top of page

Mercury 3 Speed with R10 Overdrive Rebuild Part 2

Updated: Dec 27, 2019

(A few years ago I submitted the following article to the Y Block Magazine and it was published. I have decided to post it here for those that have had questions about the transmission that is in the 1955 Ford Fairlane Club Sedan.)

Mercury 3 Speed with R10 Overdrive Rebuild Part 2

In the last issue we gave information about the R&R of a 56 Ford/Mercury 3 speed with Borg Warner Overdrive Transmission. Most of part one was about the disassembly of the unit, parts identification and assessment, and the reassembly of the main case. Now we get to the nitty gritty on what sets apart this transmission from most others in its day – the overdrive. Back when I began the disassembly process, I basically started from the rear of the transmission and worked my way forward.

The tailshaft for an overdrive is very different from a standard transmission – as you might expect. The differences include an extra shift lever, an electric governor switch, an electric overdrive solenoid switch (that engages the pawl), and the rollers/overdrive gearing inside the cover itself (more loose roller bearings – yuck!). The disassembly of the tailshaft and overdrive unit is very straightforward and most, if not all, of the manuals and diagrams I found showed excellent specifications of the sub-assemblies. However, when I removed the tailshaft casing I found red paint? Glyptal? inside of the housing. No one has been able to tell me why it was that way. Did Ford/Mercury do this at the factory? I don’t know – this is the first housing I have seen. Why would this be anyway? I decided to leave it the way it was. Nothing was peeling and all seemed to be well, but this did certainly appear to be factory applied. The tailshaft had the usual crud and goo you would expect, but a bath in solvent took care of those problems.

A word about removal of the housing – there is a very large snap ring that keeps the overdrive shaft connected to, and riding in, the tailshaft like it ought too. You have to remove a small cover plate on top of the tailshaft and use a pair of snap ring pliers to take the tension off of the ring. As you do that, you can take your other hand and slightly tap the rear shaft in the case to release it from the overdrive housing.

Keep in mind that when you unbolt the overdrive housing from the main case, you are going to hear (and hopefully see) those roller bearings for the overdrive clutch fall out. I suggest that you place a pan or a box under your transmission so you don’t lose those little boogers. The overdrive disassembly procedures are all mapped out in the manuals very, very well. Probably even better than Ford’s main case procedures for their standard transmissions, so we won’t spend any more time on disassembly – just a word of caution though – take photos and check diagrams as you go so that you can get the reassembly down correctly!

Once you have assembled your main case, you will have the front part of your transmission all buttoned up and ready to go, from the input shaft (snout, I like to call it), to your cover plate, and all the way back to the bare tailshaft sticking out of the rear of the main case. The reassembly of your overdrive gearing, parts, and housing is going to be a bit touchy so I recommend you do the following: MOUNT THE MAIN CASE VERTICALLY for reassembly. In the following photo, you can see that I chose to use my Black and Decker Workmate. It was just about the perfect height for me, and the clamping feature was a no brainer… very safe and effective.

A Workmate will keep the main case vertical as you work on the overdrive assembly.

Depending on your main case, you may have studs and/or bolts that help to hold down the adapter (the 1.5” thick casting between the overdrive housing and main case) and the overdrive housing. Get this hardware sorted out properly before you begin. We often laugh about “leftover parts” and such, but when you are working on a transmission with all of these sub-assemblies you don’t want any leftovers. Holding “extra” pieces in your hand when you are through could mean catastrophic failure. Take your time here.

As your tailshaft is now vertical, you can begin dropping on the pieces one by one as you go. Follow the sequence laid out in your manual/diagrams, and you want to make sure that you orient items like the pawl correctly. Fortunately, all of the instructions I found showed excellent information about getting the gears on facing forward, the clip locations, etc. I would assume that it would also be common knowledge to use plenty of 80W90 gear oil as you assemble each gear set on the shaft itself. At times, I went as far as immersing the particular part in oil.

As you place the gears on the tailshaft, it is a good idea to double check the rotation and action of each part as they work together. This will help you identify any errors very early on and keep you from having to disassemble everything once you are finished. (I learned that lesson with the main case reassembly.)

The re-installation of the pin that steadies the OD shift rail threw the author for a loop.

One item that I wish I had kept notes on because NO MANUAL covered it was that the small pin that steadies the shift rail needed to be reinstalled on the adapter from the correct side. Once I noticed that during overdrive reassembly, I thought, “Oh no, I am going to have to remove the adapter from the main case so that I can get behind the adapter to insert the pin from the other side.” I studied it for a while but came to the conclusion that the pin went in from the rear of the adapter and not the front.

The signs that gave this away were the discoloration on the pin itself and the interference fit of the pin when installed from the rear of the adapter. The pin had to be installed AFTER the shift rail and sun gear assembly was placed on the tailshaft itself. When you get to the clutch and roller assembly, use plenty of grease to hold your rollers, or use a rubber band to hold the rollers in place until you install the rear shaft onto the overdrive. (Thank you Dennis Leeking for that tip.)

Another note on the re-installation of the cup that the roller bearings ride in… make sure you put those spring clips back in place correctly, or you will never get the cup itself to slide back onto the shaft correctly. I had a devil of a time trying to get these to fit and then work on the shaft and then wondered what was wrong. It seems that when you look at these 3 pieces there appears no way that you could possibly get this back together incorrectly, but you can – trust me. I did find a Borg Warner Overdrive manual that had this particular all by itself in a blown-up diagram showing the correct orientation of each ring inside the cup. And what do you know? Voila! When I followed the correct setup, the pieces went together and back on the shaft just like they were supposed to.

The vertical position of the transmission really aids in the re-installation of the overdrive assemblies and the housing itself. I cannot say enough about it. The workmate made the work enjoyable as 360 degree access was provided, and most anything you set on the transmission or shaft itself stayed put so that you could install the next part in sequence. Dropping the overdrive shaft over the top of those rollers was a piece of cake as it seated properly and the full alignment was checked. When it came time to install the housing, this also was a breeze for alignment as a 90 degree orientation to the main case itself was easily seen and achieved. One word here… don’t leave out that spring that goes behind the hole for the shift rail, and whatever you do, make sure that the large snap ring is reinstalled and oriented correctly. Also, double check the installation and alignment of your shift lever because it has be installed BEFORE you reattach the overdrive housing.

The housing will only go so far before you have to get out your snap ring pliers to spread the snap ring, allowing the housing to slide down all the way. Take your time on this part and don’t force anything. All of the manuals I read discussed the need for leverage in getting this housing back onto the main case, etc. And of course that may be true. Whatever prying you may need to do, keep it gentle and light – no one is remanufacturing these overdrive housings anymore. Double check your shift rail alignment before you proceed of course.

Snap ring access for re-installation of the housing on the OD shaft – take your time

Once the housing is secure, you can bolt it down to the main case. Before you do, I suggest that you check your overdrive shift rail movement, and the movement of the gears in the main case as you “go through the gears” etc. You can check your overdrive pawl engagement with the right kind of screwdriver that will allow you to push the block in towards the mechanism, and then twist the screwdriver while engaged and then pull the engagement block back out to disengage the pawl.

Once I buttoned it all up, I put the transmission on the workbench and simulated running through all the gears. Everything seemed fine with just a little “drag” or actual force needed to turn all of the gearing and I believe we are going to have a nice little 3 speed + overdrive here. I did check out the seals to see how they stood and it looked as if most had been replaced at some point and they showed very little wear. However, I did replace the rear seal. Let me tell you that it was a bear to remove. Back in the day these transmission had seals that were meant to last. The metal casing of the seal was heavy and difficult to budge. I had to use a seal puller, chisel, hammer, air chisel, heat, pry bar, and every item I could think of plus 30 minutes! to pull out the old seal. The new seal from RockAuto installed in about 30 seconds, but seemed tight so I think we are all good there.

We have not discussed very much the operational theory of the Borg Warner overdrives from the mid 50’s. They were installed on more makes and models than our Fords. I hear Studebaker had quite a few units in use in their vehicles also. There is quite a bit of information in the old manuals and all over the internet about operation. However, I do believe that for my general use I will go with a toggle switch mounted under the dash and then a relay on the firewall. I plan to only use the overdrive on the interstate traveling at highway speed. Thankfully, the 12 volt solenoid that I received from the man who shipped the transmission to me is working very well according to the testing I have put it through. These old solenoids were very well made and are practically bullet proof. The one I have cleaned up well. Until next time, HappY motorYng!

The original solenoid and tailshaft seal display the quality production of USA made parts back in the 50s/60s. It took quite a bit of pounding, chiseling, and overall grunt work to take out the old seal - you can see how much damage it had to go through to be removed. The metal casing that housed the seal is very tough stuff. The solenoid on the left is quality as well and these things are commonly rebuilt because the hard parts are near indestructible.

The transmission was painted with Duplicolor Engine Paint, in Low Gloss Black. Hopefully she is prepared for many years of service behind a 292 Y block in a 1955 Ford Fairlane Club Sedan!

bottom of page