The Stovebolt Site Forums The Parking Lot Big Bolts Auxillary Transmission 48 Chevy

I was looking at a 48 2ton chevy with a 4 speed and a 3 speed twin stick auxillary tranny. I can pick the whole rig up fairly inexpensive. I don't know anything about the auxillary transmissions. Would it provide overdrive? Can my 46 COE with a newer 235 push an overdrive tranny. I don't really plan on hauling much weight. It would be great if I could get another 10 mph out of it.

Most 3-speed auxiliary transmissions provide under/direct/over gear ratios, which effectively turns your 4-speed into a 12-speed. There might be a data plate on the Brownie that shows the ratios. If the manufacturer's name and a model number are present, someone here can probably research the ratios. Your 235 can probably pull an OD gear unless the truck is loaded heavily or the OD ratio is too high to stay in the torque band of the engine. I'm about to install a Brownie in my 61 GMC fire truck with a 351 V-6 and a Clark 5-speed with direct drive in 5th. gear. The fire bed is coming off, and I'm going to install the Brownie where the fire pump used to be in the driveline. I'll have 15 forward speeds, and OD in 5th. gear. I'll also install a commercial 5th. wheel and a gooseneck trailer hitch.
Jerry

I went and looked at the truck, 48 chevy 1.5t. It has a Watson Aux tranmission model 42m. Can anyone tell me if this is an overdrive model. Im guessing I could get the whole truck for $400-$500. Cab is shot, engine is shot, tires are OK. the only thing I am after is aux tranny, I'd scrap the rest. Does have the deluxe stainless door window trim. What are the Watson OD units worth?

Not all aux transmissions had OD...many were Low-Low, Low and Direct. It's what the low HP trucks had back then to move BIG loads...lots of LOW gears!

Mike B

Seems like most Watsons of the era have an OD, mine is 0.85. Model 43. I don't know about model 42m.

Easy way to figure out before purchase, mark input and output shaft to the Watson and jackup a rear wheel. Main trans in neutral. Turn the wheel and count the difference in shaft speeds. A single rotation of the input will get you a good idea of ratio difference, for more accuracy do multiple rotations and a little fractional math between input and output rotations.

Good luck

A Watson Model 42 should have gear ratios:
1.49:1
1:1
0.83:1

The only 40 series Watsons listed with no overdrive are model 47 and 48.
(models 41-46 are OD with either .75 or .83)

Grigg

The literature shows a model 43 as being 0.83:1 OD

Wrenchfetcher... Do a forum search for Watson and you will find some recent posts I did with regard to the Watson. I have one in my 49 1.5 ton and it is a Model 43. It has under/direct/overdrive. You can find the designation on the right side case if you crawl under and clean off the gunk. These were a pretty common aftermarket install, often by Chevy dealers.

Grigg is right on the ratios for the Model 42. Looks Like that info I sent you has already come in handy, Grigg. :>)

Quite handy!
Thanks again,
Grigg

Well I went and did it, I drug the 48 chevy home just to get the aux transmission. It is a 5 window and has the stainless around the windows. What model of heater do I have? I'm going to pull the aux tranny and get rid of the rest. I'm going to make a post in the for sale section if you guys are after anything.

http://rides.webshots.com/album/582276439CeEbdn

Now who is going to post directions on how to shift this set up? Like running your left arm thru the steering wheel,,,,,,

Luckly the 46 GMC COE's have bucket seats. I think it would be next to impossible in a Chevy. The GMC tranny shifter comes up between the two seats and bends forward, the aux shifter will be just to the left of that. The starter lever which you push with your hand is currently to the left of the tranny shifter will have to be moved to the right of the tranny shifter. I mocked it up this morning and think it will work just fine. I'll probably have to put a bend or two in a couple of the levers.

When it is all done I will have 4 levers (tranny, aux, starter and dump bed) and 24 gears. I like levers and gears.