ago due to the rubber on the piston seals getting dry/brittle due to the heat , but other than that they work fine !
Why complicate things ???

Cheers
Phil

MAGK944

This really concerns me. You are fitting brakes that are not designed for the car, add complexity, will mess up the brake bias, may stop you running stock sized wheels and likely will have less performance than the stock brakes for what gain exactly?

V2Rocket

the volvo units are 4x38mm pistons vs 944 1x 54mm. when you do the math the total piston area is about the same so performance should be about the same. but pedal effort might drop a little.
since brake performance is about the same the brake bias should be about the same, and these fit under 15" wheels.

a few years ago these were identified as an inexpensive option to replace the NA calipers (which are boat anchors at 12lbs each btw) but the supply seems to be running out.
IIRC at the time it was hard to find rebuilt NA calipers and/or parts to DIY.

this has been on my to-do list whenever my calipers got weak but i guess i'll have to find another option.

MAGK944

Thanks for clarifying, I thought the 944na calipers were different front and rear so if fitting the Volvo calipers on four corners the bias would change substantially. Or am I missing something?

V2Rocket

Yes they are different front/rear. The Volvo units only fit front.
944 rear caliper lug spacing is 95mm vs 76mm on the fronts.

MAGK944

Understood, I seem to recall us discussing this back when the solution was first being developed

mel_t_vin

Spencer, probably irrelevant, but if those are accurate dimensions, you might consider revisiting that math.

V2Rocket

the Volvo are 4 piston monobloc calipers and each piston is counted individually.

The 944 are single piston sliding frame calipers, with one piston acting on both pads you effectively double your piston area.

((38x38x3.14)/4) per piston x4 pistons = 4534sqmm

((54x54x3.14)/4) "per piston" x2 "pistons" = 4578sqmm

mel_t_vin

What is (Pi(d^2))/4 supposed to represent?

Area of a circle = Pi(r^2)

The Forgotten On

944 NA use the same calipers as early 78-81 928s. I rebuilt the set from my 81 928 and stuck them on my dad's 87 944 NA because they were in better shape.

The 928 calipers are super easy to find and are offered as rebuilt by some venders. The rebuild kits though are like $10 and really easy to do yourself.

It's a fun afternoon project to do them yourself if you have compressed air for piston removal.

V2Rocket

D*D*pi/4 is the same result as R*R*Pi, since D=2R.... 2R*2R = 4R^2 so you divide out the 4 and get R^2.

I tend to use DDpi/4 more to skip having to divide by 2 in my head to get an R.

willrobinson

They act on both sides of the pad, but does that translate to the effort equation? It's still a ratio of master to slave area is it not?

V2Rocket

The only info I can offer on that is that people with turbo brakes and power booster delete with stock master cylinder seem to have an easier time stopping than the same setup with NA calipers, when the pedal ratios are consistent.

Master/slave setup is a pressure ratio, but since pressure is "universal" in the system the force needed to move multiple smaller pistons should be less than fewer much larger pistons. Volume of fluid displaced is another question.