Topic: 68 390 GT 9” Equa lock slips

[Benstang]

Hey!

I just rebuild my original never opened ford 9” equa lock.

The clutches looked like new. Put all together to factory specs.


On a dry road doing a burnout only one wheel spins.

On a wet road or in a corner at wot both tires are spinning.

The car has its factory not tuned 390 gt engine.

Was the original equa lock too weak for the 390s?


Is that behavior normal or is something wrong with my equa lock?

[67gt390fb]

Were you able to perform the "Differential torque check"  after assembly of the differential case?  (page 4-33,34 of 1968 shop manual)

[Benstang]

Actually I didn’t check that.

I made some burnouts after the assembly.

And I had wheel spin on both tires.

After some time maybe 250 miles later I noticed, that only one wheel was spinning.

The only two components that could cause this problem are the clutches and the Belleville spring?

Is it possible that the clutches even if they look good are bad?

[67gt390fb]

The only two components that could cause this problem are the clutches and the Belleville spring?

Yes, either weak Belleville spring and/or worn clutch plates.

You can find out the current condition of your differential by performing the "Limited-slip differential" test on page 4-2 of 1968 shop manual

[RoyceP]

Did you add Ford friction modifier to the lubricant? Your clutches look great in the pictures. The 2-pinion Equa Lock rears are not too good but yours looked fine in the pictures. Most '68 9" rears went to four pinion Traction Lock differential by April of '68. Also not too good but better than an Equa Lock.

Actually I didn’t check that.

I made some burnouts after the assembly.

And I had wheel spin on both tires.

After some time maybe 250 miles later I noticed, that only one wheel was spinning.

The only two components that could cause this problem are the clutches and the Belleville spring?

Is it possible that the clutches even if they look good are bad?

[mtinkham]

I seem to recall a some-what famous 68 390 that was filmed spinning only one wheel...I can only assume that it had the 9" Equa-lock.

[Benstang]

Hey!

Friction Mod. was  added. I assume that maybe the Belleville  spring is weak after 50+ years..?

Is there any place where I can get a new spring?

If I want a good new diff what should I buy? 

[Scott302]

https://www.npdlink.com/product/spring-washer-equa-loc-clutch-repro-1-reqd-us-made/167975?backurl=search%2Fproducts%3Fsearch_terms%3D4214-2a%26top_parent%3D200001%26year%3D

[70cj428]

I wouldn't even mess with the Equa-Loc, If you shim them tight enough to spin both wheels on a dry burnout, they wear out real quick, if you don't, they don't work. I usually just buy a new T-Lock, they have a stronger cover that won't crack like the original 69/70 ones and they are pretty inexpensive ….

https://www.quickperformance.com/Ford-9-Track-Lock-Clutch-Posi-28-31-Spline-_p_46.html