Brake drum question.

[Russell Ashley]

This has cost me several trips to the parts store and a day of lost time. My truck has a 12 bolt rear with the numbers 389486onf cast into it. It also has GM55 and A230 and CON1 cast into it at different locations. If there were ever any stampings on the axle tubes it's gone now so I can't tell what it originally came in. This was originally a four link rear. It has 11 by 2 inch brakes, with 5 on 4.5 bolt circle. The problem I'm having is finding drums for it. It seems that all of the 11 inch drums have a 4.75 bolt circle. I've searched the internet but can't find any real specs for drums that give me the dimensions. Can anyone shed any light on what GM 11 inch drums would have a 4.5 inch bolt circle. My truck has Corvette wheels and the disc brake kits I have have the 4.5 inch bolt circle so apparently this was a size that GM used at some point. My parts guy is being very helpful with this but his computer doesn't show the bolt circle, just the shoe size.

[chev3600]

Are these OE corvette wheels? I've never seen a set that wasn't 4.75. But.... if you google the casting number you have 3894860nf make the "o" a "0" you get a bunch of hits for 67-69 camaro and some others. hope this helps.

[raycow]

No GM anything ever used a 5 on 4.5 pattern except the 61-63 Tempest and those had little drums, like about 9". All other GM is either 5 on 4.75 or 5 on 5.

5 on 4.5 is the most common Ford, Mopar and AMC bolt pattern, so maybe you might want to look at one of those. My guess is that you've got some non-stock shafts in there. By any chance does the rear have C-clip eliminators? Those are sometimes used with Ford shafts.

Ray

[Russell Ashley]

I feel really dumb now. They are 5 on 4.75. I'll measure more carefully from now on and hope no one here remembers this thread.

[mr48chev]

5 on 4-3/4 is the standard "small" 5 lug GM bolt pattern that has been used since 1949 on passenger cars. The "big" bolt pattern would be 5 on 5".

Look at drums for a 69/70 Chev Impala . They came with 11x2 rear drums and were available with 12 bolt rear ends.

[Russell Ashley]

Originally Posted by mr48chev

5 on 4-3/4 is the standard "small" 5 lug GM bolt pattern that has been used since 1949 on passenger cars. The "big" bolt pattern would be 5 on 5".

Look at drums for a 69/70 Chev Impala . They came with 11x2 rear drums and were available with 12 bolt rear ends.

Thanks. 70 Impala is exactly what the parts guy came up with. I would still be interested to know exactly what the rear end came out of. The casting number indicates a Camaro or Nova, but this axle was originally a four link style and I think Camaros and Novas were leaf spring cars.

[mr48chev]

The center section may be used with several different sets of axle tubes.

Unless someone ground it off the stamped number is probably on the front side of the passenger side axle tube about in the middle of the tube. I had to carefully get the rust off a ten bolt rearend that I have to find it the other day I used a 3 inch cup brush on one of my 4.5 angle grinders.

[57picupnewbie]

Russ,

Did you ever figure your rear end delima out? I have the oringinal rear end and drums under mine. I am planning on pulling and putting in a Ford 9". If you know where you could get a Ford 9" I would consider a trade. I hope this is not against the rules to talk about trading.

[Russell Ashley]

Originally Posted by 57picupnewbie

Russ,

Did you ever figure your rear end delima out? I have the oringinal rear end and drums under mine. I am planning on pulling and putting in a Ford 9". If you know where you could get a Ford 9" I would consider a trade. I hope this is not against the rules to talk about trading.

I found out that I can ask for parts for a 70-74 Impala and get what I need. I've got it done now with new axle seals, all new brakes, new drums, new lines, and painted, so I wouldn't want to change it now.
I'm not sure about the forum rules regarding trading. I've got some things that I will be wanting to get rid of soon, either by trading or selling, so I'm going to pay the fee. Don't want to get kicked off the forum for breaking the rules.