Mitchell over drive questions

atch

atch

Senior Member
I'm in the process of buying a 1930 2-dr sedan that has a Mitchell overdrive unit installed. This is a running/driving car needing absolutely nothing. I should be paying for it and bringing it home today or tomorrow.

I've contacted Mitchell to see if I can get instructions and a maintenance manual for the Mitchell overdrive unit in the car. It's been quite a few days now with no response. Can someone on here give me pointers on this unit? I don't know how to shift it. I don't know what maintenance it needs. I'm pretty sure that there are other questions that I should be asking but just don't know what to ask.

TIA

b-t-w; I searched on here and found nothing about these units. That amazes me as I figured that there would be many posts about them.
 
Per Mitchell; Change the oil once per year or 5000 miles. High quality 85/140 weight petroleum based gear oil with a GL5 rating. No other maintainence needed

One feature I like is when you put the Mitchell in neutral, you can upshift or downshift your stock trans without double clutching.
 

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“ Shift on the fly “ ? I’ve wondered about that statement, I use the clutch before shifting gears ( mostly ) splitting 2-3 is what I love about the Mitchell OD ( up or down ) shifting the OD into neutral and then into low while still rolling is another plus !
 
Wait a time with patience. Mine also came with no paperwork (installed in the car whey we bought it). I too sent an email with no response. A package later arrived by snail mail with all the papers that come with a new unit. A+ for customer support.
 
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ModelA29 said:
Wait a time with patience. Mine also came with no paperwork. I too sent an email with no response. A package later arrived by snail mail with all the papers that come with a new unit. A+ for customer support.
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Mine was already installed when I bought the car; I didn't buy the unit from Mitchell. Maybe they will still respond to my inquiry.
 
Mitchell is very helpful. They will answer all your questions.

My Mitchell overdrive needs topping up every few months. I am not sure were the oil goes, maybe to the rear end.

Although Mitchell says to use the G5 rated gear oil, I believe the G4 rated gear oil is a better choice because of the brass components in the overdrive. Brass components can chip off with G5 because the additives are too aggressive. Make sure it is the 85W-140 grade gear oil.

Do not try to baby the overdrive. Put the clutch in and shift quickly. That is better for the synchromesh components.
 
nkaminar said:
Although Mitchell says to use the G5 rated gear oil, I believe the G4 rated gear oil is a better choice because of the brass components in the overdrive. Brass components can chip off with G5 because the additives are too aggressive. Make sure it is the 85W-140 grade gear oil.
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I asked Steve Mitchell about GL 5 Gear Oil and he said he has never had an issue using it in either the O/D or Synchro Transmission.

I have found it is hard to find GL4 85W-140 Gear Oil. What is your source?
 
atch, Here is a tip learned by experience. When you take the car out, don't try to engage O/D till you have done a few miles. Wait till the oil has warmed up for an easy shift. Besides, it does no harm to take it easy till the engine is warm anyway.
 
Synchro909 said:
atch, Here is a tip learned by experience. When you take the car out, don't try to engage O/D till you have done a few miles. Wait till the oil has warmed up for an easy shift. Besides, it does no harm to take it easy till the engine is warm anyway.
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Excellent tip!
 
The download above is what Mitchell sends out with their overdrives. If your overdrive is a few years back, there will not be hex plugs on the two front and rear tubes. The purpose to give access to the two spline couplers grease fitting inside the tubes.

I would not worry about it; a spline coupler does not normally need to be greased. If yours's does have the hex access, be careful to not drop the grease fittings inside the tube.

Tom Endy
 
Here is what RYMAX says about their G5 and G4 gear oils: https://rymax-lubricants.com/updates/the-differences-between-gl-4-and-gl-5.

I started using G4 in my Mitchell overdrive and synchro transmission when I found small brass colored flakes in the oil I drained out during the annual change. Your choice. But for my money I will play it safe.

I buy the G4 at the local auto parts dealer. If you cannot find it there then buy it online.

I use the G5 in my differential and steering box.

One more thing: Modern gear oils are much improved over what was available in 1930. I have used 85W-140 G5 in the standard Model A gearbox and it shifts fine as long as I shift slowly or double clutch going up and double clutch going down.
 
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nkaminar said:
Here is what RYMAX says about their G5 and G4 gear oils: https://rymax-lubricants.com/updates/the-differences-between-gl-4-and-gl-5.

I started using G4 in my Mitchell overdrive and synchro transmission when I found small brass colored flakes in the oil I drained out during the annual change. Your choice. But for my money I will play it safe.

I buy the G4 at the local auto parts dealer. If you cannot find it there then buy it online.
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Please show us some. I can't find 85W-140 GL-4 Gear Oil either. At the Auto Parts Store or on-line. Seems all 85W-140 is GL-5. I want the best for my Mitchell.

I did find some 140 GL-1 that claims it is best for Synchro Transmissions.
 
I’ll second (or third, or fourth…) all the above. Especially Synchro’s comment about driving a bit before shifting the O/D. Steve Mitchell explained to me that for the synchro rings to function properly they need a certain viscosity of lubricant, and (like with any multi-weight lubricant) the 85-140 needs to warm up to temperature to get to that target viscosity. He explained that the O/D works best at about 200F, and that you need to have driven a bit to have the gears mushing around (my word, not his) in the lube to get to that temperature. You should also not worry if you feel the transmission and it’s hot after you have been running it. FWIW, normal involuntary “jerk away” temperature is considered to be about 140F, so you will know the O/D is hot!

I find that my O/D is very stiff, almost prohibitively, until I’ve driven for five minutes or so. That’s at city street speeds for me. After that it’s like buttah.
 
Good video on how to use the Mitchell O/D and a nice view of the bottom of your car Paul. I see you use re-useable "cotter" pins also. I hate split pins!
 
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