View Full Version : Rotor diameter ?

12-07-2004, 10:43 AM
Hi !

I have a Camaro -69 , with Wilwood Disc brakes in the front.

The brakes were assembled in the early or mid -90īs.

They look very much like 140-7675 , but they are a bit different.

The size of My rotors are: 10,75" dia. 5 bolt , 3,88" bolt circle.

Does anyone know if itīs possible to find 12" rotors 5 bolt , 3,88" b.c.,

that will fit My car ?

Or do I have to change the complete kit?


12-07-2004, 11:20 AM
3.88" bolt circle? Are you sure that you're measuring that right? Stock Camaro would be 4.75" bolt circle and stock big-car would be 5" bolt circle... 3.88 seems awful small.

12-07-2004, 11:34 AM
Just to verify, I drew 4.500, 4.750 and 5.000, 5 bolt bolt circles and measured every which way I could think of...nothing was close to 3.88. 3.88x2 (7.76) didn't match anything either. How are you measuring this?

Salt Racer
12-07-2004, 12:55 PM
Dudes, he's talking about the bolt circle on the rotor/hub mount, not the wheel lug bolt pattern. The rotor shown below is their drag race stuff, but they used to use the same pattern on street rotors.


I think you're out of luck. Your best bet is to upgrade the whole thing. Wilwood has done fair amount of re-engineering in the last couple of years. I bet your calipers are old cast Dynalites w/ no stainless wear plates (thin stainless plates where pads backing plates make contact with aluminum caliper casting).

If you can fabricate caliper mounts, it's better if you use 1.10" or even 1.25"-thick rotors as opposed to 12.19 x 0.810" rotors that are included in their standard 12" kit. Those thin rotors are marginal on a 3500-lb Camaro for anything other than moderate street driving (speaking from my own first-hand experience here).

12-07-2004, 01:40 PM

IIRC,The newer, heavier duty kits use an almost flat plate that bolts to the back of the hub and then the rotor bolts to it. You may be able to ditch the old rotor and just get the mounting plate and new rotors and use the existing hub. Wilwood should be able to give you the fitment information.

Check out the picture at this link:

Notice the "plate" that the rotor mounts to (you can see the end s of the bolts sticking out through). That plate bolts to the back of the hub. That is the plate I was referring to above.


12-07-2004, 06:36 PM
Thankīs for Your answers !
Yes , thatīs right. I mean the rotor/hub mount.
About the caliper , I think it is an old cast Dynalite.
Part nbr: 120-1052 (canīt find it in any catalog).
Front discs are 10.75" dia.
The disc width are .81" . (Street version).
I donīt think thicker discs will fit into these calipers.
They are not wide enough.

Iīm asking these questions , because I have a lockup problem in the rear.
Itīs a Ford rear end with the same calipers as in the front.
The discs in the rear are 12.19" dia. , .81" thick .
There are 8 bolts. ( Iīm not sure about hub mount bolt circle dia.)

I have tried to adjust the propotioning valve , but I canīt get it right.
Thats why Iīd like to put on 12" rotors.
I was also thinking of the flat plate , Shane mentioned , but I better talk to Wilwood , about different offsets and stuff.

Since My car weighs , like You said , approx.3500-lb , a new brake kit would probably be the way to go.


Salt Racer
12-08-2004, 07:06 AM
I really recommend upgrading the caliper to forged Dynalite ($120 each) or even forged Superlite ($160 each), but if you want to keep what you got, Wilwood sells shims/longer bolt kit to make your calipers wider. In fact that's all they do (stack up shims between caliper halves) when you buy Dynalites for wider rotors.

You can probably keep the hubs you have, and get a pair of adapters and 12 x 1.25 rotors.

As for the rear locking up, check the caliper piston bore diameter. Front should be 1.75", and rear should be 1.38" or something. If you have 1.75" all way around, the back end will lock up big time even w/ 12" rotors on all four corners and the proportioning valve cranked all way down (assuming your front & rear tires are relatively close in size).

You can also use different pads on front and rear, like Polymatrix E compound on front and T compound in rear, for example. You can check temp vs. friction coefficient curve of each compound on Wilwood's website. I'd stay away from race pads (A, B, J, H, etc). Stopping power is incredible, but they'll eat up rotors in hurry. I've used J pads on my boss' car, and the pads took 0.030" off the face of cast iron rotors in 5000 miles (3500-lb running weight, 51% over the nose).

12-11-2004, 09:19 PM
Hi !

I have disassembled My calipers and I found 1.75" caliper piston bore dia. , both front and rear.
So , larger rotors in rear. Same caliper piston size , both front and rear .
And slightly larger tires in the back.
Back :(295/50/15) 26.6" Dia.
Front : (265/50/15) 25.5" Dia.
Not a good combination.

I also looked at the pads :Gator Pads (green)pn: 150-2391 (front)
Pads rear: 44004 AG (Beige color) (not sure if itīs Willwood ???)
Maybe a switch would help ?

I keep trying to identify My propotioning valve .(Canīt find it anywere)
It says " KN " on the adjusting knob.

I read "Jegīs Hi Performance "catalog , where they described Wilwood prop.valve :
" .....fine tune the front to rear braking balance by proportionately decreasing the rear (or in some cases the front) brake line pressure."

Is that possible ,to connect the prop.valve in the front brake line??

What do You Guys think ??


Salt Racer
12-13-2004, 07:25 AM
Installing proportioning valve in the front line is a bad idea. For more info, go to this thread (https://www.pro-touring.com/forum/showthread.php?t=2771).

Looks like you're on a relatively tight budget. I don't blame you, especially since you reside in outside of US. But think about it this way - spending $1000 on brake upgrade now is much cheaper than hospital bill, fixing sheetmetal, and upgrading brakes later.

That said, here's bare minimum of what I would do...
- new rear calipers w/ 1.38" pistons
- 12.19 x 0.810" rotors for front: Wilwood has everything you need to upgrade, but like I said, if you can fabricate go with wider rotors.
- Polymatrix E pads for the front. You can keep old tan (beige) pads in the rear if there's sufficient material left, or get Polymatrix T pads.

These should make your brake substantially better than what you have now. But I'm not a brake engineer and I cannot be held responsible for what I said, so your best bet is to consult with Wilwood.

12-13-2004, 10:18 AM
Tight budget. Yes!
When buying parts from US , will cost almost the double ,before it gets here(Sweden).Shipping , customs fee and 25% tax on top , is tough.
So I want to be sure ,to get the right stuff , from scratch.

Thankīs to You Guys , I have a lots of information , about disc brakes.

Thank You once again.

Michael :icon996: