Disc rear converted to Drum?
 

OK,

Couple questions here. Car is a 1986 Trans Am. 5.0 TPI

1st the car came stock with disc brakes in the rear. Nice option. Only it now has a drum rear. The previous owner said the disc was a terrible design so he traded his for a drum rear. Bolted it up but never hooked it up. My assumption is that the combination (proportioning valve) would need to be changed to give it the correct amount of pressure.

So naturally I would rather have a disc rear back in the car. Not much for 3rd gen available around me (at least in my price range).
However there is one from a 93 Camaro.
So my question is if I can use the same Combination valve that is still in the car with a 4th gen rear?
I would assume being that the car alread had a disc rear and that the 4th gens are so similiar it would work but wanted to make sure I am not overlookng something.

I do understand the width differance and that I would need to use later wheels to avoid them sticking out a couple inches. Also spacers to be used to accomodate the modern wheels up front as well.

Re: Disc rear converted to Drum?
 

The standard J65 combination valve, used with 10.5" rotors and iron Delco-Moraine calipers, 82-88, has a different bias than the one used with the so-called 1LE set-up with 11.7" rotors and alum PBR calipers, 89+. Typically, members use the 1LE valve (you'd need the first-design valve for your 86) or an adjustable when swapping in those brake components.

For more info about the above and other considerations, such as the speedo gears and parking brake, check the link below:

https://www.thirdgen.org/forums/tran...-10-bolts.html

JamesC

Re: Disc rear converted to Drum?
 

I had read through the Sticky on 10 bolts but they only mentioned drum to disc needing the valve changed thats whey I was wondering if going to the 4th gen would be ok seeing as the car already had a disc rear originally.
At this point I may end up finding a combination valve for a drum rear. Shouldn't be too hard since most want the disc setup anyway.
It will be an easy way to get the car road worthy and see what other issues there may be.
Thanks.

Re: Disc rear converted to Drum?
 

Actually, disc to disc is covered in the 10-Bolt FAQ:

If I Swap From a Drum to a Disc Rear End Do I Have to Change the Combination Valve?*

and

If I Swap From Standard Discs to PBR's Do I Have to Change the Combination Valve?

JamesC

Re: Disc rear converted to Drum?
 

Now how did I miss that?
Thanks.
Now I have to go check on the 9 bolt disc rears as I found one of those to see how that swap would go.
I just don't want to drop $400 on a rear for this car. Actually saw one for sale that was taken apart for $350.
Really wonder why he would have taken out a good disc rear to put in a drum?

Re: Disc rear converted to Drum?
 

Many drum-to-disc swap people never touch the prop valve & are perfectly happy. Many do swap & say it is "essential". I say swap the rear ends then decide for yourself.

As for the tires "sticking out", they will still be under the fenders. Ever noticed just how far the tires are in to start with? They will come out to flush with the upper portion of the fender lip, so 4th gen wheels are not "required".

Re: Disc rear converted to Drum?
 

with that in mind maybe I will hook up the drum rear thats in there to see how it brakes.
If I works well I may leave it as is until I can find a rear I really want.

Re: Disc rear converted to Drum?
 

Your brakes will certainly work, but will they function as well as they might with the correct valve--that is a valve designed for a specific braking application: there's a valve for the disc/drum set-up, another for the standard disc/disc set-up, and yet another for the disc/1LE set-up).

When you've come to a decision on which rear end is best suited for you, I'd suggest the correct valve.

JamesC