noises and wriggling from the posi rearend at low speed

[Whateverman]

mostly i'm just wondering if anyone else's truck does the same thing or not

-alright here's the story: i'm running the original 1969 issue ford 9in with 3.50 gears & 'traction -lok'

-say i'm creeping around a parking lot at low speed,upon turning the rearend will let out some "clunks" with the butt end of the truck shimmying with every 'clunk" its more inclined to do the dance when i've driven aways and got the gearlube warmed up

it went away for quite awhile when i dumped a jug of posi-trac additive into the pumpkin about 16yrs ago,and whenever it started happening again another bottle of posi additive would take care of things ,but since the truck sat for a couple of years and hasn't really been driven all that much since, the shimmy and shake is back again

i've had this same "issue" with the rearend in my truck for the last 20yrs and i've put around 300 thousand miles or more on it this way -hasn't gotten really any worse,but its just as annoying as ever - ....and especially so because even tho' she's experienced many times over many years the old lady is sure that shes gonna have to walk home everytime it happens ....

any similar experiences,thoughts or warnings about the tradgedies that may occur unless this situation is quickly resolved?

[ultraranger]

The term, "Posi" is used by many as a generic term to describe any differential that directs power to both rear axles. For a Ford though, this is technically incorrect. "Posi" (short for Positraction) is a General Motors trade name for their differential.

The Ford 9-inch rear end first came out in 1957. The first differential Ford used to direct power to both rear wheels was called the Equalok. Sometime by the '60s, Ford introduced the Limited-Slip differential. The only difference I can see between the Equalok and the Limited-Slip is possibly just a name change.

1969 was the first year Ford redesigned the differential and called it the Traction-Lok. While the Traction-Lok is similar to the Equalok/Limited-Slip, it is still different. The Traction-Lok is a much better design than the previous units. The 1969 model Traction-Lok, however, is the worst year for the Traction-Lok design due to the design of the differential case half on the drivers side of the unit. It has 4 large holes in the casting that makes it weak. They are prone to cracking between the holes.

If the diffential case is broken in this area, the unit will continue to work, but each time the clutches apply and
disengage, it causes the case to work back and forth in the broken area which grinds small metal particles loose that get
circulated through the gears, bearings and clutches.

To fix your differentials problem, it may be a simple matter of pulling the 3rd member out of the housing to dump the
gear oil, reinstall the 3rd member, add the 4 oz bottle of friction modifier and top it off with fresh gear oil.

If it's a case that the differential is broken, then you will need to replace it and check the condition of the ring and
pinion gears. --while you have the 3rd member out, to dump the gear oil, it will give you a good opportunity to check
the differential to see if it's cracked on the drivers side case half. If it is cracked, you'll need to replace the differential
with the '70-Later version.

Ford redesigned the differential in 1970 ('70-'85) to a differential case with a solid casting on the drivers side half of the
casting.

If the differential is not cracked, add your friction modifier and gear oil then make 10 tight turns to the left then 10 tight turns to the left to work the oil/friction modifier into the clutch plates.

I'm currently at work and don't have access to photos of what I'm talking about, in regard to the differential casting design, but will post some photos of the differences in the '69 Traction-Lok differential casting vs. The '70-'85 version after I get home this evening.

[ultraranger]

Difference in '69 Ford Traction-Lok differential vs, '70-'85 Traction-Lok differential. 1969 differential on the right, '70-later differential on the left. Notice the (4) large holes in the differential casting on the right vs. no holes in the differential casting on the left:



'70-'85 Traction-Lok on left, (broken) '69 Traction-Lok differential on right. As you can see, the holes create a weak area that allows cracks to run from one hole to the next...to the next...

[BobbyFord]

What you are describing is normal. My truck does it also.

[Whateverman]

What you are describing is normal. My truck does it also.

right on! good to know that i've spent the last 20yrs wondering if i was tempting fate for no good reason!

[Whateverman]

and thanks to ultraranger as well that was a pretty interesting read -

[ultraranger]

Some 9-inch rear end information from my website, (I first published this information on there in 2001, pimarily for Mustang & related Ford owners), but there may be some information of interest for anyone that would like to check it out, since any 9-inch 3rd member will fit any 9-inch housing, ( car or truck ), as long as the differential spline & axle spline count is the same (28 or 31-spline).


1. http://ultrastang.com/info2.php

2. http://ultrastang.com/info6.php

3. http://ultrastang.com/info5.php

4. http://ultrastang.com/info4.php

5. http://ultrastang.com/info3.php