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Author Topic: 1973 rear drum to disc brake conversion  (Read 11539 times)

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frbformula

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1973 rear drum to disc brake conversion
« on: October 15, 2008, 03:57:28 PM »
im trying to find anyone who has or who knows how to do a rear drum to disc brake conversion using stock GM parts so i can go to auto zone and get replacement pads/rotors and not need to order any special parts.

thanks.
« Last Edit: December 31, 1969, 07:00:00 PM by firebirdclub »

78tahitman

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Re: 1973 rear drum to disc brake conversion
« Reply #1 on: October 17, 2008, 10:44:38 AM »
They do sell rear disc brake conversion kits for about $600 to $800. Probably the easiest thing to do is find a disc brake rear end from a 1979 to 1981 Trans Am and do a swap.  It will be a direct bolt in replacing your stock rear end from the 1973. You will typically spend about $200 on the full rear end.  By doing this swap you will be using all stock parts and GM parts which you can get replacement parts from any auto store.  Now once you do this there will also be some other things to consider.  First thing you have to do is also buy a new master cylinder and proportioning valve and replace those as well, usually about $110 for both from places like The Rigth Stuff Detailing or Inline Tube.  The other thing is the rear end gears that are in there.  I don't know what set up you have, but I am guessing it might be a 2.42 or maybe a 2.56 rear end in there now.  The disc brake rear end that you will get might have a 3.08 or a 3.23 rear end gear.  So you can leave it as is, but your speedometer will be off due to the gear difference.  You can swap out the gears from your rear end into the new one, or change your speedometer and drive gears in the transmission to match the new rear end.  If you swap your existing gears into the new carrier on the disc brake rear end, I would highly suggest that be done by a professional in order to get it set right.  But if you change the speedometer and drive gears in your transmission, that can be done yourself.
Brett Campbell
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frbformula

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Re: 1973 rear drum to disc brake conversion
« Reply #2 on: October 20, 2008, 08:15:27 PM »
Thanks. but i wanna keep the 8.5 gm rear end in it and not go to a 7.5. the only reason i need the rear disc breaks is because i got 3.73 gears and a 3000 stall converter and the drum breaks wont hold the tires past 2300 rpm. im just lookin for a little more holding power at the line.

78tahitman

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Re: 1973 rear drum to disc brake conversion
« Reply #3 on: October 23, 2008, 10:41:46 AM »
From 1979 to 1981, it is still a 10-bolt 8.5 inch rear end.  So your guts from your existing set-up will fit in there.
Brett Campbell
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1978 Trans Am, 1989 Trans Am, 1998 Trans Am

frbformula

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Re: 1973 rear drum to disc brake conversion
« Reply #4 on: October 25, 2008, 05:10:49 PM »
is there any way that i can just take the brakes off the later 8.5 rear end and just put the discs, calipers and brackets on the 8.5 in my firebird

Todd Stahr

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Re: 1973 rear drum to disc brake conversion
« Reply #5 on: April 20, 2009, 12:32:50 PM »
is there any way that i can just take the brakes off the later 8.5 rear end and just put the discs, calipers and brackets on the 8.5 in my firebird

Yes, its a bolt on deal if you find a disc rear. You will need the parking brake cables as they are different, along with everything hitman said.

There are 4 bolts that hold the backing plate to the housing, to get the plate off you need to pull an axle. To pull an axle, you remove the rear cover, then remove the pinion pin retaining bolt (it has a long unthreaded end after the threads that tends to break), push the axle shaft in and remove the C clip. Once the C clip is off, you can pull the axle and continue the brake swap.

Last I checked you can get the rotors at a parts store, the calipers are a bit tougher to find, the backing plates will need to come from a disc rear, I think I have two or three sets of backing plates, one set of calipers and no rotors. Some parts are tougher to find than others, so its best to do as hitman said and find an entire rear.

There is also a way to utilize S10 Blazer rear discs on 10 and 12 bolt rears, if I can find it in the next few days I will post the details.
Performance and general repair tech. Traditional Pontiac V8 is my specialty, as well as automatic transmission repair/diagonossis. 2nd gen speciality, and with the addition of the 98 Formula 4th gen LS1 I am getting to know them real well. Holley and Qjet advice as well.

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Re: 1973 rear drum to disc brake conversion
« Reply #5 on: April 20, 2009, 12:32:50 PM »


 

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