1967 M-21 and Posi-Rear End Lube

[Salvatore I.]

I have 3 very basic questions:

1. How can I replace the lube in the M-21 transmission housing and in the rear end on my 67 327; in other words, what is the best method that has been used to extract the lube from the housings of the tranny and the rear end? Is there a special type pump/suction device that hase been used for this process?

2. What are the specs on the lube that should go into the tranny and the rear end (with Posi)?

3. Where can I find these lubes, are they available in any reputable auto parts store or do I need to order from one of the Corvette specialist websites?

Thanks for the feedback!

[Joe C.]

Re: 1967 M-21 and Posi-Rear End Lube

Sal,

All items needed are found at your local auto parts store.

You'll need a suction tool to extract the old lube. This looks like a large syringe (about 1 quart capacity)with a flexible hose to insert into the gearbox/diff. There are dirrerent types, but the least expensive is manual, and is as I described.

Any gear lube API spec GL4 or preferably GL5 will work. Probably the best viscosity for normal use, is 80W-90 with mineral based oils, and 75W-90 for synthetics. Use the same lube for the trans, and the diff.

With the diff, you MUST add 1 tube, or 4 ounces (minimum)of friction modifyer ("posi additive")if it is not already blended into the gear oil. Sometimes 4 ounces is not enough to prevent clutch chatter, especially with old, or worn clutches. Best results are obtained with adding the smallest amount of additive. Start with 4 ounces, but leave room for more if needed. Drive to a parking lot, and make a series of figure-eights to distribute and mix the additive between the clutches. If they chatter, add 2 more ounces of additive, if not, top off with gear oil.

SOME gear lubes already have the friction modifyer added, particularly some synthetics. CHECK THIS BEFORE ADDING ANY ADDITIVE TO THE DIFF. I use Valvoline gear lube, 80W-90 mineral based, because I know that it contains no friction modifyer.

Joe

[Salvatore I.]

Re: 1967 M-21 and Posi-Rear End Lube

Thanks Joe

I will take it from this point...thanks for the feedback...

Sal

[Duke W.]

Re: 1967 M-21 and Posi-Rear End Lube

GM recommends GL-5 in both the transmission and axle. You might get away with GL-4 in the transmission, but NOT in the axle. There is not a hypoid gear axle on the planet that will live a full life on GL-4.

To be on the safe side, use GL-5 in both - any name SAE 80W-90 GL-5, commonly known as "gear oil" will do, and it's widely available.

For Positraction axles add one four-ounce bottle of of friction modifier additive, 1052358.

Duke

[Salvatore I.]

Re: 1967 M-21 and Posi-Rear End Lube

Thanks Duke for the info

Sal

[J M.]

Re: 1967 M-21 and Posi-Rear End Lube

I just did mine. Got a cheap suction hand pump and a flexible piece of clear tubing to stick in the hole. Worked real well. But, man does that old fluid stink.

[Salvatore I.]

Re: 1967 M-21 and Posi-Rear End Lube

How much lube is added to the rear and the tranny? I was going to fill the tranny to just under the plug hole....is this correct?

The mystery to me is the rear-end...the posi red label is located high on the casing...fill with lube to just beneath this plug hole too?

Thanks for the feedback....

[Joe C.]

Both Same....Under Plug Hole *NM*

[Duke W.]

Re: 1967 M-21 and Posi-Rear End Lube

Four speed transmission capacity is 3 pints; axle is 3.7 pints. This data is in owner's manuals, service manuals, and AMA specs. Everyone should have copies of these docuements and refer to them as necessary.

Use these quantities, which should bring the level to slightly below the bottom of the fill plugs. When hot the oil will expand slightly and should be right at the bottom of the fill plugs.

Duke

[Salvatore I.]

Re: 1967 M-21 and Posi-Rear End Lube

Thanks to everyone...your feedback and guidance has been very helpful....

Sal