LS1 Rear Discs
Back to working on the Firebird. This is the first part of several posts I will have of updates to modernize the car. I have had most of the parts for several years but Covid quarantine gave me the excuse to get a few of these changes on the car. Up first is the 98-2004 LS1 rear disc upgrade. For the most part this is a simple upgrade to get a 12" rear disc for your 10/12 bolt rear end using mostly factory parts. There are a few of ways to do this such as using two backing plates from the same side to get shock clearance. However, I choose to use a right and left backing plate and relocate the shock to get the clearance I needed. This allows me to use the factory second gen e-brake routing for the emergency brake cables.
After removing the c-clips from my axles, I disconnected my wheel cylinders, e-brake cables and pulled the drums off uneventfully. I then mocked up the left and right LS1 backing plates, left and right calipers and rotors. I ended up needing a .200 shim to push the caliper outward to align it correctly over the rotor. I had a set of moser bearing retainer plates from an old project which turned out to be the perfect width to make a shim after grinding out the center hole to fit around the OD of the axle tube.
Next issue was the lower shock mount on the driver's side. That needs to go toward the front of the car about 3/4" for clearance between the caliper and shock. I drilled the hole in the spring plate where I needed it and added a grade 8 "thick" washer under the upper shock mount to kick the shock forward and into the newly drilled hole. The only downside I can see to this is that the hole is no longer in a flat area of the spring pad, the lower shock bushing is not loaded evenly and will likely see premature wear.
I just cut my previously bent hard lines, added a new tube nut and ran a new braided flex brake line from Earls to each caliper. I needed longer wheel studs from the aluminum drums, just never put them in and with the axles out, I replaced the studs with slightly longer 7/16 wheel studs from Doorman.
The final issue which is a bit unresolved are the e-brake cables. The internet lied here and led me to believe the LS1 backing plates were the same as the Blazer/LT1 backing plates except they fit a 12" rotor. I can tell you that is completely wrong. The LS1 backing plates lack the cast in mount for the e-brake cable the Blazer/LT1 plates have. So if using LS plates, you are going to have to fabricate something up to secure the e-brake cables. Additionally, you will have to remove the e-brake lever from one of the plates and flip it around using one of the adjustment clips from the opposing side if that makes any sense. This will give you the calipers mounted behind the axle with e-brake cables that pull forward just like your stock second gen F-body. Your LS e-brake cables are way too long but are the same diameter so I will simply pull the LS cables through the second gen F-body cable housings and reattach them to the factory second gen e-brake cable.
If I had to do it over again, I would definitely go with the LT1 or Blazer system. I would have lost 1" in rotor diameter but in exchange, I would not have to be fabricating a bunch of stuff to get my e-brake to work. Finishing up the e-brake is going to need to be a project for another day.