The Stovebolt Site Forums The Shop Area Engine Shop '55 and '56 od units

i came across a '55 station wagon and a '56 sedan a few weeks ago that had original od units; t-bar pulls. and looking in my '68 manual, it gives breakdown/repair steps but not operational info. knowing that they had solenoids, i thought that's how they're turned on and off, but when i saw the mechanical lever on the vehicles and in the manual, i'm not following the use of both. my old jeep's saturn od was strictly mechanical. ?

The overdrive unit is a Borg Warner like is used in Ford and Mopar. When you pull the T-handle under the dash, it is locked in direct and locks out the free wheeling. When you push the handle it allows the solenoid to shift into OD. The governor in the rear of the tail shaft only allows the solenoid to shift at speeds above 28 mph. I have had Ford overdrives for 45 years. I prefer to pull the handle when I drive around town and it is like driving a regular transmission except that you have the pep and engine braking effect of 3.89 or 4.11 gears or whatever Chev uses. Also, the free wheeling at speeds of 28 mph is kind of awkward. Once I get to a cruising speed, I push in the handle, let off the gas and it shifts into OD. Ford has a kickdown switch under the gas pedal. I think Chev is in the carb. Mashing the pedal to the floor will cause it to shift back into direct.

The Borg Warner overdrive essentially works the same, regardless of what it is in. The T handle on the dash only operated the lockout for the freewheel. The solenoid is powered up whenever the ignition switch is on. When the handle is pulled out, the freewheeling clutch is locked, and it also slided a blocker that prevents the solenoid from engaging the overdrive gearset. In thsi position, it drives just as a standard 3 speed would.
Pushing the handle in unlocks the freewheeling clutch, which is nothing more than a one way roller clutch. It also shifts the blocker out of the way of the solenoid pawl. At speeds under 28 mph, you have freewheel action when you let off the throttle (no compression braking_ which allows for easy coating off throttle (saving feul) and also allows for clutchless shifting from second to third. Once you get over 28 mph, the governor grounds out, which allows the solenoid to engage. It doesn't drop into overdrive right away, there's a blocker ring that prevents that. You have to let off the throttle, which allows the blocker ring and overdrive componets to properly synchronize together. Once the overdrive pawl has locked in, you have overdrive. You also have compression braking, as the overdrive locks the freewheel clutch when the solenoid is engaged.
Here's the operation description from the '55 Truck manual.

thanks for the link lb - and man that sounds like a complicated operation, but maybe only bec it's being red vs doing it

It's actually not that bad to understand, but it is alot easier to see what's going on when you have the parts in front of you. I have a spare overdrive unit that I picked up for parts, I'm thinking about mocking things up and doing a vid on how the innards operate. Just gotta get the time to make it reasonably operable.
Crenwelge, you are correct about the kickdown on the Chevrolet. It mounts to a bracket on the carb, and is actuated by a tab that is attached to the rod coming from the bellcrank to the carb on 6 cylinder. That switch is somewhat hard to get, and expensive when you do. I find it really isn't necessary to have it. Never have had to get into it that hard with mine, pulls just fine in o/d.

if you need any impetus, a confirmed audience, to do the vid, i'm all eyss and ears

what's so special about the switch? within reason, wouldn't just about any switch that has the options for normally closed/normally open do the trick?

The switch has 4 terminals on it, 2 are normally closed, 2 are normally open. The 2 closed terminals connect the ignition switch power to the relay. The 2 normally closed terminals come into play when the kickdown is used. First, it breaks the connection to the relay, which allows for de-activation of the everdrive, second, it enregizes the pull in windigns, which actually pulls the solenoid pawl out of engagement, third, it interupts the ignition for just an instant to unload the driveline, allowing the solenoid pawl to come out easily.
As I said, I've never had to use it, as my engine pulls hard enough to not need it. Also, if I do need a bit more grunt, I'll downshift to 2nd and keep the o/d engaged, it's more gear than 3rd, but not as much as 2nd without overdrive. I figure it's pretty close to having a 4.10 rear gear. It certainly is a good hillclimbing gear, and is fun for driving on curvy roads.

and actually, 2x2s are also available, but you idea sounds better to me

where might i see the internals of an original switch?

I have used a late model GM cruise control switch for several OD installs, about $10 at Napa. The wiring would be the same as the factory switch. Lower terminals (plunger end): pink to govenor and orange to relay. Upper terminals: green to #6 on solenoid and black to neg side of coil.
Fred

rfs - would ya happen to know the stock number on that switch?

Napa SL199 switch. You will also need 2 ea 1/2 24 NF jamb nuts.
Fred

One of the nice operational features I really enjoy with the Chevy 3 speed overdrive installed in my 1954 3100 is described in the City Traffic Driving Section of the 1955 manual that Longbox55 kindly linked in his reply above. When driving around town and in traffic in overdrive you can take off in second gear and then release the gas peddle (above 28 mph) to shift into second gear overdrive to keep up with traffic. If you come to a stop, just put the clutch in. You can start and stop all you want to without ever touching the shift lever. In the next section, Use of Clutch Pedal, the manual describes how you can shift through all the gears (except reverse) without using the clutch when going under 28 mph. Above 28 mph you can only shift second to third without the clutch, as stated above. Very functional and lots of fun.

rfs - thanks for the #

and man tc43, reading that a second time, it sure does sound convenient. an automatic stick on the lines of the old veedubs