Rear Brake Upgrade

[baja 911]

I have a 65' 911 with a 78' 3.0 set up for off road. My problem is the car doesn't stop very well. Yes, there has been some exciting moments. At this point I would like to upgrade to larger rotors in the rear. The fronts are not as much of a concern at this time.
The master cylinder is stock. The rear rotors(vented) are 68' I think. I get 1200-1500 PSI at the calibers. I was told that since I have large tires I need larger rotors.
Is there any bolt up kits? Or specific car/years to swap from?
Being I'm a new Porsche owner. I don't know much and any help would be appreciated.

Thanks...Baja 911

[Flieger]

Can you lock the wheels? If yes, then try better cooling, good fluid, and experiment with different pads to find one you like. If no, then you need more brake torque. Different pads will have different friction coefficients. This is one way to get more torque. If you go to a larger rotor, you get more leverage and torque but the rotor is heavier and has a greater moment of inertia to slow down, similar to putting larger tires on.

Heat management is the key either way since brakes turn speed into heat to slow you down. Cooling and fluid and pads that are up to the task are wise any way you go.

What wheels are you running? You could use PCCB carbon-ceramic rotors for more torque and less weight at the same time if you have large wheels and an even larger wallet.

[ix0ifan]

I am not sure what you have on the front but if you have fitted later Struts and calipers the brakes will be badly balanced.

The stock set up on a 1965 car would be solid discs all round, M type Front Calipers with 45mm dia pistons and 3" mountings. The rears would be an L type caliper (very small pads), 35mm pistons with a 2.25" mounting.

If you have vented rear discs, which would be 285mm dia they would have come initially from from a 1967S and on an A Programme car should have an small spacer bolted to them. The pistons are likely to be 38mm dia if the calipers have been changed to the slightly later S. I would assume that you may also have the ventilated M Type Caliper on the front.

The master cylinder should be a single circuit 19mm diameter unit.

Fitting larger rear discs could well unbalance the braking system and cause serious oversteer problems and could be risky but there are some other issues to consider.

Can you find a suitable disc with the correct spacing for the handbrake drum?.

The depth of the the early disc is only about 70mm. I would imagine that it is quite difficult to find soemthing that will work.

The next issue is that the clearance between the rotor and the caliper is only about 2.5mm and you will need to pace ount the caliper if you do fit a larger disc and you may have wheel clearance issues.

Swapping rotors from later cars is difficult as the SWB Banana Arms make it very tricky.

Itis possible to shorten later LWB Arms but you need a jig and considerable fabrications skills.

I would tend to agree with Flieger about heat management but I would make sure that you do have rear calipers with the 38mm dia pistons as the 35mm jobbies are limiting.

I would also add an adjustable pedal box which will allow you to increase the rear bias until just before locking occurs. This again is tricky as low cost cylinders such as Wilwood are limited in terms of the choice of diameter. Tilton are also restricted and tend to be limited to 0.625" diameter which I think is a bit too big for a SWB Car and would produce a 'wooden' pedal.

AP Racing make a short cylinder of 14mm dia which would be a better choice. A mechanical pedal ratioof between 6 and 6.5:1 is also a good idea for SWB cars.

[baja 911]

Cooling is not a problem and no I cant lock it up. The fronts are an off road product from Neal with Wildwood calibers. The whole front end is a VW based mid travel design. Being able to lock up the rear brakes is preferable in the dirt.

Thanks for the tips...Baja 911

[ix0ifan]

We build gravel rally cars and have to use more or less stock calipers for the pre 68 class that we enter.

The standard vented system from the early S with M type cast Iron fronts and the 38mm rear calipers work well with a bias bar pedal box and will certainly allow the rears to lock if adjusted correctly.

We also have a Hydraulic Fly Off handbrake fitted for those extreme moments.

A plate type lsd is also a good idea and we use a 40 degree coast ramp with a 65degree power ramp for gravel with preload set to give a slip torque of just less than 30 lbsft so the understeer is managable.

We have recently fitted some shortened late steel banana arms as they are much stronger and less prone to bend. The M type rear caliper with 38mm pistons uses an larger pad and gives slightly better balance adjustment.

We are currently using Pagid RS4-2 pads all round with Stainless Steel pistons in the calipers and Motul RB660 Factory Line Brake Fluid

[Flieger]

Pad area does not increase brake force. Piston size and pad compound do. Pad area just gives longer life and more heat capacity.

[TRE Cup]

Sent you a pm
Dave

[ix0ifan]

Originally Posted by Flieger

Pad area does not increase brake force. Piston size and pad compound do. Pad area just gives longer life and more heat capacity.

Originally Posted by Flieger

Heat management is the key either way since brakes turn speed into heat to slow you down. Cooling and fluid and pads that are up to the task are wise any way you go.

[ttweed]

Originally Posted by baja 911

The fronts are an off road product from Neal with Wildwood calibers.

Don't know how big your Wilwood front calipers are, but it is possible to put 3.2 Carrera rear brakes on a '65-68 SWB car with the proper adapters. Mike Moran made a kit awhile back, but it was a short run and he sold all of them I think. There's an old thread on the Early S Reg forum about it. Some people may have bought some and not installed them, so you may still be able to pick a kit up, or get the original drawings from Mike to fab your own, if the Carrera calipers and rotors would be a good match in the rear for your Wilwoods in the front. They are a LOT bigger than the stock SWB brakes and can still work with a stock 19mm master cylinder.

[Flieger]

Originally Posted by ix0ifan

I did not say that bigger pads were not a benefit. Just do not expect more brake torque if you stay with the same compound.

[TRE Cup]

We make an adaptor kit for the swb cars that accept the boxster calipers. They would balance out the front wilwood units for a better system.