Early 3" strut caliper upgrade kit - why not?

[jmcjunkin]

I have been looking to find struts with 3.5" bolt spacing so that I could go to SC or Carrera calipers, but here is an upgrade kit that works with the 3" spacing. Larger 3" bolt spacing calipers for $275 -- Parts Heaven claims same caliper area as SC/Carrera. This is much cheaper than changing to 3.5" struts and calipers. What's the catch? Has anybody used these? Al at Parts Heaven commented that they are "really popular with the track guys around here."


http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33563&item=2458525887

[Oldporsche]

I guess I missed something like the dimensions.

I know that there are some boxter front calipers out there that are modified for the 3" spacing. It think that there are some guys out there using BMW calipers also as an upgrade.

Good luck,
David Duffield

[jmcjunkin]

these apparently are bmw or bmw oem calipers. I do not have exact dimensions. Curious if any bay area people have tried them.

[jmz]

Probably nothing wrong with them unless you are trying to stay in a particular class for auto-x. For instance that wouldn't fly with the update backdate rule for street prepared.

[Bill Verburg]

here is an upgrade kit that works with the 3" spacing

Whether or not it is an upgrade depends on what you are trying to achieve.

I believe that they are BMW sourced calipers, the only + is that the pad area may be somewhat larger than on an M caliper. This really doesn't get you much if any better braking.

[MikeSid]

If you can lock your wheels on dry pavement, you don't need a slightly larger pad area. You need a larger tire patch on the road. IMHO brake upgrades for light sports cars are the snake oil of the future. All you'll do is lock your wheels faster. And the engineers can weigh in on whether that decreases braking distance at all. Yes track cars have huge brakes. But they also have huge tire patches gripping the road. I think these upgrades (tire size and brake pad size) go hand in hand and upgrading one and not the other is pointless.

[zotman72]

One 911T data point and an expensive one. Learn from me how not to do this 3.0"-->3.5" upgrade.

Round 1
Heard on Pelican about 2 years ago about this BMW 320i caliper upgrade. Several California parts vendors were touting it.
Went to junkyard, found said source vehicle (75-77), pull the 3" spaced ATE calipers and bought 2 rebuild kits. Got excited, the pads were about 25% larger than the M caliper pad size. But nuts, the calipers was for solid rotors, not vented! Got the wrong car apparently (BMW not consistent within the model years) and I did not realized it at the time of extraction. Further, I was throwing my car out of PCA/RMR Challenge series class as these were not Porsche OEM calipers. This would be the similar situation with PCA Club racing as well. Well I sold the BMW calipers to a California 914 pilot here on Pelican after I rebuilt them and painted them nicely! Lost about $80.

Round two:
Bought a set of "Boge 3.5" struts from another RMR/PCA club member that had Koni Sport adjustable inserts and RSR ride height spindles at our annual swap meet ($300). Double mistake. I wanted the Boges so I could use my Bilstein sport inserts I had already in my Boge T 3" struts. My new (to me) "Boge 3.5" struts turned out to be Boge Hydropneumatics and my Bilsteins did not fit! Worse yet the ball joints were different (old style) and the struts would not work with my twelve 15" wheel collection. Boy was I quite torqued. Not exactly a happy camper. Track season was soon to start too.

Solution: Bought a set of new Bilstein RSR struts with 3.5 spacing and some SC calipers from Dart Auto. With race pads, ATE slotted rotors and a cooling kit, my 911T braking is much improved on the track and street. Yeah M calipers are ok on the street but with sticky tires on the track(DEs), the Ms just do cut it.

Moral: Upgrade your struts and skip the 3.0" kludges. HTH

[jmcjunkin]

I hear the comment about "if you can lock up your brakes" you don't need a brake upgrade, but isn't there another dimension?

I have raced motorcycles and mountain-bikes, and the most important thing for me there on slippery terrain was brake modulation -- or the ability to break and restore traction. On all brake systems I could lock up the wheels but on the best brake systems I had good modulation. I am new to pcar driving, but isn't the same true? SC/Carrera calipers may not dissipate more heat but I have found the modulation to be better....

[Bill Verburg]

I have raced motorcycles and mountain-bikes, and the most important thing for me there on slippery terrain was brake modulation -- or the ability to break and restore traction.

I was very involved in m/c racing and am an avid bicylist as well. There is a huge difference in the manner in which brakes are applied between the 2 and 4 wheel worlds. In the 2 wheel world there is a built in extremely sensitive and adaptable ABS sysyem that is continually monitoring and adjusting for variable conditions, this ABS can independantly vary the brake toque at one end or the other form 0 to max. This ABS is you.

In the 4 wheel world, where cockpit adjustable bias valves are rarely used actively, let alone even in existance, you must start w/ decent native bias. Then modulate as best you can w/ your leg. Things that will improve the ability to modulate brakes are

• pads that have appropriate friction/temperature characteristics
• approprite temperature range achieved in the system
• larger m/c
• elimination of compliance from the mechanical/hydraulic portions of the system
• Appropriately sticky rubber in its temperature range

[911ctS]

I had these exact calipers on my T before i changed to 3.5" spacing and I loved them. they were a HUGE improvement over the M calipers. they are basicly the same as an "A" (SC) caliper but 3"

BTW you can get them alot cheaper if you just call NAPA or somewhere like that. I used to sell these kits on ebay and I got my calipers fom NAPA for like $175/pair

[cstreit]

In the 2 wheel world there is a built in extremely sensitive and adaptable ABS sysyem that is continually monitoring and adjusting for variable conditions...This ABS is you...

Bill, mine never worked very well. In fact the first time I used it on my first 10-speed, I ended up on my head.

[Bill Verburg]

Chris, sounds like my first ride w/ clip ins ouch

I didn't say that it works best right out of the box, it does need some time to learn, the school of hard knocks is the best out there. Maybe the public schools should take a lesson?

[Jim Richards]

Well, I for one am confused as ever about brakes / brake upgrades. 2004 will be my first full season of DE. I'll be driving a stock 73E narrowbody with 6x15 (f) and 7x15 (r) wheels and probably 205/50/15 RA-1s (soon to be purchased). I imagine at my experience level and with a stock 911E, I can do nicely with the stock M calipers. Next winter I'm going to rebuild the motor to 2.7RS MFI specs. In 2005, I'll be somewhat more experienced and I'll be tapping 40+ more HP with the engine upgrade. Should I expect to upgrade to S calipers, or even the Carrera calipers/rotors before the 2005 DE season, or stay with stock M calipers? Thanks for the advice and please forgive me for veering this topic a bit from its original direction.

[Bill Verburg]

Jim, try it w/ what you have but do use fresh, quality fluid, high temperature pads and try to get some cooling air to those poor rotors.

IFF you find that to be inadequate, then the next step is either S or A calipers in the front(3.5" struts), this is only an incremental improvement that will distribute the heat load over a slightly wider area. That is likely all you need or want especially if you wish to stay in a stock class.

[Jim Richards]

Thanks Bill. By your use IFF, you must be an engineer or mathematician.

I've got the fluid and pads under control. About cooling...is there a good economical solution? Do you cool all 4 rotors or just the fronts? Thanks again!

[911ctS]

I agree with Bill, that is all that you will need for a lightweight car like yours. Carrera rotors probably arn't necessary and will just add to your unsprung weight.

[911pcars]

As I recall, the M calipers with 3" bolt spacing came only with solid rotors (?). If so, these bimmer calipers (w/vented rotors?) are a definite upgrade; go for it. Increased thermal mass is what we're aiming for, yes? Depending on your application, this might be all that is needed for a lighter vehicle. I'm pretty sure the brakes don't care if the calipers bolts are 3" or 3.5" apart. Do these use M pads? They're slightly smaller in area than the A or S pads.

Sherwood

[Jim Richards]

Nope, my 73E's rotors are vented. I don't recall when the change was actually made to vented rotors for the T and E models, but I think it was 1970 (or late '69). The S models were vented starting in 1967 (or late '66).

[Bill Verburg]

Sherwood, the earlist cars '64-67 w/ M front & L rear caliper used the non vented rotors as did the '68T w/ M & L combo and the '69T w/ M & M combo, but all the other 911s thru '83 used the same vented f/r rotors

[Jim Richards]

Now about brake cooling...