Sure grip issue

[70 Sport Suburban]

Since you already have your old rear end and the first one you tried, measure the width of the axle capture point on both carriers, if your 2.76 is wider, you have identified the problem, the axles are too short. That probably means that both of the 3.91 rear ends were out of something other than a C-Body as the sport suburban uses C-Body axles which should mate up to a C-Body carrier. Other axles are not going to help if you have a B-Body carrier installed in a C-Body housing. You will need to find a C-Body carrier.

The other issue is that you are going to beat your engine to death running a 3.91 gear set at highway speeds. A 3.23 set came standard for that reason.

Dave

So the 1st set of 3.91s they were in my friends 71 Sport Fury GT. So i looked up what size axles and diff measurement and were gonna measure if there is any difference in the 2.76 vs 3.91s but i measured my axles and they were around 30 3/4 wasn't my wagon supposed to be 31 or 31 21/64 could that make a difference?

 

[polara71]

Wagons have a wider rear track ? Is that what your asking?

 

[70 Sport Suburban]

Wagons have a wider rear track ? Is that what your asking?

Just trying everything that people are saying for help. I measured my alxes and they don't match to what i found online mine are shorter. My housing backing plate to plate is the right length so somewhere in the past someone took the 3.23 open out and possibly put shorter axles and the 2.76 that was in it. So should i look for longer alxes on Fri at the yard?

 

[Big_John]

So the 1st set of 3.91s they were in my friends 71 Sport Fury GT. So i looked up what size axles and diff measurement and were gonna measure if there is any difference in the 2.76 vs 3.91s but i measured my axles and they were around 30 3/4 wasn't my wagon supposed to be 31 or 31 21/64 could that make a difference?

Every reference I have says the wagon axles should measure 31-21/64" and everything else 30-5/8".

If you have axles that are too short, it seems to me you would have problems setting the axle play when you did the swap. The play would not have been right with the open rear in it either.

There's no difference between the 2.76 and the 3.91 for width. The thrust spacer in the center would be the same width on them too.

First thing I would check is to make sure that someone hasn't swapped a sedan rear housing in the car. Check the width, should be 64-3/8 axle flange to axle flange. But I'm thinking that the axles were changed and they were wide enough to catch the spider gear splines on the open rear. Not wide enough to catch the splines on the spiders with the sure grip, but wide enough to engage the outer splines.

Any chance these axles have "green" bearings? That would mean no tapered, adjustable bearings and probably the only way this ever worked to begin with.

 

[70 Sport Suburban]

Every reference I have says the wagon axles should measure 31-21/64" and everything else 30-5/8".

If you have axles that are too short, it seems to me you would have problems setting the axle play when you did the swap. The play would not have been right with the open rear in it either.

There's no difference between the 2.76 and the 3.91 for width. The thrust spacer in the center would be the same width on them too.

First thing I would check is to make sure that someone hasn't swapped a sedan rear housing in the car. Check the width, should be 64-3/8 axle flange to axle flange. But I'm thinking that the axles were changed and they were wide enough to catch the spider gear splines on the open rear. Not wide enough to catch the splines on the spiders with the sure grip, but wide enough to engage the outer splines.

Any chance these axles have "green" bearings? That would mean no tapered, adjustable bearings and probably the only way this ever worked to begin with.

Ok ill measure with the axles in i did measure backing plate to backing plate and it was 57 which meets what I've seen online. My axle didn't have the piece to adjust axle play either.

 

[Big_John]

Ok ill measure with the axles in i did measure backing plate to backing plate and it was 57 which meets what I've seen online. My axle didn't have the piece to adjust axle play either.

If you can verify without putting the axles back in, that's great.

If this helps: Mopar Rear Axle Dimensions

 

[Davea Lux]

Ok ill measure with the axles in i did measure backing plate to backing plate and it was 57 which meets what I've seen online. My axle didn't have the piece to adjust axle play either.

If you have tapered axle bearings, the adjuster is essential to get the end play set up properly as the axles butt up against each other. The adjuster moves one axle in or out to be sure the bearings mate properly. Without the adjuster, you would have excessive end play and lots of clanking and other noise coming from the rear end and probably failed seals as well. Your axles are not to spec for a wagon rear end as noted in the previous posts. I suspect that someone has probably switched sedan axles into the wagon rear housing which might have engaged enough to operate (poorly) with the 2.76 gear setup. The sure grip would need the extra length to fully engage the spiders and operate properly. The squealing noise you were hearing was probably the axles rubbing against the disengaged spider assembly. You should probably check the oil and housing for metal shavings. If someone updated to the "green" type bearings, no end play adjuster is needed, but you will need to find axles that are the proper length for the wagon rear. Still need to check the housing and oil for metal shavings.

Dave

 

[70 Sport Suburban]

So i wanna thank everyone for there help with my sure grip issue. I took my axles out and measured them and yup someone switched them out. I got lucky and went to a yard the guy had a parts book looked everything up and found out what wagons and trucks and vans i could use. A buddy had just got a 73 van for parts and it had my axles so i put them in tonight and everything works like it should now and i did check for metal before putting it back together.

 

[polara71]

These guys diagnosed that unbelievably well

 

[78Brougham]

If it ain't broke don't fix it. This is why I leave some things alone.

This would've drove me berserk. Lol

Unbelievable the knowledge here! And the willingness to share it!

 

[3C's & a D?]

Glad you resolved the issue. I just wanted to throw this out there- last year I had to change one of the axles in my '71 New Yorker which had pitting where it meets the seal. I had recently parted a '71 Polara and figured I'd be able to use one of it's axles. Nope, too short, one out of a '71 Newport, right size. So while I didn't realize that there was a wagon,sedan/hardtop difference, I was made aware of the Dodge/Chrysler difference. Not sure where Plymouth fits in here. The more you know!!!

 

[Darter6]

Yeah, never say never when it comes to Ma Mopar.

 

[70 Sport Suburban]

Glad you resolved the issue. I just wanted to throw this out there- last year I had to change one of the axles in my '71 New Yorker which had pitting where it meets the seal. I had recently parted a '71 Polara and figured I'd be able to use one of it's axles. Nope, too short, one out of a '71 Newport, right size. So while I didn't realize that there was a wagon,sedan/hardtop difference, I was made aware of the Dodge/Chrysler difference. Not sure where Plymouth fits in here. The more you know!!!

I got lucky with the guy that runs the junk yard he pulled out his book and let me take a picture of what i needed to look for.

 

[3C's & a D?]

Just checked, had it backwards. '71 Dodge Polara, 741 case, 2.76 suregrip, 60 inch axle housing, flange to flange, 29 1/8 inch axle length (end of shaft to dust boot plate). '71 Chrysler Newport, 741 case, 2.76 suregrip, 57 3/4 inch axle housing, flange to flange, 28 7/16 inch axle length (measured the same). Now that I think about it, I'm guessing the reason is due to the over hanging quarters on the Chryslers. Don't put a Dodge axle in your Chrysler!

 

[3C's & a D?]

I got lucky with the guy that runs the junk yard he pulled out his book and let me take a picture of what i needed to look for.

View attachment 148069

Ok, so what is the difference between a (removable) vs. (non-removable) center section?

 

[Snotty]

8.75 Rears have a removable "third member," one you can remove by simply removing the axles. They are a "quick-change" type. Very similar to a Ford 9". Other rears, that have the cover that come off, require an entire rebuilding of the pumpkin to change the gears.