I have the 7 1/4 rearend, thinking of switching to 8 3/4 rearend. I think this one I'm looking is the casting number 2070741 (small pinion shaft, 1965 to about 1972). It is single traction, the mounts for the u-bolts are 43 inches center-to-center, just like my '67 dart's 7 1/4, so I think it's from an A-body. It has the small bolt pattern (as mine does) and 10 inch drums. This should fit my car yes? I think the total width might be a bit wider, but not much (I'll have to take that into account when choosing offset in wheels I think).

I suppose I have to shorten/rebalance my drive shaft for this change, larger U-bolts, anything else? Leaf springs different for the different rearends? Does the brake line on the 7 1/4 use a junction block like the larger rearends...

Any other considerations? Forgive my ignorance, I haven't done this in decades.

BG

Are the universal joints the same or is that another thing I'll have to swap out? Do I do that when I shorten and balance my drive shaft (i.e. mate a larger u-joint assembly to the old shaft)?

I think you will have to shorten the drive shaft, and most likely the 8 ¾ uses a lager U Joint then 7 ¼â€￾ rear-end.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Both 741's that I had used the same small "7260" u-joint as the 7 1/4" rear. Leaf springs should not need changed. Shorten the drive line and bolt the rear in with the 8 3/4 shock plates and U bolts and you should be ready to go. Can't remember about the junction block?

Rick

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Anyone know offhand how much to shorten the drive shaft? According to the measurements found here, http://www.crankshaftcoalition.com/wiki ... 's_guideit looks like about 2 1/4 inches will be about right

1.75-2" should be safe. 2.25" might be a bit too much.

Lou

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Home of Slant6-powered fun machines since 1988

Any others have experience with doing this, have a number for how much to shorten, where to make the cut, etc?

Thanks again.

Brian

As I recall, the end (caps) slide into the "pipe" like a sleeve and are welded in place. I could grind away the weld and remove the end, cut the pipe, reinsert, weld and balance. Is that how it's done? I can have a shop do it just to be safe; just curious how people do it.

bg

Generally a driveshaft is shortened by being placed in a large lathe where the yoke-to-tube welds are cut. The tube is then shortened in the lathe so as to be square, the yoke is re-inserted into the tube, clocked the same as the opposite yoke and welded into place. The tube is checked for straightness, straightened if needed and balanced. I don't have access to a lathe this large nor any balancing equipment so I pay to have it done.

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Joshua

You see how long I've been out of this....I called them end caps instead of yokes...

Yes, I have seen people cut the pipe in the middle and leave the yoke weld intact, but this seemed so silly to me. Even if one has precision equipment the chance of error/imbalance is much higher than if one does it at the ends. Also, welding must be much more precise than if one is simply rewelding the seam where the yoke that has been tapped against a nice squarely cut end of the shaft....crazy.

Another question. I seem to recall seeing someone put a cup of tranny fluid inside the shaft before welding it shut, to dampen noise/vibration in the shaft during operation. Anyone heard of that? Seems like it would work OK, as long as it never solidified, say in Alaska on a really cold day...that sounds like a recipe for universal joints shattering in the cold. That said, I believe the freezing point of tranny fluid is about 65 below zero Fahrenheit.

Brian

Is your shaft 2 piece and the rear yoke bonded with rubber?. I have had 2 67 Darts and both had the bonded rubber tube/shaft.
Your driveline shop may tell you to eliminate the bonding and replace the tube. Just a thought..

I've done a couple of these swaps. 1-3/4" is a happy number to use for cutting the shaft.

It is a good idea to measure for sure before you have it cut.

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Official Cookie and Mater Tormentor.

The first driveshft I had done to convert from B&T joint to slip spline, and get shortened, had the rubber. The driveshaft shop said it was easier and cheaper, to just use a new tube. The only thing they used from my old shaft was the rear yoke (I call them u-joint ears)

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Charlie,

Do you like double posting?

Do you like double posting?

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Brian,
I went conservative and cut off 1.75" and used the larger U-joint. Yes, the brake line junction block on mine was the same and I replaced the brake line hose.

I installed a 1969 8 3/4 in my 74 Swinger. It has 10" drums and a 742 case with Sure-Grip. One of the best mods I have done....I just got tired of changing 7.25" rear ends. I went through 4 rear ends in 6 years just driving back and forth to work, 120 plus miles a day.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG