Carrera Boxter Brake Upgrade Question

asphaltgambler · 05-09-2006, 04:47 PM

On my '85 Targa project I have decided to go with boxter front brake upgrade. I have sourced the calipers and purchased the adapter/mount kit from TRE. I'm using new drilled front rotors.

My goal was mainly for bling factor plus they do add stopping power. But some here have argued to what % improvement. I do not plan to race or autocross, just occassional spirited street driving. I like the fact that the only 'cobbing' part of the upgrade is the mount which looks very well made. All else is stock stuff, so no hassle there when replacing

The guy at TRE suggested that I also should go for the rear boxter set-up as well. I'm not sure if I want to $$ bling out that much more. I was planning to use the OE rear brakes, just freshen.

Does anyone here already have the front and rear Boxter brake conversion? If so what do you think?

For the guys that have only upgraded the front, what do you think?

Thanks!

asphaltgambler · 05-10-2006, 07:00 AM

Bump

Vipergrün · 05-10-2006, 01:54 PM

I am sure Bill V will chime in. The Boxter fronts use a Carrera rotor anyway, at least mine did. However, the pad area is a bit larger. I did notice a bit of unbalanced feel when I had the Boxster fronts and SC rears. I now have Boxster rears as well and it feels much more balanced. I am not sure which rotors are on the rear as TRE did that as part of my backdate project, but they are either Carrera's or pretty close to it by visual inspection.

Jim Smolka · 05-10-2006, 01:58 PM

asphaltgambler,

Do you know the piston sizes of the front and rear Boxster calipers. The brake bias can then be determined. From the data, one can then determine if the rear Boxster are a good idea.

Bill Verburg · Bill Verburg's Garage

If you want matching calipers use the Boxsters in the back otherwise use the Carrera rear calipers, they both use the same Carrera rotors.

hmd · 05-10-2006, 03:46 PM

I had a setup with both front and rear boxster calipers and carrera rotors. The car stopped really well but I find there was way too much bias on the rear. Even with a bias bar with setting all the way to the front.

I would stick with carrera rears.

Jim Smolka · 05:36 PM

If you have Boxster front brakes and 84-89 Carrera rear brakes the brake bias is 37.9 % to the rear and 62.1% to the front (Not factoring in the proportioning valve).

If one has SC rear brakes and Boxster front rotors, then the brake bias is 33.3% of the pressure to the rear and 66.7% goes to the front

If one uses the Boxster front brakes and Boxster rear brakes, then the bias is 36.8% to the rear and 63.2% to the front.

asphaltgambler · 05-10-2006, 05:05 PM

Thanks All!! - Jim, I don't know the fluid volume differential between the boxters and the Targa's. But it's a safe bet that the boxter uses more volume of fluid.

HMD your case is what I'm talking about. The last thing I'd want to fiddle with is a bias valve that turned to the point of almost cuting out the rear just to balance the fronts.

Anyone else have this setup with reccomendations??

hmd · 05-10-2006, 05:14 PM

My car was a bit different from the norm. The PO had twin MC and a balanced bar setup, he had never got the balance with the boxster at fronts and rears right either. So it definitely not the driver

I wouldn't know what it would be like with a standard MC setup.

Elombard · 05-10-2006, 06:01 PM

Where did you source the calipers from?

Jim Smolka · 05-10-2006, 06:43 PM

If one is going to be tracking the car a good bit, the 930 MC is a good option if one is increasing the size of the calipers.

With a dual MC system and a balance bar, another factor to condider is the volume the MC's can push. Assuming the F/R brake bias is OK and the fronts are still not braking enough, then the front MC may not push enough fluid through to the caliper pistons.

asphaltgambler · 05-10-2006, 06:50 PM

I purchased them from Oklahoma Foreign / $300 for the pair.

hmd · 05-10-2006, 09:20 PM

Jim,

You may have a point there.

asphaltgambler,

Try front with carrera rears first, from all report I hear that the best combo.

mshriner · 05-10-2006, 10:41 PM

This thread is very timely for me as I am about to convert my rear brakes to boxster calipers. (They have to be better than the BMW 320I calipers I have) Since I didn't buy the TRE kit. I did not get bolts. (Timmons Billet)

Anybody know the bolt size? I was told, 2 - 12 x 1.5 x 60mm AND 2 - 12 x 1.75 x ???? (missed the last part) I am hoping to track down some bolts and get to the project this weekend / next.

Matt S

Shocker · 05-10-2006, 10:44 PM

I am doing something very similar on my '77. I am using the Boxster fronts with Carrera rotors and Carrera rears with Carrera rotors. A new 19mm stock MC, SS lines and a Wilwood bias valve. The rotors are new Zimmermans and I am running the Axxis MetalMaster pads.

Dave at TRE said that the bias valve was a requirement to get the balance right. I PM'd Bill and he said not necessary. The 77 doesn't have the bias valve like the later cars.

Anyway. I bought the Wilwood just in case, but I am going to try it Bill's way first.

The install will happen sometime this spring after my new shop is built. WOOT!

Mike

asphaltgambler · 05-11-2006, 07:47 AM

Also the guy at TRE (in a round-about-way) said that if Boxter calipers were used at all four corners master cylinder volume could be an issue. As in: you should think about bolting in the 930 master

Jim Smolka · 05-11-2006, 09:22 AM

One problem with the whole brake bias things is what works well for one 911 may not work well with another. Such factors as shocks, tire combinations, brake pad friction factors, ride height, etc, can factor into the equation. IMHO , for a track car having more rear bias is better because one can then reduce the pressure with a bias valve or proportion valve

asphaltgambler · 05-11-2006, 01:12 PM

I'm leaning towards boxter front and stock Carrera rears for now. I believe that someone a few weeks ago posted that they had the same set-up as above it worked great for them.

Bill Verburg · Bill Verburg's Garage

Thee is little difference in bias between the Boxster/Boxster and Boxster/ Wide Carrera M.

The Box/Box is slightly more front biased, a p/v would only exacerbate that

neither would want or need a p/v unless tires or suspension were way out of wack ie a very unusual combination unique to that particular car.

Jim Smolka · 03:45 AM

Looking at the brake bias of an SC with 48mm caliper pistons in the front and 38mm pistons in the back, the brake bias is 38.5% to the rear and 61.5% to the front. Not factoring in the 84-89 Carrera's proportioning valve, the brake bias of 911's with 48mm fronts and 42mm rear pistons results in a brake bias of 43.4% to the rear and 56.6% to the front. Therefore the Boxster front and Carrera rear setup has about ~0.6% more front bias braking than the original SC setup.