944T calipers on my 911

[KTL]

Souk,

It looks to me that VCI uses the "widget" spacer because of their 1-piece front rotor choice. The rotor they use is not a custom application. Their rotor is that from the '86 951. The 2-piece rotor method allows you to establish the necessary o/s with the rotor hat instead of the "widget" spacer?

I'm sure Chris reminded you that you have to file the ball joint cup on the A-arm a tiny bit too. Even when the spacer's in there. I didn't like the spacer idea myself because of how the grease seal sticks out a bit. Just my opinion. Far be it from me to question VCI's design. It obviously works because Chris has no problems.

By Souk:

Anyone use a 3.2 Carrera rear rotor (290x24 mm) with a 944T caliper in the rear of a pre-Carrera car to retain e-brakes (as oppose to the 930 rear caliper)?

Why not use the 930 rotor with the 964/944T caliper like Bill recommends? It retains the p-brake. Cost? Unsprung weight? But the answer to your question is that the VCI kit uses that exact rotor (290x24 911 part)!!!

The caliper hole spacing is 3.5" O/C. That's why the holes are welded and redrilled for your 3" O/C spacing. See how the holes are further inboard to the caliper C/L?



Bill,

Could you point me/us to some references on brake sizing, biasing, design, etc? Seems like you have to repeat yourself so often regarding these issues.

[KTL]

Originally posted by Souk

(Talk about a one-man thread! ...four post in a row!)

What the heck do you expect when you're posting at 3am? Even I don't get up that early! You switch jobs and become a garbage man?

[MotoSook]

Originally posted by KTL
Souk,

It looks to me that VCI uses the "widget" spacer because of their 1-piece front rotor choice. The rotor they use is not a custom application. Their rotor is that from the '86 951. The 2-piece rotor method allows you to establish the necessary o/s with the rotor hat instead of the "widget" spacer?

------------------------------------------------------------>Souk
I believe the 951 front rotor is a good choice beause they are cheaper than a custom 2-piece..right?

As for the widget spacer...why didn't they just back the caliper inboard by 1/4 inch with their axial-radial adapter? Or will that cause the rotor interference with something else?
<------------------------------------------------------------

I'm sure Chris reminded you that you have to file the ball joint cup on the A-arm a tiny bit too. Even when the spacer's in there. I didn't like the spacer idea myself because of how the grease seal sticks out a bit. Just my opinion. Far be it from me to question VCI's design. It obviously works because Chris has no problems.



Why not use the 930 rotor with the 964/944T caliper like Bill recommends? It retains the p-brake. Cost? Unsprung weight? But the answer to your question is that the VCI kit uses that exact rotor (290x24 911 part)!!!

-------------------------------------------------->Souk
That's what I wanted to confirm I guesss. That the VCI rear rotor is indeed the Carrera rotor. Comparing a couple of sites (SW's and VCI, their rotor measurements are not identical..understandable..even stated as "rough" on SW's page) it was not clear to me that the rear rotor was a Carrera rotor. You got a used rotor off the Unicorn for me?

Edit: So I can use the Carrera rotor and retain e-brakes...right..dang I'm dense!

The 930 rear rotor is 310mmX28mm. It would require grinding the rear 944T caliper, and won't it create an undesired rear bias since the 951 front rotor is just 299mmX28mm? I don't have that spreadsheet handy to compare pad contact area, but a smaller pad area in rear would eliminate any rear bias concern.

<----------------------------------------------------

The caliper hole spacing is 3.5" O/C. That's why the holes are welded and redrilled for your 3" O/C spacing. See how the holes are further inboard to the caliper C/L?
--------------------------------------------------->Souk
I recall two contradictory statements made by Bill V. I hope to clear that up...

One statement indicated that hogging out the calipers to make them fit a 3.5" bolt spacing in front was not recommended, but then he made a statement that VCI could have just done a similar thing with the rear instead of machining for an adapter. Please clear this up Bill....

<-----------------------------------------------------

Bill,

Could you point me/us to some references on brake sizing, biasing, design, etc? Seems like you have to repeat yourself so often regarding these issues.

Bill's be a great resource, and I hope he never gets tired of replying to our idiotic, non-self researching lazy arses.

[MotoSook]

Originally posted by KTL
What the heck do you expect when you're posting at 3am? Even I don't get up that early! You switch jobs and become a garbage man?

Genius minds are restless Imagine if all those garbage men...put their heads together..we'd cure cancer and walk on Jupiter!

[KTL]

I'm assuming the front rotor choice by VCI was based on cost issues. I'd agree that the 951 rotor is cheaper than 2-piece. Can't make the kit cost too much I guess. Apparently their kit is a slight compromise in that sense? Not as much heat management as Bill's setup, but still an effective upgrade?

Moving the caliper via the axial-to-radial adapter still doesn't address the rotor interference with the ball joint cup on the control arm.

Mark might have a used Carrera rotor for you. I can check today. If not you can borrow one of mine. I have take off the RR caliper anyway to replace a torn dust boot. Just so long as I get it back stickyfingers................

Pad area 964 4 piston calipers both F/R = 86 cm^2
Pad area 930 calipers = 94 cm^2

It appears that the fronts need the adaptors to get the caliper spaced radially outward far enough for rotor clearance? That's how I understand it from Bill's quote:

By Bill V:

The AP or Brembo rotors shown above would be used w/o machining in the 280x28mm size. The 290 or larger sizes would require machining and adaptors.

The beauty of radial mounts is that rotors of different diameters can be swapped in/out by swapping adaptors.

VCI also likes to machine radial mounts into the rear calipers. I don't think that this is necessary but do understand their perspective.

So you can hog the front calipers, but you can only use the 911 24mm thk. rotor in doing so, which is bad. Using the bigger (28mm thk.) 951 rotor requires the adapter (and "widget" spacer)because of the 951 rotor hat o/s? That's my best guess. Where the heck is Chris? He's got the darn things.

[Bill Verburg]

Sheesh go skiing for a few days and everyones shorts get knotted up.
CHP-POR

What reference points are used for determining the size of the adaptors so that they will position the calipers properly for the diameter of rotor chosen?

When using the 964/944 calipers it depends on who machined the calipers, they don't come from Brembo as radial mount, same for axial positioning. IF the holes are drilled correctly everything just lines up. What are the CAM dimensions? that's propriatary and you pay Powerhaus for the answer.

Maybe I missed it in earlier threads, but isn't a larger diameter rotor a significant contributor to more effective braking because of a longer moment arm?

Yes, thats one reason that you need a matching rear setup.

I acquired some Brembo 944 caliipers some time back that I was told were turbo, but after measuring (what's sticking out past the the dust boots) I think I got something else based on the varieties you have listed.

You do not measure the part sticking out, get under the dust cover and measure there. The most common fronts are 36/40, the moct common rears are 28/30 or 30/34. The small piston always leads. The #s posted mean nothing to me.

[MotoSook]

Originally posted by Bill Verburg
There are 2 ways to do it
the wrong way(potentially dangerous) by hogging out the mounting holes and fitting over Carrera rotors.

[Souk] The above statement appears to be an attachment concern, not a heat or bias concerns (issue nevertheless)

The right way by machining the calipers to accept axial/radial adaptors and using 930 rotors

[Souk] I plan to go the VCI attachment route. That is, machining the front calipers and using adapters and widget spacers.

The rear is actually easier in some respects as long as 930 rotors are used

[Souk] 930 or Carrera rotors, I want e-brakes which both should provide. Seems the 24mm Carrera rotors in the rear should be adequate.

In addition the m/c needs to be updated.

[Souk] Why are some guys reporting adequate (firm and no spongy feel) pedal feel with the 19mm master cylinders?

[KTL]

Souk,

Your quotes make my brain overheat like a 24mm front Carrera rotor under a 964 caliper....................

[Bill Verburg]

Souk

Can you elaborate on the 944T rears in back...I don't have one in hand (yet). Is the mounting hole spacing 3 inches? And will the unmodified 944T rear caliper bolt onto a 911 (say 76) while using a 930 rear rotor to retain e-brakes?

The trailing arm bolts are 3" O.C., the original Brembo is 94mm(close to 3.7". For rear use the original holes need to be plugged and redrilled @3" and slightly further from the lower end of the mount. One of these days I'll make a template, but haven't gotten around to it yet. VCI will do the same type of mod as used at the front. The other issue is that the throat/pad box of the 944/964/993 rear is ~2mm narrower than it should be to fit over the 28mm wide 930 rear rotors. So some minor mods are needed in this area and some pad thickness needs to be removed. An unmodified 944/964/993 rear caliper cannot be used on a 911 trailing arm. The above mods are for use w/ am oem 930 309x28mm rotor, yes the parking brake is retained in it's stock form and operation. The 930 rotor just replaces the 911 after the backing plate is removed.

Chris does not have this setup. He has the calipers modified by VCI for use with smaller 944 or 951 rotors. That was all he needed on his very light car.

The 930 rotors are the ticket for heavier and or faster cars.

the rotor steps are[list=1][*]282.5x20 &290x20 mostly thru '83[*]282.5x24 & 290x20[*]282.5x24 & 290x24 '84 htru '89[*]299x28 & 289x24 Chris' setup 944t rotors[*]304x32 & 309x28 930[*]322x32 & 322x28 993tt[/list=1]

[MotoSook]

I don't know how to do it otherwise! Bill's back!!!!

[Bill Verburg]

SprintStar,
There are a whole bunch of issues w/ installing 930 brakes on a swb car
first- the front struts need to have 3.5" ears
second - Warren says that the trailing arm mounts are 2.5". I don't know if that is true or not but 930rear calipers require at least 3" mounts. Now I alway thought that was what was used on those cars but I have never worked on one so don't really know.

[Bill Verburg]

What's confiusing is that there are several possible ways to do this sort of thing. and the front and rear are different.

My head hurts as well.

[MotoSook]

Bill, I expected Kevin's pea brain to hurt, not your's

OK! In a nut shell:

In the front:

I'm going to maching (or have VCI do it) 951 front calipers and make r-a adapters. I'll machine a spacer for the rotor too. Use 951 front rotors.

In the rear:

I'll hog out and make a filler "clam shell" for the rear calipers and use the 24mm Carrera rotors. I understand this is less desireable than the 930 rear rotor setup, but my car will not be a full track car. I won't have to machine the inner face of the calipers to fit the 28mm 930 rotors.

Use my stock 19mm m/c.

OK?!

Approval:___________________

[Bill Verburg]

No matter what you will want a 23mm ATE m/c. Steve Weiner is a good source for these. You want the kit which includes the rod and fittings.

I know of no way to use the 944/964/993 Brembos in the back w/ the Carrera rotors. They are too small in diameter.

[MotoSook]

Originally posted by Bill Verburg
I know of no way to use the 944/964/993 Brembos in the back w/ the Carrera rotors. They are too small in diameter.

Bill, do you mean thickness or diameter. The numbers above indicate the 84-89 Carrera rotor diameter is 1 millimeter more than a 951 rear rotor. Both have the same rotor width...seems like it should work, yes?

[Bill Verburg]

do you mean thickness or diameter. The numbers above indicate the 84-89 Carrera rotor diameter is 1 millimeter more than a 951 rear rotor. Both have the same rotor width...seems like it should work, yes?

Thickness of 24mm is not an issue for 944/964/994 rear caliper. But the diameter is an issue. VCI's method still leaves some pad overhang because the rotor has too small a diameter. The 944 mounts are not the same radial distance form the axle centerline as the 911s. ie the 944 rotor has too small a diameter.

The redrilling method for use w/ 930 309x28s also moves the holes about as close to the top of the caliper as is practical. That means that 309mm is about the smallest diameter rotor that can be used in this way.

[MotoSook]

That (!) clears it up. Thank you once again Bill!

[cstreit]

Bill,

THere is actually abot 4mm of pad overhang with the 84-89 rear rotor...

...but while this is true, I have yet to find anything negative about it. (other than wasting 4mm of brake pad. )

I would have preferred thicker rear rotors since they are only 24mm but while I consider myself harder on brakes than your average bear, I have not had any overheating issues since installing the VCI kit.

I have mixed feelings abotu the 23mm master cylinder though.

1) Since the sellers are re-selling it, they charge too much for what I know is a basic Mercedes truck m/c. I understand why, just don't like it.
2) The pedal is SO FIRM, that it makes it more difficult to modulate.

[SprintStar]

Originally posted by Souk
Still looking for answers....

Anyone use a 3.2 Carrera rear rotor (290x24 mm) with a 944T caliper in the rear of a pre-Carrera car to retain e-brakes (as oppose to the 930 rear caliper)?

I have not tried but I bet you it's the same. Same thickness. The difference between the 951 and 3.2 rotor is the how deep the hub is. But both will use the same handbrake assembly. In fact, if you cross-reference numbers, you will see the handbrake pads have the same part number.

Sprint.

[Bill Verburg]

THere is actually abot 4mm of pad overhang with the 84-89 rear rotor...

Your car, your choice, doesn't sound like something I would want on mine. The correct native rotor thickness is 24mm for that caliper and the rear does so relatively little braking that one can get away w/ a lot back there.

The pedal is SO FIRM, that it makes it more difficult to modulate

Not true!! Ergonomic studies have shown that the human leg is better at modulating pressure at a fixed position, than at varying positions. The larger the master cylinder the more closely the system approximates that ideal. This is the reason that the factory has always used larger master cylinders on their sporting and race cars. The larger m/c is not hydraulicaly necessary after a point but it does improve the ergonomics for the driver.