Technical LET'S TALK OVERDRIVES

If you leave your car in gear when you park, be sure to DISENGAUGE the OD or it will roll away! You can guess how I know.

 

Just a little story about the BW T85. This is what I used in the El Caballo, and it worked better than great. I tortured that bugger.
Now for the story. Way back in the late 50's early 60's, I had a friend who built Y-Block Fords. He had a 292 in a '56 Ranchwagon which was waaayy overbuilt. He O-ringded the heads/block and ran 13:1 compression. I don't recall the cam, but he ran a mag, and a homebuilt highrise with 2-4-bbls. The runners on the manifold were about 12 " tall, and so much of it stuck out the hood.
Now for the best part..... The T85 case is virtually identical to the T10 case. Sooo, my pal used the entire gear set from a T10 in his T85. He eliminated the O/D, but it also eliminated the reverse gear. The first time he ran it, he was protested. You can't run a 4-speed in a his class unless it came that way. Whooaaa, back the truck up, so to speak. The rules said you must run the original case with at least 3 forward speeds. Nothing about a 4th gear and nothing about reverse.....
Sometimes you just gotta be creative......

 

They will do it for a while, but in the long run…if you run your overdrive transmission in low gear….much…..you will be replacing parts wit a transmission that was not driven in low gear! Just the facts….like them or lump them….it is still the facts!





Bones

 

It's easy to find a replacement switch IF you're not going after oe application or position. You could use a momentary contact switch with a relay if you can't find a dual contact switch. But with the option to engage at will (w/o the governor) I didn't need the kick down function.....I wasn't passing anybody with the old 230. The only reason I use the kick down now is to get on the freeway when the o/d is already on, to pull hills I just downshift into o/d second gear.

 

BTW both panel trucks had 4.11 rears. The '64 had 235/75 r15 (28.9") and the '56 has 215/85 lt16 (30.4), the '56 does around 70mph at 2000 rpm in o/d and if I remember correctly the '64 was like 65 mph at 2000 rpm. 2000 rpm was the sweet spot for both 6s for mpg.

 

I've had 3spd overdrives in various cars since 1971.
The first few were wired with all the factory features, governor, passing kickdown, lockout cable, etc.
Eventually I just decided to control it myself.
The pull cable to lock out the o.d., and a dash switch to kick the o.d. solenoid in and out were the only controls I wanted.
Of course I had to remember to turn off the solenoid, and remember to pull the cable to let me use reverse, but that wasn't a big deal any more than rememberng to push in the clutch at a stop sign...

ALSO- DITTO what Boneyard said-
if you start using the o.d. in the lower gears, not just in high only, the multiplied torque of the lower gears will wipe out your o.d. rather quickly. Even the tough T 85s will give up their planetary gears when you really pour on the coal...

 

Is there an adapter to adapt a gm od to flat head engine?

 

There's a fair amount of misconception here about how the OD works.... They really do work best if installed as designed.

First, engine braking. You have engine braking ONLY when the OD is disengaged AND LOCKED OUT MANUALLY WITH THE CABLE. If the cable is pushed in, it'll freewheel in all forward gears, it won't matter if OD is engaged or not. The caution about the car rolling away when parking is very real. There is an internal manual interlock that shifts the trans out of OD when placed in reverse, if using the trans as the parking brake do this or pull out the OD cable to lock out the OD. If you have an OD conversion of some sort (R10 or R11 added to a four speed for example) that interlock may not be present. Some guys will claim there's a 'small amount' of engine braking in OD, but that's just 'stiction' from the gear lube. If you're going down a multi-mile long grade, it's a good idea to lock the OD out or you'll be performing an unintended brake test with possibly bad results. AMHIK...

The OD cable DOES NOT engage the OD. Pulled out, the OD is locked out. Pushed in, it is enabled but the electrical controls/solenoid do the actual shifting of the OD in and out. You can push the cable in enabling the OD at any time, but you can only pull it out disabling the OD under specific conditions. You can pull it out anytime you're fully stopped. If moving, it's a bit trickier. First, the trans needs to drop out of OD. This can be because the governor opens when speed drops low enough (generally around 23 MPH give or take) and your coasting, unloading the OD. Once it shifts out of OD (and you'll usually 'feel' this), apply power to load the trans. This will 'lock' the overrunning clutch, you can now pull the cable out. DO NOT pull the cable out while coasting, this is the equivalent of putting an automatic into park while the car is still moving and can damage the OD. If using the kickdown mode, once the downshift is complete and with power still applied, you can pull out the cable. Failure to follow these directions can and probably will damage the OD unit.

Shifting without the clutch while in OD. I'll pass on the advice given me years ago by the guy that furnished rebuilt transmissions to me... DON'T DO IT! After having a couple of them turn into 3 speeds of neutral, he told me to knock that off and I wouldn't have any more trouble like that. It will work for a while until it doesn't. Apparently, it's hard on both the syncros and the overrunning clutch. He was right...

Lastly, the electrical controls. I hear guys wanting something 'simpler' or 'more control'. First, the wiring is elegant in its simplicity as I'll show below. Very clever design. As to 'more control', why? As-designed, this offers seamless operation with interlocks to prevent damaging the OD from operator error. Now, 'back in the day' it was considered 'cool' to split-shift them for 'six' speeds. The reality is there's really nothing to be gained. If you do the math, you'll find there's little difference between 1st OD and 2nd standard, same goes for 2nd OD and 3rd standard. As an example, the low-gear ratios used in '56 Fords were 2.78, 2.57, 2.49 and 2.33. Multiply by .7 and that gives you 1.95, 1.79, 1.74 and 1.63. Standard 2nd gear ratios were 1.61, 1.59 and 1.48. Not a great deal of difference. Comparing 2nd OD to 1:1 high gear is even closer; 1.13, 1.11 and 1.03. Any possible performance gain will be lost to the time it takes to effect the shifting in-and-out of OD between gear shifts. Wouldn't it be easier to simply downshift? As to the 'cool' factor, with the proliferation of 5 and 6 speed transmissions these days, no one will notice anymore... LOL

On to the control diagrams. I've simplified these for clarity by erasing the non-pertinent wiring...


This is shown de-energized, i.e. OD is not engaged. Pretty simple. The governor (the on-off switch) supplies the ground connection for the relay after passing through the normally-closed contacts in the kickdown switch. The governor contacts close, the relay contacts close and power is sent to the OD solenoid to engage OD. Several things to note here. Relay/circuit power is supplied off the ignition terminal on the ignition switch. It could be any switched 12V source, although switching with the ignition is a good idea as the only time power is needed is when the engine is running. A relay is used to reduce arcing at the smaller governor contacts. These contacts can be exposed to oil contamination from leaking into the governor from the trans, the governor can be disassembled and the contacts cleaned/filed to restore operation. You also have two sets of contacts inside the solenoid, one set controls the solenoid coils. There are two coils, a high-current pull-in coil and a reduced-current holding coil. Once the solenoid pulls all the way in, a set of contacts opens and disconnects the pull-in coil. If your solenoid won't pull in, don't assume the coil is bad, it may be these contacts need cleaning/filing. If your trans works normally but won't engage the OD, the problem will most likely be here. Note that that this circuit is in operation whether the OD is enabled or not, and the OD is held in electrically by the solenoid, not mechanically.

This is the 'ignition defeat' circuit to allow downshifting under load. First thing you should notice is it doesn't disconnect power from the ignition. When the OD is engaged, the contact shown in the lower left corner of the solenoid is closed. Remember, an ignition spark isn't produced until the points open (a loss of power), so when you step on the kickdown switch and close its normally-open contacts, the coil now thinks the points are closed and no spark is produced. When the solenoid returns to its de-energized position, those contacts open and normal ignition is restored. You DO NOT want a spark produced while the OD unit is in the process of shifting as damage could occur.

I do think I can answer one question that comes up regularly in relationship to this; what if you have electronic ignition? I'm 98% sure that if you're using a two wire, in-the-distributor conversion like a Pertronix that this circuit will still work just like the points would. If you have a separate box type like a MSD, more research will be needed.

Like I said in my first post, these are a truly great cruising transmission when used right. And while these aren't particularly fragile, I'll agree with other posters that they don't suffer abuse very well.

 

Steve’s write up is about as good as I’ve ever seen. Particularly the part about pulling the handle when disengaged and under load. It’s exactly the way my Dad taught me when I was 16 in 1966. I added a drop out switch to allow me to dis engage without using the kick down and full throttle. Same cautions about long steep hills on compression, and shifting without the clutch when free wheeling. Dad had broken enough of them to know, and didn’t really want to have to teach me how to rebuild them too.

 

I can still hear my Dads keys jingling , when he would turn the ignition off and back on, on our 53 Ford station wagon! Flathead wit a three speed overdrive!





Bones

 

I can say that with a Pertronix setup in a stock distributor that it works fine (just like points). When I said "turn it on" I should have said "enable the system by pushing in the cable". Also I'm not 100% sure what you're saying about engine braking IN o/d, but once you're in o/d (fully locked in, cable in, solenoid on and above 23 mph) it does have normal engine braking. I still like being able to control it at will for the reasons I stated before, BUT you really have to be careful and pay attention......this use is NOT for everyone. I always went under the impression that the cable needed to be pushed in only under the governor enabling speed of around 23.

 

Or put it in reverse. Shifting to reverse locks out the overdrive, which is why it's safer to use the original wiring and solenoids/switches--backing up with overdrive engaged is a very bad thing for overdrive parts.

 

I have put a bosch relay on the old housing of a burned out relay so it looks original. You can buy a repro wiring harness for 49 up Ford with overdrive which is cheap and simple to install.

 

You can push the cable in while moving (forward) but don't pull it out while moving. An example of driving with the cable out would be in town stop and go or hilly terrain speeds under maybe 35. This way the transmission works like a regular 3 speed with compression braking all the time. When you get back out on the road, you can push the cable back in and go back to "electric" overdrive.

 

Overspray, thanks for posting that!

 

First, thanks for the write up. about the ability to use the ignition cut out with other ignition systems, I guess you could use a Bosh relay and just turn off and on the 12v positive going to it. But I have points anyway so I can wire up as it should.
Thanks again.

 

I ran an overdrive R-10 many years in a couple of early MoPars with a toggle switch to control the relay/solenoid and no governor. Those transmissions have a low geared second (1.83) so the use of second gear overdrive was quite useful ratio in mountain driving. Never had a problem with that setup.

 

I imagine you saw my video is driving my Model A, and I see that is what you are biulding. I used a 39 Ford steering column and box with the 51 Ford column shift tube and linkage. It gave me more room having the column shift in the Model A, and it fit like a glove. I hooked up the column shift linkage rods to the trans and only had to slightly "tweak" (bend) them to make it shift smoothly. I mounted the kickdown switch to the firewall with a small "L" bracket to actuate it from the carburetor linkage (Fenton 2X2 94s). I could have mounted on the carburetor like most stock GM, Chrysler, and Studebaker kickdown switches. I also mounted my relay under the dash.

 

Related question: Will the BW R10 overdrive ignition cut out circuit work correctly if I'm using a Stromberg Efire distributor? It still uses a coil, and I think the cut out briefly stops power to the coil.

 

The ignition defeat feature in the OD wiring DOES NOT disconnect power to the coil. Doing so will produce a spark, which is what you're trying to prevent.

The Stromberg distributor is switching the power to produce spark, while the OEM ignition switches the ground to produce the spark through the points. The OD wiring mimics the points being closed, preventing any spark. This distributor won't work with the OD wiring and because of how it's built the OD wiring can't be easily converted to do so.