The Stovebolt Site Forums The Shop Area Engine Shop Back up light thingy

Over the weekend I found my brackets for back-up lights on the SM420 in my 48 3100. I need to push down on the cover at the top of the shifter rod and turn it to replace it. Is there a trick to that? Do I need to take the cover off the transmission to remove this plate?

Thanks.

Push down, turn about 1/8 turn counter-clockwise, it should pop up. If it's really crusty, soak it good with a penetrating oil like PB blaster or WD-40.

Thank you very much.

how does the back-up light switch mount? you wrote that you found brackets and that you need to get the shifter out. I have not seen that before (for a SM420). How does it work? Thanks

Yeah Dennis, how does that work???? I've never seen a backup light accessory for an AD truck with an SM420 trans. From you post it sounds like there is something inside the transmission??? Pictures please.

Denny Graham
Sandwich, IL

IIRC, there's a bracket that mounts to the shift lever with a push-to-contact switch on it, or a switch on the shifter housing and an operating lever that's attached to the stick. Pretty primitive, but it works. They were a very scarce option.
Jerry

Jerry hit it. The bracket I spoke of replaces the cap at where the shifter rod goes into the top of the transmission. It has a tab where the push-button contact mounts. Then there is a paddle bracket that mounts to the shifter rod. When the transmission is shifted into reverse the paddle bracket pushes down the contact and the back up lights come on. Simple contraption.

I bought the whole system years ago and put the column set-up on my 55 TF. I will put this system on my 48 with the floor shift (SM420).

It is pretty neat. Now I need to find 2 back-up lights from the early 50s car.

Pardon my dumb but I still can't picture what your discribing, sure appreciate a photo.
DG

Yes, it would be interesting to see a photo of an original SM420 backup switch?

Novak Transmissions website: "The last year of the SM420 (1967 [maybe 66 & 67]) had a backup light switch installed in the top cover to meet that year's federal mandates." Novak installs a switch on their transmission rebuilds but it does not look like they sell a kit for others to install. Maybe they install a conversion as described below.

Old Stovebolt.com thread on adding a back-up lights switch.

Here's another conversion.

heres a pic of the SM420 backup light assembly

http://carphotos.cardomain.com/ride_images/2/2877/4121/19692060221_large.jpg

Maybe a dumb question, but what's an SM420 transmission? Might that be the four speed that is in my '39 3/4 ton?

Gary

SM420 is the 4-speed GM started putting in trucks in 1948 and used through 1967. It might be the one in your '39 but only if someone has performed a swap.

OldSub

OK. I think mine is the original '39 transmission. Putting in the backup light switch is still an interesting project, and may well work on the old box, too.

Thanks,

Gary Fossen

Just dug up this old thread...and have a question about the switch needed for this set-up. I have the bracket, and depressor paddle piece, but lack the actual switch. Does anyone know of a replacement switch that will work? I have found NOS ones, but they are too rich for my blood ($100.00) I'm sure there is an aftermarket switch out there that would work, but not sure where to find one. To make matters worse, I don't have the original one to use as a comparison. Has anyone encountered this problem, and can you hook me up with the part #???? Thanks!

A push-to-start button should work, if you can figure a way to mount it to the shift lever. Any good FLAPS should have a listing for a generic starter switch, or one of the aftermarket suppliers like Cole-Hersee will definitely list one. Try a boat shop or a marina if necessary for a push-button horn switch- - - -same thing.
Jerry

A push start button is a good idea, but I'm not sure it would have the correct amount of reach?? It is something to consider however, and I will look into it.

I'm still here, but a long way from the backup switch. I'm in the process of painting the cab, and that seems to be a rather steep learning curve...considering it's my first. Just the same, thanks for the responses.

Gary

Something just occurred to me...I think there are spring loaded toggles available, too. The longer paddle would make them somewhat adjustable for length of throw...