Problems with 1961 rear differential...need advice

[Captainfab]

There is a thread on here that has the rear differential codes and what they are. I believe you can find it in the '60-'66 FAQ Index. The HC is the code.

Edit: I found the thread here: http://67-72chevytrucks.com/vboard/s...d.php?t=327764

Looks like you have a '65-'67 3.73 posi rear differential. Of course this is assuming nothing has been changed in the last 40+ years. I'd pull the cover and have a look. More than likely the oil needs changed anyway. It'ss just cost you a couple quarts of gear oil, a bottly of friction modifier and a cover gasket. Then you will know for certain what gears you have, and the peace of mind knowing you just serviced your differential, and all is good inside.

[par4tom]

Great info again Cap!

The HC is a 3.67 Positraction Unit

8 06 means it was manufactured in August of 66

W means is was from the Warren Plant.

This helps a lot...I'll live with the gearing, service it and set out to work on transmission.
T

[par4tom]

Originally Posted by par4tom

Great info again Cap!

The HC is a 3.67 Positraction Unit

8 06 means it was manufactured in August of 66

W means is was from the Warren Plant.

This helps a lot...I'll live with the gearing, service it and set out to work on transmission.
T

Bearing retainer on SM420 is 4 11/16 and on the NP 440 is 5 1/8. I'll machine down the retainer a bit to get it to fit. My bellhousing is 4 3/4 opening...

[Captainfab]

I'm not sure if there is enough meat on them to be able to turn them down that far. If not you could open up the hole in the bellhousing. Or you could change the bellhousing for a '67-'72 bellhousing. But then you would have to deal with adapting the clutch slave cylinder to the newer bellhousing.

Originally Posted by par4tom

Bearing retainer on SM420 is 4 11/16 and on the NP 440 is 5 1/8. I'll machine down the retainer a bit to get it to fit. My bellhousing is 4 3/4 opening...

[MusicMan70]

Post #18 shows one that's been turned down.

[MusicMan70]

Here's a better photo comparison; Ebay photo and another of mine.

[Captainfab]

Thanks for clarifying. I did not realize the one you posted had been turned down. That will be easy enough to do for someone with a lathe.

[par4tom]

Nice photos...I see what you mean on turning that down.

BTW, did you use an RTV sealant behind the retainer and on the bolt threads?

[MusicMan70]

par4tom,

I had my unit gone thru by a reputable transmission shop. I can only assume some type of sealant was used. I have not had any leakage issues and followed the instructions from the Classic's Truck article.

[par4tom]

Another question...I have secured a cast-iron NP 440 transmission (off a 4 wd), and the transmission shop is going to completely go through everything once I give them the go ahead. The only thing missing is the tail housing for a 2wd which the guy is trying to track down.

He is also going to machine down the bearing retainer to 4 11/16 to fit the bell housing. So in that regards, I'm making progress. ("Thanks" for the pictures)

Can anyone point me to finding a tailhousing for this? Or, can you let me know what specific tailhousing I will need here?

And I would like to confirm, it is a 10 spline on the OUTPUT shaft as well, correct?

[MusicMan70]

Well here is a complete unit...

http://www.ebay.com/itm/Chevrolet-4-...df9545&vxp=mtr

... with shifter and HD shift rods and bellhousing. This is what you will need and it has the correct tailhousing AND Shifter too, cheaper as well, should you decide to go this route.

Output shaft towards engine is 10 spline; to driveshaft I think is the same as a turbo 350 (30 spline?)

Here are some tailshaft pics

[Captainfab]

I assume that the trans guy has verified that the output shaft is the correct length and spline for a 2wd application? Typically when converting a 4wd trans to a 2wd trans, the output shaft has to be changed also. This may or may not be the case with this trans. Just trying to make sure you don't end up with something you can't use.

[par4tom]

I went over to his shop this morning and he was pleasantly surprised with all the homework I had done (thanks to you guys!)

Anyway, the input shaft is correct and should fit. He knows that the bearing retainer needs to be machined down to 4 11/16 to fit. So on the front end, we're good.

On the tail, evidently there are numerous tail housing units that will fit this transmission and I'll let you know which one he decided to use.

I'll document this whole install and post it on here once I'm done and maybe it can help someone else.

But from what he can see from the pictures on this thread and from what I've told him, we appear to be good to go. I ordered the transmission today and it should be up to Fresno from LA here in the next couple of weeks.

[par4tom]

Ok, I'm stuck.

The transmission guy says he is having trouble finding a tail housing to fit a cast iron NP440/MY6.

Can someone help me on which tailhousing(s) will fit?

Tom
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[MusicMan70]

Tom, Is the bolt pattern different then the posted photos? If so can he send you a pic of the bolt pattern?