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> Rear Brake Rotor options
Eddie914
post Oct 19 2006, 10:50 AM
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Worn rear wheel bearings and the concern about 914 CV joint longevity with the torque of the 3.2 liter Carrera engine motivated me to upgrade the rear drive components on my '71 3.2 six conversion.

Previously, I had utilized stock 914 1.7 axles and re-drilled 5 lug hubs used with 911SC rotors, calipers and an 8mm wheel spacer between the rotor and hub. It was difficult to center the rotor and therefore the rotor would at times rub the brake pad retaining pins. The wheel bearings were worn and hard right turns would result in increased rubbing

Here is what the upgrade involved:

- 911SC Transmission output flange (coarse spline)
- 944 Turbo inner CV Joint
- 914 axle with extended spline shoulder
- 944 Turbo outer CV Joint
- 911SC Stub axle
- 914/6 Wheel bearings
- 911T Wheel hub
- 85mm Bullet nose wheel studs
- 911SC Brake rotors
- 911SC Brake Calipers

The brake rotors are still hitting the brake caliper mounting ears. What are the options? Spacers? Washers? Different rotors? Grinding the ears?

What are the diameter, thickness and offset of 914/6 rear brake rotors compared to 911 rear rotors?

How much space is needed between the rotor and mounting ear? Is heat transfer from the rotor to the mounting ear a major concern if the rotor is very close (0.010") to the mounting ear?

I'd like to eliminate the spacer. Fender clearance when running 911 turbo 16 x 9 BBS RA wheels with 245/45/16 tires is minimal. With the old worn rear wheel bearings the clearance was less than minimal under hard cornering, i.e. most of the raised letter on the tires has been worn off!

Thanks

Eddie
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davep
post Oct 19 2006, 10:57 AM
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The spacer between the hub and rotor should be 4mm, 8 is way too much. The 4mm is the difference in offset of the 911 rotor and 914 rotor. Offset is the difference between the inside working face of the rotor and the face that the hub mates to.
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Mueller
post Oct 19 2006, 11:01 AM
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I just made some 1/4" spacers that go between the rotor and hub for SirAndy's car, not really sure why since I've never seen the problem..had something to do with centering of the calipers to the rotor...of course that solution won't be ideal for since it'll make your tires move closer to the fender
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Mueller
post Oct 19 2006, 11:03 AM
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QUOTE(davep @ Oct 19 2006, 09:57 AM) *

The spacer between the hub and rotor should be 4mm, 8 is way too much. The 4mm is the difference in offset of the 911 rotor and 914 rotor. Offset is the difference between the inside working face of the rotor and the face that the hub mates to.



I have EricS rear vented /4 kit and it came with the 5mm spacers. For SirAndys application, 5mm was not enough (IMG:style_emoticons/default/confused24.gif)

edited post to change 4mm to the correct 5mm (IMG:style_emoticons/default/smile.gif)
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davep
post Oct 19 2006, 11:21 AM
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Did Sir Andy have the brackets for the water shield installed between the caliper and the trailing arm? If not, that changes the equation. You have to compensate for each and every change in the set up.
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Eric_Shea
post Oct 19 2006, 02:44 PM
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Mine are 5mm for that reason. Not sure why Mark stated 6mm was the measured distance. It never made sense to me but... I have to go with it. (IMG:style_emoticons/default/confused24.gif)

If you use the 5mm and then do what Ferarri does, shim the mounting ears, you should be able to get it exact. Ferarri has a bunch of varying thickness washers just for that purpose.

Sorry Eddie, didn't answer any questions really. The rotor hitting the pad retaining springs is due to the fact that you probably haven't turned the rotor down. You should take 4mm off the edge. Find a local machine shop with a lathe large enough to turn that edge off. The mounting ears on the 914 control arm are made for 914 and 914-6 calipers and rotors. With the SC rotor you have a larger circumference. I've never had a 911 rotor hit the mounting ears... (IMG:style_emoticons/default/confused24.gif) Maybe they're not 911 rotors?? My 914 is sitting on 911 rotors right now. No spacers.

If you'd like to eliminate the spacer, buy bolts that are 5mm longer and add 5mm spacers under the caliper mounting ears. This will bring your rotor back to the hub and bring your wheel in further giving you the fender clearance you need. With 911 calipers you should have plenty of room for this procedure.

The only other question I would have is the 911T hub. It should be identical. If it's later then a 911T then you would have another 4mm off the face hence your 8mm spacers. Are you sure it's the 911T hub? If it's the wrong hub, it would also explain why you're hitting the mounting ears. I've got $buckage$ on it being a later model hub.
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Dave_Darling
post Oct 19 2006, 02:55 PM
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For the record, 914-6 rotors are almost completely identical to 914-4 rotors. They're a tiny bit thicker (I think 1mm or so), not vented, and a little tiny bit larger diameter.

Your SC rotors are very much thicker, as they're vented.

--DD
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Eric_Shea
post Oct 19 2006, 02:58 PM
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That aint the issue as he's using SC calipers on them (IMG:style_emoticons/default/wink.gif)

There's only 4 things that come into play on this end of the driveline:

Calipers
Rotors
Hub
Spacers

There's only two things that need to be variable:

Rotors
Spacers

Of those two the rotors need to be turned down. Once that's accomplished, it's easy to mock up the system, slip a pad loaded caliper over the disc and take a set of digital calipers to the caliper mounting ear and the control arm mounts. Determine the spacers needed and the new length of the mounting bolts.

(get the proper hubs first) (IMG:style_emoticons/default/biggrin.gif)
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Eddie914
post Oct 19 2006, 03:47 PM
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I'll do a bit more measuring this evening. The 911 hubs seem very close in dimension to the 914 hubs except for inner splines and hole count and boss location.

Hubs came from steel 911 trailing arms. Seller has two long nose 911 conversions ... a 911ST and 911RSR ... I'm not sure which donor the arms came from. I know one was originally a Sporto.

Thanks All!

Eddie
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J P Stein
post Oct 19 2006, 04:30 PM
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I spaced out....no, wait...I moved in the caliper with spacers....4-5mm.
Been workin' for years.
The hub centers the rotor raidialy...a spacer in there.....doesn't.
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McMark
post Oct 19 2006, 11:22 PM
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It's an easy explaination. (IMG:style_emoticons/default/rolleyes.gif)

5mm spacer did NOT center the rotor in the caliper. I haven't put the 6.6 mm spacers in yet, but I expect them to work fine. NOTE: Andy is using a custom axle/hub/cv/etc setup on his car and this is what I'm blaming for his 'special' case.
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Eric_Shea
post Oct 20 2006, 09:08 AM
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I be believe'n you I just couldn't figure 6.6mm out. Now that you say it's a different hub then that makes sense. What hub is it?

Send the 5mm's back and I'll re-loot you. (IMG:style_emoticons/default/wink.gif)
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Eddie914
post Oct 20 2006, 03:54 PM
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Thank you everyone, for all your comments, information and suggestions.

I did some measuring and finished putting it all together this morning before work (got a 4:45 am start ... kids to school at 7:25 and in the office before 8:00 am).

I took a drive over my lunck break and the teener seems to be working very well.

A 5mm spacer between the rotor and hub was used. The caliper seems very well centered with no adjustments. I drilled the spacer so the two rotor retaining screws could be used to help keep the rotor centered. The rotor diameter was NOT turned down and does NOT rub the brake pad retaining pins.

There will still be minimal fender clearance with the 245/45/16 a032r Yokos on the BBS Mahle 16x9 et+2 930 wheels in the rear. I'm guessing that the old wheel bearing was allowing wheel deflection that was exacerbating the rotor/caliper and tire/fender clearance issues.

Looks like a 2mm spacer could be used. That should gain about 1/8". not much but it might eliminate the rubbing.

The next track day I'm planning is October 28 with the IRDC at Bremerton. Any PNW teeners interested?

Thanks again.

Eddie
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Eric_Shea
post Oct 20 2006, 04:01 PM
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(IMG:style_emoticons/default/smilie_pokal.gif)

I guess it's just with teener calipers that you need to turn it down. Glad everything is working.

Now... how much clearance do you have with the mounting ears? Mine don't rub w/o spacers so you may be able to eliminate the rotor spacer and space out the caliper by 5mm. Almost 1/4" is almost 1/4" (IMG:style_emoticons/default/wink.gif)
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sixnotfour
post Oct 20 2006, 08:19 PM
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5mm .200
6mm .240
1mm.03937
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Eric_Shea
post Oct 20 2006, 09:32 PM
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(IMG:style_emoticons/default/tongue.gif)
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SirAndy
post Oct 20 2006, 10:25 PM
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QUOTE(Eddie914 @ Oct 19 2006, 09:50 AM) *

The brake rotors are still hitting the brake caliper mounting ears. What are the options? Spacers? Washers? Different rotors? Grinding the ears?


i just went through this on my car ...

early 911 hubs, '85 carrera calipers and '85 carrera vented rotors.

the rotors would hit the caliper mounting tabs (just barely). i had mueller make me a set of 6.6mm spacers that go between the rotor and the hub, moving the rotor out 6.6mm.

that puts it right in the middle of the caliper!
(IMG:style_emoticons/default/smash.gif) Andy
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Eric_Shea
post Oct 21 2006, 10:09 AM
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Ahhh. it wasn't the hub, it's the Carrera Rotors. Another 3mm in total thickness larger... right?
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