[Formula jg]

I'm sourcing a rear disc setup but am confused about axle flange offset measurement. Here is a link to Wilwood site with various flange diagrams:

http://www.wilwood.com/BrakeKits/BrakeKitApp.aspx

I don't see a 10 bolt diagram.

I had new custom axles made (no installed yet) and the shop suggested a 2.75" axle offset for the new axles because it was the most common with the aftermarket disc brake kits, so we went forward with that dimension.

Does anyone know what the oem offset is for '79 Firebird with drum brakes?

thx

[Scarebird]

2.81" is what is normally used.

[Formula jg]

Scarbird,
So if I order rear brakes that have a 2.81" brake register offset and my actual offset is 2.75" then I would have to shim to get them centered over the rotor properly?

[HWYSTR455]

Most rear disc kits have a requirement for a particular flange and center register diameter. Will depend on the kit. Read the install instructions prior to purchase. For example, the Right Stuff Kit I just used on a non-C-clip BOP 10 bolt uses a axle flange diameter of 6 3/8 and a rotor center of 2.915 for the hole.

My axle flange pattern for the A body is a 3.375 center to center top bolts, and I don't see it listed on the Wilwood site. Yours should be a 3.125 on your 'bird, and I don't see that one listed on Wilwood either. I think their' chart may be off, might want to call them. Pretty sure they have rear kits for 10 bolts.

.

[Formula jg]

HWYSTR455,
That's correct, my rear axle housing flange measures 3.125" and it's not shown on Wilwood website. I had already spoken to them twice (hope their products are better than their customer service/tech reps) and after each call I didn't feel confident with the accuracy of the information they provided. I trust and rely on the memebers here to help guide me.

Anyone install a Wilwood rear brake system on a late 2nd gen coporate 10 bolt?

thx.

[HWYSTR455]

You called Wilwood and they couldn't tell you if they had a caliper bracket for a 3.125 10-bolt?

Call and ask for post-sales tech, tell them you have the kit for the 3.500 axle, and ask why it doesn't fit. They may be able to give you a better answer!

.

[Formula jg]

Called Wilwood (3rd time) no rear kit for corporate 10 bolt. They suggested I contact one of the axle mfg. like Strange or Moser to see if they have their own Wilwood brake kits.

[Bigger is Better]

They do make a kit, or did, I have one on my TA. Well kinda, I had the same challenge and it was about 5 years ago so I suprised they still dont have a kit marketed to it.

I dealt with "HotrodUSA" in washinton state and they understood the whole 12 bolt/10 bolt issue. I also talked to Wilwood and had to get to some senior guy to get it figured out. At the end of the day I believe it was the "Forged Dynalite Rear Parking Brake Kit" for a 12 bolt that is what I used.

I will have to check my records and post back as to the kit number and offset. My kit was a bit special as HOTRODUSA had an Wilwood "exclusive" where the rear rotor setup with a hat/rotor where the standard kit is one piece. I just checked and it looks they are out of business now (?). That said they were all off the shelf Wilwood parts (it used to be there standard kit) and if you asked them they asked you to buy it from Hot Rod.

The one issue I did have with the kit was that there is a small "pilot"/register that extends past the axle housing flange, I geuss to center the rear brake OEM bracket. The Wilwood parking brake/drum backplate did not have a relief machined in it, or the big enough, for this pilot so it doesnt seat properly so you have to shim the caliper a fair bit to center it on the rotor. When I called Wilwood on it they had not heard of the issue before so am I am not sure if it is specific to the 10 bolt. I just took apart the backing plate and had the relief lathed into it.

If I can find the info I will post it soon.

[Bigger is Better]

OK, so I found some of my original information. The kit I bought was Wilwwod 140-6293S (staggered shock), 2.75 inch offest. As I mentioned this kit was a special Wilwood kit for HOTRODUSA but it was basically the 12 bolt internal brake kit for 2.75 inch offset but with a two piece hat/rotor as compared to the standard Wilwood kit.

The issue I ran into was the pilot on the diff was 2.84 inches and the brake kit had a relief for a 2.725 inch pilot. If you look at the Wilwood flange diagram it lists the pilot OD that I have as a "12 bolt late" and not the standard 12 bolt. At the time I measured two 1980 4 wheel disc 10 bolt TA diffs so I am not sure if those were unique, I didnt think so. The top bolts are also around 3.072 inches center to center (??).

Thats all from a trail of emails I had so I cant garuntee its accuracy. I recommend that you measure the offset of your axles but also the register OD. From there you should be able to talk to Wilwood about a matching kit, it might be for the "12 bolt late" application.

[Formula jg]

Bigger,
Thanks so much for taking the time to post this info and pic.

I checked that Wilwood part no. and it was not valid. I spent some time today getting more precious dimensions and found 2.81" axle shaft flange to axle housing flange, here is a pic:

I also measured the axle housing flange center-center bolt holes here is a pic (note that I had a lot of difficulty determining exactly where the center of the bolt holes were so these are approx. dimensions):

Is the "pilot" your referring to the axle tube O.D. that protrudes through the axle housing flange? If yes, mine measures smaller (2.540") than any of the 3 shown on the Wilwood diagrams (2.725, 2.840 or 3.150).

[Bigger is Better]

Your picture reminds me of the issue i had. The register i was talking about is actually in your axle offset picture. If you look at the axle tube where it comes threw housing flange there is a small step that is a larger diameter then the tube and protudes a small amount past the flange. You want to measure that because if the relief in brake bracket is smaller it wont seat against flange. Wilwood had no idea what l was talking about when I asked them about it.

Its ok if bracket is bigger as it does not need be perfectly centered.

[Formula jg]

Bigger,
See attached pic:

Is this the area you had some trouble with? If yes, I will have to measure it come this weekend.

[Bigger is Better]

Yes that is it. Also I assumed you wanted an internal parking brake kit, those have a drum like backing plate which can have an interference issue. The non parking brake kits I believe have a more standard bracket caliper mount that might not be a full backing plate and have more clearance.

Eitherway i think you should measure that.