Rear Brake drag with 911 Conversion, Caliper spacing wrong? Options

[agrump]

My car has rear calipers from an 83 911sc. I am experiencing an odd groaning noise from the rear of the car once the car has been driven a bit. This usual happens when turning but sometimes when going straight, just not as loud. I believe it is coming from the brakes as it immediately goes away once I apply them. I checked the rear axle bolt and found it to be properly torqued. I noticed that the calipers are not exactly centered to the disk, one piston is father out then the other.. There is a 5mm shim between the caliper and the spindle but it looks like this should be a bit thicker to center it. What size spacer should there be and could this account for brake dragging?

[jim912928]

Did you do a 5-lug conversion or are you still running on the 4-lug setup?

Not exactly your problem..but when I converted my rear end to 5-lug (used 911 vented rotors) I had to space my calipers so the disk was centered within the caliper. Otherwise I was getting a "grinding" noise as the disk rubbed into the side of the caliper. I just used washers on the inside of the caliper mounting stubs to space the caliper appropriately.

I'm guessing that once you apply the brakes and things slightly adjust (heat/play) that they are rubbing the calipers? Can you see any rub/grinded marks on the inside of the caliper where the disk might be rubbing it?

[jim912928]

I'd also check your wheel bearing wear...if you jack up the car do you get alot of play/movement by grabbing the tire and wiggling it back and forth?

[agrump]

It is a full conversion to a 5 bolt hub. The rotor is not touching the caliper but the caliper is not centered. There are 5mm spacers between the caliper and the mount but I thnk they should be thicker.

I checked for play/movement and did not find any. The sensation is like the pads are not retracting enough once they get warm. I don't think the rotors are warped because it is a continous noise and it does not do it when you first start driving

[davep]

You really need to get the rotors centered in the calipers. Heat in the rotors can change the clearances. Did you use vented rotors, and if so did you reduce the rotor diameter? That is critical.

[jim912928]

Davep is right if you used vented rotors...they are a larger diameter then the stock 914 rotors and even larger than 914-6 rotors. I had to take mine down to a machine shop and have them turned down some. I just took a stock 914 rotor along and told them to make them the same (forget how much they shaved off).

[davep]

I don't have my data with me, but I recall :
vented 290mm
914/6 286mm
914/4 282mm

With 911 calipers I would use 286mm since they are the same as the 914/6.

[agrump]

I did not do the installation so I am not sure if the rotor was turned down. They are vented. I'll check the diameter tonight. I didn't notice any clearance problem or abnormal disk wear caused by misaligned pads but I'll check regardless.