Rear Diff Noise

[69'Net]

This may be a bit lengthy but I'll do my best to explain. I've got a road runner that is mostly done being restored. Sorting out all the issues now. I noticed it's got a fast shudder or vibration above 60 mph. It has a 3:91 suregrip out of my dart, had no issues in that car. So first thing I did was jack up the rear of the car put it in gear and noticed it sort of binds at higher speeds at the U joint. So I replaced it. Here's where I developed a new problem. Not even sure it's related to the U joint. I drove the car down a long stretch of road, vibration still there at higher speeds. Did fix it. But I did a tight U turn to come home and developed almost like a whine or rubbing noise from the rear diff area. It's not a tire or anything like that. Definitely rear end area. So I came back jacked up the rear again rolled the tires didn't hear anything. Drove the car lightly around for almost 40 min, no noise. So I decided to try the tight U turn again, noise came back and made noise on every turn back home. If I jack the car up and roll the tires it will go away. I'm kinda stumped. Could it be a green bearing not liking the tight cornering? I've always heard they're junk.

 

[gtxrt]

did you put the sure grip additive in.the gm one is the best.

 

[69'Net]

I put lucas oil in it, the bottle says you don't need it.

 

[GTXDAN]

Go to O'Reillys and get this and dump in it.


Motorcraft Friction Modifier - XL3
Part # XL3 Line:


$11.99Each

 

[1STMP]

I had a sticking suregrip as
you describe. Fresh rebuild.
Added the friction modifier
and turned a few figure 8's
on an asphalt parking lot.
The noise stopped.

 

[69'Net]

Ok I'll run by tomorrow and give it a shot. I'll be pretty happy if it's that easy of a fix

 

[1STMP]

Please report back.
Thanks!

 

[SgtSuperbird]

Definitely try a rear differential additive. I could have saved myself a flatbed towing bill from Ohio, back to Michigan, about a dozen years ago - if I had known about this magical fix. I hope it works for you.

 

[Jerry Hall]

Those old sure grips need the friction modifier regardless of what Lucas says. And old school 80W90 gear oil. New things are not necessarily better in our 50 plus year old cars.

 

[hunt2elk]

I always use the Ford friction modifier stuff as well. Basically because Cass aka Dr Diff recommends it.

 

[gtxrt]

my point was you need to have an additive in there. ford or gm ac-delco are better than the chrysler additive. do not use synthetic lube. what weight is the lucas ?

 

[AR67GTX]

Another voice to second that you still need a friction modifier even with a rear lube like Lucas that says it is for a limited slip differential.

 

[69'Net]

Update. Friction modifier didn't fix it. I still have the noise.

 

[1STMP]

Update. Friction modifier didn't fix it. I still have the noise.

Did you try turning a few
figure 8's? Force the lock
side to side.

 

[69'Net]

I didnt do that. Just a bunch of tight U turns. Sometimes it does it. Sometimes it doesn't

 

[1STMP]

I didnt do that. Just a bunch of tight U turns. Sometimes it does it. Sometimes it doesn't

Figure 8's will work better
as you're forcing the locker
to engage from side to side.
Make them as tight as you
can. You don't have to be
burning rubber to do this.
You don't want wheel spin.

 

[steve340]

If you have green bearings did you remove the axle spacer from the sure grip carrier?
Something must be different if the head was OK in another car.

 

[4406bbl]

If you have green bearings did you remove the axle spacer from the sure grip carrier?
Something must be different if the head was OK in another car.

Good catch^^^^

 

[69'Net]

Both cars have green bearings

 

[jdsgtx]

This may be a bit lengthy but I'll do my best to explain. I've got a road runner that is mostly done being restored. Sorting out all the issues now. I noticed it's got a fast shudder or vibration above 60 mph. It has a 3:91 suregrip out of my dart, had no issues in that car. So first thing I did was jack up the rear of the car put it in gear and noticed it sort of binds at higher speeds at the U joint. So I replaced it. Here's where I developed a new problem. Not even sure it's related to the U joint. I drove the car down a long stretch of road, vibration still there at higher speeds. Did fix it. But I did a tight U turn to come home and developed almost like a whine or rubbing noise from the rear diff area. It's not a tire or anything like that. Definitely rear end area. So I came back jacked up the rear again rolled the tires didn't hear anything. Drove the car lightly around for almost 40 min, no noise. So I decided to try the tight U turn again, noise came back and made noise on every turn back home. If I jack the car up and roll the tires it will go away. I'm kinda stumped. Could it be a green bearing not liking the tight cornering? I've always heard they're junk.

Had the same problem in a 70 Challenger. My started exactly as you described and then turned into a clunk at low speed acceleration while turning. The rear end needs to be checked for proper clearances on the pinion to differential case and axel shafts to differential side gear splines as well as differential side gear to pinion. Also check for worn thrust washers