This thread is in response to a question on another thread about an overdrive I built a few years back.

In 1995 I started relocating from CA to MD. My tow rig was a '65 Merc that my Dad picked up at the factory, pulling a tandem-axle trailer that grossed 7,000 pounds, so with some stuff in the car I was pushing 12,000 CGVW. The first trip was with the original auto, but I figured I'd get better mpg and have fewer problems with a manual. I had a T-98 I had rebuilt for a cousin which was still in good shape after we parted out the '60 F-100 it was in. I had saved a T-85 OD for some 20 years for just such a use. (This was my second OD splice - I put a T-86 OD on the back of a T-10 in 1968 and it is still in a '56 Ford Victoria in Kansas.)

The T-85 OD ratio is an almost perfect split for all four gears of the T-98 and it worked great. I used it for ten cross-country trips. I had 3.00 rear gears with a TorSen limited slip unit, so I could only use top gear unloaded at 70 & above, but I used all 8 gears a lot of the time. Even unloaded it was great to be able to hit the right gear to roll effortlessly through a small-town speed trap. I did manage to break it about half-way through my travels and after one trip without being able to split gears I HAD to fix the OD. (I broke it by accidentally backing up while in OD - a big NO-NO. The original OD tranmissions had a reverse lockout, but mine did not.)

On my 13th trip, I had a roll-over accident on I-5 which totalled the car. I brought it home and kept all the running gear. Since then I have been doing Ford pickups.

I'll take some pics and discuss the technical aspects tomorrow.

 

thanks very much I am very insterted in this.

 

I am going to tell the "long version" of my 4-speed/OD story because I learned a lot that I think would be useful to share. I will break it up into a series of "bite-size" posts. WARNING: Do not subscribe to this thread if you are easily bored.

Overdrives had a mystique about them for over half a century. They are associated with combining good economy with performance. In pure mechanical analysis it is arguable that a straight trans with more gears than a three-speed should give an equal combination of economy and performance if it had the proper ratios. It would be simpler and perhaps a little more efficient if the top gear was direct, with no gear losses. From a assembly-line point of view, the three-speed overdrive transmission was attractive because it could be an extra-cost option that would more or less directly replace a three-speed, using the standard column shift.

With a normal three-speed, the overdrive usually only offers a fourth top gear for the highway. First OD and second OD are rarely used and are usually not an even split of the gears. When applied to a close-ratio four-speed, the only additional ratio is the top gear - all the others are redundant. Still, in 1968, the idea of an overdrive on my T-10 was attractive. After enjoying the small rpm drops on my Isky-cammed 312, in a ‘56 Vicky, I decided that the only way to get anywhere on the highway with a 4.56 9” Ford rear end was to put an overdrive on the back of the T-10. I am going to discuss this trans before the T-98/T-85OD because there are a lot of useful “lessons learned”.

Feel free to add thoughts or disagreements - this is a conversation.

 

Here is a link to a picture:

https://www.ford-trucks.com/user_gal...146712&width=0

If the link does not work, look at "Archie's Tech Album" in my user gallery & please PM me so I will be able to learn how to solve the problem.

 

I had numerous T-86 three-speed/OD transmissions - I had to have spare parts to as I managed to “blow up” two. (I had a friend who went through TWENTY-FIVE T-86’s before his first and only T-10 - true story.) Neither of us ever had a problem with the T-86 three-planetary overdrives, so I figured the little OD would hold up. (The T-10/T86OD trans I built is still in a Vicky in KS - so far, so good - almost 40 years.)

How to do it? Well I acquired a T-10 tailshaft that had suffered greatly when a drive-shaft was thrown following a rear U-joint failure. The last four inches of the tailshaft was gone. I also managed to acquire a T-10 mainshaft that had failed just in front of the splines. Now I had all the parts I needed. About that same time I helped my Dad put a 289 engine in his ‘63 Jeep cab-over (FC-170). I know now that I could have swapped in a Ford T-98 input shaft, but in those days we were ignorant of such things and took the direct approach. One of the great old LA hot-rodder machine shops was Henry’s Machine Shop, so I drove the 200 miles to see if they could splice a Ford T-10 input shaft onto the Jeep’s input shaft. They said no problem and did the job for something like $35. They also shared their method which had been used successfully on many drag machines of that era.

The Henry’s method is to use a lathe to drill & ream a 1/4” hole dead on center in the shafts . In the same setup turn bevels in preparation for welding. A hardened dowel pin is used to assemble the two halves and a very high-quality weld is built up going round & round. If necessary the weld is ground flush. Also, if necessary, the shaft is straightened.

I later had occassion to use this method “rescue” a twin-V-8 tractor pulling rig that broke a trans shaft in the first day of a two-day event. Even though they broke, they took that round because of a fault on the competitor’s part. They were still in the running if they could repair the shaft. We did the repair overnight using the Henry’s method and they took their class the next day. I don’t know how much longer that shaft lasted, but they made a number of pulls with it that day.

 

Now that the shaft was made up, there was still the problem of how to manage the case connections. I could have put a double-bearing carrier and yoke on the front an overdrive and mounted it after a short drive-shaft, but I wanted an integral mount. I had my broken cast-iron T-10 tailshaft and I scrounged through my junk pile for a T-86 main case. I then spent many happy hours on a Bridgeport mill making most of these two parts into piles of cast iron chips. When done, I had a very short T-10 tailshaft, with a flat surface exactly parallel to the front surface, right behind the rear motor mount boss. I made even more of the T-86 case into chips - I reduced it to a flat plate consisting of only the original rear of the case. I had a very good professional welder (who also did my shaft) use nickel rod to weld the two cast iron components together. I aligned them in the machine shop and delivered them to the welding shop clamped together. With a long bead on the outside diameter there was a lot of weld. I was not there to observe the welding, but I assume the entire assembly was pre-heated.

I then assembled the 4-speed and overdrive. It worked great - best of both worlds, but there was one lesson to be learned. The original design for all these Borg Warner overdrive transmissions includes a “gutter” cast into the main case. This gutter catches gear oil thrown from the gears and it is carried back into the heart of the planetary gear assembly. I thought if I filled the overdrive through its separate fill hole, it would have adequate lubrication. Well, I was wrong. After about 4,000 miles, the overdrive started “singing”. The sump level in the main case was much lower than the overdrive and slowly the oil all ended up in the front case. For the next 4,000 miles the solution was to top off the overdrive before making a highway trip. Finally I tore it down and put a seal between the cases. This was easy because there was a bearing bore that was empty, so all I had to do was press a bushing on the shaft and turn it true to the seal’s ID and find a seal with the appropriate OD.

 

The final test. When returning to the Army from leave in 1971, I was taking US-54 from KS to NM. In those days it was a pretty lonely stretch of two-lane road. I came upon a bunch of locals with a early 60’s chevy who were on the shoulder. The car looked like a classic “low rider”, but it was just because the shoulder was soft after a rain - they were “high-centered” with the whole frame on the ground. They had a chain and I had a cable, so we hooked up with my car on the hard pavement with 3 or 4 of them sitting on my trunk-lid for traction, I eased out the slack nursing my 11” Shaefer all aluminum clutch & flywheel. (Some may remember that these clutch/flywheels were bronze-faced.) I slowly let the clutch out while feeding in more throttle until I was at full throttle at 3,000 rpm, at which point the chevy slowly was sucked out of its mud hole. The tires never broke loose and “OH, that’s right!” - the welded shaft in the trans held. (Only afterwards did it occur to me that if I broke my welded shaft, I was a marooned few hundred miles away from “home” and would be AWOL.)

 

A few decades later, I found the need previously mentioned, to have more gears for towing. I had worked out the ratios on paper: 8.71, 6.40, 4.21, 3.09, 2.30, 1.69, 1.36, 1.

These jumps average 1.36 which is pretty good for the wide torque band of a 390FE. I had saved up several core T-98’s and acquired a T-98 I had previously rebuilt. Even though I had never broken the welded shaft, I decided that I would avoid a possible point of failure. I decided to NOT cut either the T-98 mainshaft or the T-85 mainshaft (which was the “input shaft” for the T-85 OD).

In order to use the shafts full length, the extra length made for a long adaptor - over a foot long. This was OK because there was already plenty of space in the car application and it would let a long-bed F-100 get by with a one-piece driveshaft and no carrier bearing. Next post I’ll go through the details of coupling the shafts without a weld.

 

Avoiding a welded joint meant using a mechanical coupler. The output shaft of the T-98 was splined and the front of the the T-85 mainshaft was also splined, so a splined coupling could have been machined out of one piece of steel. I had access to a fully outfitted machine shop, but I am lazy enough to take a short cut when one is available. In this case, I used the companion flange that was bolted to the T-98 originally - I was half-way there. In the T-85 trans the 2nd-3rd synchro hub is installed on the front spline of the mainshaft. With a minimum effort I reduced this hub to a flange with the splined center. I then machined up a spacer which had counterbores that insured perfect alignment. I drilled the spacer and cut down synchro hub to the same bolt pattern as the T-98 companion flange. This whole assembly was held together with four grade 8 bolts.

One small point is that I did not want or need the coupling to float on both shafts. I wanted to use the original T-98 nut, but how could I tighten it with the smaller diameter through the rear splined hole. My solution was to machine the spacer such that I could assemble the coupling with the nut AND a 1/2” drive socket inside. This socket stays in the transmission, but allows tightening up the nut by using an ordinary 1/2” extension on the torque wrench.

Lesson learned: The nut I used was a fiber-locking nut. After about 10,000 miles, this nut slowly backed out - it was, after all, USED! I had to pull the OD off the trans in the car and re-assemble with a new, locktited nut. No more nut problems.

 

The other main task is the adapter housing. This time I fabricated it from scratch, starting with a large-diameter piece of thick-walled steel pipe. I turned up a pair of end plates about 3/4” thick and 2" larger diameter than the pipe OD. I faced both ends of the pipe square, with bevels for weld penetration, and then welded the flanges on the ends of the pipe. This was my first experience with 7018 (low hydrogen) stick welding rod and I loved it. As I remember, I did a root pass in the bevel and another broad pass on top of than followed by a pass on each side nailing down the edges. I am very confident that this part is over-welded. (I am not paying myself, so I consider over-welding better than under.)

The entire weldment was normalized in a furnace. I then faced the one end to match the trans, including necessary counterbores and, in the same setup, I turned true the entire OD of the pipe. This gave me a reference surface to use when setting up for the facing operation on the other end, insuring that all bores were co-axial and both ends were parallel.

Next post, I will discuss the all-important issue of lubrication.

 

By now I knew that lubrication could not be an afterthought. My earlier solution of sealing the OD in its own chamber worked, but an OD actually holds a very small amount of oil and a planetary assembly is not the best for “dip/splash” lubrication. In all the Borg Warner overdrives, the solution is to use the transmission with its large and lower sump to oil the overdrive. The gutter catches a continuous supply of oil thrown off the gears and delivers it to the heart of the planetary gearset. In this case I used the same approach with my adaptor housing. It had its own sump level at the same height with the main transmission level. I installed the old T-85 1st-reverse slider gear on the shaft as the “oil pump”. It threw oil into a angle-iron gutter welded inside the adaptor housing which delivered the oil to the proper hole & into the center of the OD gears. I also used a piece of external tubing to carry oil back from the fill hole in the OD to the adaptor so that the oil would circulate and maximize cooling. I felt this was necessary because I would be using this OD for more than just a top gear. I used it to split all gears, although I was gentle with it when in 1st & 2nd where I probably could have broken it if I went full throttle. (Say 300 ft.lbs. times 6:1 in “grannie” - this is asking a bit much for an overdrive designed for a car.) The hardest work the OD had to do was pulls up the first half of long grades in 3rd over at full throttle. This really worked well and there were few grades that I ever had to drop any lower than 3rd direct. Having the right gear was also great on the down-grades, allowing me to compression brake enough that I ever had to touch the brakes. Up or down grade, you can always use a lower gear, but I hate to be going up or down in 2nd and watch the idiots close up to me in my lane at 70 and swerve around me when they realize how slow I am going. Sooner or later I figure I’ll end up with one of them plastered to the back of my trailer. (At 12,000 CGVW, they would know they hit something!)

This all worked very well, but I did find a way to break it . . .

 

Those of you that are familiar Borg Warner overdrive transmissions know that there is an interlock for reverse that disengages the OD even if the lockout cable is not locked out of OD. I did not have an interlock on my first (T-10/T-86) OD and never had any problems, but ONCE, in heavy traffic after coming off the freeway, I accidentally left the overdrive toggle switch on. At the time I was towing a trailer with a D-2 CAT on board. When towing, I try to “drive ahead”, watching for possible problems ahead, but this time someone made a U-turn that they could not complete and the traffic closed up and there was “gridlock”. I had room to back up and started to do so, but noticed some “resistance” and then there was no reverse at all. (I did not apply very much throttle or hear any sound.) The traffic cleared while I was wondering what happened and then noticed that the toggle switch was in OVERDRIVE!

The way these Borg Warner overdrives work, there is an overrunning (one-way) clutch that provides direct and then, when the shifting pawl is pushed in by the solenoid, the sun gear is locked, the clutch overruns, and you have OD. In reverse, the planetary gearset provides an OD ratio, but the clutch does NOT overrun, locking things up. Bottom line: something has to give. I learned what the weak point of these transmissions is. The splines were literally all sheared out of the planetary carrier which is NOT hardened. Thanks to the overrunning clutch I could drive and completed the three miles left to get home (without backing up).

As an interim measure I did a repair via welding which did not allow for overdrive, but made direct work, including reverse. I missed my gear-splitting so I located another planetary carrier and put it all back together. This trans made quite a number of hauls cross-country and was still working fine when I rolled the vehicle (another story for another time). My current solution is a New Process 540 5-speed in my ‘68 F-350, which will be replaced by a Roadranger 10-speed as soon as I can get everything else out of the way and get it installed.

I hope this provided some of you with some entertainment. I am ready to answer any questions or discuss similar projects.

 

Thats quite a read acheda. I've always been obsessed with overdrives since I started driving my 86 f150 wth an AOD tranny (learned to drive on that truck). Theres something refreshing about not running out of rpms. I now have a second truck that is a diesel and even with 3.08 gears (which I put in) I will still be putting an E4OD tranny in.

For the longest time I was under the impression that the AOD was the earliest overdive tranny that could be found in a ford (1980). But I later found out about earlier ones that go as far back as the late 60s?? Were they ever offered in trucks of that era?

Since you mention that you have a 390 engine (one of my personal favorites), I was wondering what sort of milage you get with it. I've been toying with the idea of swapping a 390 in place of the 302 that my truck has right now, but I've never come across anyone that has an overdrive behind a 390. How do you like the engine and how does it perform at say 2000rpm or less? Right now, my truck is turning about 1850 rpm at 70 mph.

 

The 51 F-1 that I learned to drive on had an overdrive that was originally installed in a '56 F-100, so I know that Ford pickups had overdrives at least as far back as '56. The first car that I bought was a '50 Ford sedan and it had an original overdrive. Both of these were T-86 3-speed overdrives.

In a '65 Merc passenger car with automatic, I have pushed 18 mpg by cruising at 55 mph and taking care on the open road. This was the original high-compression ratio engine. With a low-compression 390 built to survive heavy towing, I would only get around 12 mpg empty, but once hauled a Caterpillar D-2 from CA to MD (2800 miles). I kept track of every drop of gasoline, including fill-up at the end and got 9.3 mpg with a GCVW of almost 13,000 pounds. A high-compression 390 in a '65 F-100 with 3.70 rear gears (& no OD) would only get around 15 mpg at best because it is pushing more air than a passenger car.

I didn't have a tach in these vehicles, but the Merc with the T-98/T-85OD had a 3.00 rear axle ratio and I could only use the overdrive at speeds over 70 mph in top gear in the trans. For 75 mph out on the western interstate highways, it was a nice combination. At these speeds, 12 mpg (with an empty trailer - 2,000 pounds) is pretty good. A 390 is not ever going to be a mileage engine - they have other things that they do well. This is one reason I am going to try a 300 in my '68 F-350.

My advice to you if you want to set up a 390 with an overdrive would be to stick with the smaller Edelbrock 4-barrel intake, small valve heads, dual exhaust with stock manifolds. Then it should be happy with your 1,850 rpm cruising speed.

 

Thats does it, I am now convinced that automotive technology is going backwards, not forward. It blows my mind to think that in 1956 you could get an overdrive.

I think you would be hard pressed to find a gas powered truck built today that could operate at 13,000 pounds and get 9.3 mpg. The best I ever got with my f150 (see sig) was 13 mpgs, and the AOD has a lockup function.

Thats too funny, right now I'm looking into the 300 l6 as well (and the 351w). Its not like I really nead to liquify the rear tires anyway. I agree 12 mpg at 75 mph with an empty trailer is not bad at all, I'm just not quite sure which engine to go with if I decide to swap for somethong better.

I'll be keeping the propane system, so I may also consider 10:1 compression. I probably won't run out of power with a 390 thats for sure, but I'm hoping to build for a more fuel efficiency if at all possible.