Rebuilt 8.75 Sure-Grip - resistance and clunk

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Tylinol

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Hey guys, just wanted to make sure nothing is screwed up before I go any further.

I just finished an 8.75 sure-grip swap in my '69 Barracuda. The transmission ship rebuild the center section for me and they tend to do good work. I've finished putting everything together (including axles with the sealed green bearings) and I've noticed there's a lot more resistance than there was on the old 7.25. The car will sort of bring itself to a stop when I left off the gas while rolling slowly. I also heard and felt a clunk when I turned slightly to the right. I'm hoping this is all just the LSD stuff needing to be broken in, but want to make sure there's nothing else I could be missing.
 
it it a clutch or cone (less likely) I think you can set the preload on the clutch packs (maybe with shims?) Have you filled with a SG rated fluid or added the SG modifier to the fluid?
 
A fresh suregrip will pop and chatter around turns until its broke in. Put some miles on it and see if it gets any better.
 
any rear wont slow you down as its basically a one piece when both wheels are turning the same rate.
 
my builder suggests multiple figure 8's in opposite directions..
 
I needed two bottles of friction modifier to quiet and smooth out my new suregrip and gear set. Smoothed out and quieted after a short cruise around town.
 
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He said it slows the car down when coming to a stop. Turning is not going to fix anything.. You can't get tighter than a spool going straight and a spool doesn't drag...
 
MoparLeo said:
He said it slows the car down when coming to a stop. Turning is not going to fix anything.. You can't get tighter than a spool going straight and a spool doesn't drag...
Click to expand...
Exactly. If the car slows itself in a straight line, something's WRONG. I can see it trying to bind in a turn, but not going straight.
 
he also stated it pops when turning so breaking it in doing some turns (figure 8 for both clutch directions) will possibly wear in the clutch pack. Dragging brakes is possible as well as a super tight preload pinion bearing. What is the casting number?
 
With green bearings did you remove the centering pin or block in the sure grip ?
 
What was the ratio before?

What is the ratio now?

Does it do the same when in neutral?

You might just be feeling more engine braking due to a different ratio!

If it does it in neutral I would check the brakes.

With both rear wheels off the ground get it up to about 50 and put it on neutral, do the tares slow at an expected rate?
 
Jack it up, start and put it in gear. Release the brake at idle and see if the wheels turn. If they dont, start by looking at the brakes.
 
So, I got the car off the ground and the wheels off. I was able to remove the wheels with the car fully off the ground - in other words, it took at least 70ft/lbs of torque to get the wheels to even spin. Removed both brake shoes and the driveshaft.

I think a good part - possibly all - of it was the brakes dragging. I think the pop *might* have been the brake letting loose. That, or it's the lash switching between forward and reverse. I think that's when the pop/clunk is actually happening and the turning was coincidental. I only made it 20 feet out of my garage and back, so the "turn" was very slight. There does seem to be a very, very small amount of lash at the axle, but no more than my 7.25.

With the brakes off it still doesn't "spin" - ie it takes constant force to rotate it, but my 7.25 is the same way. The 7.25 definitely takes less force, but maybe this is just down to bigger, sure-grip diff vs open diff?

Edit: the 7.25 is 2.76:1, the 8.75 is 3.23:1. Green bearings are the ones from Mancini racing and axles are factory. The thrust pin was removed by the shop.
 
So, the wheels will turn free enough now - I can spin them with my hand and they'll drag to a stop but not stop immediately. My only worry now is the play. I can rotate the wheel back and forth about 5 degrees, and when rotating it back and forth to the beginning and end of the "dead zone" there's a soft clunking sound from the center of the rear end, almost like lash between the ring and pinion?
I have no idea if this is normal - this is my first 8.75 and first live axle car too. Everything else I've owned has been transaxles with CV joints.
 
Tylinol said:
So, the wheels will turn free enough now - I can spin them with my hand and they'll drag to a stop but not stop immediately. My only worry now is the play. I can rotate the wheel back and forth about 5 degrees, and when rotating it back and forth to the beginning and end of the "dead zone" there's a soft clunking sound from the center of the rear end, almost like lash between the ring and pinion?
I have no idea if this is normal - this is my first 8.75 and first live axle car too. Everything else I've owned has been transaxles with CV joints.
Click to expand...

Post #7.
 
So, both the shop and some testing on my old rear end would indicate that the rotational play is normal. That said, I took it on a longer (as in around the block outside my driveway) drive and something has got to be wrong.

I found a big parking lot and did a dozen low-speed figure-8s. Each time the inside wheel chirps, hops, and bangs 3-4 times. It didn't get any better with more figure-8s, if anything it got slightly worse. The car puts up quite a fight when making a tight turn, especially on the inside wheel. Going straight feels bit better, but there's a whine on coasting that sounds exactly like a police siren.
 
Clutch type. And, to clarify, the drag going straight seems to be gone - that turned out to be the brakes being adjusted too tight.
Some of the remaining "drag" I was feeling is that the rear end stutters really badly if the car is turning even the slightest bit, and binds up the inside wheel really really badly going around corners.
 
Per conversations with Dr Diff the gear oils that come with the friction modifier already mixed in, don’t have enough of the additive.
Contact the shop that installed the unit to find out what lube they put in, if they did not add an additional bottle of friction modifier, do that and then see if things improve.
 
It may be that somebody set the turning torque all wrong, and now your diff is acting like a spool.
AND the backlash on the C&P is supposed to be less than .010 at the tightest point, and should not vary by much all the way around. Usually .007 gets the pattern darn close. The pinion will never clunk if set up right! (see note-1), AND Ima thinking something is bent, or the one-way clutch in the back of the trans is not working right, or the U-joints are seized.

I would start with dropping the driveshaft, and testing the sprag and checking the U-joints. While the shaft is off I would retest the turning force at the axle ends, in the same manner as you previously tested. (see note-3)
Even if the SureGrip is bound up solid;...With the wheels and drums off, and the recommended small axle-bearing end play; greater than zero/less than .007;......you should be able to rotate the pinion by hand, with very very little effort.
If you cannot, then remove one axle shaft (See note-2), and try again. If it is still dragging, remove the other one and try again. If it is still tight! remove the pumpkin and send it back.
But if it loosened up with either axle out, or both, then something is bent, or the bearings are NOT all on the same axis; that is to say; the axle bearings and the case bearings. This points to a bent banjo housing.
If when you remove either axle, it doesn't practically jump out of the housing, this also points to a bent housing.

Note-1
The only things inside the cone-type third member that can clunk, are the spider gears climbing up and down on the cross-pin or, the crosspin slamming around in the saddles or, the crosspin is too long and is hitting the pinion; NONE of which should be happening! in a just rebuilt unit.
Note-2
I say remove the axle, but mean just far enough to pull the splined portion out of the sidegears. The trouble with only going this far, is that the outer end of the axle will now be resting on the seal. That could be bad. So I say take it out; but when you do, it will make a mess so have a bucket or tub available to capture the drippage. Alternatively, you can support the axle flange in some way to prevent the weight from going onto the seal.
Note-3
BTW the installed driveshaft only likes to turn one way, due to the sprag in the back of the trans. When you spin it in reverse direction, the sprag locks and forces some of the transmission guts to turn, and one of them drags on the L/R band, which creates the major part of the resistance that you will feel. In the opposite and normal direction, the sprag slips and the only moving parts are the planetaries which you can barely feel.

best of luck to you.
 
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