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9/10/2017 7:07 PM  #1


Resr end noise

Hello all, Robby 13 here. 67 mustang fastback .
Ive been hearing a grinding noise on left and right turns, nothing straight ahead. At first i thought it was the rear bearings, but they would be making noises all of the time, right? So im figuring maybe rear end? It does have a limited slip 3.25 gears. How and what should i be checking for? I installed a new unit from Just Rear Ends about nine years ago. First thing ill check is gear oil, but what after that? Thanx again.

 

9/10/2017 7:30 PM  #2


Re: Resr end noise

Where is the noise coming from?  Grinding noises when turning sounds like front end.  Remember you can't always tell the source of the sounds.  Recently, I had a strange whirring sound coming from under the dash.  Turned out to be the electric fuel pump in the rear cavitating because of a clogged fuel filter.


Original owner - 351w,T-5, 4whl disks, power R&P
 

9/10/2017 8:57 PM  #3


Re: Resr end noise

When you installed the limited slip, did you add friction modifier to the gear lube??


.......common sense is a flower that doesn’t grow in everyone’s garden.......
 

9/11/2017 1:02 AM  #4


Re: Resr end noise

Although there are several friction modifiers available on the market, the Ford stuff is the only way to go.  If you used something else, drain and refill with fresh oil and Ford friction modifier from your local Ford dealer.  Specify that the limited slip is in a 1967 vehicle.
Best
Al


Classic cars are full of surprises and almost none of them are good ones!
 

9/11/2017 7:05 AM  #5


Re: Resr end noise

Al is right on, back when these were new/newer, I worked at the Eaton Proving Grounds where the engineering was done for the limited slip units. All the materials used back then were different especially the friction materials since they contained good old asbestos. Ford used a lot of those units and had about the best friction package in their rear end lube for those units. I only have used the Ford stuff in the limited slip units and have no problems.

 

9/11/2017 3:14 PM  #6


Re: Resr end noise

Agreed....the Ford stuff is the best..wear latex gloves when handling that stuff..smells bad and is not easy to wash off if you get it on you..


.......common sense is a flower that doesn’t grow in everyone’s garden.......
 

9/11/2017 8:10 PM  #7


Re: Resr end noise

Time to go old school--and I'm going to date myself by making the following suggestion...
Have a helper, small in stature, get in your trunk or crouch in your back seat. Drive the Mustang to create the exact sound you are describing. Have them tell you exactly where the sounds come from.

I've ridden in the trunk of many cars (no jokes please) to track down sounds. FYI, if the weight of a dead man in your trunk makes the sound change or go away, it's suspension (dry rot shock bushings). Another similar test will tell you if it's early signals of u-joint failure.

It's amazing how noises from the back of a big old T-Bird change when buddies are stuffed in the trunk and going to the drive-in.

 

9/12/2017 9:19 AM  #8


Re: Resr end noise

Definitely rear end, sound dissapears while going straight, the smaller the turn radius gets, the more noise it makes. Will check friction modifier situation. The unit is only 9 yrs in, the company, called just rear ends is pretty reputable when i was searching. Ill check for leaks also. Ok.0, will check back-thanx.

     Thread Starter
 

9/12/2017 3:02 PM  #9


Re: Resr end noise

If its making noise during turning only that's absolutely a differential issue.  That's when the differential has to work.  I would start by draining it and refilling with fresh lube and a bottle of friction modifier.  Test drive and see if the issue gets better.  If it gets better, but still isn't 100% gone; add a little more friction modifier.  I've had to do that on one or two rears over the years.  Some brands of differential, etc. just need a bit more of the modifier to operate seamlessly. 

Last edited by TKOPerformance (9/13/2017 4:54 AM)

 

9/12/2017 3:24 PM  #10


Re: Resr end noise

Grinding sound on turns from a limited slip rear gear setup points directly to failed friction modifier, not to the quality of the gear builder.  Only other thing to cause your noise is bad spider gears due to the pinion pin having shifted in the carrier housing.  That is usually caused by continued heavy dumping of the clutch or by attempting to "drift" the car a lot.  Most 9" today have 4 pinion carriers and can handle just about anything you do; however early 9" and all 8" Ford carriers were two pinion and could be damaged.  New aftermarket carriers are all 4 pinion.  Aftermarket limited slip carriers of other than track lok design use different locking philosophies, but your noise is classic track lok dry clutch.  Ford's first 9" track lok in 1969 had a very weak clutch case that could fracture and possibly cause a noise.  I have serviced several of those and found the broken clutch housing but none of them were producing any tell-tale noises.
Best
Al


Classic cars are full of surprises and almost none of them are good ones!
 

Board footera


REMEMBER!!! When posting a question about your Mustang or other Ford on this forum, BE SURE to tell us what it is, what year, engine, etc so we have enough information to go on.