The Stovebolt Site Forums The Shop Area Engine Shop 228 GMC MY6

Hello, My name is Erik, this is my first thread here.

I am wondering if any of you have put the New Process MY6 behind a GMC 228.

I have a 1950 GMC 100 project I'll be starting on soon and I want an open drive, overdrive trans. I'm not determined to go manual at this point, but I'm leaning that way. The MY6 looks like the easiest manual overdrive to install, I'm just wondering if anyone has tried that as with the smaller displacement I thought the ratio spread might be a bit wide.

I did search, but I didn't find this answered.

That's more commonly known as an A833, and it has been done a few times. Try searching for it that way.

There is a thread on www.oldgmctrucks.com on that very conversion. I think that transmission would be overkill on a 228 engine in a 1/2 ton pickup. I would be leaning more towards the T5. If you were planning to put a built 270 or 302 in your truck someday the A833 would be a great choice. Too much transmission isn't really a bad thing, as it will probably outlast the truck, but the t5 will give you 1 more gear to get you rolling.

The MY6 is a great tranny to use behind a straight 6. The MY6 will bolt to the original bell housing AFTER the bell housing is bored to fit the MY6's larger input bearing +OR+ the input bearing housing is turned down to fit the smaller bore of the OEM bell housing.

An A833 is a Mopar transmission made by New Process, just like the MY6. However, be advised the A833 will not directly bolt up to the OEM bell housing without major modification, including making a spacer to go between the tranny and bell housing to accomodate the longer input shaft on the Mopar tranny. I have a Mopar tranny in my basement (thinking it was the same as a MY6 to prove all this).

Your rear end ratio will make a huge difference in this swap. I am running a 261 bored .030 with a stock 261 cam in my half ton 51 Chevy. I am running a Ford 9" rear end with 3.50 gears. This yields about 65-68 mph at 2000 rpm in overdrive. First gear is nice to start out in--you don't have to slip the clutch a lot to get moving. Reverse is bearable also.

Back in 1981, my cousin bought a brand new half ton pickup with a 250 six and this transmission. In overdrive at 60 MPH the engine was turning about 1200 RPM. The rear end ratio must have been 2.40(?). This pickup was virtually unusable as you really had to slip the clutch to avoid killing the engine and overdrive was only practical once you hit about 80 mph. Some years later we changed the rear end to a 3.42 and that made a world of difference.

BTW, the rear slip yoke is the same as a TH350. I ended up shortening the driveshaft from a 1977 LIncoln Mark VI about 2", using a combo u-joint to adapt the slip yoke to the FoMoCO driveshaft.

I've been running this since last June '07 and have had NO problems at all.

Thank you all, I would probably hop the engine up later (I'm thinking a turbo on the 228 would be different) but at first a pair of carbs and split exhaust are probably all it's gonna get.

I was most concerned about having too big of a dead space between gears.

If a +.030 261 is doable with this with a 3.50:1 9" then I should be able to do this with a 228 and say 3:73 or 4.11 for 65 between 2200-2400.

Thanks again.

Sounds to me like you are better off building a 270 or 302. The cost will be about the same, but there is no substitute for displacement. 228s were rated between 85 and 105 HP from the factory. 302s came off the line with 160 HP. I don't have the torque numbers, but when it came to torque the 302s are suppose to be monsters.

Yes, the 302 is famous for breaking everything in the drivetrain of a 1/2 ton. I can come up with either, but I have the parts for a turbo 228, and a 228 so...