The Mitchell is IN!

Hoogah

Well-known member
A few weeks ago I sought the experiences of Ford Barn members about installing their Mitchell overdrives, and received some helpful responses, including copies of some relevant articles in the Restorer together with a great set of photos sent to me by Tom Endy (thanks, Tom!).

I’ve taken the plunge and installed a Mitchell in my ’28 Phaeton and thought that others might be interested in my experience, as I haven’t found a thread that discusses this here.

Not being a confident mechanic, I sought the help of Alan, a retired “vintage” mechanic in Portland VIC, 70 miles down the road from where I live. Alan’s got a Model T amongst his collection. In honesty I should say that I helped Alan to do the job – not the other way around!

The Mitchell comes with a brief set of instructions which assume that the installer has a fair bit of knowledge and can figure his way out of problems. I’d like to see the instructions beefed up to address some of the issues commonly encountered, and some good quality diagrams or photos to illustrate the brief instructions at each step. I don’t think this is an unreasonable expectation for an item of this considerable cost.

At the very outset we were faced with conflicting advice about removing the rear spring. Mitchell said to drop the rear end with the spring attached to the axle, but Tom’s advice was to leave it attached to the chassis and remove it from the axle using a spring spreader. For some reason, Alan decided to have a buck each way (!) and attempted to remove it from the axle without the spreader (which we didn’t have on hand). Tip No. 1 – DO NOT DO THIS! It broke a shackle and could have inflicted serious injury when it finally let go. The photo shows how we ended up – spring attached on one side and the rear end out of the car. You can see how far the spring “snapped” from its spread position attached to the axle.

Rust Alert: From this photo you’ve probably already worked out that my car is no fine point trailer queen. It’s a survivor, so you’re going to see plenty of the flaky stuff if you keep reading. . . .

1RearEndOut.jpg

There was no way we were going to get the spring back on without a spreader, so we hastily arranged for one to be sent overnight, on loan from Henry’s Model T & A Parts in Ballan VIC (thanks, Keith Eastwood!). Meanwhile we set to on removing the tail shaft with the puller we’d borrowed from Keith. 86 years of tight fit sure took some pulling. Tip No.2 would be to make sure that your puller is heavy duty. Ours had to be bent back into shape after using it to pull the tail shaft and pinion gear out of the diff, and again after pulling the pinion gear from the tail shaft.

Pressing the newly assembled rear shaft and pinion back into the diff also took some doing, and I was glad to be the “helper” as opposed to the key decision maker at this time. We referred to Tom’s articles and photographs frequently during the whole process to shed light on Mitchell’s scanty notes.
2RearEndWithODInstalled.jpg

Day 2: The spreader arrived and we managed to re-attach the rear spring to the axle. Both rear bushes were found to be quite worn, so it was just as well we’d dropped the spring out. One of them had to be completely cut through internally with a hacksaw before it would let go. 86 years of “rusted on” takes some shifting! New shackles and bushes all round.
3ReattachingSpring.jpg

Re-attaching the rear end with Mitchell back onto the universal joint was also pretty awkward for just two people. Even using two jacks (under the diff and under the front end of the drive shaft), the sheer weight of the rear end plus the extra weight of the overdrive gearbox made lining it up with the universal physically difficult. At that point I’d have given anything for an extra elbow joint and bicep in each arm!
4ReinstallingRearEnd.jpg

Installing the linkages came pretty easy, although the Mitchell instructions ignored any mention of the RH Drive adapter that had been included in the package. But my man was all over it! I had given this issue no thought at all until I was driving the car to my mechanic’s house and reflecting on how little knee room there is, even for a short (5’7”) guy like me. It suddenly occurred to me that if the shifter ended up on the RH side of the gearshift, it was going to be very crowded on my side! I didn’t need to worry.
5Shifter.jpg 6ShifterLinkageOnTrans.jpg

Tom’s photos provided an excellent template for making a template (!) to position the hole in the floor for the shifter. The shifter has plenty of adjustment to enable it to be set at such an angle to clear the seat when in Low Range.
7FloorTemplate.jpg

Floor back in and good to go!
9CabinWithShifter.jpg

After 18 hours over three days, the Model A is back on its wheels and under its own steam with an extra set of gears. We were finally happy campers. That’s my man, Alan, on the left. Thanks mate!
10AllDone.jpg

I traveled the 70 miles home with a blustery tail wind in squally rain – not ideal open car driving conditions! We sat on a comfortable 55 mph at around the same revs that the engine was pulling at 45 mph without the Mitchell on the way over. I think I’ll be happy at 50 – 55 mph on the open road (if safe to do so), and my wife will be more likely to join me for longer journeys - this was a major consideration in undertaking this modification. For my wife it’s more about getting there rather than the journey!
I love my survivor car, the options that the Mitchell gives me, and the fact that the installation is totally reversible – not that I ever see myself removing it!
Last picture was taken back at home, safe and sound, with the Mitchell sitting happily underneath after its maiden voyage – the only shiny thing under there! (Note to self, remove the lawnmower before backing the car out of the garage.)
8ODUnderCar.jpg
 
A Mitchell is a wonderful thing indeed.
Great car, also, I happen to like survivors. They are original only once.
And the info and pix you get from Tom Endy are irreplaceable.

Glad you only broke a shackle. You could have easily broken way more than that.
There have been numerous warnings on this forum about the rear spring.

It is never too soon for another reminder, so here goes:

WARNING there is a massive amount of kinetic energy stored in that rear spring and it could take off your hand, arm, or head. It is dangerous to work with even with the proper equipment. Be certain to have a decent spring spreader and the knowledge to use it.

Good roads!
 
Very nice report. I am glad no one was hurt when the shackle let go. The other rear spring hazard, besides the shackle, is the 3\8" center bolt. It was never meant to hold all that energy even when it was new. After 86 years it could be rusted with the head ready to pop off. Had it done so instead of the shackle breaking the top leafs would have flown 20 feet in the air and taken your head with it if you were standing over it. If that didn't happen you need to run like the devil, because they are coming back down.

Thank you for posting the photos of the broken spring. I down loaded them and added them to my collection rear spring horror photos.

I agree that the Mitchell instructions are scanty. That is why supplemental articles concerning the installation are useful and available.

Fortunately with a 28, you did not encounter the early 370:1 pinion gear that is not compatible with a Mitchell installation.

Tom Endy
 
Your turn to help another with his install. in short order you will use the mitchell like original equipment. Thanks for the detailed and well written narrative. C clamps and logging chain are useful. as soon as the rear spring drops down during removal of the differential assembly I install 2 c clamps as high up as I can.
The logging chain gets wrapped around the center bolt area as soon as the full assemble is exposed. Never again remove the bare spring as Tom Endy cautions. You made me real nervous standing next to the rear end with the spring spreader in place.
Bet you swallowed hard when the shackle bolt failed.
Hope you bought a lottery ticket after the shackle broke.
 
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very nice.. I have taken my A up to 72 with my mitchell...BUT now i drive comfortably at around 60-63 and love it.....Enjoy
 
Hi Hoogah, are you okay for me to write up your story in our club newsletter, as it is very informative and may well assist others in their installation of the overdrive?

Paul
North Island Model A ford club
New Zealand
 
One of the joys of having a Mitchell is not always going 60 mph plus, but cruising 50-55 so quietly. The first time I rode in a car with one, my mouth dropped when it was shifted into OD about 45 mph....it was so quiet and smooth.... Just amazing. Once you experience one, all the comments by the naysayers tend to be quickly forgotten, and you realize you would never have an A without one.
 
I agree with Terry. The main thing I want is lower engine speed, rather than more car speed.

I'm thinking I'd like to build a spare rear end with 3.27 gears.

My 50 Stude has a 4.55 rear end with an overdrive, which kicks the ratio down to 3.19, but even at that, it sounds and feels good when driving 50 MPH.
 
I think I was kinda lucky not to have done more damage to the car or myself in removing the rear spring! I'm not too proud of having this photo added to Tom Endy's hall of fame for rear spring horror photos :(, but if it helps someone else I'm happy enough! :)

I like Brentwood Bob's advice about trying to somehow contain the rear spring any time it is removed from the car. I wonder if I should have replaced the centre bolt while I had the spring out and "relaxed"? Would this have been a simple remove and replace task? We were both nervous spreading the spring to re-attach it to the axle, having realised the energy we were adding to the spring with every turn of the spreader adjustment.

I'm also OK for Paul_nz to reprint this story in his club newsletter. It's the kind of thing I was looking for on here before I embarked on the installation, but couldn't find.

And, Bruce in Southern OH, I'm sorry but I don't really know what ratio my diff is - I guess it's whatever Henry put in there! I only acquired my car recently and haven't done any rebuilding. What did Henry put in his standard '28/29 Phaetons?
 
Was 3.70 confined to the AR? Although I have an AR body, it is mounted on a later '28/29 chassis and running gear. Is there a way I can tell what diff I've got without pulling it apart?
 
A bit harder than other cars because of the enclosed tail shaft.

There may be a proper way for the model A, but I would jack one rear wheel up and put the crank handle in and move crank to exact top for reference.

Then mark wheel and move it backwards to take up any driveline slack , and in 3rd gear, turn the crank 3. 78 times .

The one wheel will rotate twice around, and if it is 3.78 , the mark will be at the same spot .

If it goes past the wheel mark, do it again at 3.70 engine revs .

A bit of trial and error .

I suppose some would remove plugs and turn the rear wheel and count engine revs, would get the ratio correct without guessing it is 3.78 but more time consuming .

Always best to have one wheel up and one on ground so your spider gears don't move and give you a false reading.

Your one wheel will just turn twice around .
 
Pooch! Are you extracting the urine?
Crank the engine 3.78 times versus 3.70? That difference translates to just 29 degrees. I'll have to get my protractor out! :confused:
 
Well you could always do it 37.8 times and count .

That would be more accurate or 378 times even .

Hoogah, when you next drive your mitchell, can you give us a report on OD gear splitting.

I would be curious to see what ratios you have with effectively 6 speeds forward.

Eg, what is 2nd OD ratio like , is it close to 3rd direct or a usable extra gear ?
 
Yeah, 378 cranks sounds good! :D Better start now!
I'll give you some feedback on the performance in splitting second gear when I'm out next and find a suitable hill.
 
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