C body 8 3/4 rear end into a B body

[deleof57]

I have something really strange now. Before I went to a swap meet this morning, I measured the width of the spring perch on my Roadrunner. Just being cautious even though its a B body mopar and it has a 47.3" measurement. It measured out to 46"!? It has a E body 8 1/4 rear end on it. I measured 3 times to make sure. I checked the placement of the springs to the body and it wasn't modified. Have any of you ever seen that before? I wonder if this is going to make it easier or harder to find that 8 3/4 rear end?

 

[moparman73]

deleof57, you got me curious. So, I went out and measured my 73 Charger. A rough measurement with a tape measure from the outside of one spring to the outside of the other was 48.75". My springs are 2.5" wide, so center to center distance would be 46.25". Then I measured the perches on a C body 8-3/4 that came out of a 67 Fury wagon and it measured 46" center to center. It looks like it would work fine to me, the extra overall width is not a big concern to me either since I don't intend to install really wide tires.

 

[old tired rebel]

I'm not a fan of yurcking the springs over a 1/2" to fit the wrong rear end. Lots of A-bodies have 68-70B rears cause the perch spacing is 1" different. Same with the E and 71/4B. It puts a twist load on the shackels. I've bent factory shackels fairly easily while removing them. Also has a twist load on the bushings. Just was not designed that way.
Lots of guys will "say been driving it that way for years" still doesn't make it right.

No we didn't have to move the springs 1/2 in over. It bolted in with no problems

 

[cueball446]

I hope it helps. I actually like the fact that it pushed the tires out a bit, I could still fit 295s with no problem. The early 70s c bodies will bolt in with not issue except, I believe the e brake cable on the c body is longer so you will want to swap it out for a shorter one. You can still get the c body differential pretty easy. I would love to see a pic of your car

 

[cngordon]

I also could not find an 8.75 that would fit my 69 Sport Sat, and ended up buying one off the web. Did all my measurements, did the research on the web, had the seller measure everything exact. Cost me about $150 for shipping. Would have cost me the same again to return when it arrived and was a rear out of a c-body instead of what he said he was selling.
My mechanic fellow convinced me to get the housings and axils shortened and the spring perches re-welded in the correct spots. They did a very nice job and it works but now I have 3.23 gears in a old rear end that i spent too much money on. I still want to replace the gears as those highway numbers make my launches at the track soft.
I suspect that had i spent a just a bit more I could have ordered a complete aftermarket setup with gears of my own choice.
This was my first go at putting an old car back on the road so just one of my lessons learned.

 

[deleof57]

I appreciate everyone's input, really helpful. I've decided to buy the rear end off the Monaco and take the perches off and put some new ones on that will fit the spring placement on my RR-46". I went and looked at the rear end and it looks good. The owner said he drove to the spot where it's at now, so it should be in working condition. I am going to swap out the 742 for a 489 case. Plus I got it at a great price $250. Thanks again for your advice and opinions.

 

[deleof57]

Okay fellas, now that I have the C body rear end, I am going to take the 489 open pumpkin and have it changed over to sure grip with a 3.55 ratio. I think I am locked into getting an Auborn Gear unit since I am not rebuilding a sure grip and there aren't any new Dana's being made and I'm okay with that. My question now is, is there anything that I have to watch for now that the rear end is going onto a B body? Such as shims, pinions or yoke size? We already covered the rear end width, now what about pumpkin to drive shaft differences? I don't know what the 489 came out of or if it makes a difference. A friend of mine who is a mechanic will do the job for me at his shop. He has all the tools and has rebuilt differentials plenty of times. He told me to get the specs and he'd do it. I don't know have a clue what the correct specs would be. Again, I appreciate ALL your answers and responses.

 

[YY1]

I'd do one perch at a time, so you can use the other one to check the angle.

I've seen people clamp the housing onto two jack stands, so that the perches are level (using a bubble level).

Also might want to double check that the pinion angle (perch angle) is the same between the two housings before you start. Just in case.

This is just back yard stuff, and I'm sure there are others with more "correct" tech knowledge and terminology, but it's what I've seen work.

Do you already have an SG in the 742? If you do, I'd just swap it in, unless you plan on 600+ HP and slicks.

The diameter of the U-joint bearings could be different between the 742 (smaller) and the 489 (could be small or large IIRC). Should be easy to tell by test fitting. There is a "conversion" U jont available if this is the case.

Driveshaft length could be an issue if you're taking out a 7 1/4 or 8 1/4 unit.

There are still driveshaft shops around that can shorten the shaft, although I think most of their work these days is CV shafts. Shouldn't be too expensive, maybe an hour labor.

 

[deleof57]

YY1, yes i did I think about doing it one perch at a time. I would really be screwed if I would have taken both perches off at the same time. Unfortunately the 742 doesn't isn't a sure grip and the rear end in my RR now is a 8 1/4. And if i need work done on the drive shaft there is a drive shaft shop 5 minutes away.