9" posi question

[69MyWay]

I have a 9" in my 69 Camaro. I am running standard rear gear oil and the POSI additive.

Problem is, the clutch in the posi unit is WAY too aggressive and it binds/catches very strong in slow speed turning. It makes the back of the car feel like it is going to tear off.

Question is - if the clutch is too aggressive, can I tone it down by changing fluid and NOT adding posi lube? Correct me if I'm wrong, but doesn't the posi lube help the posi clutch get friction - or is it the other way around?

[AllSpeedAndy]

What posi unit is in it?

[69MyWay]

What posi unit is in it?

Good question. It is a clutch style, and I was told "carbon fiber" clutch disc. I didnt' pick it out. I had it build based on some trading and swaping to fit my 69 Camaro. However, I can't tell you the brand or anything beyond that.

This is really strange. This morning it is a record low temp in Florida (low 20s). When I backed out of the garage and then went out of the driveway, I didn't notice the horrific grab/snag/bump that is so typical and especially the more warmed up the car gets. By the time I was at work it was doing it again.

[chicane]

What fluid are you running ?? And... which friction modifer are you using ??

I doubt you are going to be able to run the diff without using the friction modifier... unless the lube you use has it added to the base oil itself. Then again... you may just need to add a little more fric mod to subdue your issue.

Most differentials need 4oz of fric mod... but if the clutches were not soaked in fric mod to begin with (at the time of differential assembly) it will need time to mix with the base oil for it to do its job.

[69MyWay]

What fluid are you running ?? And... which friction modifer are you using ??

I doubt you are going to be able to run the diff without using the friction modifier... unless the lube you use has it added to the base oil itself. Then again... you may just need to add a little more fric mod to subdue your issue.

Most differentials need 4oz of fric mod... but if the clutches were not soaked in fric mod to begin with (at the time of differential assembly) it will need time to mix with the base oil for it to do its job.

I can't remember the weight of the oil - I looked up what would go into any stock Ford 9" application (oil weight wise). I added the fluid modifier that you can buy at the local auto parts stores. This has been an ongoing problem for a couple of years, but I have been driving the car everyday to keep miles off my new truck and it is driving me crazy!

[AllSpeedAndy]

When it is cold first thing in the morning, the oil is going to be thickest...
and by the time you get to work it has warmed up and problem came back.

This tells me your diff. likes the thicker fluid, now either what you have in it has broken down, or you need something of better quallity in there, like Royal Purple or another brand of performance fluids...As chicane said, I wouldn't
go with out the friction modifier, be sure to put that back in. But I would try a higher quality fluid than the general parts store stuff, before tearing in to it.:thumbsup:

[69MyWay]

I wonder if I should use GM posi additive (perhaps two bottles) and a quality fluid - and or thicker fluid.

Like a dang idiot, I didn't drill and tap a drain hole in it - so I have to figure out how to syphon the old stuff out :mad:

[chicane]

Use a quality straight (minimum) 90wt (I like their 140wt myself) and only use the OE Ford friction modifier... not the junk off the shelf at the local parts store. There is a big difference in the composition of the fric mods available and Ford makes the best parrafin based stuff there is... and RedLine makes the best synthetic based stuff there is.

I might also recommend that you use a 'better' differential lube as well. The cheaper parts store brands (to include Valvoline) do not tend to homoginize with the friction modifiers very well. When they seperate... you get noise.

My personal recommendation for lube is in this order:

1. Schaffer, #209 with the suspended moly

2. Torco, RGO 85/140

3. LE... Amsoil... and all the rest.