Jeff 63ValiantConvertible
Active Member
So, I would have to replace the entire housing or can I just swap axles and gears...thank you for responding
An accurate 8 3/4" rear axle width list
- Thread starter 72bluNblu
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Jeff 63ValiantConvertible
Active Member
Thanks
moparspares
Well-Known Member
FYI here is another one to the mix. Australian Dodge Phoenix which is based on your Plymouth Fury is 57 3/4. I have 3 of these and they all measure the same from late 60's to early 70's Phoenix. Its weird they changed ever so slightly but may have to do with the cars having to meet a certain amount of Australian content - Maybe?
STRorange
Well-Known Member
Mother Mopar was deffo weird when it came to 8 3/4 axles.
Three different diffs is a start then there's the wide variety of axle widths and shafts to go with them!
Mainly because of the 'opposing bearing system' (back to front) so the side force transmits from one side, all the way over to the other when cornering...
Now mostly converting folks have to dual roller GREENs eliminates the EXACT axle shaft length as before.
Some of the early A-Body YUKON axles were TOO short from the manufacturers!
When used with an early detroit locker they were shearing the splines, as the shafts were approx 3/8" short!
Think the SHAFTS were labelled as 28 INCHERS for the stock A-bods?
Seen loads of even 'experts' get it wrong with the 8 3/4 specs too.
They forget the thickness of the brake back plates and array of shims etc.
Me I think its easy, just lay the shafts on the ground (splines ends together) with a 1 1/2" spacer between them and measure to the bearing plate.
Then allow 1/4'' 'LESS' for backplates and shims and thats your axle case width.
A little more tricky with the 'old style' bearings but you should be changing them out anyways...
This only applies when you have fixed length axles, the 'cut to size' are easy peasy...
Three different diffs is a start then there's the wide variety of axle widths and shafts to go with them!
Mainly because of the 'opposing bearing system' (back to front) so the side force transmits from one side, all the way over to the other when cornering...
Now mostly converting folks have to dual roller GREENs eliminates the EXACT axle shaft length as before.
Some of the early A-Body YUKON axles were TOO short from the manufacturers!
When used with an early detroit locker they were shearing the splines, as the shafts were approx 3/8" short!
Think the SHAFTS were labelled as 28 INCHERS for the stock A-bods?
Seen loads of even 'experts' get it wrong with the 8 3/4 specs too.
They forget the thickness of the brake back plates and array of shims etc.
Me I think its easy, just lay the shafts on the ground (splines ends together) with a 1 1/2" spacer between them and measure to the bearing plate.
Then allow 1/4'' 'LESS' for backplates and shims and thats your axle case width.
A little more tricky with the 'old style' bearings but you should be changing them out anyways...
This only applies when you have fixed length axles, the 'cut to size' are easy peasy...
@72bluNblu I see a few additions on later threads. Has your original chart been edited? (from page 2)
The chart I posted has additional measurements compared to the one at Moparts, yes. I have measurements for the 7.25 and 8.25" A body and the 8.25" F-body rear axles because I was able to measure them myself. But I haven't edited the chart that I originally posted in this thread. I've confirmed a few more measurements myself since I posted it, but I don't have any more additions.
According to the chart axle length for a body 8 3/4" is 27 11/16" and housing length is 52 5/8". Why is the drum to drum measurement different between the bbp 57 13/16" and sbp 57 1/8"? I'm assuming that the drum measurement is taken where the wheel contacts the drum but the chart doesn't say. Thank you.
I don't look at the charts as gospel but more of a guide. Over the years I've found the housings and axles vary even when they are under the same year body and style. Parted a lot of cars in the 70's and started paying attention to rear ends 
in the 80's.
in the 80's.
You are correct, the chart should have a second entry for the BBP A-body axle length. The one in the chart is for a SBP factory axle. The BBP axles have a different axle flange offset, so that length is different and that is also why the wheel mounting surface measurement is different. You can see the reason illustrated here
I only added the mounting surface measurements because I use them to figure out wheel backspacing, I never bothered to add the different individual axle length because I buy all of my BBP A-body axles, since they never came that way from the factory.
The original chart should have been more clear, when it says "flange to flange" it means the mounting flanges on the bare housing, and "drum to drum" means wheel mounting surface to wheel mounting surface (wms-wms), like you said the area where the wheel actually contacts the mounting surface of the drum. I probably should have updated it when I copied it from Moparts, but I didn't.
I don't look at the charts as gospel but more of a guide. Over the years I've found the housings and axles vary even when they are under the same year body and style. Parted a lot of cars in the 70's and started paying attention to rear ends
The only differences outside of factory tolerances I'm aware of come from different axles. For example, a factory A-body 8 3/4" (SBP) has a different width than an A-body 7.25" (SBP) for the same year. And a factory BBP A-body 7.25" is different from both the SBP 7.25" and 8 3/4". The same is true for the '71 B-bodies for sure, the 8 3/4" and 8.25" are different widths too. A-body 8.25's are the same width as the BBP A-body 7.25's (or so close I can't tell the difference in measurements).
My own measurements have always shown the housing widths to be very close to the list at the beginning of this thread, I've measured half a dozen different 68-70 B-body axles and found they were all pretty much dead on, less than 1/16" different anyway which can easily be a measuring error if you're just using a tape measure. Same for the couple of E-body, A-body and C-body 8 3/4's I've had in my possession at one point or another. The big differences are all from different style rear axles. Obviously there is a factory tolerance on the housings themselves, but at least from what I've seen that tolerance is much tighter than anything related to the frames or body's on these cars.
I agree about the tolerances being tighter than what the body and chassis was!! The biggest differences in housings/axles that I found were mostly from the 66-67 B bodies. The ones I parted out still had the original rear ends (kinda hard to tell if they were swapped out in the 60's though) and some of those differed as much as 3/8ths inch. Even that isn't much but it can make a difference if someone is buying new axles for an existing housing and goes by a chart instead of measuring it....and yes, doing accurate measurements is very important. The cars that I parted the most of were E and B cars....and running a 68-70 B rear in an E body was a popular swap and sticking one in from a 66-67 did well too.
So 28 1/32" for bbp axle length? Thank you.
69FBCuda
Stand back 10' for your viewing pleasure & Safety
Does anyone know the min/max space for the pin w/buttons installed for the Suregrip to function properly? Proper spider/disk engagement, not as critical on the one piece spider-disk as it is on the two piece.
I posted this so members converting from open to suregrip can get an accurate assessment as to weather the existing axles will be adequate for use as is/was the case for @Miszny where the old axles were to short causing additional troubleshooting and removal/replacement. I'm sure I would have made the same mistake
New axles too short?
screenshot credit to drdiff
I posted this so members converting from open to suregrip can get an accurate assessment as to weather the existing axles will be adequate for use as is/was the case for @Miszny where the old axles were to short causing additional troubleshooting and removal/replacement. I'm sure I would have made the same mistake
New axles too short?
screenshot credit to drdiff
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dukeboy440
Well-Known Member
There's no minimum or maximum 'space' for the pin. The center pin is is 1 1/2" long and with the right axles for the housing, you should be able to adjust them for the proper clearance cold. IIRC, it's around .010" but man, I've been adjusting them all my life just by feel and have never had an issue. Also, the thrust pin doesn't have much to do with the proper functioning of the SureGrip and associated parts. It's job is to take up the space between the axles so they have the proper bearing preload....which really isn't much until they warm up but it's enough to make them work.
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69FBCuda
Stand back 10' for your viewing pleasure & Safety
Typical A body 8.75 with stock axles(image courtesy drdiff)
57.675-(28.0875x2)=1.5" gap. Okay that's a given for stock axles, what if yours are shorter? is there a minimum/maximum you can get away with.
And yes I am beating this to death just to make it simple for future generations. I'm sure a lot of builders just keep this info in the back of their head somewhere.
57.675-(28.0875x2)=1.5" gap. Okay that's a given for stock axles, what if yours are shorter? is there a minimum/maximum you can get away with.
And yes I am beating this to death just to make it simple for future generations. I'm sure a lot of builders just keep this info in the back of their head somewhere.
If your axles are too short, then you will have to make your own thrust pin if you want to keep on using the Timken bearings but many will just go with the Green Bearings (ball bearings) and not worry about the thrust pin. Also, there's so much tolerance in the housing that you have to pay attention to what the widths are vs axles. Don't know about the 'A' body rears but I've run across B rears that vary from the same model car. I've had some that were 1/8" to the side shorter. That's a 1/4" total. If you pick up a short housing and then find some axles that are a tad long....well, the tolerance can stack up on ya. Measuring to the decimal point is......usually pointless.
Building a custom 9" rear and I would like to have equal length axle shafts. Would having a 2.25" offset pinion be a bad thing?
dukeboy440
Well-Known Member
When I had my Dana cut down, I left the offset to factory. Didn’t see a reason to change it
The intent of having equal length axle shafts is to make having spares easier. The result of building a 9” to have equal length axle shafts is a pinion gear offset about 2.2”.
My question is…. Is having that much offset (about an inch more than a 8.75) a bad thing? If so, why?
dukeboy440
Well-Known Member
Well to me, a pair of axles cost the same regardless, so I just ordered a second set and called it a day. The odds of me breaking a dana 60 35 spline axle at my power level is slim. Your mileage may vary
Having spares in pairs or cost isn't the concern. I am used to minimizing spares where I can from my days of racing offroad. Simply put, I would rather have equal length axle shafts if I can. That way if I am at the drag strip and break an axle shaft, I can swap it out and keep running. If I break another axle shaft, I can swap it out and keep running because my pair of spares work on either side. If having equal length axle shafts causes an issue due to putting too much offset to the pinion, then I will build the axles to have zero to factory offset and stick with unequal length axles.
So back to my question.... Is having a pinion offset by 2.2" a bad thing?
dukeboy440
Well-Known Member
I doubt the 2.2” offset affects anything, worst case, you shim the engine and trans to be straight in line with the pinionsl
metalbender58
Active Member
I just picked up an 8.75 LBP housing and axles for my 73 Dart swinger at Mopars in the Park. It did not come with backing plates and I am thinking the original 7.25 shock mounting plates will have to be swapped out also. I haven't checked axle tube diameters. I'd like to run 10 inch rear brakes. I am assuming 10 inch backing plates off any 8.75 will bolt up to the housing, but do I need to worry about shoe width. should I be concerned about this?
The 7.25” has a smaller tube diameter, the shock plates will not work on an 8 3/4 without modification. Better to get the right shock plates.
Any 10” backing plate from an 8 3/4 will work, but you absolutely have to pay attention to shoe width. The 5x4” and 5x4.5” bolt pattern axles use a different flange offset, and 10” SBP backing plates will not work with BBP axles or vice versa. Backing plates for 10x1.75” brakes have a different offset than backing plates for 10x2.5” drums.
How to measure the offset and different measurements for the different backing plates here
Converting rear drum brakes from SBP to BBP
And the difference in the axles here
dukeboy440
Well-Known Member
Yes and no. Width matters so pay attention. Backing plates usually interchange. Though Your best bet is to get a back plate drum set.
No the 7.25 mounting plates will not work in your new 8.75. 2.25 inch diameter tube versus 3 inch. I tried to hog my plates out but the shock mount itself hit the axle.
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