My 89 Formula has a drum rear. I would like to convert the brakes to the late model disc. Is there any way to adapt/modify the backing plat so that i can put the disc brakes on? I really don't want to get a whole new rear.. i recently swapped it. Bad planning on my part, but i would like disc brakes!!

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• 89 Formula 305 WS6
  SFC's, LCA's, Air Foil
  Spohn Panhard Bar
  Flowmaster Cat Back, Tranny Cooler
  A/F Ratio Meter (not a mod but it sure spurs interest)
  Trans Temp Gauge
  Most "Free" Mods
  3:73, Zexel Torsion Posi
  !cat
  CAI W/ K&N
  
  15.559 @ 88 MPH
  (Not good enough)

 

If you can find a disc rear, check out the mounting flanges on the ends of the axle tubes as compared to your drum rear's. The drum uses a rectangle, the disc uses a square. Something could probably be welded up. Who knows, the drum rear's "rectangle" might be able to get cut down and re-drilled to copy the flange of a disc rear.


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-Tom P (Hot rodded 1986 Firebird 2.8l)

 

Hmmm.. thanks.

I just saw on ebay a guy selling these plate things that do the job, he wants some stupid amount of money for them.. $80ish.

Is there a difference in the backing plate of the older version compared to the "new" version of the rear discs?

<edit>

Part numbers for the assy would be very helpfull!!!
Does anyone have some new version backing plates or the entire assy laying around?

[This message has been edited by Omega (edited August 28, 2001).]

 

I've got a pair of 89-92 disc backing plates sitting right here.

 

I could be wrong, but it seemed to me when I had one of each laying side by side, that the "flange" thing that was welded onto the housing was MUCH smaller on the disc housing than the drum one. It looked to me like there was absolutely no possible way to interchange them. Although, it might be possible to cut the drum one down to the disc size somehow. But it's like ¼" steel, not fun to cut.

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"So many Mustangs, so little time..."
ICON Motorsports

 

The backing plates are easier to change than it would be to modify. The toughest part is catching the old gear lube. All you have to do is take the cover off the pumpkin, remove a bolt that holds in a shaft, push the axles in enough to remove the c-clips, and yank those bastiges out. Then, 4 bolts hold the backing plate to the axle flange. Since yu have to get the rest of the stuff ( discs, calipers, e-brake cables, etc ) you may as well hunt for a whole rear. Except that you probably want to keep your 3:73s, it is easier yet to swap the whole kit and kaboodle.

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88 IROC with cobbled together (not by me)drivetrain, 86 (?) TPI unit,CE subframe connectors, Edelbrock strut tower brace, polygraphite bushings all around...it handles like a dream, but man is it hard to push!!

 

Yes, the plan is to keep the rear that i have now. I have put quite a bit of work into it and i don't want to change it unless i REALLY have to. I know that there is one huge bolt and 2 smaller ones on a drum rear. I don't see why GM would make the entire rear different just for a disc version. I just hope that its possble.

Thanks guys.

 

They did make the housing ends different. Disk brake ends use 4 bolts around the flange to hold the caliper mount on while drum brakes as mentioned above use 2 small bolts and one large one at the top of the backing plate.

I don't have a drum housing around anymore since I cut off all the brackets to put on a 9" housing. It could be possible to drill the 4 holes in the drum brake mount so that the caliper mount could be attached. I'm pretty sure the bottom 2 bolts won't line up with the drum holes.

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I wonder if the flanges were welded in the same location on the axle tubes... I should check out my drum rear; it's still in the backyard. I might plant some flowers around it...

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-Tom P (Hot rodded 1986 Firebird 2.8l)

 

If you could let me know it would help.. ya know, i also have a rear sitting in the back yard. The ends are sealed but it would look pretty funny having plants come out the end