psychodiagnostik

Is there a way to know whether a D36 is a 2 series or 3 series? I'm looking at one for sale locally. It came out of a '92 automatic, but I don't have a way to see the option codes to know whether it came with 2.59 or 3.07. The owner sent me a photo of some casting numbers but I don't see an obvious way to know from these.
thanks!

WVZR-1

Not many of the D36 assemblies came with the information etched into the bottom of the housing BUT some did. The way you confirm the ratio if you can put "hands on first" is to rotate one of the axle shaft flanges one complete rotation and count the rotations of the pinion flange. It should be a rotation of either just over 2 1/2 times or just over 3 times, you need to watch for 2 3/4 turns (2.73) ratio also. Very simple since it's out and on the ground. Remove the cover and the information will be on the ring gear and you could count teeth and do the math. Out of the car and on the ground you've many options.

Can the guy provide you with the VIN? If yes take it to a GM dealer parts counter and ask them to confirm the axle ratio RPO for you. That isn't definitive in your case but it's a potential confirmation.

If the housing was etched from the Dana assembly facility it would have three or four lines of code, the ratio, the GM assembly # and the Dana "bill of materials" 605490-4 (2.59), 605490-1 (2.73) or 605490-2 (3.07). If it had a BOM of 605321, 605260 or 605239 it's much older. If it's 605172/605180 you for sure DO NOT want it. That build would indicate '84 and the weakest of all.

psychodiagnostik

Thanks, the seller did this over the phone before I even got back in touch with me, he told me he kept getting "almost four" turns of the pinion for every one turn of the axle.

I went ahead and picked it up, after confirming that sure enough it looked like this is the ratio. I just checked it on the bench, marked everything with a sharpie, checked it 3 times and and sure enough, I get about 3 and 1/4 turns exactly of the pinion for every one axle turn.

It looks like a 3.73, which obviously never came in a D36 but I know it's available in the aftermarket. The seller said he got this complete assembly thrown in along with a complete '92 automatic Vette he bought.

arbee

3 and 1/4 turns would not be a 3.73. Did you mean 3 and 3/4??

WVZR-1

LOL - I caught that also but the OP mentioned that "seller" mentioned almost 4 so I so I just smiled and moved on. I'd think the OP needs to maybe pull the cover and "DO THE MATH"!!!

arbee

Yep, probably a typo. Wanted to point it out for him so he doesn't maybe think he has something he doesn't.

WVZR-1

I made sure in my first post I mentioned "removing the cover" because the OP mentioned this: how to tell for sure

He needs to anyway before installing and confirming the "gear pattern" or having someone who understands check it for him, particularly if it's thought maybe to be an after-market build.

drcook

Also while the cover is apart, the thickness of the ring gear can be examined. If it is a "thick" gear, then originally a "2" series, a thin, then was the "3" series.

Yukon gear sells both. A call to them would clarify the dimensions of "thick" -vs- "thin"

https://www.yukongear.com/partslist....26+Pinion+Sets

Divide the nbr of teeth on the ring gear by the nbr of teeth on the pinion will give the ratio.

psychodiagnostik

Sorry yes it's three and three quarter turns. I'm hoping once I get the cover off I can see for sure the number teeth, brand if it's indeed aftermarket etc.

A Peter C4

Almost all ring gear have ratio stampted on them, I've never seen a ring gear that wasn't stampted with ratio.

psychodiagnostik

As an update, I did take the cover off, here's what I found out:

Stamped on the ring gear is USA 012 G 05 878373C 41-11 A .

It looks like this matches the US Gear catalog for a 3.73 ratio for the carrier that came with 3.07. 41 tooth ring 11 tooth pinion. I've never heard of US Gear, only Richmond & Yukon, does anyone have experience with US Gear?

I don't see obvious problems, the fluid inside was dark but I didn't see trash or evidence of damage. I'm thinking of taking it to a local shop that does diffs to see if it's set up right. I'm not really operating at the level necessary to check the gear pattern, backlash, etc.

Also, I have a new FelPro gasket, however it looks like the cover/batwing was put on with only RTV. The gasket was the one AdvanceAuto's system shows will fit, but I haven't taken it out of the box to test it. Should I just seal with a bead of RTV/permatex or whatever? Is one brand/temp range the best to use for this?
Thanks