Rear Wilwood Kit on '77 Firebird

[GoreMaker]

I bought a rear Wilwood disc brake kit for my '77 Firebird with a stock GM 10-bolt rear end. I'm running into some problems that are confusing me, and I figured I'd ask about it here first before getting in touch with the reseller or Wilwood directly.

The kit is 140-14400 which has 11" rotors with parking brake drums and staggered calipers.

When trying to install the backing plate, the bore doesn't fit over the lip on the flange of my rear end (flange registration diameter). It's not even close. The lip is 2.840" diameter, and the hole on the backing plate is 2.725". There's no way the backing plate could lay flush against the flange. If I tried to tighten it down, it would just bend. This isn't a tiny difference, it's 1/8". Do I have the wrong backing plates? Or do I need to get them machined out to fit around the lip on the rear end? I wasn't counting on that extra expense.





Also, my understanding about the goal of the staggered kit is to keep the calipers away from the shocks. These backing plates came pre-assembled with the parking drum shoes and cable brackets. However the way they're setup right now, the calipers would be on the same side as the shocks on both sides. Are these assembled backwards? Or am I wrong about where the calipers are supposed to be?

[GoreMaker]

So NOBODY has any insight into this? Not even the forum category sponsor?

I tried calling Wilwood multiple times today. Each time, I got hung up on in the middle of the call and nobody bothered to call me back. This is not the Wilwood experience I was expecting.

[toddz69]

The trouble is that there aren't a lot of people on these forums anymore. I'd give it a few days and see if someone knowledgable chimes in. And hopefully Wilwood will call you back!

Todd Z.

[GoreMaker]

Finally got through a conversation about this with a Wilwood tech.

Regarding the center register bore size, they feel my application is an oddball. I definitely have the original 10-bolt rear-end for this '77 Trans Am. They DO have a backplate with a 2.84" bore size, it's just not what's included in this kit, even though that's specifically the one recommended for my car. Their solution was to sell me 2 new backing plates (part number 250-6874). They're sold individually, so that would be a $100 extra purchase, plus waiting time for it to be delivered.

Instead, I went to my local engine shop and had them machine the bore out to 2.84". They did it on the spot in 30 minutes, it cost me $50, and now it fits perfectly.

So for anyone looking to buy this brake kit for a 2nd-gen F-body, check the diameter of the register (raised lip) on the flange to make sure you're getting the right backing plates. It could be 2.725" or 2.84". And be absolutely sure you've scraped away all the rust before measuring, that's exactly where it likes to accumulate.

As for the staggered-ness, I was wrong. The way they're assembled is correct. I just forgot that the shocks attach to the car at the opposite end of where they attach to the rear end (ie, the left shock attaches to the car in front of the axle but attaches to the leaf spring plate at the rear of the axle). I forgot this fact because the rear end is off the car completely. So the backing plates were in fact assembled correctly to keep the calipers away from the shock. However I had to take them apart anyways to have them machined.

[toddz69]

Glad you got it figured out and solved so quickly! For some reason I can't get onto the Wilwood site at work but was looking at their tech site on my phone and the 2.84" registration on the 1993-2002 Camaro (10/12 bolt Late). Weird that yours is the same in '77.

Todd Z.

[GoreMaker]

That's actually how I knew there was a 2.84" register backplate available, I saw it on 4th gen kits. But 4th (and 3rd) gens are coil-sprung axles while 2nd gens are leaf sprung, so I'm not sure why mine would have a 2.84" register if 2.725" is the more common one. I wonder if Wilwood just has the year cut-off wrong for 2.725" rear ends. I don't have any other 2nd gens on hand to verify.

[red78firebird]

I've been having the same issue on my 78, 2.84"

How do you like the kit?

Mike

Finally got through a conversation about this with a Wilwood tech.

Regarding the center register bore size, they feel my application is an oddball. I definitely have the original 10-bolt rear-end for this '77 Trans Am. They DO have a backplate with a 2.84" bore size, it's just not what's included in this kit, even though that's specifically the one recommended for my car. Their solution was to sell me 2 new backing plates (part number 250-6874). They're sold individually, so that would be a $100 extra purchase, plus waiting time for it to be delivered.

Instead, I went to my local engine shop and had them machine the bore out to 2.84". They did it on the spot in 30 minutes, it cost me $50, and now it fits perfectly.

So for anyone looking to buy this brake kit for a 2nd-gen F-body, check the diameter of the register (raised lip) on the flange to make sure you're getting the right backing plates. It could be 2.725" or 2.84". And be absolutely sure you've scraped away all the rust before measuring, that's exactly where it likes to accumulate.

As for the staggered-ness, I was wrong. The way they're assembled is correct. I just forgot that the shocks attach to the car at the opposite end of where they attach to the rear end (ie, the left shock attaches to the car in front of the axle but attaches to the leaf spring plate at the rear of the axle). I forgot this fact because the rear end is off the car completely. So the backing plates were in fact assembled correctly to keep the calipers away from the shock. However I had to take them apart anyways to have them machined.

[red78firebird]

That's what threw me, it has the measurements of the 92 to 02 which is way after 1978 .... the issue is the later 10/12 kit isn't for staggered shocks.

Glad you got it figured out and solved so quickly! For some reason I can't get onto the Wilwood site at work but was looking at their tech site on my phone and the 2.84" registration on the 1993-2002 Camaro (10/12 bolt Late). Weird that yours is the same in '77.

Todd Z.

[GoreMaker]

I've been having the same issue on my 78, 2.84"

How do you like the kit?

Mike

It's been great! I run it with 12" front rotors (using more recent B-body spindles) that are 1.25" thick (using 94-96 Fleetwood J55 calipers). I'm using a dual-cylinder manual brake setup with a balance bar that's set at practically 50/50, but slightly biased toward the rear. Pads are Wilwood BP20 all around. Balance and brake force are absolutely perfect for the tires I run (255 front, 275 rear). For a street car, I don't think I could do any better than this setup.

[red78firebird]

It's been great! I run it with 12" front rotors (using more recent B-body spindles) that are 1.25" thick (using 94-96 Fleetwood J55 calipers). I'm using a dual-cylinder manual brake setup with a balance bar that's set at practically 50/50, but slightly biased toward the rear. Pads are Wilwood BP20 all around. Balance and brake force are absolutely perfect for the tires I run (255 front, 275 rear). For a street car, I don't think I could do any better than this setup.

awesome, thanks for taking the time to comment ..... ordered all my parts and have started the tear down

[79T/Aman]

It's been great! I run it with 12" front rotors (using more recent B-body spindles) that are 1.25" thick (using 94-96 Fleetwood J55 calipers). I'm using a dual-cylinder manual brake setup with a balance bar that's set at practically 50/50, but slightly biased toward the rear. Pads are Wilwood BP20 all around. Balance and brake force are absolutely perfect for the tires I run (255 front, 275 rear). For a street car, I don't think I could do any better than this setup.

Hello Frank, you got the dual master set up on the car I assume?