Overdrive for a 52 F-1 flathead

K

ken-r-mer

Senior Member
Ok, I need some assistance from the flathead w/ 3 speed overdrive experts on this site.

I got my hands on a 51 Mercury 3 speed overdrive from the bell housing to the tail shaft including the flywheel, clutch, pressure plate, and clutch linkage to the pedal. All the gears show no evidence of missing or chipped teeth.

This winter, I'm planning to replace the standard truck 3 speed column shift mainly for the economy and higher cruising speed ability of the overdrive. I also want to retain the "cool factor" column shift. Reading the Van Pelt Sales trans chart, the gear ratios and spline count (16) on the main shaft are supposedly the same between the 51 Merc and the 52 F-1.

I see that the clutch linkage setup exiting the bell housing of the Merc unit appears the same as my 52 F-1 (a rotating shaft with a flat key-type end exiting the side of the bell housing, in lieu of the pivoting type lever as seen on other setups). Will the complete linkage of my stock 52 F-1 work? Or, do I have to do some creative massaging and manufacturing?
What about the trans tail mounting location?

I know the drive shaft length has to be modified but that will be done after the F-100 9" rear w/ a 3.5 ratio goes in first (phase 2).

Also, I'm gonna put in a new clutch disc regardless of the existing units condition, but, how do I tell if the pressure plate is still good? Or, should both be replaced at the same time?

I've always driven manuals my whole life and averaged over 175,000 miles on each car/truck and have never had to replace one, yet, due to wear.

Phew! Thats enough for now.
 
I'm no expert but I know a fair amount about the early Ford/Borg Warner O/D gear boxes. In the 1951 Mercury model year there were two types of overdrive transmissions used. In early 51 they continued with the 49-50 type units until they had used reserves. The late 51 Mercury models used a new transmission that was based on the earlier 49-50 standard ford units. The easiest way to tell which is which is by the bell housing. Early 51 still used the half bell with a shallow bell on the trans case. The later 51 had a separate full bellhousing but still retained the early style clutch release shaft set up. The late 51 and on trans had no bell shape to the case at all.

Which unit do you have? There are also differences in the type of clutch plate and trans input shaft splines. Early still had 1 3/8 X 10-spline and late had 1" X 10-spline.

Kerby
 
I am not an expert on the nuances of clutch/pressure plate sizes from year to year, however, I have had a lot of experience in upgrading various vehicles to later model engines, transmissions.etc..
As a general rule, it is best to have all of the original equipment, nuts, bolts etc. when trying to modify any component. I would think that if you have everything from the Merc, bell housing to yoke, kick down switch and the disengaging cable, the conversion should be a slam dunk. Of course you will need to shorten your drive line and maybe replace the u-joint with one that is compatible with the OD yoke.
You might have to consider re-gearing your differential to something around 3.89 with 600x16 tires. I am not sure what the standard OD gearing was in the F-1 series trucks, I do know that the F100's in '57-60 had 3.89 as a standard OD gearing, with 3.72 as the standard for non-OD trucks.
 
I have what appears to be a cast iron bell housing that is separate but bolted to the trans case. The bottom of the bell housing is flat and has a metal plate across the bottom (inspection plate?) as well as the starter mounting plate. I just was wondering if the linkage of the Merc will work with the linkage of my 52 F-1. Both have the thick rod linkage and connect similiar just outside the bell housing. Maybe its just a matter of taking some measurements and if its close... just improvise.
 
If you want to install this transmission you will have to cut out your cross member. The solinoid on the oversdrive will sit right in the middle of the cross member. I think a better solution is to use a 3.25 ratio axle, since you are already planning on changing axles.

If you do decide to chop the cross member, use the stock 3.92 ratio rear axle or a similar ratio axle. The 3.92 and overdrive gives a final ratio of 2.74, which is tall for a flathead. My personal preference for a rear axle ratio for overdrive in that truck is 4.11, this gives a final ratio in overdrive of 2.88. The 3.50 is too tall for overdrive and a flathead.
 
When I went to several websites to evaluate gear ratios, rpms, tire diameters, and speeds, I found that with: a .70 overdrive ratio, a 3.50 rear end ratio with the 26" (29.75" is stock) diameter tires on 16" rims that I currently have, my speed at 2,000 RPM will be about 63 MPH. I'm just looking to be able to keep up with traffic during those few times I need to get on the highways. I look at the overdrive as a 4 speed but keeping the column shifter feature.

In situations where I don't need the overdrive it can be manually locked out. Then the numbers would be 44 MPH at 2,000 RPM in 1:1 top gear. Am I correct from my memory that a stock flattie V8's max torque is near 2,100 RPM?

What I like, when reading about the overdrive, is that at speeds under approximately 28 MPH a governor kicks it out of overdrive. Likewise, when the gas pedal is fully depressed (passing speeds or hard acceleration).

Also, I will be rarely hauling anything heavy...besides passengers.
 
You have the later 51 mercury set up and it is compatable with the clutch equalizer set up on the 52 F1. The 1 inch 10-spline transmissions can use the 9.5 inch Long type or the later Mercury B&B 10 inch clutch. There most likely will be an issue with the O/D control solenoid but I'm sure it could be modified to work. I've seen some pretty wild modifications to get the old Lincoln overdrives in the early fords with the x-members so an F-1 crossmember mod should be much easier to overcome.

My experience is with the earlier Mercury set ups and they have a 3.92:1 rear axle ratio with the both the Dana 41s & 44s. They are a heavy car and that ratio works really well for all around driving. The 3.5:1 is going to drop the rpm even more so the first gear start out is going to require a little more throttle. It should work OK but you may want to keep a heavy clutch set up on your flywheel to help with start outs.

The Ford/Borg Warner R-10 O/Ds aren't the stoutest transmissions out there but when everything is working correctly they are really nice to drive. It takes a bit to get used to a standard transmission that coasts when you let off the gas but it's not that much different that driving an automatic only there is no torque converter and you still have to shift & clutch. In the old Mercs you can start out in second on a flat street and never have to shift while driving in town. Its like a 2-speed auto except you have to clutch at stop signs.

Kerby
 
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Maybe I'll keep the 3.92 rear axle for now to see how it goes once the overdrive is in and running. I can always change the axle at a later date.

This trans install is my 2010-11 winter project. Between now and the first snowfall I should have all the pieces necessary to start. In the mean time I can replace the seals and gaskets in the overdrive unit.

I'm just looking forward to not hearing the engine scream as when I was on the interstate or rural roads trying to do 50 MPH. I don't think the stock truck gearing was ever meant for the faster speeds. It always feels like it's looking for that next gear even when I was doing 40-45 MPH.
 
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