rearend swap questions
 

First time poster, long time learner.

I have the said '65 below. Some number of years ago, I swapped out the original rearend for a '70 c10 5lug with 3:08 non posi. A few years ago, found some great original ralley wheels. When I put them on, the wheels tires wouldn't fit under the rear fenders, there was about a half inch sticking out past the fenders on each side. Since attempting to put them on, I took the fenders off to figure out what the deal is, but to no avail. The only thing I can think of is there is a size difference between the years I didn't account for or know about. Ralley wheels I got are 15x8 with tires of 255/60. Something isn't adding up in my brain here.

Heres the questions, are the rearends different sizes (backing plate to backing plate)? I was told there is a spacer or adapter that needs to be removed, but I don't see one, so where would it be? Finally, if the rearend I got came out of a '70 Suburban 1/2ton, is there difference there as well?

Would appreciate any assistance.

Bret

Re: rearend swap questions
 

Width of the rears ends changed sometime after 70...+ 1.5 inches(I think)


Luc

Re: rearend swap questions
 

5 lugs didn't start until '71 but yes the rears got wider sometime in '70 by 3/4" each side, still shouldn't be enough to cause a problem. what is the back spacing on those 8" rallyes. I'm still running the PO's 8" rims with a backspacing of only 2 inches and the PO had to flatten the fender lip for clearance. normal backspacing is 3 1/4" I think which should give enough clearance.

Re: rearend swap questions
 

You may have 4x4 rallys. I think they have a more centered type backspacing. Rims that have a deep look to them probably wont work. You need a set that has like 4 to 5 in of backspacing. Too much backspace and tires will hit the wheel tub towards the center of the truck. Do some measuring. Go to the junkyard and look for newer truck rims. They have more backspacing. Here is a picture of ones im looking for. Late 90's, 2000's rims. They look to have at least 4.5 of backspacing.

Re: rearend swap questions
 

Guess I should have re-read my post before putting it up. The rearend is in fact out of a '71 not a '70. Thanks for the correction as well.

I'll check the back spacing on the wheels. The wheels are 5 on 5 I do know that for sure. At the same time as I measure back spacing, I'll get the backing plate to backing plate measurement.

Is it a common theme having to roll the fender lip with any new(er) wheels?

Edit: Wheel back spacing is 4 1/4". Backing plate to backing plate appears to be 56 3/4" (inside dimension of backing plates).

Re: rearend swap questions
 

Done some more looking into this rearend. The rear end I have came from a '71 Suburban. From backing plate to backing plate my tape shows 56-3/4 inches. Wheel mate surface to mate surface (WMS) shows 64-3/8 inches.

Not sure if it's a date stamp inside the wheel, but it says 8 20 84.

All said, I'm still at an impass with the decision, but at least I know more of what I'm up against.

Re: rearend swap questions
 

The WMS to WMS measurement on the '63-early '70 rear differentials is 62". The late '70-'87 rear differentials are 63 1/2". If yours measures 64 3/8" that may be a '88 and up differential. Those are wider yet, but I don't remember the exact measurement. This may explain your tire fitment issues.

Edit: Another thread got me thinking....that 64 3/8" wide rear differential might be out of a Van. Van rear differentials are wider than truck rear differentials.

Re: rearend swap questions
 

Thanks Captfab, and all others. It is looking more and more I'll be finding a '65-'69 rear. Things on the this " '71 rearend" don't seem to be making much sense, unless I read the tape wrong, that's possible. I'll update when I can afford a rearend or convince someone to swap locally.

Appreciate the help.

Bret

Re: rearend swap questions
 

Hi, Bret.
If you find your diff. is 63 1/2": (Cap Fab correctly stated this dimension.)
7-inch rallys will clear with max size of 235-75-15 w/a lowered rear....I just confirmed it about 6 PM tonite on my 66 w/63 1/2" diff. I couldn't use my 265-60-15's on ANY wheel! Your 8 inchers MAY clear w/the 235-75-15??? May go "some" wider w/stock height. GM made rally's in 8", 7", and I believe 6.5's. The 6.5's(?) look kinda wimpy imho.

If you use a 65'ish rear end:
(I think your years are correct: 65-69. Maybe even a 64?)and get a set of 5-lug rallys that are 7 inches wide, you should be able to use 235-75-15, or a tad wider, IF rear has been lowered significantly. If rear is at stock height the 8 inch x 5 lugs should work & may accept bigger/wider tires than 235-75's.

Should you use the older rear w/6 lugs, pull your axles & take them along with drums to a machine shop. They can re-drill flanges & drums to accept the "newer" 5 luggers. Have to plug only one of the 6 holes, as 4 will locate on 'virgin' metal; that 5th one drills into an original of the 6 holes. While there, ensure the drum you take them fits over the 'register meat'(the stick-out ridge on axle-flange that centers the brake drum's center hole); else the m/shop has to cut ridge down to match--like if you find a '71 drum w/5 holes already: its centering hole is smaller than the 6-lug's. Also don't let the fins on a 71 drum fool you into thinking they are wider: brake surface is same as 65.



Good luck & have fun.
sam

Re: rearend swap questions
 

Thanks luvbowties, I appreciate the information.

Re: rearend swap questions
 

Another option may be a custom offset from one of the replica wheel manufactures.

David