What Rear Brakes?

[bobswei]

Hi, I've upgraded my front brakes on the race car and now have way to much in front and feels like nothing out back. I went from stock, late 70's S brakes all around to Wilwood Ultra Lites, 4 piston calipers on front. I was told that Carrera rear calipers are a match but they seem very similar to what is there now. Would that be a good choice? Or what would be a better option? Car is about 2K lbs, all fiberglass and carbon fiber (if this is important).
Thanks for any suggestions.

[Brad Roberts]

Can you give me ALL the specs on the system? Piston size/MC size/Pad compound F+R? An engineer I work with created an Excel spreadsheet that we use to determine proper piston sizing for the MC and calipers so you have a matched system. It is setup for dual MC's or single MC. The car doesn't matter, but the weight does as well as the size and compound of slicks.


B

[Mahler9th]

Bob:

Nice to see that you are back at it.

If you visit the paddock at Sears Point next weekend (26-27 June), the PRC will be there and you can see some examples of setups. A number of us with light cars run a 930 rear caliper up front with a simple and cheap lightweight Wilwood rotor and either a Carrera rear caliper with Wilwood hat and super light rotor (my car), or a Boxster caliper with a Wilwood hat and super light rotor. With the Boxster rear calipers you need adapters. All with a readily available master cylinder. Simple, light, cheap and balanced. There are maybe a half-dozen cars with this configuration.. .maybe even more.

If your Wilwood front is similar to a 930 rear, then you may be able to run almost the same thing. I have the Wilwood rotor part numbers (we buy them from Summit). Wilwood rear hats with an appropriate offset are hard to find... I have a brand new set available if they can work on your car.

I will be there all three days.

- Mike

[KTL]

I'd be interested to see your setup/specs Mike. Sounds like a very simple solution to brakes that a lot of people really struggle with in putting it all together.

[bobswei]

Thanks for the responses. Brad, I'll see what info I can give you without tearing the car apart. Single MC I believe is 19 mm (stock early 70's). Front brake pistons are 1 1/4" (rough measurement while still on car) x 4 pistons. Rear are stock M calipers (69' to 83' I believe) but not sure of piston size and they will be going away. No idea on pad compounds. I have an extra set but no markings on them. Is this good enough for a starting point?

And Mike, I like the idea of Carrera or Boxster rear calipers. Carrera calipers should bolt on to my SC swing arms? But the boxsters need adapters and a new MC? Price is a concern and I wish I had my original S calipers back.
Here is a photo of my fronts. If someone has input weather they are similar to 930 rears, maybe I have a direction to go with this. Brad's spreadsheet could also shed some light.
And, I'm close to being back at it. I've been working weekends for the past 4 years and tough to get a Sat or Sun off. I've been to about 2 NASA events in the past 3 years. But shortly, I will have Saturdays off so that's why I'm sorting out the brakes. Wish I could be at Sears this month.

Thanks,
Bob

[KTL]

You're not really gaining anything by using those calipers, except for unsprung weight (lighter caliper). I'd switch back to the Porsche calipers- use the Carrera A calipers since it appears you have the larger Carrera 24mm thk rotors installed. The Wilwoods don't look like they're functioning well either- more piston extension on the outboard side than the inboard.

If nothing else, i'd get a proper caliper retaining pin in there. That cotter pin isn't necessarily bad, but it looks like a hassle to bend, pull, and reinstall when a pad change is needed. Proper smooth pin with a retaining clip should be easily available from Wilwood.

Ideally you'd switch to SC calipers

[Bill Verburg]

Originally Posted by KTL

...it appears you have the larger Carrera 24mm thk rotors installed. ....

Nope, he still has stock 20mm rotors and stock 19mm m/c

Originally Posted by KTL

If nothing else, i'd get a proper caliper retaining pin in there. That cotter pin isn't necessarily bad, but it looks like a hassle to bend, pull, and reinstall when a pad change is needed. Proper smooth pin with a retaining clip should be easily available from Wilwood.

this whole setup is such a kludge that that is almost irrelevant, but you are correct

Originally Posted by KTL

Ideally you'd switch to SC calipers

Best idea in this thread, or as I outlined in the parallel thread in 911, I wouldn't go so far as to say "ideal" but at least that is a well engineered system.

[KTL]

My diplomatic govt employee/vistor friendly nature rubs off on the forum......

I guessed at the rotors being Carreras because typically the SC rotors have a more ovoid vent no? Or maybe i'm thinking of the rears by memory.

I won't debate that it's a makeshift system. That cotter pin is the cherry on the makeshift sundae....

[bobswei]

Well, after all the feedback, I'm a little overwhelmed. I'm thinking to get it done as simply as possiable. Anyone want to trade some Wilwoods for a pair of S calipers? I don't have the budget to make this work right and look right with the calipers I have now. Or, maybe I can find matching Wilwoods for the rear. I checked out Summits website and prices are all over the place for these things. Or maybe I will shelve the idea for now since I'm still working weekends at the moment. At least I have a few directions to go.... Thanks for the ideas.

[Bill Verburg]

Originally Posted by bobswei

Well, after all the feedback, I'm a little overwhelmed. I'm thinking to get it done as simply as possiable. Anyone want to trade some Wilwoods for a pair of S calipers? I don't have the budget to make this work right and look right with the calipers I have now. Or, maybe I can find matching Wilwoods for the rear. I checked out Summits website and prices are all over the place for these things. Or maybe I will shelve the idea for now since I'm still working weekends at the moment. At least I have a few directions to go.... Thanks for the ideas.

The simplest and cheapest to get done is a set of 3.2 Carrera front rotors and calipers. It's all a bolt on works perfectly w/ the M rears that you have and w/ the 19mm m/c and will give you factory bias. The thicker rotors even help w/ the heat issues a little

[bobswei]

Bill, that sounds like it might work for me. I just got a line on some front Carrera rotors so I'm half way there. I like the idea of bolt on and proven that it works. Thanks for all the input.
Bob

[Walt Fricke]

The cotter pin retainer is really pretty practical. To remove, grab with channel locks and yank out. A slight rebend of the end, and a pinch with the fingers, and it will go back in easily. A little twist with a screw driver, and you are back in business.

At one time Wilwoods came with these cotter pins. Doesn't this model still?

The first Wilwoods made for 3.5" mounting centers in the late 1980s, and which would fit our 911 front struts with a little futzing with spacers between the caliper and mount to center things, came with four equal sized pistons. As a result, pad taper wear came on rather quickly.

Those Wilwoods had a reputation, whether deserved or not, of being flexy (like the S calipers did, I suppose).

I'm running an offshoot of the Wilwood called Bremtek (now many years out of business).



It has differential piston sizes top to bottom (with the rears being smaller) and has been very reliable. The seals, for instance, have run fine for about 15 years. I think the newer Wilwoods have this valuable differential.

In any case, the pads are a lot larger and thicker. I use pads sized for the Wilwood, so I am very glad they are still making and selling these. If your Wilwoods have differential piston sizes, I'd keep them. And work on getting rears with appropriate piston sizes. I don't think Wilwood makes a similar Ultralite with 3" mounting and smaller pistons, though it would be nice if they did because being able to use the same pads front and rear is really nice (the inner rears need their ears sawn off).

I didn't have to do much figuring with my Bremteks, as they came sized appropriately F/R for 911s and for a 19mm MC, plus I have a balance bar to adjust the bias. They work so well that I just went from two 0.75" MCs to a pair of 0.70s with no apparent loss of pedal (though not quite as much reduction in pedal effort as I was hoping to achieve).

I don't know what motor you have in that car, but I like the large pads (thickness I see you have dealt with by spacers) for my track only car, which is slowly getting below 2,000 lbs without me in it. I'd not want to go back to much smaller pads and heavier calipers. Nominally pad size doesn't count for instantaneous braking, but it sure seems to help in terms of longevity and heat while racing.

So, with all deference to those with other opinions, I think going to 3.2 brakes is a step in the wrong direction for a race car.

[armandodiaz]

Originally Posted by Mahler9th

Bob:

Nice to see that you are back at it.

If you visit the paddock at Sears Point next weekend (26-27 June), the PRC will be there and you can see some examples of setups. A number of us with light cars run a 930 rear caliper up front with a simple and cheap lightweight Wilwood rotor and either a Carrera rear caliper with Wilwood hat and super light rotor (my car), or a Boxster caliper with a Wilwood hat and super light rotor. With the Boxster rear calipers you need adapters. All with a readily available master cylinder. Simple, light, cheap and balanced. There are maybe a half-dozen cars with this configuration.. .maybe even more.

If your Wilwood front is similar to a 930 rear, then you may be able to run almost the same thing. I have the Wilwood rotor part numbers (we buy them from Summit). Wilwood rear hats with an appropriate offset are hard to find... I have a brand new set available if they can work on your car.

I will be there all three days.

- Mike

Mike I was looking into a Wilwood alternative for my 85 Carrera. But I'm not sure what hats or rotors to use (under my 15s). Do you have any suggestions? I'm mostly upgrading for weight but would like to upgrade the calipers also. One thing I'm worried about is having too much brake. My car is 2K lbs and would not like to spend my time on the track locking up wheels.

[Bill Verburg]

Originally Posted by armandodiaz

Mike I was looking into a Wilwood alternative for my 85 Carrera. But I'm not sure what hats or rotors to use (under my 15s). Do you have any suggestions? I'm mostly upgrading for weight but would like to upgrade the calipers also. One thing I'm worried about is having too much brake. My car is 2K lbs and would not like to spend my time on the track locking up wheels.

w/ a 2k# car the A or S front on 282x20 stock rotors and M on 290x20 stock rears is usually perfectly adequate, use wide A calipers and rotors(282x24) in front as a slight upgrade

[armandodiaz]

Originally Posted by Bill Verburg

w/ a 2k# car the A or S front on 282x20 stock rotors and M on 290x20 stock rears is usually perfectly adequate, use wide A calipers and rotors(282x24) in front as a slight upgrade

What about my original Carrera brakes and rotors. Are they good?

Also, what about the rotor weight? They are pretty heavy. Would it be worth it to replace the Carrera Rotors with equally sized Wilwood hats and rotors?

[Bill Verburg]

Originally Posted by armandodiaz

What about my original Carrera brakes and rotors. Are they good?

Also, what about the rotor weight? They are pretty heavy. Would it be worth it to replace the Carrera Rotors with equally sized Wilwood hats and rotors?

3.2 Carrera fronts are the wide A calipers and rotors(282x24) I referred to above. leave the back alone

[armandodiaz]

Thanks Bill I'll leave things alone. One question though....

If the Carrera brakes are good enough for my 2k# car then why does Porsche use these HUGH 6 piston and carbon fiber rotors in the LM2 Spyder? Isn't it only 1700#? I'm not comparing my car to the Spyder but the main reason I guess would be the speeds?

[962porsche]

i just did a full race volvo S60R last week that the owner added bigger front brakes . he over looked one little thing a brake bias ajuster( cockpit proportioning valve )!

[Flieger]

Originally Posted by armandodiaz

Thanks Bill I'll leave things alone. One question though....

If the Carrera brakes are good enough for my 2k# car then why does Porsche use these HUGH 6 piston and carbon fiber rotors in the LM2 Spyder? Isn't it only 1700#? I'm not comparing my car to the Spyder but the main reason I guess would be the speeds?

They have sticky tires and so can generate more brake thrust. Combine that with higher speeds (kinetic energy is (mv*2)/2 ) and many laps of hard braking without rest, and the heat tolerance of the carbon rotors and pads is necessary. They also weigh alot les!

[mattsctr]

Hi, just to be sure are you saying your fronts lock up long before your rears? Do your rears lock up at all?

I'm assuming (always dangerous) that your looking for more even braking front to rear but are happy with your fronts abilities?

If that's the case, do you run a brake bias? If so have you tried adjusting it? If not then this would possibly solve your problem.

Sorry for all the assumptions, as someone who has been through brake balance set up many times I'm just trying to help.