Hoping for the Hand of God...

[Guest]

aka Big Brakes

I finally got my car back today with its new brakes [][]yippee[][]

The story so far has been one of constantly improving the std brakes. If you follow the forum then you will have some idea of what I have done over the past couple of years - new calipers, new discs, race pads, race fluid, remove dust sheilds, duct air thru under a-arm scoop to rotor centre and install hub block-off plates. It works ok but a 1989 G50 car is surprisingly heavy with a tank of gas, 11 litres of oil, sundry litres of windscreen wash, tools and a spare wheels - some 1330kg [:'(][:'(]

While I never failed to stop or had a very soft pedal on the track, the pedal was often disconcertingly long and never inspired full confidence. Now that my car has the full big torsion bar suspension, 225/245 r-compound track rubber and has dieted to the tune off about 50kg it seemed like a good time to give in to the upgrading monster and fork out for some big brakes.

The obvious candidate are 1978-1989 Turbo brakes. With big 917 derived calipers and fat 28/32mm discs they are good for 500hp track cars. But the cost is big once you get the requisite zero offset mounting bells and front discs. You also have to find some Turbo calipers, replace the master cylinder and it really is massive overkill for a trackday 231hp car.

In my opinion the ideal in terms of heatsink and modern stiff calipers would be a 964 brake system or a 944Turbo system. After all, this is what Porsche did when it turned the 3.2 into the 964. I have often looked at 964s 944Ts and thought I would like a set of those brakes. Well, a thought has become reality. After lots of careful research and chatroom trawling I found that VCI (in the US) offer just such a kit - but the price makes you weep. So how do you do it cheaper?

The guts of the kit is a set of 944T front discs (28mm thick vs 24mm for 3.2 and a little larger in diameter) and a pair of 964 or 944T front calipers. VCI recommend you also use a 944T rear caliper on a standard 3.2 rear disc (same 24mm thickness as a 964 or 944T and similar diameter) but this results in a little pad overhang. So time for more research.

First a picture of the new to me 964 front caliper.

 

[Guest]

Research into the various Porsche brake set-ups showed that the early 964 C2 came with 2 piston rear calipers that were virtually the same size as the 3.2 rears. Those in the know will be aware that 3.2s have oversize rear calipers but run a proportioning valve to ensure the bias is correct and not too rearward biased. After a chat with Neil Bainbridge it became apparent that using the 3.2 rear calipers and removing the proportioning valve would give a bias similar to the 964 - close enough to tune with different pad compounds anyway or if that fails an adjustable bias valve.

So, job done? Just bolt on the 944T discs and 964 calipers, chuck out the proportioning valve and Bob's your father's sister? No. For some reason the calipers have a different bolt spacing. Now you can just elongate the bolts holes a bit and bolt them on but all the Porsche gurus said you should suck up the cost and pay for them to be machined and have a bolt on billet aluminium adapter made. Rather than pay for someone to invent how to do it, I sent them to VCI. The Post Office charges £55 to send two caliper and USPost charge USD30 to send them back - and the Post Office still can't make a quid !![:'(]!!

Six weeks later and here is what you get:

 

[Guest]

I will put up a few more pictures so you can all see the lovely billet aluminium bits. Ooo Errr.

 

[Guest]

And another:

 

[Guest]

I have lots of other pictures and I took all the measures but fate was to strike and make that all rather irrelevant because VCI put the wrong adapters on ![][]!

So, I had to get a new pair of adapters sent out (VCI's cost) direct to my mechanic who now had the car in bits on a hoist. Somehow Doug at VCI (nice bloke) sent rear adapters despite these being front calipers and despite my buying a pair of 4mm bearing spacers from him that are only applicable to the front wheels.

Did I mention bearing spacers? Forgot that. The spacers are necessary so the discs don't foul the suspension. Only problem is that you lose 4mm of offset and hence 4mm of tyre clearance. Fingers crossed that the 225mm front tyres don't rub ! Its kind of out of order but here is the photo of the clearance.

 

[Guest]

Hmmm, tight fit, no? Strangely the RHS looks even worse - but then the RH fender was thoughtfully dented by an anonymous neighbour (ie., he/she did a runner) and has been gently persuaded back into shape with the help of a BFH. Here it is.

 

[Guest]

As usual great write up Richard!

 

[Guest]

So what's it like? Well, I haven't driven it yet [&:]

Car got delivered and my mechanic said it was mega. He said the car just sucks into the road. I can report that the pedal feels nice and stiff - the first time it has ever felt that way since I bought the car. I can't wait to have a decent drive at the weekend. I will also take some wheel-off shots.

In the meantime, the only downside is the price of pads and discs. Genuine Porsche discs at £200 a pair and Pagid Blues at £160 per axle. Gulp. I may be going to Eurocarparts for replacement discs !! Still, they should last a while as Pagid Blues are quite disc friendly. The pads are twice the size of the 3.2 fronts so they should also last a while. Fingers crossed and no telling SWMBO.

The calipers ended up getting a precautionary rebuild and the labour came to 4 hours total - not bad I say.

Here is the finished product:

 

[Guest]

There really is only a nats whisker of clearance. You couldn't get a bigger disc/caliper combo under a 16x7 Fuchs wheel. So I am rather chuffed.

Richard

 

[bones]

Stop it Richard ....you're tantalising us with snapshots of your car! The word for you is Carnographer.

 

[Guest]

.. thats better than what most people call me.

 

[IanHighfield]

Richard,

Great write up as always - thank you. Looking forward to feeling how well the car now brakes (Bedford).

If you don't mind, what cost could we expect to pay for good used 944T Disks and Calipers, and how much to they charge to modify the caliper). Trying to get a feel for the conversion cost.

 

[Guest]

New discs are £70 each from discount places and £100 each for OE Porsche. No point in doing second hand really. I got a full set of 4 964 calipers for about £120 IIRC but you would normally expect perhaps up to £200 from wreckers yards. Factor in the cost of rebuild as well.

Richard

 

[Guest]

Here is the "wheel off shot" borrowed from elsewhere in my archives. Sharp viewers will spot that this is not my car in the picture due to 2 inconsistencies - but the view of the brakes is identical. Torrential rain and work prevented any car related activity last night [][].

RB

 

[Guest]

One more picture to help complete the story. This is a picture of the wrong way to modify the caliper ie., just elongating the mounting holes.

 

[Anil]

Does anyone know how these 4 pot calipers work?

Do only 2 pistons engage first and then all 4 when the pedal is pressed harder, or do all 4 pistons press the pad at the same time?

Cheers

Anil

 

[Guest]

All 4 pistons press on the pads at once. If we ignore the fact that these calipers have differential piston sizing, the pressure is transferred thru the essentially incompressible brake fluid medium equally to all four pistons and an even pressure applied to the pads. There are no valves or anything to delay pressure from any of the pistons or to create a sequential effect.

The differential piston sizing means there is slightly less pressure applied to the leading edge of the pad (I think but I'm not certain if its leading or trailing edge) which I think creates more even pad wear.

HTH,
Richard

 

[Anil]

Thanks for the clarifcation Richard.

One other question...Do you know if the 964 calipers you have installed will fit behind the standard 6x16in Fuch alloy, or would I need to move up to 7x16in in the front?

Anil

 

[Guest]

They just fit behind the 7x16 and I haven't tried the 6x16 wheels I have. At the worst, you may have to install longer studs (you have the hub off anyway when you do the brakes and the studs are only about £6-7 each) so you could run the necessary spacers for clearance. With 6x16 and 205 tyres you could run at least 20mm of spacers before you have any clearance issues. I am running 7s with 225s and a 5mm bearing spacer with 1.5 degrees negative camber and no clearance issues - although it almost looks like the wheels are protruding outside the wheelarches.

At some point in the future I will see if a 6x16 fits but it won't be for a while as I have a full calendar for the next few weeks.

RB

 

[Guest]

I hope this isn't boring people too much, but I promised to report back after track testing.

Short answer is, I am very pleased. On r-compound tyres, I can brake really hard and late. This is how I always wanted my Porsche brakes to be. Comparing notes with other 3.2 owners and taking a couple for rides the consensus is that the brakes are quite a lot better - probably "dramatic" is a better description.

It is still possible to get a little of the old soft pedal syndrome but its better than before. At the very end of the day I had a good session without a passenger and that little less weight made a big difference. Brakes felt great for 30 minutes - at which time I had to stop to pack up and go home. Accordingly, I will be hunting for a little more weight reduction....

On the downside, the bias isn't quite perfect. On road tyres, it is too easy to lock the front brakes. I put this down partly to having brand new road tyres that seem to have a serious lack of grip. Lock-up has not been apparent on the road - just on track. I think I will have to try some more aggresive rear pads.

Over and out,
Richard