Auxiliary Transmissions / Overdrives

[sret43]

I'm hoping that this thread might bring together a collection of knowledge and experiences concerning older auxiliary transmissions and overdrive units. I haven't got much to bring to the table as I have just purchased my first aux trans for my learning curve.

I have a Watson Model 46 - Serial #Z64732. It's a straight cut gear under/overdrive unit. The overdrive ratio appears to be 50% over.

What are some of the more sought after overdrives out there? Something from the 1960's with helical gears and 23% to 27% overdrives.

Steve

[maineSS]

Does this mount back of the transfer case- it seems to have a shaft brake. It also seems to have PTO openings- interesting, you could have multiple shafts running all directions under your truck!

[sret43]

That is a parking brake drum on the back but I don't have the associated parts for it. This came off of a 1958 Dodge D400 2wd long wheel base. I just bought a Watson 2021 2 spd at .73 overdrive. It also has the PTO covers but is a much smaller unit than the Watson 46. I'll pick up the 2021 this coming weekend and will post pics & more info about it.

There's another Brownie I just missed in an auction near Salem, OR. It's a 2 spd at .73 overdrive and an even smaller unit with no PTO mounting.

I've been messing around with a spread sheet trying to figure out all the ratios formulas. I still can't figure out how to post the information from a spread sheet yet.

[sret43]

Watson 2021

Well, I spent 11 hours on the road Friday night riding my Beemer and traveled 646 miles to pick up this Watson 2021. It only weighs in at 80 lbs. and seems to be in real nice condition. It's a 1:1 and 0.73:1 and can be reversed mounted to be either OD or UD. I'm wondering if I'll be able to gut the thing and reverse install the gears so the housing will clear my muffler.

[sret43]

Watson 2021

This is a cable operated unit and Napa carries several replacement parts for this overdrive. The gears seem to be in great shape. We'll see how the bearing surfaces look in a couple of weeks.

[maineSS]

What kind of input torque are they rated for? The downfall of the Denman seems to be instant wipeout if you forget and shift into low range or reverse. Also, how much would you have to shorten up the driveshaft? Hopefully you wouldn'f steepen up the angle to the point where universals w9ould start breaking.

[sret43]

Watson 2021 Torq

I haven't found any specs on the 2021 or the 46. My brother-in-law says he has a few old shop manuals for various overdrives so I'll just wait and see what he's got. Judging by the beefyness of the 2021 I'd say that my 354 hemi ain't gonna break it.
I haven't looked at a Denman, yet. Got any pics of one?

[sret43]

I've looked everywhere and about the only Denman overdrive I could find would be round, made of rubber and with a large circumference. :)

[maineSS]

I've never seen one. They're a British Laycock unit, modified by Dennis Gronan in New Jersey. Don't know what they were originally used on, but sound somewhat too light for PW duty.

[Tom Petroff]

Here's mine. behind a stock 230.
I'm very pleased with it.
If needed I can change it back to a stock driveshaft in under 20min.

Know of one friend has one behind a 318 powered FFPW.
Good friend in TX has one,another in Maryland.
There stronger than you think. Have all worked them hard with no problems.
Gear vendors copied the Laycock unit.
Notice the comparison.
TGP

[sret43]

What a great looking unit. When you say GV copied this, does the Denman do the coast downhill like the GV? What is the OD ratio? I can't quite see how you mounted it but that sure is a clean install. Thanks!

Oops, just spotted the front bracket.

[sret43]

Tom, after searching through the web, I was wondering what model type your overdrive might be. From what I've learned so far these Laycock ODs can be very bullet proof.

[Chewie]

I don't know about older auxilaries, but here's a link to Spicer 3 and 4 speeds. Handwritten lengths and torque specs, too.

http://webpages.charter.net/jlbarnes...f/auxboxes.bmp

The link came from TheDieselStop forum.
Chewie

[maineSS]

It would be interesting to see what the Laycock can handle for input torque.
The 230 has a gross max torque around 180 lb-ft, 1st gear is about 6:1, reverse is about 7:1. Since the unit is behind the t-case, it would be looking at 1080 lb-ft in 1st, or 1260 lb-ft in reverse at the 1:1 t-case ratio, or 2117 lb-ft/2470 lb-ft at the 1:1.96 ratio. If you forgot to shift out of OD when you parked, and started up in low/reverse, it will see some heavy-duty torque figures, and the vehicle weight won't cut you any slack.

[Chewie]

Found another link.

http://www.ford-trucks.com/forums/58...ie-thread.html

I know, I know, it's a ford link. But there are 130+ posts about auxiliary trannies. Lots of info.
I've had a 5831 on my wish list for a few years...
Chewie