Narrowing a 8 3/4 diff.

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Coldlakedodgegu

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Hello everyone,
I posted some videos up to YouTube of my differential narrowing. I'm not done yet but I'm hopeful to have the housing completed this week.
Perhaps it can help someone out.
Maybe if there are some guys on here that have done this before, they could chime in and let me know their opinion if I'm screwing this up.
This is my first time doing this.
 
Nice job so far. If you need an alignment bar there's a vendor on ebay that makes a nice set of bushings for a reasonable price. I bought the Dutchman setup and now wish I'd gone with the ebay...same quality but much cheaper.
 
451Cuda said:
Nice job so far. If you need an alignment bar there's a vendor on ebay that makes a nice set of bushings for a reasonable price. I bought the Dutchman setup and now wish I'd gone with the ebay...same quality but much cheaper.
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Thanks 451 cuda. I made my own at work on the lathe. I don't know if they'll work great or not. I'm going to try. I drilled the centre hole only .002" larger than the shaft. I hope it slides in free enough.
 
When deciding width...keep in mind big bolt backing plates n drums are wider than A body...
Make sure you do the math you are after on final wheel placement.....
 
joesnow said:
When deciding width...keep in mind big bolt backing plates n drums are wider than A body...
Make sure you do the math you are after on final wheel placement.....
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@joesnow I intend to put 11" drums on it. Do you mean that the bearing placement on the axle shaft is different for big bolt and bigger drums? I don't have any reference around for that knowledge. From the backing plates I do have it looks like it's stamped deeper. Meaning the drums will go further into the wheel well.
I will want to make sure before I do it. If you have some more info I would appreciate it.
 
The offset of the backing plates are different SB to Lb
Just measure twice, cut once :)
Bearings are the same.
 
I know it doesn't help you, now. And I realize you're doing this in your garage, in the great white North and all. But, the machinist in me, tells me I would have done this (part 1, anyway) differently. I would have chucked up one end of the hsg in a lathe in a four jaw chuck, with a live center/cone in the other end. Then I would have cut rings in the OD of the tube for running a steady rest. Then I'd place the same end in a steady rest, and removed the tailstock. Then I would cut the tailstock tube end off with a parting tool. I think I'd try (if the tube is thick enough)to cut a precision register on the tube end. This will mate with a female register I'd cut in the shortened brg end just removed. The other side would be pretty much a repeat.
 
rustycowll69 said:
I know it doesn't help you, now. And I realize you're doing this in your garage, in the great white North and all. But, the machinist in me, tells me I would have done this (part 1, anyway) differently. I would have chucked up one end of the hsg in a lathe in a four jaw chuck, with a live center/cone in the other end. Then I would have cut rings in the OD of the tube for running a steady rest. Then I'd place the same end in a steady rest, and removed the tailstock. Then I would cut the tailstock tube end off with a parting tool. I think I'd try (if the tube is thick enough)to cut a precision register on the tube end. This will mate with a female register I'd cut in the shortened brg end just removed. The other side would be pretty much a repeat.
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@rustycowll69 i appreciate the feedback. I only have access to a lathe for small periods and projects when workload permits. I'm not a machinist by trade. I wish I could do a lot more there. I'm actually a non destructive testing technician. So I usually critique others welds for a living.
This time I will try to get my final welds x ray'd and show them in the final video. I don't think the factory tolerances were do tight either.
From these pics do you think the housing was friction welded together?

IMG_0155.JPG


IMG_0153.JPG
 
in no way, am I denigrating what you've done. I applaud your ingenuity and ambition. yes, some of the oem welds, are crude at best, but I've probably owned 30 or 40, and probably worked on 30 or 40 more 8-3/4" rear axled cars, and I don't recall a single one leaking from the seams. LOL
 
rustycowll69 said:
in no way, am I denigrating what you've done. I applaud your ingenuity and ambition. yes, some of the oem welds, are crude at best, but I've probably owned 30 or 40, and probably worked on 30 or 40 more 8-3/4" rear axled cars, and I don't recall a single one leaking from the seams. LOL
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@rustycowll69 by no means did I take offence to what you said.
I was only commenting, I suppose the problem with "text" it's impossible to read emotion or context sometimes. I appreciate all feedback, even if it's negative. Thank you.

On a side note, I think the 1 weld was leaking on this diff I just didn't think friction welding would've been used during the 60's.
I ground off the outside and ran a bead down. A little grinder and paint to make me the welder I ain't!

Cheers Kevin
 
If you are putting BBP brakes on it, they move the axle flange out about 5/16 on each side compared to the SBP stuff. The 57 1/8 becomes about 57 3/4 when you get finished if going with a 52 5/8 housing flange length.

I bet the tube is bent about where your straps are located on your stand. Pretty common, especially on pass side tube.

I always like to have my wheels and tires and work backwards to my axle overall and housing lengths. I have a spreadsheet that does a really good job. It has a sheet to calculate backspace for A body stuff with stock tubs, mini tub/relocation and the offset shackle set up.

I always grind that porosity out before proceeding. I even grind out the tack weld where the weld is going to start before doing any welding. Weld up to the tack weld. It can be done in 4, 1/4 turn passes.

Cool videos
 
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@crackedback I appreciate the feedback. Where does the extra length come from on a big bolt pattern set up? I have 11" brake set up from the C body, I intend to use. I was just going to do the math backwards from what a stock set up is minus the difference and order axles. I would like to know what you recommend, should I build up the rear brake set up than measure? Or measure the old axles bearing stack up and figure it out somehow that way?

I suppose in hindsight I would have done a few things different with welding in the ends, but here I am. I inspect welds daily and professional welders fail everyday, Not they would've messed these welds up. I chalk mine up to being amateur and will learn from it.

Thanks again for the feedback.
 
It's the distance from housing flange to axle flange, known as brake standoff.

SBP is about 2.25" and BBP is about 2.525" IIRC.

I lost my excel program and can't open the spreadsheet I have.
 
I used to weld up ship propeller shafts, and unless you're a very talented professional welder, it would be most difficult to get as pretty a weld like the manufacturer has on those housing ends. I am sure those are done by a machine rotating the housing at a scienced-out rotational speed, heat and weld wire feed.
 
I'm no welder by trade but I narrowed the 8-3/4" under my Dart some 5 years ago and it hasn't come apart yet.
I did find that welding thick iron, with the welder on full bore, seemed much easier then 'tacking' thin iron/sheetmetal.


20111129-RearAxleShortening-IMG_1671.jpg


20120101-RearAxleShortening-IMG_1674.jpg
 
Coldlakedodgegu said:
@crackedback I appreciate the feedback. Where does the extra length come from on a big bolt pattern set up? I have 11" brake set up from the C body, I intend to use. I was just going to do the math backwards from what a stock set up is minus the difference and order axles. I would like to know what you recommend, should I build up the rear brake set up than measure? Or measure the old axles bearing stack up and figure it out somehow that way?

I suppose in hindsight I would have done a few things different with welding in the ends, but here I am. I inspect welds daily and professional welders fail everyday, Not they would've messed these welds up. I chalk mine up to being amateur and will learn from it.

Thanks again for the feedback.
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Which Lincoln machine are you using? I can see it's a MIG but not the amperage or model number.
 
rustycowll69 said:
in no way, am I denigrating what you've done. I applaud your ingenuity and ambition. yes, some of the oem welds, are crude at best, but I've probably owned 30 or 40, and probably worked on 30 or 40 more 8-3/4" rear axled cars, and I don't recall a single one leaking from the seams. LOL
Click to expand...

Off topic here but the housing in my car now is leaking from the seam weld. First one I've ever seen
 
good job there

to bad you are so far away Im in quebec

because if you would live closer you would have a dana to do lolll
 
Each side of the joint should have been ground to a 45 degree to about half of it's thickness, creating a nice "V" for your initial weld. Trying to burn a heavy enough weld to penetrate your overall thickness is not good technique, and is why you have voids in your welds that shown in the X-ray. You're not wrong, there are just better practices to follow.
 
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