Posi Traction?

Hi Guys

It's getting cold here now so time to start my winter tinkering. First on my list is looking at my rear axle - it behaves like a locked diff on slow, tight turns and low speed manoeuvring (juddering etc.) - worse when I have a heavy load in back.

Then yesterday when leaving a gravel car park it dug two holes before moving so I'm guessing it is a limited slip differential of some kind.

My plan is to drain it down, refill with oil & additive and test it again with some tight turns - any tips or anything I should be looking out for? Do these axles have any weakness's?

Thanks - my other question is in another post

Just take a close look at the inside when you have the cover off. If it gets worse with a heavy load in the back it sounds like it may have a spool in it or its locked up for some reason. Mine acts like that but I know its because I shimmed the clutch pack a little too tight when I rebuilt it.

M1D

Thanks M1D

I'll have a check - hoping its a fluid thing as previous owners put a lot more money into the stereo and interior than any kind or servicing.

yes could be old or wrong fluid type.

So, unless I'm mistaken, this is a Positraction unit?

https://i.servimg.com/u/f60/20/05/18/39/img_6210.jpg

Looks a bit like other LSD units I've seen. Seems overkill for 155bhp but I like that!

Its quiet and the gears look unworn so I'm going to clean up and pop the cover back on with new oil and some additive - any favourites or recommendations of brands?

Thanks

I used a 90W for limited slip, Valvoline I think. The rear made weird noise's while moving slow with the engine off. I remembered back in the '70's the Chevy dealer sold a special "Pos-A-Trac" oil that was red in color. I went to a local dealer and the parts guy said they don't have that anymore but he did sell me a additive for the posi rear end.(about 8oz.)
No more funny noise's, seems to be working well.
My Posi unit.

Non Posi unit.

Thanks Russell

Looks pretty similar - I can get the 90W no problem but may struggle to get anything designed specifically for Posi over here although any additive for this type of LSD would do I guess.

You don't have a Chevrolet dealership? Pos a trac is different than limited slip.

"Pos-a-trac" is simply Chevy's name brand for their limited slip differential. Pontiac called theirs "Safe-T_Track". Ford called theirs "Trac-Lok" Mopar called theirs "Sure grip" or "Power-lock" all marketing terms for the same thing. Like calling a tissue "kleenex"

Any limited slip additive will be fine. Many of the higher end gear oils already have the additive in them.

Thanks guys

Russell - GM over here are Vauxhall mainly and Chevrolet are just rebranded Daewoo.

Kooky - yes, thought it couldn't be too different, its just that you guys get cool names for stuff when we just get LSD!

do not just add any 90 weight oil.

The wrong oil will change the coefficient of friction on the clutch plates and make the clutch pack stick or slip too much. That is exactly what the GM additive is for was to modify the oil so it would not making it compatible with the clutch friction material.

The weird noise, clunking or chartering sounds is exactly that the clutches are not de-clutching smoothly.

The wrong oil is probably what is making you posy not unlock as it should.

The correct oil will be a hypoid oil specifically for limited slip differentials. 90 weight is good and you may also need the additive.

If it was the wrong oil your clutch plates will be saturated and in may take quite a bit of cornering braking the clutch pack free to make them move and work the new fluid into the clutch material.

By the way, you see those two big 1/2" holes one either side of the case on plane with the axles. do not block them with a cheaply made gasket as they are part of the oiling system.

m1D

Thanks Guru

I've put in two litres (quarts-ish) of 80-90W GL5, so that's cool and I have some Red Line additive on its way via Amazon - when that's in, I'll go for a tour of local roundabouts!

Gasket was a decent looking Felpro with slots in it to match the oil holes, so all good there too. Little by little this old van is getting better all the time.

Good plan! we don,t have many roundabouts here, but now you have enlightened me what they are used for.

You van does look pretty sweet:)

Thanks Guru

I used to live near the roundabout capital of the UK - it was modelled on the US city grid system but using mostly roundabouts, hundreds of them!