Rotor Clearance

[kupcar]

Hi Guys, I have a 76 930 with a Big Red brake upgrade. The problem I have is that the rotor is maybe 1mm from the front a-arm. I just changed out the oem struts to rsr struts. I don't think this should change the geometry other than raised spindles. With the old struts, I had a bit more space. The hub is the same. Anyone have any ideas why the clearance is different? Is it ok to do a bit of grinding on the end of the a-arm to create more clearance between the rotor and a-arm? Thanks, Jeff

[Bill Verburg]

Originally Posted by kupcar

Hi Guys, I have a 76 930 with a Big Red brake upgrade. The problem I have is that the rotor is maybe 1mm from the front a-arm. I just changed out the oem struts to rsr struts. I don't think this should change the geometry other than raised spindles. With the old struts, I had a bit more space. The hub is the same. Anyone have any ideas why the clearance is different? Is it ok to do a bit of grinding on the end of the a-arm to create more clearance between the rotor and a-arm? Thanks, Jeff

This is all you need

[kupcar]

Bill, Thanks for the help. I maybe have half that now. Is it ok to grind a bit off the a-arm? Thanks again, Jeff.

[Bill Verburg]

Originally Posted by kupcar

Bill, Thanks for the help. I maybe have half that now. Is it ok to grind a bit off the a-arm? Thanks again, Jeff.

I'd look into why the rotor is so close to the A arm,
are all these parts in place? It's very common to find #23 missing

[TimT]

I just changed out the oem struts to rsr struts

This coupled with the larger dia of the big red kit rotors can cause interference between the a-arm and rotor..

As the spindle moves up the strut... the back of the rotor gets closer to the a-arm.. In some instances the a-arm/rotor foul. You can grind the end of the a-arm, or space the hub out..

[kupcar]

Thanks a bunch guys. I will first take it apart to see if all the parts are there. If they are then maybe a quick grind to get a bit more clearance. Thanks, Jeff

[911pcars]

Originally Posted by Bill Verburg

I'd look into why the rotor is so close to the A arm,
are all these parts in place? It's very common to find #23 missing

Bill,
What is part #23 called? What's the purpose of it? Approx. thickness?

thanks,
Sherwood

[DRACO A5OG]

Hey Sherwood,

I think it is the inner Bearing Seal from memory

[911pcars]

Originally Posted by DRACO A5OG

Hey Sherwood,

I think it is the inner Bearing Seal from memory

You sure? Bill's response seems to indicate a spacer of some sort that if missing would position the rotor closer inboard, toward the a-arm.

However, the oil seal is typically installed flush with the hub and wouldn't affect the position of the rotor.

Sherwood

[DRACO A5OG]

Well, I was wrong PAG Katalog calls#23 an O-Ring:

.75 cents



Pelican Parts - Product Information: 999-701-084-50-M104

Damn, I don't remember seeing that when I replaced my front bearings, well I do need to change my rotors so I guess i will place it while I'm in there, re-packing the bearing too . Thanks fellas for another weekend chore. I really need stop logging on, it always cost me Well $1.50 ain't bad to be in spec.

Question? won't this o-ring cause some play due to it's compound??? That is all I need more slop in front Ivangene, another Derlin idea? eh???

Jim

[911pcars]

Originally Posted by DRACO A5OG

Well, I was wrong PAG Katalog calls#23 an O-Ring:

.75 cents

Pelican Parts - Product Information: 999-701-084-50-M104

Damn, I don't remember seeing that when I replaced my front bearings, well I do need to change my rotors so I guess i will place it while I'm in there, re-packing the bearing too . Thanks fellas for another weekend chore. I really need stop logging on, it always cost me Well $1.50 ain't bad to be in spec.

Question? won't this o-ring cause some play due to it's compound??? That is all I need more slop in front Ivangene, another Derlin idea? eh???

Jim

Jim,
You're right. it's an oil ring (for speedo drive), and wouldn't have a bearing (pun) on the rotor position. It being rubber wouldn't be on the race/hub/bearing axis which requires everything to be stacked.

I think one of the aftermarket brake upgrade companies has metal spacers which could be used to space the rotor further outward. However, this poses another issue with the rotor remaining centered between the caliper halves.

Sherwood

[TimT]

That o-ring fits in a chamfer behind part 24 and the spindle. P/N 24 rarely gets removed

[haasad]

I too had this issue with my big brake conversion detailed on ddk ( uk)

The o ring fits behind the spacer on the stub axle. The standard spacer isn't usually removed so the presence of the o ring isn't obvious. The spacer is a very tight fit on the stub axle and the o ring sits in a chamfer feature on the spacer . I understand its function is to seal the interface between the spacer and the stub axle preventing corrosion setting in. In no way does it allow any compliance within the assembly.

I made new spacers to push the rotor out as far as possible whilst retaining sensible bearing contact on the stub axle and a full hub nut depth . I made my own adaptors to fit the 944 turbo sourced calipers and accomodate the new offset requierd to keep the caliper central on the rotor

In the end I couldn't get enough clearance to ensure no fouling between the rotor and the balljoint when lock was applied so I raised the spindles on the struts and corrected the bump steer by setting the steering arms to compensate.

I wasn't happy to grind away material from the ball joint feature on the a arm.

andy

[kupcar]

Well it looks like all the parts are there. I have maybe the width of a dime clearance between the rotor and a-arm. It almost looks like it touches when the car is off the lift. Never had this problem with the oem struts. The rotor is perfect with no indication of touching. What is a safe distance for clearance? Thanks, Jeff

[KTL]

The part that spaces the hub outboard a slight bit is #24- a spindle collar. Even with that collar in place, there can be some clearance issues with a rotor slightly too wide or a bit to much offset. VCI makes a little widget spacer that you install behind #24. You can see it in this picture



It's a simple circular spacer with a chamfer on the back side of it to avoid squashing the o-ring on the spindle. The fit is a light press fit. You heat the spacer with a heat gun and it slides right on. Same goes for removing the spindle collar. Heat it up a bit and it will pull right off with a small two jaw gear puller

You could have a machine shop make these spacers very easily. Just give the diameter of the spindle and they would make the spacer a teeny bit smaller ID press fit

[kupcar]

Hey Kevin, thanks for the tip. This might solve the problem. Any idea what they call the part other than a spacer? Tinley Park, I have in-laws that live off 171st & 80th. Small world. Thanks Again, Jeff

[911pcars]

Originally Posted by kupcar

Hey Kevin, thanks for the tip. This might solve the problem. Any idea what they call the part other than a spacer? Tinley Park, I have in-laws that live off 171st & 80th. Small world. Thanks Again, Jeff

I recall VCI calling theirs a "spacer", about 0.040", the one they recommend to install 944 turbo rotors on matching 944 turbo calipers. Let us know the current availability and pricing if you can.

Sherwood

[TimT]

VCI want $70 for the spacers according to the website...Not sure you could have one offs machined locally for less than that.... unless you have an in with a machinist

[DRACO A5OG]

Just a thought, if place that spacer, will also need to space the caliper mount so the caliper sits center of the rotor? I was just looking at OP's pic trying to see if the current set up was off???

[KTL]

Yep VCI just calls it a spacer. Here's a pic taken from their site



The spacers are the rings above the master cylinder. VCI provides these in varying thicknesses depending on your need. I think I recall them being 3, 4, 5mm thick. I have a few sets of these and ended up using the thickest ones on my '87. The clearance was still pretty tight but there was no problems. I still shaved the nose of the A-arm a slight bit just for peace of mind .

DRACO,

You make a good point about spacing the caliper mount. However that's theoretically not necessary in the case of using the VCI kit as a whole. The VCI caliper mounts, spindle spacer and '86 944T rotor are a "matched" group that are dimensioned to get everything lined up right.

That said, in this case where the spacers are used without VCI's caliper and rotor setup, the caliper is most likely not going to be centered atop the rotor. I have seen even the VCI installation not always perfectly centered on the rotor. In that case some washers of suitable thickness are helpful to move the caliper inward and center it on the rotor. If it's off by a lot, a new adapter should be made of a greater thickness or a full width spacer should be used instead of washers. I don't like the idea of the caliper adapter teetering atop a stack of washers against the spindle mount.