The Stovebolt Site Forums The Shop Area Engine Shop sm420 with overdrive on back?

I see the Ranger overdrive goes on the front of the sm420 tranny, but it would require moving the sm420 back to the seat or there abouts. I have a chev car overdrive. Does anyone make an adapter to attach the car overdrive to the back of my sm 420? Or, can someone tell me how to make it myself. I have access to a guy in a machine shop. Also, which overdrive is best? Thanks - Scott

You should just get a 5 speed.

check around in the forums...i think this topic has been discussed before. and i'm pretty sure someone has made this work, the OD tailshaft to a 420/465 4 speed. just a few minor mod's i beleive.

Not much luck with my search Rhinelander.

still looking

The OD tailshaft mod (car overdrive) works on a later Saginaw 4 speed (the sideloader with external shift levers), but not on a SM420. If you already have a Chevy car overdrive, your options would be:
1.) Use the 3 speed chevy car overdrive
2.) Get a Saginaw 4 speed and adapt it to fit the car overdrive (just needs a hole drilled).
3.) Sell the car overdrive and buy a differant rearend gear and use the SM420.
4.) Sell both the overdrive and the SM420 and install a 5 speed tranny.

How do you adapt the overdrive piece to a sm420 tho. Is it a custom plate in between with a yoke adapter? What machining is needed? Thanks - Scott

Scott, you can't put the saginaw 3 speed overdrive tail on the muncie 420, sorry.

If you want to keep the granny low 4 speed. You can spend a bunch of money on a gear vendors OD for the tail ($2500+). You can put a ranger in front and then bend a custom shift rod ($1500). you can buy the advance adapters dodge NV4500 to chevy adapter kit and have an input bearing custom machined ($ depends on how cheap you can get the tranny).

I think I'm going with a ranger. If you decide that's the way you want to go let me know, I may have a pricing break.

Chris

Or you can find a watson or spicer 5831b overdrive and put it behind the sm420. The watson is a very small overdrive - only 11.5 inches long. I am about to put one on my 59 when I get a few other projects out of the way.

What about a Columbia OD? Will that work? GMCustom - I am a big fan of keeping the 4spd as opposed to getting a 5 spd. The granny is awesome for Seattle hills and pulling the boat out of the water. You can cruise around town in 3rd gear from near stop to 35 and never have to shift gears. It's even more fun to let the fentons sing between 30 - 40 yeee haaa! The drawback is a loud truck on the freeway if you want to go faster than 62. That's why I'm interested in this conversation. I know that Columbia overdrives work well on early F#*@s, but how about our Chevys?

Bumping this conversation...

If I'd like to leave the 4 speed...and add overdrive what are the options. Just thinking about this now as my ears were ringing after a 25 minute highway drive.

(Yes, I know I need that tar paper stuff in cab, and I have a 5.17 rear which is probabaly not made for 60pmh, and I have the bais plys on split rims...so maybe this isn't the answer, but was just wondering.)

I still haven't completed this yet, but we kept the sm420 and we bought a few used parts to do this, but we don't seem to get to it. Come out of the back of the sm420 with a shorty transfer case drive shaft. Go into the overdrive part off an old overdrive transmission. It needs a 6 spline yoke like on tractor stuff to do it. Fleet Farm has some of the stuff. The overdrive tranny half needs a plate on the front to keep the lube in and the plate needs to have a bearing hole in it. That's the plan, but as I said, we haven't done it yet. We have the parts, but the short drive shaft between the sm420 and the od tranny half needs to do a yoke switch because they are designed so that people can't just hook up cars stuff to tractor stuff. I don't know why tho. - Scott

I commend you for being creative, but I'll give you a little warning about that overdive unit if yoy hook it up this way. Whatever you do, make absolutly certain to lock out the overdrive befroe you try to use reverse. If you try to reverse with the od freewheel clutch engaaged, you'll destroy the unit. On the original trans, there's a lockout pin that prevents this by disengaging the od when the trans is in reverse.
When you get it together, post some pix. The project sounds intersting.
You also mentioned the Columbia in an earlier post. I didn't see a responce, so I'll tell you what I know about it. The Columbia, or at least the ones I've seen, install in the rear diff, not the trans. I seem to recall that it actually replaces one of the axle bell on the ford housing. It works somewhat like the planetary 2 speed axles on big truck, just with an overdrive ratio instead of a low gear. If I can find more, I'll post it.

Longbox, Thanks for the reverse tip, It could save me. Advise to Sab... Get the tallest tires you can find. Mine gave me a 13% speed increase at the same rpm. It is more than some of the rear end upgrades will do, but I like looking down on some of the newer trucks anyway!

Since this post began, I installed a Gear Vendors O.D. to the back of my SM420. I can now travel 80 mph in 4th over at the same rpm as 60 in 4th. The split between 3rd and 4th is pretty cool as well. Just what that tranny needed. Anyway, I'm tickled pink about it. I'm also broke. I did the O.D. first, drove it a while, and then switched to radials. That also made a HUGE difference in how the truck rides and handles. Then a little dynomat in the cab, new shocks and now my truck rides like a modern truck on the freeway.
I also found out since then that a Columbia O.D. is basically a 2 speed rear for the old Fords. My neighbor is rebuilding 2 right now.

Hey bigmacdaddy, what happens on hills? Can you still get it up? The hills, that is.