A-833/NP440/MY6 transmission on a BOP bellhousing?

[Bonnewagon]

I am looking at one of those Mopar A-833 overdrive transmissions that GM used in the '80's. They called it the NP440 or MY6 and it was in various Chevy vehicles like Blazers and Sierras. I know the main case, tail housing and input shaft were changed so they could bolt up to a special Chevy dual pattern bell housing. But is it true the hole in the bell housing is a bit larger than the standard GM housings because the input gear cover is larger than what GM usually used? And the dual bolt pattern housing- was that a Chevy only item? Was it also Chevy/BOP? So to use it behind a Pontiac 400 I would need to enlarge the input gear cover hole? And what about the bolt pattern? Is there enough meat on a BOP bell housing to just make new holes? I would not want to use a Chevy-to-BOP adapter. Anyone try this?

 

[fleming442]

Nope, haven't even heard of it.
Is putting Mopar parts in worse than Ford parts?🤔

 

[Bonnewagon]

Ha ha, well it is a Mopar transmission that was made and modified by New Process Gear to fit GM. From what I read it is pretty bullet-proof. The Mopar regular 4 speed version was used behind Hemi engines and the 440. But by the late '70's it was relegated to slant 6's and 318's. They changed 4th gear to overdrive for fuel economy. GM used them from like '81 to '87 or so in pickups and vans until OD automatics took over. I think it would be perfect for a Pontiac 400 or 455. A 3:09 first gets going easy and .74 OD gets good highway manners.

 

[fleming442]

I'm intrigued; is it a 3+OD or 4+OD? Is it widely supported?
I have an Autogear M22W gearset in the red car. 4th is still 1:1, but you get the M20 2.56 1st and M22 straight cut gears. 4th OD would be cool, but it conjures up visions of the Ford 3+1, granny gear 1st, transmissions in the old 6 banger F150s.

 

[ssn696]

It's a really weird hybrid. I think I read that it was an iron case 4-speed, with 3rd gear swapped for an overdrive. Not sure how that worked for shifting. I have a transmission book...I'll look and see what I can find.

 

[Bonnewagon]

It is a 3 + OD. 3rd is 1 to 1 and it actually is very similar to the HD Borg Warner T-16 that came in my '67 Firebird 400. With the torque of the 400 I used to stay in second gear all day, it was that flexible. I only needed first to get going and 3rd on the highway. But the '67 had 3:55 rear gears and man, would an OD 4th have been the best ever. I crunched some number and if I used this in my Bonnewagon that has 3:23 rear gears, 26.85" tall tires, at 2000 rpm I would get almost 70mph. And an overall 1rst gear ratio of 9.98 would be effortless take-off. Paul Cangialosi has it in his HP manual trans book.

 

[fleming442]

Sounds good as long as you have enough torque to pull the OD.
I couldn't do it; wrong on too many levels. 😊

 

[Bonnewagon]

That is why I love Pontiac V-8's. You can practically climb a tree with the torque of a 455.

 

[olds307 and 403]

I also considered this trans. I found mixed info, some say it is bullet proof, others say it is weak. I need something to survive 450+ ft/lbs. I was wondering the same thing about the bell housing. Trouble is finding a decent strength trans with a better first and overdrive that doesn't cost a fortune in manual or autos a tall order. I do like that they come with a factory Hurst shifter on them all.

 

[DRIVEN]

I've had several of them. They are really sturdy and would be a great match for a torquey 400. I have one behind the 327 in my El Camino but really liked it with the 400 SBC that was in there previously.

Here's what you need to know; There are several versions of this oddball. First, it comes in 2wd and 4wd. The extension housing and main shaft is different (I used a 4wd for parts). Second, they come in cast iron and aluminum versions. Third, there are 2 different bolt patterns where they mate to the bellhousing. One is std. Muncie/Saginaw/T10. The other is std on the driver's side but looks like a Mopar on the passenger side. You would need the corresponding bellhousing to match. The version with the std GM pattern uses a stud and nut in place of one of the bolts -- no big deal.
Fourth, the front bearing retainer is "truck" size but there is enough meat left to put it in a lathe and turn it down to "car" size if you use allen head bolts to bolt it on. I've done it.

So for your application, look for one with the std GM front pattern and turn down the retainer. It'll bolt right in place of the Saginaw. Easy peasy.

These stupid things seem to fetch a premium anymore but you can still snag them if you're patient. Also, they don't shift as quick as a Muncie so they aren't ideal at the dragstrip. Those big, heavy gears are hard to synch. I've found GM Synchromesh fluid works best. ATF shifts a little quicker but they are noisy. 80/W90 is too heavy.

Hope that helps.