Redrill rotors to different bolt pattern

[Beck]

Does anyone have suggestions to accurately redrill front brake rotors to a different bolt pattern. I'm working with '84 Chevy 1/2 ton rotors. These are 5 on 5. Since I was looking at swapping the rear axle with a narrower one from a car I was wondering if there was an easy fix for the smaller bolt pattern for the front rotors.
I am doing a "spring flip" on the rear so I am mounting different spring pads on the bottom of the axle. I want to run deeper dish wheels on the rear to make the tires look wider. It is too expensive to narrow the stock rear so I thought I would shop for one a few inches narrower. The stock rear measures 63 1/2" from wheel flange to wheel flange. If I went with a big GM car axle the bolt pattern is still 5 on 5 right? I do NOT know how wide one the the rear axles is from a Caprice, Caddy, or similar type car. Does anyone have one laying around they could easily measure? I have also considered the bigger Ford cars and trying to find an older one with a 9".
Another problem with the axle swap is the gear ratio. I have a 2.73 in the truck and want to stay with that. I have to keep the RPM down on the engine. Were there any gear ratios higher than that (2.50) readily available?

Thanks, Beck

[sirstude]

That is a really wide rear, should not be too hard to get narrower.  In a 9" Ford, the early Galaxy's, have a rear that is 61.5 inches wide.  That same rear is in almost all of the Econoline vans from the 60's so can be had pretty cheap.  When I redrilled the stuff for my Olds, I just used one of those plastic bolt pattern finders.  I put it on the hub and used a centering punch set to mark where the correct bolt pattern would go.  The just used my drill press to drill them.

Doug

[enjenjo]

There is no direct interchange on the front rotor that I can find. If you machine the inner bearing race down .125" a 94 Camaro 12" rotor will fit with a GM big car caliper in the stock mount.

On the rear end, 78 to 85 full size GM rear is 60.5" face to face with a 5" bolt pattern. 57 to 59 Mercury and Edsel senior series is 58" wide with a 5" pattern. 78 to 85 full size GM has the same ring and pinion as an 84 truck. Ford 9" goes down to 2.47.

[Beck]

There is no direct interchange on the front rotor that I can find. If you machine the inner bearing race down .125" a 94 Camaro 12" rotor will fit with a GM big car caliper in the stock mount.

I already have good rotors with new bearings and seals. The calipers on the truck are new also. I hate to pitch all that to swap rotors.

On the rear end, 78 to 85 full size GM rear is 60.5" face to face with a 5" bolt pattern. 57 to 59 Mercury and Edsel senior series is 58" wide with a 5" pattern. 78 to 85 full size GM has the same ring and pinion as an 84 truck. Ford 9" goes down to 2.47.

The full size GM sounds like the way to go. Especially since it has the same bolt pattern. The 57 to 59 Merc and Edsel would probably require swaping out the backing plates and drums. I had a 57 Ford rear in a rod and had a problem finding drums. I thought the ring and pinion on the truck was different than the car, or is that just the 12 bolt. Mine is a 10 bolt.
I just had a 9" rebuilt for my 32 (used the same gears). My cost was $275. The same guy gets $450 to do a GM. I set a 9" up twice and it still made noise a few years back. Then I had a different shop "build it". It was still noisy. I decided to have a pro do this one. I haven't driven it yet. The noisy one was 4.11 ratio which I understand is often noisy. This one is a 3.50. It was loud before I pulled it so I thought a rebuild was in order. The difference in rebuild price makes the 9" more attractive.

[tonto1]

On the full size GM cars like the Caprice, I thought the standard cars had a 4 3/4" bolt pattern and only the station wagon and police cars had the 5" pattern.

[enjenjo]

On the full size GM cars like the Caprice, I thought the standard cars had a 4 3/4" bolt pattern and only the station wagon and police cars had the 5" pattern.

For Cbevy, yes, but Pontiac, Olds and Buick used the 5" pattern on most models.