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pat64tbird
03-22-2016, 09:47 PM
Hello Members,

While I take car of my brothers 64 Thunderbird I myself own a 1967 Chevrolet Impala. The previous owner had the rear differential changed to a 12 bolt positraction unit. The rear end does have GM stamped on it. My question is: Do I need to add a limited slip additive to the new rear end fluid that I'm putting into it? Thank you for your help.

Sincerely,

Patrick

simplyconnected
03-22-2016, 11:17 PM
Yes. The clutch packs need the friction modifier additive. Later on, you will need it again if you hear RE chatter. - Dave

pat64tbird
03-23-2016, 06:14 AM
Thanks Dave.

Patrick

OX1
03-23-2016, 07:48 AM
I'll ad yes if it is a stock or stock type limited slip with clutches (probably is). If it is an aftermarket, say gear driven diff, like this

http://www.eaton.com/EN/Eaton/ProductsServices/Vehicle/Differentials/detroit-truetrac/index.htm

then no.

pat64tbird
03-23-2016, 03:41 PM
Everything that I see in the rear end is gears. My question is: I put 400 miles on my car with just 80/90 hypoid oil. Did I do any damage?

jopizz
03-23-2016, 04:57 PM
Those GM rears are pretty bullet proof. I drove my '66 Impala for four years with a bad pinion bearing. It was still going strong two owners later.

John

pat64tbird
03-23-2016, 05:39 PM
Thanks John,

I never knew that my positraction rear is also limited slip. I was originally given wrong information about the oil, that's why I put 80/90 hypoid rear end oil in it.
Tomorrow the part store will have the gasket so, keeping my fingers crossed there will be no noises.

Patrick

OX1
03-24-2016, 06:14 AM
Everything that I see in the rear end is gears. My question is: I put 400 miles on my car with just 80/90 hypoid oil. Did I do any damage?

If the rear tires felt/sounded like they were "chattering" (screeching) on every turn, you may have worn the clutches a bit, but doubtful anything catastrophic.

If you really want to check, put car in gear/park and jack up one wheel. Put old style torque wrench (pointer type, not digital or click type) on a lug and look around on net to find LS breakaway torque of that differential. Attempt to spin that one tire until it starts to move. Read torque wrench pointer and see if LS breakaway matches spec. If it is much lower, than the clutches have worn some.

Or if the car spins the tires, do a short healthy burnout on dry pavement and see if you get two tire patches (my preferred method of LS diff checking:D)

pat64tbird
03-24-2016, 07:50 AM
Thanks OXI.

Patrick

pat64tbird
03-24-2016, 02:28 PM
Thank you for all the responses. I put the correct oil and additive in the rear end and everything is running smooth. No noises or vibrations.

Patrick