More than one bottle of differential additive?

[Lonnie Wiggins]

If I stop my '69, and then start up again, or, if I stop and reverse...sometimes I'll get a thunk and shudder from the differential (I presume, as everything else seems tight - checked the differential to frame snubber/bolt assembly).

I know the differential contains one bottle of additive. Could it need two?

Has anyone ever seen an situation where more than two were needed?

[Terry M.]

Re: More than one bottle of differential additive? *TL*

The 1969 Corvette FSM, I believe, calls for one bottle, but those of us with late model Caprice/Impala B-bodies routinely use two in spite of the applicable FSM calling for one. The limited slip mechanism is very different in the B-bodies than the Corvette, however. I don't think two bottles will hurt - other than your wallet.
How long has it been since you changed the differential fluid? After years and years the fluid, and positraction additive, need replacement. You might try that as a first - least costly - option.

[Terry M.]

Re: More than one bottle of differential additive? *TL*

The 1969 Corvette FSM, I believe, calls for one bottle, but those of us with late model Caprice/Impala B-bodies routinely use two in spite of the applicable FSM calling for one. The limited slip mechanism is very different in the B-bodies than the Corvette, however. I don't think two bottles will hurt - other than your wallet.
How long has it been since you changed the differential fluid? After years and years the fluid, and positraction additive, need replacement. You might try that as a first - least costly - option.

[Duke W.]

Re: More than one bottle of differential additive?

If you don't know the last time the fluid was changed, change it using the GM axle oil and one four ounce bottle of the additive. Also measure the circumference of the tires. If they vary more than about 1/2" that can cause problems with the positraction.

If the tires are okay and it still makes noise, add a second bottle. If that doesn't cure the problem, then it's probably something else - maybe an internal problem in the axle.

Duke

[Duke W.]

Re: More than one bottle of differential additive?

If you don't know the last time the fluid was changed, change it using the GM axle oil and one four ounce bottle of the additive. Also measure the circumference of the tires. If they vary more than about 1/2" that can cause problems with the positraction.

If the tires are okay and it still makes noise, add a second bottle. If that doesn't cure the problem, then it's probably something else - maybe an internal problem in the axle.

Duke

[Mark Ring]

Re: More than one bottle of differential additive?

Yes I did need more than 1 bottle but it was in a Camaro. I had the differential swapped out and the new one would snap on freeway cloverleafs etc. The second bottle did the trick.

-Mark.

[Mark Ring]

Re: More than one bottle of differential additive?

Yes I did need more than 1 bottle but it was in a Camaro. I had the differential swapped out and the new one would snap on freeway cloverleafs etc. The second bottle did the trick.

-Mark.

[Wayne W.]

Re: More than one bottle of differential additive?

I routienly use two.

[Wayne W.]

Re: More than one bottle of differential additive?

I routienly use two.

[Steve D.]

Re: More than one bottle of differential additive?

Is differential additive used in all posi-traction differentials, or just later models?

[Steve D.]

Re: More than one bottle of differential additive?

Is differential additive used in all posi-traction differentials, or just later models?

[Duke W.]

All

The additive is a "friction modifier" that prevents "slick-slip" friction that causes the chatter we can experience.

All Corvette positraction axles require it for smooth chatter free operation, and automatic transmissions fluids have a similar additive to keep their wet clutches operating smoothly.

The additive appears to degrade with time, which is why the fluid should be replaced with new fluid and additive every 30K to 60K miles.

It's best to use the least amount of additive to eliminate chatter because too much will reduce the effectiveness of the positration unit.

There are several types of limited slip differentials. The "clutch" and "cone " type as used by GM require the additive. Purely mechanical types such as "ratchet" (Detroit Locker), the worm gear type (The name escapes me for the moment.) and the "viscous" type do not need the additive.

Back in the fifties and sixties the additive was whale oil based and the old Type A Suffix A ATF had a whale oil additive. With the outlaw of whale products in the US in seventies an alternative petroleum derived product was developed.

Duke

[Duke W.]

All

The additive is a "friction modifier" that prevents "slick-slip" friction that causes the chatter we can experience.

All Corvette positraction axles require it for smooth chatter free operation, and automatic transmissions fluids have a similar additive to keep their wet clutches operating smoothly.

The additive appears to degrade with time, which is why the fluid should be replaced with new fluid and additive every 30K to 60K miles.

It's best to use the least amount of additive to eliminate chatter because too much will reduce the effectiveness of the positration unit.

There are several types of limited slip differentials. The "clutch" and "cone " type as used by GM require the additive. Purely mechanical types such as "ratchet" (Detroit Locker), the worm gear type (The name escapes me for the moment.) and the "viscous" type do not need the additive.

Back in the fifties and sixties the additive was whale oil based and the old Type A Suffix A ATF had a whale oil additive. With the outlaw of whale products in the US in seventies an alternative petroleum derived product was developed.

Duke

[andy#34338]

Just had to add a second to my new 3.55 in my 60

I put a new 3.55 in my 60 an after a couple hundred miles it started making binding noises mostly on turns. Added a second bottle and no more issues.

Andy

[andy#34338]

Just had to add a second to my new 3.55 in my 60

I put a new 3.55 in my 60 an after a couple hundred miles it started making binding noises mostly on turns. Added a second bottle and no more issues.

Andy