new 8.25 shudder in low speed turn

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rich006

rich006

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I replaced my 7.25" rear end with an 8.25" sure-grip from a salvage yard car, and now I have a shudder at very low speed when turning slightly. It seems to go away at higher speeds or in a full turn. Also, it seems to go away after driving a few miles but comes back next time I start out.

Before installing the rear end I changed the pinion seal. I restored the bearing preload very close to what it was before, about 7 in-lbs required to turn the pinion by the nut with the axles clipped in but no wheels installed. I did not change the axle bearings but they looked OK to my novice eye as did the axles and the differential (I pulled the axles to change backing plates). I filled the differential with 2.2 qts of 75W90 gear oil with nonslip additive.
 
Sounds like SG clutch shatter. You may need to add another additive to it( a good quality one) I use the additive from NAPA. Then find a open parking lot and do figure 8's to work the additive into the clutches.
 
What Roy said ^^^^^^ and possibly you may need to just drive it some more so the clutches get saturated good.
 
Did you add a bottle of friction modifier to the gear lube?

Regardless of what the label on the bottle of lube implies, you must add friction modifier when used with a good limited slip differential.

If gear lube does not smell like friction modifier, it contains very little, if any, additive.
 
I didn't add friction modifier because I've read elsewhere that you don't need to if you get the "limited slip" oil, but I'll try that. I don't know what it smells like either, but I guess I'll find out. :) I'll also drive a little bit more to slosh the lube around a little bit. I've probably gone less than 30 miles since putting the new rear in, and it was thoroughly drained at the time.
 
Try and squeeze a extra can of posi lube in there, that's a cheap fix.
 
rich006 said:
I didn't add friction modifier because I've read elsewhere that you don't need to if you get the "limited slip" oil, but I'll try that. I don't know what it smells like either, but I guess I'll find out. :) I'll also drive a little bit more to slosh the lube around a little bit. I've probably gone less than 30 miles since putting the new rear in, and it was thoroughly drained at the time.
Click to expand...

Trust me, one time is all it will take you to identify the friction modifier. Smells like A$$.
 
IMG_1272.png

This worked instantly. It didn't smell as bad as I feared; in fact, it smelled similar to the Valvoline gear oil that I had already filled the diff with. Anyway, the chatter is gone. A little dab did me...
 
Turns out the problem isn't gone. After I added the first bottle of Mopar friction modifier, the chatter went away for a while but then came back. I added a second bottle with the same result. Now it's been a couple of months and a few hundred miles, and still every time I back out of the garage it chatters as soon as I start to turn. Any ideas?
 
Are you sure it's coming out of the rear end? Torqueflites when they start giving you issues will chatter in reverse.
 
I restored the bearing preload very close to what it was before, about 7 in-lbs required
Click to expand...
Did you check gear pattern, backlash? Anytime, ANYTIME, you change one thing in a gearing system, something else also changes. Pre-load is bearing preload only, even allowing drag from a seal. Doing it with axles installed has thrown the readings to the wind. I would check for pattern, backlash, and metal contaminants; and also verify u-joints.
 
Sounds like your gear lube is contaminated.

1. Drain the original gear lube.

2. Re-fill with conventional 85 W 140, GL-5 grade gear lube, plus 1 bottle Ford friction modifier additive.

3. Run the car on jack-stands for 10 minutes.

4. Let the car sit overnight before driving.
 
Luv the Ford XL3, decent price too. Doctor Diff, is letting it set over night after mixing on jack stands as good as doing figure 8's?
 
I prefer to run the car on jack-stands. Cutting figure 8s can tear up a chattering clutch pack.
 
Recently I found my newly replaced pinion seal was leaking. Rather than replacing it myself again, I took it to a shop for a full teardown. It cost me a lot more than I wanted to spend, but they did find that the side bearings were bad. With all new bearings in the differential and new oil, the chatter is completely gone.
 
For posterity, I should add that the new oil is non-synthetic 80w90 GL-5 without limited-slip additive. Unfortunately, since so many things were done at once I don't know why the chatter is gone now--it could be the new bearings, could be the change of lubricant, it could be simply that the old oil was contaminated, or it could be that they increased the pinion bearing preload when they replaced the seal (it was about 7 in-lbs to turn the pinion, and they set it to 15 in-lbs).
 
Well, the chatter is back--mild when cold but now really bad when warm. It started after I had a new tailpipe and muffler installed--I assume the exhaust work didn't cause the chatter, but the trip to the exhaust shop was the first extended highway driving after rebuilding the rear end. What now? Should I flush the oil again? Try a different lube? By the way, this is a cone-type differential and the cones look pretty good.
 
rich006 said:
I replaced my 7.25" rear end with an 8.25" sure-grip from a salvage yard car, and now I have a shudder at very low speed when turning slightly. It seems to go away at higher speeds or in a full turn. Also, it seems to go away after driving a few miles but comes back next time I start out.

Before installing the rear end I changed the pinion seal. I restored the bearing preload very close to what it was before, about 7 in-lbs required to turn the pinion by the nut with the axles clipped in but no wheels installed. I did not change the axle bearings but they looked OK to my novice eye as did the axles and the differential (I pulled the axles to change backing plates). I filled the differential with 2.2 qts of 75W90 gear oil with nonslip additive.
Click to expand...

The good side to all of that.... The System is nice and tight.... It will wear in with time.... Just means "It's working good"... Just my 2 cents..
 
per post 18, there is currently no additive in there?Why?
Start by putting some in.
If the problem persists get just one rear wheel off the ground and perform a turning torque test. Attempt to turn the one wheel in a forward direction. If you can easily turn it, there is a problem.The cones will have to be lathe-cut and the spring pressure restored. I set mine up for street, on the workbench, with about 120ftlbs turning torque, with the proper oil-mix in the case. With the above test, you have to be a pretty powerful guy to rotate the tire.But too loose does not chatter.Too tight might.
If it is currently set too tight,more than say 140ftlbs turning torque it will want to spin the inside tire around nearly every corner. From the driver's seat, this can be interpreted as chatter.
 
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Per phone call to Dr. Diff I got the following tidbits, some of which he stated in a post above (thanks Doc!):
- cone-type sure-grip needs friction modifier just like clutch-type
- one bottle of friction modifier/additive is all you need
- Ford additive seems to stop chatter better than Mopar additive
- if it's chattering, the oil is contaminated; drain it and add new oil with the additive
- cheapo GL-5 oil is as good as the fancy stuff (80W90 is good for most US climates)
- after filling, "drive" the car on jackstands for a few minutes and then let it sit overnight to "set" the friction modifier before driving

I haven't driven the car yet, but the Ford stuff smells much worse than the Mopar stuff, so it must work better... I'll report back after I drive a little bit.
 
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