930 Rear control arm question

[77turbocarrera]

Does anyone have experience with drilling the second set of caliper mounting pads on the rear 930 trailing arm for caliper mounting?

I am working on a 993 black caliper swap and it seems that the mounting pads line up to the stock 993 mounting holes. This seems easier than filling and drilling the 993 caliper.

Is there a benefit to mounting the caliper behind the wheel?

[Bill Verburg]

Originally Posted by 77turbocarrera

Does anyone have experience with drilling the second set of caliper mounting pads on the rear 930 trailing arm for caliper mounting?

I am working on a 993 black caliper swap and it seems that the mounting pads line up to the stock 993 mounting holes. This seems easier than filling and drilling the 993 caliper.

Is there a benefit to mounting the caliper behind the wheel?

The rear caliper mounts are set up for 3 1/2", the 993 will want 94mm mounts(~3.7") this is off the top of my head but I think it to be correct.

you will have to measure for radial spacing.

There is no particular advantage to trailing mounts vs leading mounts in back, in front there is a slight advantage to trailing over leading

[77turbocarrera]

Hi bill, I think I may give this a try in the rear since I really don't have anything to lose by drilling the mounting pads if they are in line.

I will get a 78 930 rotor and mock it up, either way I need the 930 rotor regardless of the mounting position.

Thanks

[911st]

The pre 78 turbo's had casting for front or rear caliper mounts. However only the front's were drilled for the 911S calipers. It was not until the 78's that the rear tabs were drilled for the big 930 calipers. I think they were surface milled to for a square and proper depth surface, not just drilled.

This makes for the opportunity you note.

Might be best to do it on a mill to get every thing square and proper.

Is there and advantage. Not really. However in front of the wheel might lower the unsprung weight a very little bit.

Also, if the calipers were set up for one side of the wheel and are moving to the other, I think you need to turn them upside down the piston stager correct and then you have to flip the bleed valve and tube's end for end.

It would be a nice set up. However might be easer to have the calipers modified.

Not a brake guy so I could be wrong.

[bkreigsr]

to answer your question, yes I have drilled and tapped the rear ears on my 77 - the hard way.
The easy way would be to remove the stub axles and e-brake assembly and drill from the outside in, but rather than do that, I did it from under the car and drilled outward.

The drivers side on may car was already drilled out, but not tapped. I enlarged the existing holes and inserted helical inserts for the M12 bolts.

The passenger side was different. After drillling the holes and tapping and doing the time-cert thing, I found out then when I went to mount the caliper, the ears had to be milled another 3-4mm in order for the caplier to straddle the ears and the rotor. I was able to get it one ear pretty close with a 4 1/2" grinder.

I gave up at this point and retained my VCI modified calpiers on the leading edge. Besides, after all that, my engineer son said I was better off leaving the calipers on the leading edge for better weight distribution/center of gravity.

Bill K

[77turbocarrera]

This guy did it on his 930 - its a 996 caliper, but that only changes the mounting orientation. The 993 caliper actually has the correct mounting ears.

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bkreigsr, I plan on removing my rear rotors and drilling from the outside.

[Bill Verburg]

Originally Posted by 77turbocarrera

This guy did it on his 930 - its a 996 caliper, but that only changes the mounting orientation. The 993 caliper actually has the correct mounting ears.

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bkreigsr, I plan on removing my rear rotors and drilling from the outside.

That is not a 996 caliper, it does appear to be a modified 993tt or 993RS rear caliper.

the modifications appear to include machineing off the stock axial ear type mounts and converting the caliper to radial mount w/ an adapter. The adapter probably has 3" axial mounts.

here is is hat it would look like unmounted, the left caliper is an unmodified 993tt rear, the center is a 993RS modified as described above for use on 911 3" rear mounts, the right is a 993tRS/tt big red front, the 993tt and 993Rs rears are the same except for piston size


same 3 calipers from the top

[Bill Verburg]

A 996tt rear would be far easier to mount as it is already a radial mount design and is perfect for 930 309x28mm rotors. The only issue is the smallish pistons used on the 996tt rears, but that can be lived w/

996tt/GT3 rears

[bkreigsr]

Originally Posted by 77turbocarrera

bkreigsr, I plan on removing my rear rotors and drilling from the outside.

removing the rotors still will not give you full access to the ears.
it's not possible to drill the ears without removing the e brake assembly, which entails removing the stub axles. - take another look from under the car.

Bill K

[bkreigsr]

a picture is worth a thousand etc...etc...
pic #1 - finished drilling, milling, and threading
pic #2 - both mounted at once.
Bill K
note the e-brake backing plate behind the holes

I presume that the lower orientation of the leading one also does more to improve the of center gravity than would the trailing and higher caliper.

[Flieger]

That ought to stop well

[77turbocarrera]

Looks good, I'm going to try and mount the 993 caliper there, going to get the fronts finished first.

[bkreigsr]

Originally Posted by 77turbocarrera

I'm .... going to get the fronts finished first.

I would do the rears first, that way if things don't work out, you won't have to back into an alternative, i.e. finding another pair of rears to match the fronts using the 3" rear spacing.
Bill K

[77turbocarrera]

If it doesnt work out I will mount them in the stock location and do the required machine work.

Thanks