Correct transmission and differential fluids?

blubob

blubob

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I have a '68 Firebird 400 with the Muncie 4 speed and the low gear rear end. I think it is 4.11:1 or close to it. All original, and I am running a mild cam and Holley 4bbl putting out about 400 hp. I just had the clutch replaced, and would like to replace the transmission fluid and differential fluid myself. Does anyone have any recommendations on what fluids to use on these original parts? I was going to go with 80/90 in the rear end, but wasn't sure. Also, is there a tutorial on how to swap the fluids in the tranny. I know how to do the diff. Thanks.
 
unless you have an M22 version of the Muncie there is no drain plug. You have to buy a hand pump to remove the old fluid thru the fill plug on the side of the case. make sure the rear end fluid is for a limited slip differential. Use any brand name fluid for both.
 
Thanks Mel! I called RedLine Oils today and they have a 75/90 for the rear end that requires no posi additive, as well as a 75/90 NS for the tranny. I ordered some today. The tech I talked to said it was only 2.5 pts for the tranny and 4.8 for the rear end. Does that sound right? I haven't looked at the tranny to see if I have a drain plug or not. Can you recommend a pump kit for this purpose?
 
the fluid capacity sounds about right, in both cases with the trani or rear level fill it till it just starts to pour out of the plug. There is no specific pump what ever the local store has is fine.
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Thanks. I am going to try to get on it after I get new tires and an alignment done Friday. 11 year old tires with 12,000 miles on them so they gotta go. And I never aligned it after I replaced the front springs last summer. Then I need to install the '69 disc brakes after I rebuild the calipers. Hopefully by summer it will be ready to go. Any thoughts on where to get rebuild parts for those calipers? Ames the best?
 
Thanks for the help. I gotta take off for a business trip for a few weeks, but I was able to get new tires and an alignment done before I leave. I also had the front bearings repacked, as they were loose and out of spec for the alignment. I think when I get back I will get to work on the brake conversion. I think if I buy a fork I can do it all myself, and then just take it in to get aligned again. The place I had it done will do it again no charge.
 
I pulled the rear diff cover, drained the fluid. Smelled burnt, but no metal, and the inside of the diff looks like a swiss watch. Couldn't find a gasket, so I went with black ultra silicone. Re-installed the diff cover, hand tightened the bolts. Little bit of ooze of silicone, just right. Am waiting an hour for it to set up then going to torque, but dont have the value. I thought it was 25 ft. lbs., but am not sure. Anyone have an idea? I am going to pump in 2 qts and see if that fills it. If not I need to order another quart from RedLine.
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25 is the correct value
 
Thanks. I torqued it down last night, filled it with just under 2 qts, and ran it. No leaks, and the silicone has a nice thin rib all the way around the cover. I was surprised it took less than 2 qts before oil started coming back out the fill plug hole. Now I have to pump out and replace the tranny fluid. I found a square bolt head about 3/4 of the way up the side of the tranny, on the passenger side. Is this the fill plug? I am going to have to put it up an the lift to get at it. I ordered another quart of RedLine 75/90NS, for a total of two.
 
Yes that's the plug. You might notice a protrusion a few inches below it. Thats where the second plug would be if you had an M22.
 
Thanks for the fill plug info. I found an OEM washer fluid pump in the Ames book for $55 so I will need to replace that this spring also. Does anyone know the size of the bolt that holds the front or bottom of the flywheel cover? Mine is missing, and the cover is open a little bit.
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it might be 1/4-20x7/16
 
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