Gm Sm420 Vs Condiesel (gama Goat) Sm420

That fill plug will be fun to use!! Maybe swap cases?
Can I ask what you had to pay?
Thanks
Jay

 

My guess is it will be similar. The d218 offset is the d18 offset and Novak usually tries to clock the transfercase as high as they can.

 

$1100. A good bit more than it would have cost for me to rebuild one, but a good bit less than a complete rebuild unit from Novak.

 

I would not swap cases. Only swap what is needed into the goat.

 

A case swap would negate half of the reason that I bought the NOS ConDiesel trans, which is that I don’t have to rebuild it.

The fill plug might be easier to get to once I hit the reinforcing ribs with an angle grinder. We’ll see how that turns out. Also, any ‘64+ cases should have the same reinforcing ribs, whether they’re from civilian trucks or Goats.

 

If the rib is the same as on mine it’s not bad at all with the fill plug. I have not even shaved mine down.

 

Drill and tap the pto area for a fill plug. Make sure it is level with the fill and clear of the gears.

 

I don't have the tools nor any experience with that, but I could probably learn if need be. However, I did just send the top cover to Novak, and it has a nice flat spot where the reverse light switch would've gone on a '67 case. Perhaps I could ask them to drill and tap that for a vent.

Is the point of a vent just to relive pressure when the fluid gets hot? Or is there a reason to have it level with the fluid level?

 

After some research myself, SM420s vent through the not-well-sealed Shift tower. If you want a proper higher vent, you will need to seal the shift tower with some sort of rubber boot (maybe a Honda CRV rear CV boot, they are really small), and the drill/tap the top cover somewhere to run a line up under the hood.

In the case of my flatfender, the shift tower will be a good 35" above the ground, and almost 12" above the floorboards. I don't plan on fording water deeper than that, so I'm leaving it alone. This does mean I might lose oil through the shift tower if I flop the Jeep. But then I probably would through a vent anyway depending on the routing of the hose.

 

I have a shift boot of sorts from Novak that (AFIK) seals the shift tower. Never thought about the pressure change before now, so I didn't think about a vent.

I'll see if Novak can drill and tap it to the same size as the D18's vent, once I can figure out what size that is.

There might be a way to make a sort of catch can that the vents could run into that could hold the oil if you drop it, but I can't picture how to build one in my tired state. I'll probably figure it out at some point when I wake up in the middle of the night. Of course, is it really worth the effort to build one and the space that it'll take up under the hood?

 

Found someone selling a NOS ConDiesel SM420 on ebay. I believe this is how mine originated. Mine have the same gray/green topcoat, the blue paint underneath that you can see in the scratches, and the same contract number that you can see on the box. The seller who I bought it from told Dad that he had bought them from John Doe, and that John Doe had gotten them originally packed up in foam in crates. Seems this may be how mine started life. I wonder if "-10/84" is a date. If so, these transmissions were manufactured (or at least packaged) quite late.

Here's the link:https://www.ebay.com/itm/173062241576?_skw=gama+goat+transmission&itmmeta=01JF4EPYAW9G7QDHRYQQ04XNCS&hash=item284b503d28:g:7akAAOSwmNxaZ9Ex&itmprp=enc:AQAJAAAA8HoV3kP08IDx+KZ9MfhVJKkIkLAaDfY4gymzqQcCYfY2fp6L6WtsW7D/PJc6YlEMwhs7CDQ1he4HFFIGbbITPi3lbH5Vr3OcT9uJuOR2xQaFmkAgX1MWissEwqXGcm2nfsyCJKwIZsSdzvgmeZGTyHU3UHcXVectgYR81hv/VDLqRUaw51B4/uuqP4qfTh0HNSAAsdDLNW821kuvXaC6Korw2SLJ5i0OOut7ipD+F+VzVsCDcGHUgFhdsZ4Jhl8B6X3KEjhZ9bjpoQ2EeZaRXGI/MSrucHwcDzqOKcpKiqt+QFjxuVIPlocPfB0zTnYPaw==|tkp:Bk9SR8Ll2475ZA

 

You only need about a 1/8" npt vent. Like the front axle. That's all the sm465 got. You can go larger later if needed.

There's nothing to it really. Buy 1/8" NPT drill and tap set. Make a wooden guide with the bit to help square and steady the drill while drilling on the sm420.
Then use a hand drill or two handed tap wrench to tap. Another wooden fixture would help a lot with this. While tapping turn the tap forward a half turn or so and back up just enough to break the chips.

 

On my SM 420 I fill the transmission by removing the shift cane, pull out the fill plug and fill it from the top till it runs out the fill plug. The retainer for the shift cane is just a spring loaded quarter turn cup.

also, the shift cane and retainer is not sealed, so this talk about vents is moot.

 

Yesterday I was contacted by a forum member who wanted to inform me of some of the troubles he faced in swapping in a Gama Goat trans behind a Dauntless. His particular trans seemed to be an earlier Gama Goat trans, and he said it was cast with GM, not ConDiesel IIRC. I may be explaining this poorly, but the problem he faced was that his bearing retainer had a shorter length from the base of the retainer to the end of the tube that the throwout bearing rides on. The overall length of the retainer was the same as a normal bearing retainer. But basically the throwout bearing could not travel as far back on the Gama Goat trans as it could on a normal SM420, and he could not get the clutch to work correctly because of it. He eventually figured out the problem, and had to get the bearing retainer machined down so that the throwout bearing could slide all the way back.


Here is a pic of his bearing retainer, followed by a standard SM420 bearing retainer. Note the shiny part, which is where his was machined down to.


It seems I've gotten lucky and my bearing retainer allows for more throwout bearing travel than a standard SM420. Perhaps it's because I have a very late-production (1983?) transmission, and he has an earlier, GM-produced unit. Here are some measurements of his transmission (post-machining), my ConDiesel, and my donor Early SM420, respectively, for comparison:


(AFAIK the total shaft stickout is the same on all of these transmissions. Note that I measured off of the throwout bearing to account for the bevel on the input bearing retainer)

In the case of my transmission, the throwout bearing can travel farther backward on the ConDiesel than it can on the Early SM420, so mine should work.


He also brought it to my attention that normal SM420 input bearing retainers should not be interchanged with Gama Goat SM420 bearing retainers. The oil hole (the bulge on the input bearing retainer) on the Gama Goat trans is at roughly 6.5 o'clock, while the normal SM420's oil hole is at roughly 7.5 o'clock.

 

Just to follow up on the whole vent thing, I contacted Novak and their little shift tower boot doesn't seal the trans completely, and it can still vent through the tower, so no vents needed.

 

To follow up here I got the whole trans, case, and clutch assembly together and into the Jeep. Everything fit together just fine.

I bolted the ConDiesel trans directly to the bellhousing that came stock behind my Dauntless-powered '66 CJ5, and I used a LUK 01029 clutch kit. I drilled the lower mounting holes out per Novak's instructions, and it all fit together. I used Novak's GM to Sm420 pilot bushing and that worked just fine. On the other end, I used a Novak 422-4-6 SM420 to Dana 18 adapter kit, as I have a large-bore (4") case and a 6-spline input on my Overdrive.

The only thing that was less than great was that I couldn't get one of the Novak-supplied D18 to adapter bolts to work because it was hitting the Novak D18 oil pan I have, so I had to use the stock (slightly shorter) shorter bolt for that hole.