The Stovebolt Site Forums The Parking Lot Big Bolts Aux Trans anyone recognized this??? ID-ed Aux Trans

I just picked up an auxiliary trans today...now I need to identify it.

It bolts directly to a SM420 transmission.

Trying to add pictures to post.

http://s1253.photobucket.com/user/GMCPic/library/Gear%20Box?sort=3&page=1

Oh yeah it was free, a friend is cleaning out his garage and asked if I wanted it.

I had hoped it would bolt up to one of my Clark 5 speeds, but no luck there. It bolts to an SM420, I checked. Bolt pattern matches the rear bearing retainer of the SM420.

Serial/ID plate is gone.

Case casting number is 5057-2

I am thinking that it is something somebody maid from the rang box section of a transfer case.
Have you been able to determine how many gears it has?
Or how it shifts?

Yes, it is a 3 speed aux w/Direct-drive, Over-drive, Neutral and Under-drive.

This is a factory unit from GM, all the casting have GM part numbers.

If you look at the photos enlarge #5 and look at the shift pivot point and the 2 rods below it. The 2 rods are the shifting mechanism for the gear box. The inner rods has 3 positions, IN, center & OUT. The outer rod has 2 positions, IN and OUT...OUT matching the center position of the inner rod.

There are in the neutral position now.

Definitely a cool piece I would love to find something like it in a three speed overdrive. That would turn an SM 420 into a 12 speed overdrive.

A 3 speed over must be a real auxiliary transmission I have never seen anything like it that is really cool

I have a 48 GMC 1Ton with a SM420 in it. May be I will put it in the 1ton. I had been thinking of putting in a Clark 5 speed, but this may work better.

More realistic is 9 speeds forward, not counting low gear.

I'm not familiar with it either.
Try your question here as well, someone there may recognize it.
http://www.4btswaps.com/forum/forumdisplay.php?22-Transmission-Adapter-Transfercase-Discussion

Isn't that thing cool Grigg???
GMCpic you have found something really cool I am really curious to find out more about it definitely keep us informed as to what you find out.

Pardon for the dumb question, but if you are not sure what model it is, how do you know it is an overdrive unit? I have a spicer 4 spd aux and they made a few different versions so I had to make sure my model was an OD because they offered straight drive and underdrives for them. It would have no use to me if it was not OD.

Just asking as I have never seen one like you have here.

Was this to go in a torque tube app or is that a slip yoke setup on the rear?

It has 3 positions for the shift rods, plus neutral.

I shifted each possible position and rotated the input shaft and walla under, direct and over.

I checked it out before making the statement about it being an 3 speed under, direct and over auxiliary trans.

Plus I verified that it does bolt directly to the rear of an SM420.

It is for an open drive-line setup and seeing as how it does not have the ability for a drive-line E-brake.
My thinking is that it may be for 3/4T or 1T open drive line, with cable E-brakes at the rear wheels.

It looks like a regular 'Brownie' that some clever person mated to a 420, probably also fit a 465.

All the castings have GM part numbers. I am told it will only bolt up to a SM420 because it replaces the rear bearing retainer on the SM420.

Added another pic:
http://s1253.photobucket.com/user/GMCPic/media/Gear%20Box/14081_58_1.jpg.html?filters[user]=127999858&filters[recent]=1&sort=1&o=0

It was probably only used by Chevrolet, I was informed that all the Advanced Design Chevy s (larger than a pickup)came standard with SM420, that a 5 speed was only a later option.

It only weights 95 pounds...not 200.

It would be interesting to see what the input shaft looks like, as well as the adapter plate. If the shaft is not welded, perhaps somewon would like to copy it. If you ever have it apart, it would be nice to see.

Very interesting, still not something I've ever seen or heard of.

Grigg

Still wanting to know more

Well today I did a little more inspection of the Auxiliary Trans.

The casting on the front of the aux. trans is the same as the casting for an enclosed drive-line. I did comparison an test fit the splines.

All you have to do is have an old SM420 enclosed drive-line laying around (which I do). Use the rear trunnion (U-joint assembly)from an enclosed drive-line. And have two rear yokes from an open drive-line. One for the front input shaft of the aux. and one for the rear output shaft. Which I have.

Oops, almost forgot move the Speed-o cable drive to the rear of Aux Box.

Remove the ball joint housing from the enclosed SM420 or the bearing retainer from an open drive-line SM420. Replace with the front casting off the Aux. Trans. Connect the Rear trunnion back on the SM420 output shaft with a bolt and washer, then using a standard U-joint connect one of the Yokes and the trunnion together. The yoke floats free on the input shaft of the Aux. Trans. With new gaskets reassemble the SM420 and the Aux. Trans.

Install as one complete unit assembly as shown in the last picture I loaded.

Oh yeah the rear of the Aux. Trans needs a bearing or drive-line hanger. This thing has to be well supported. even through it only weights 95 pounds. The casting are not that strong to support the weight.

I was going to put a Clark 5 speed in my 1Ton. It has the long wheels base with a 12 foot factory flat bed and 18 inch dual rear wheels. But I would still only have direct drive in high gear.

Now by adding the Aux. Trans instead I will have an overdrive for puttering down the road. Now to figure out exactly what the actual Gear rations are, but no hurry there.

I only wish I knew who made the thing, I am hoping someone out there with a lot old Chevy truck service manuals runs across this thing.

All is well in Paradise.

All Hail Klaatu and Gort

The input/output shafts are the same as the output shaft on an SM420.

Wouldn't need to use a U-joint as a coupler, would be handier, though, if both splines were the same, Mark Williams can broach items like that. If not use a U-joint, then not need to use closed driveline rear bearing retainer, just couple front and rear retainers of some kind.

When mounting the rear of it it should be in rubber or on a leaf spring such that the mount shares the weight but doesn't restrict the movement much. The engine is mounted in front and side mounts on the bellhousing, those are your primary mounts. If the back of the trans is mounted too solidly you'll break stuff as the frame flexes and or have vibration issues.

Curious what the factory mounting solution is if you can find a parts diagrams or pictures of an original one?

Also, I agree that a u-joint is not the ideal coupler because in this case it wouldn't have any angle to operate through, it'd be straight. A U-joint with no movement soon wears flat spots on the needles and corresponding groves on the trunnions. I suppose if it's a bushing type u-joint (no needle bearings) there is more leeway, still though that's not as good a junction in this case as a straight splined coupling would be.

Grigg

Seems I miss spoke here. The input shaft is the same diameter and spline count, but GM used a tapered 10 spline while the gear box are straight spline. The output shaft is 1 1/2" 10 spline.

But I do have some good news for those ho have been following this thread.

The Aux Gear Box is. . . hold you breath now.

Is a Watson from H.S. Watson Co. of San Francisco CA., but it was manufactures by...TA DA drum roll please Brown-Lipe of Toledo Ohio for H.S. Watson.

New pix have been added to my collection.

http://s1253.photobucket.com/user/GMCPic/media/Gear%20Box/WatsonGMCrecommend.jpg.html?sort=3&o=0

All hail Klaatu and Gort

It is a Watson...from H.S. Watson Co. of San Francisco CA. But it was manufactured by Brown-Lipe for Watson.

Input shaft is 1 3/8" 10 spline by 2 1/2 " long.

Now I know what it is...and my local drive-line shop can and will help with the U-Joints and splines needed. I am going to install this "Watson" 3 Speed Auxiliary Transmission in my 1948 GMC FC-253 1T. In stead of using one of my Clark 5 speeds. The 1TON has a 1956 GMC 248 CID in it.

I took the ends and side cover off today to check out the inside, It was so clean I was going to eat my lunch on it.

I had the drive-line specialty shop check it out with me. So next week we get started with getting the splines..I had the U-joints. Also, will fabricate a rear mount (rubber) for it.

I will take pix tomorrow.

I will have to change seats from the standard bench seat to a pair of single seats, because of the new location for the shift lever being slightly off center, to the left and rear of the SM420 shifter.

As far I can tell it is a Watson 30 series, which preceded the 40 series. Which was used on lighter trucks like 1ton and 1-1/2ton. I found a Watson Model 31 it was a 2 speed which could be mounted in either orientation for Direct and Over, or Direct and Under.

Also found a Watson 39-M1 which is a 3 speed like mine, but does not mount directly to the trans, but rather just behind like most other aux boxes.

Hopefully the ATHS (AMERICAN TRUCK HISTORICAL SOCIETY) [http://www.aths.org/] will be of more help...apparently they have a Master parts manual for Watson Aux Gear Boxes.

Watson Aux Gear Boxe where used by all the light and medium duty truck manufacturers, i.e. Chevy, GMC, Ford, IH, Dodge, Reo...etc. etc. mostly pre-1960, but not all.

The one I have is perfect for splitting gears on either the SM420, SM465 and the Clark 205V & 207V, it works in true progressive fashion mounted behind the main box. I was just lucky enough to find one that is married directly to the main box, my SM420.

I will add another picture later tonight.

All Hail Klaatu & Gort

Lucky is hardly the word for it man you're golden!!!!
I would love to had made a find like that. So if it is truely progressive it should give you 12 gears forward and 3 in reverse That is just too cool.

Not at all surprised it turned out to be a Watson.
I am surprised they made a directly mounted auxiliary, that's something I hadn't seen from them.

Nice find,

Grigg

As far as I know Watson was the only manufacturer of this small of an auxiliary, but I wasn't aware that they made one to be married to a SM420. As wide as the splits are on a SM420, there is a good chance that it will be progressive. But I can't imagine what you would do with 12 speeds behind a GMC.

Ok Guys here are a couple of more pix.

http://s1253.photobucket.com/user/GMCPic/media/Gear%20Box/tson39-M003.jpg.html

http://s1253.photobucket.com/user/GMCPic/media/Gear%20Box/tson39-M009.jpg.html

So far as far as I can tell the ratios are: 1:49, 1:1 & .75.

Going to put it in My FC253.

Man that is a cool setup it would be super cool if you could build a set of actuators and mounts to air shift it from the main boxes shifter knob.

Lets not get to far this is going into a 1Ton, not a semi;)

All Hail Klaatu & Gort

Grigg why did you not suggest a Watson, would have made my life a whole lot simpler...;)

I didn't suggest a Watson because you were so sure it was a GM unit with casting numbers and all.
And I'd not seen a direct mounted auxiliary like it of any sort that old. Spicer did later have some very direct mounted ones making what they called a "compound" transmission.

Grigg

The air shifter idea or even a cable shifter would solve the problem of having to modify the seat because of the second shifter location.

Are you sure you can't use a lever and just bend it to suit so it misses the seat?

Air shift is not worth it, more complexity than necessary and you loose the feel of the shift. The trans is not synchronized so feeling the shifter as it slips in gear (or grinds) is a helpful. There were air shifted auxiliary's and even air shifted main transmissions but that aspect of them is nothing special.

If bending a lever won't work perhaps borrowing a shifter and linkage from a Chevy COE would work. I've searched for some pictures with no luck.

Grigg

I don't think Watson made it, I think some handy gentleman made it in his shop. Too bad it is not sturdy enough for a 6BT. Fine for a 6 cyl. gasser, though.

Just to add my $.02.I have a Watson in my "53 wrecker that is a three range divorced style, all under drive.In my area it was a common installation for farm trucks to give them slow speed but a lot of low end power.With the 4 speed,the Watson and a two speed rear I have 24 forward and six reverse.It fits nicely with the original seat.

Hi Grigg,

I did some measurements today, Grigg you are right, the Aux Box will fit with a little effort. I do not have to move or replace the seat. The lever pops-up just in front of the seat frame.and is bent forward

The local Drive-line specialty shop is making-up a new front drive-shaft and a new U-Joint to go between the SM420 and the Watson Series 30.

But I am having trouble finding a shift level. The GM's I have found so far, are too large. The lever I need has a ball swivel which is only 1-3/8" diameter.

Did you see this info previously, and here's some references to check and explain. http://www.stovebolt.com/techtips/driveline/setup/index.html

The shifter bracket looks much like some of the later Spicer auxiliary shifters, they may have that smaller ball size.
You could machine or have made what you need to fit if you can't find an old one.

Was vaguely aware of the possible U-Joint problem.

AS yet no final decision has been made about whether or not to use a enclosed drive-line u-joint/trunnion or a straight spline coupler.

Will not be using a U-joint with needle bearings in any case that was the first thing out the door.

Found spline couplings a W.W. Granger 1-3/8" 10 spline by 3 inches long $89.00 ugh.

The spline on the output shaft of the SM420 is also 1-3/8" 10 spline...but the splines are not cut square, the sides of the splines are at an angle.

Also if we do not use a enclosed drive-line yoke the the coupling will be floating...no way to bolt it on to output shaft of the SM420 to stop it from floating. Sure wish I could find an old GM manual. that covered these things.

All your info is of great help...please keep it coming.

Also I actually took out my measuring tape today and measured the location of the Aux Box shift lever in relation too the Main Box shift lever. Exactly (almost) 12 inches to the rear and to the left 6 inches. The hole for the shifter will be in the trans floor plate...just need my trusty hole saw.