Mitchell OD In MY AA - Update

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emf
Posts: 46
Joined: March 21st, 2016, 5:21 am
Body Type: Firetruck
Model Year: 1928
Location: Hudson, NY

Mitchell OD In MY AA - Update

Post by emf » August 21st, 2017, 12:18 pm

I posted this on the Ford Barn, but since I said I'd report back here, here it is...

Sorry for the long post...

I thought I should bring everyone up to speed on my Mitchell Overdrive installation in my early 28 AA Firetruck. This is a 36% overdrive unit with a 3 speed transmission and a high speed rear.

The 110 pound box arrived by UPS and I was ready to dive in. The front torque tube with the shaft installed was attached to the gear box, along with the rear torque tube. The rear shaft and its coupler were not installed. This needs to be installed by the user. The unit was shipped with a cable shift linkage that was intended to be clamped to the standard shift lever. I thought this looked too modern, so a call was placed to Mitchell. They agreed to replace the cable linkage with a shift lever type. It was explained to me that hard linkage using clevises and a rod on AA trucks may not be desirable, since the box sometimes jumps to neutral when hitting bumps or pot holes with these heavily sprung trucks, so they have gone to a shift lever with cable. Since they have never shipped a kit for a firetruck, they had no way to determine the length of the cable needed to get around the large firetruck pump that sits between the transmission and the second universal joint. They shipped an ‘off the shelf’ length of cable and suggested that I try it. If modifications were necessary, we could do so once the unit was installed.

The parts went together without issue and I was surprised how quickly it was all assembled. I assembled the unit on a spare rear end assembly so as not to lay the truck up for an indefinite amount of time. This is parade season… I would say that the total time necessary to remove the old drive shaft, torque tube, and radius rods from the old assembly was 1 ½ hours. The assembly of the new parts to replace those removed was about the same. Working on a lift was a tremendous advantage.

The hardest part was connecting the cable linkage between the box and the handle. After much consternation, and since they did not have an off the shelf front cable bracket for the AA, I decided that the easiest method would be to fabricate my own hard linkage using rod and clevis. This forced me to extend the bell crank at the transmission end by about 4 inches to get below the large frame cross member just behind the pump. Once I made that decision, the rest followed without issue.

Results. I am amazed at the workmanship of this unit. It is quite well made and my guess is that I’ll get many years of great service. It shifts very smoothly and is almost effortless. I can guess at my top speed in overdrive is about 40-45 mph. I need to have someone follow me and clock my speed. I’d do it again in a heartbeat.
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Stakebed
Posts: 1076
Joined: June 14th, 2007, 7:29 pm
Body Type: Grainbox
Model Year: 1929
Location: Illinois

Re: Mitchell OD In MY AA - Update

Post by Stakebed » August 21st, 2017, 4:27 pm

she looks pretty - in your opinion do you think the linkage would fit an AA with the dual high? How did you attach your shiftier to the crossmember? I could see how mitchel would be concerned about it popping into neutral if the rearend flexes enough.

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emf
Posts: 46
Joined: March 21st, 2016, 5:21 am
Body Type: Firetruck
Model Year: 1928
Location: Hudson, NY

Re: Mitchell OD In MY AA - Update

Post by emf » August 21st, 2017, 4:55 pm

I don't think my pump takes up any more space than the dual high does. I have one on the shelf and it extends down below the shaft centerline about the same as my pump. The shifter is attached via a special cast aluminum adapter supplied by Mitchell. The adapter bolts to the shift tower and is used for any 3 speed transmission. The big issue is the length of the bellcrank that meets up with the linkage. I lengthened it to get the rod below the cross member.
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Stakebed
Posts: 1076
Joined: June 14th, 2007, 7:29 pm
Body Type: Grainbox
Model Year: 1929
Location: Illinois

Re: Mitchell OD In MY AA - Update

Post by Stakebed » August 22nd, 2017, 7:06 am

I replied on your forbarn post as well but right where that linkage is is where the foot pedal and linkage for the dual high is located so i dont think you could run both in this setup. If the rod and arm were off the right side of the trans theres tons of room. I dont remember my photo sharing account otherwise id post a pic....

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emf
Posts: 46
Joined: March 21st, 2016, 5:21 am
Body Type: Firetruck
Model Year: 1928
Location: Hudson, NY

Re: Mitchell OD In MY AA - Update

Post by emf » August 22nd, 2017, 8:00 am

When they shipped the unit to me, the shift mechanism was a cable set-up with the shift plunger attached to the original gear shift lever by using clamps. With this, connected via cable, it would avoid the dual high pedals.

Frank

Stakebed
Posts: 1076
Joined: June 14th, 2007, 7:29 pm
Body Type: Grainbox
Model Year: 1929
Location: Illinois

Re: Mitchell OD In MY AA - Update

Post by Stakebed » August 22nd, 2017, 8:15 am

ooh ok, yea it shouldnt be too hard to make a similar bracket and attach to the passenger side area. Already pretty crammed in the drivers side foot area as is haha

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