The Stovebolt Site Forums The Shop Area Driveline 1959 LCF powermatic six speed trans

I was online reading about a 1959 chevrolet Viking LCF truck.
Sources said an optional package with a 283 was a six speed
Powermatic transmission (not powerglide) with a 3.73 or 3.55
rear end. I have never heard of this before. I bought a chevy
manual for Powermatics. So that will take 42 weeks to get
here.
Has anyone heard of this, and can you tell me anything more
about either the transmission, or the package with a 3.73 rear?
On a huge Viking LCF truck??? I just had no idea that the beast
existed. Thanks for any details. Mike.

Mike - You can dive into details on the 1959 Chevrolet Viking LCF and optional equipment here in the 1959 Chevrolet Truck Data PDF from the GM Heritage Center.

Here's another resource, 1959 Chevrolet Truck Engineering Features to add to that info above.

Happy reading. Let us know if there's more you'd like to know.

Mike - After a little more digging through resources, it looks like the initial offering of a V-8 (265) and 6 speed Powermatic transmission package was in the 1956 Chevy LCF line HERE.

As '56 was the first year offered, the 1956 Chevrolet Truck Engineering Features pamphlet has a detailed section with most anything you may want to know about the "Powermatic". By '59, the information wasn't included in that year's pamphlet as it was considered "old news".

I couldn't find anything that indicated '59 LCF's (5000-9000 Series Trucks) were equipped with 3.73 or 3.55 rear axle ratio's. The axle ratios for both standard/optional single speed and 2 speed rear ends are specified in the previoulsy linked 1959 Chevrolet truck Data PDF.

So the "beast" with a V-8 and 6 speed Powermatic's exist, just not with either of the axle ratios you mentions.

Thank you Gdads51! Just what I was looking for, and a lot more.
The gear ratios include 3.31, 3.55, and 3.70; so close to what the
online comments were suggesting. Close enough for me anyway.
I assume 3.31 would use lower RPMs at highway speeds, and a
3.70 would yield better acceleration, with 3.55 being an in
between compromise. I'm wondering if all of this implies a one
speed rear end instead of a two speed rear end with a power
matic transmission? For a driver, not a heavy hauler, what gear
ratio would anyone choose? Thoughts? Now, where would a
person find a powermatic? They were made at least from 1956
through 1960. Thanks again!

If the specs show only one gear ratio per option, it is a single speed rear differential. If you are looking at a truck to purchase and it has a Chevrolet V8, it will bolt up to any Chevrolet spec'd automatic tranny, power glide, turbo 350, turbo 400, 700R4, 4L60, 4L80, and more.

Mike - I'm not sure what "sources" you're referring to, but the LCFs are "Big Bolt" trucks (1-1/2 ton and up) and those gear ratios you just mentioned were not available for the big trucks. In fact for 1959 the only ratios listed being offered for the 1/2 ton trucks is a standard 3.90, and optional 3.70, 3.38 and 3.92 Posi-track gear sets. None of the 3 ratios you list were available in Chevy LCF trucks for 1959, with or without the optional Powermatic as that transmission was only available for the "Big Bolts".

As far as your understanding of the affects of each of those ratios for engine rpm and acceleration, your not wrong. There's just no connection between those ratios, that were all single speed axles in pickup/panels/Suburbans and the Powermatics and "Big Bolt" single or 2-speed axles.

With all that being said, I'm going to move this thread to the Driveline forum as that's the best place to continue discussing transmissions and rear axles.

The Powermatic transmission is actually an Allison 6-speed automatic with a retarder pedal located where the clutch pedal would normally be (looks like a gas pedal), this allows the transmission to be use for down hill speed reduction saving wear on the brakes.

There were changes/improvements made over the years from it's introduction in 1956, for example in 1958 they added a second Drive range and changed the look of the shift tower.

The different applications are identified by the color of the Allison Data Plate (like red, green, yellow) that were riveted on the side of the trans case.

Mike B

It was offered in 1957, and the truck shop manuals from then on had the overhaul info in them, up until it was not an option anymore.

The Powermatic (Allison) 6-speed automatic was first offered in a Chevrolet truck starting in 1956...It's also in the 1956 Supplement Shop Manual.

Mike B