Dropping out of 4th

AA Ford Discussion Group relating to the repair and restoration of your AA Ford.
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Posts: 8
Joined: January 21st, 2016, 9:44 am
Body Type: recovery
Model Year: 1929

Dropping out of 4th

Post by motorclubaa » March 15th, 2018, 9:21 am

W e are in UK with a '29 recovery truck which drops out of 4th very regularly, the only answer being a passenger to hold it in!
Have tried suppliers here but they only seem to have shafts for the A. No springs or balls. The springs for the A appear to be bigger and no-one has balls (?)
Does anyone know if they are available in the US?
We bought springs but they were much too big.
We guess AA shafts will be different because of the extra gear?
anticipating help

Bob C
Posts: 1255
Joined: April 24th, 2003, 11:50 am
Body Type: Mail truck, Stake tr
Model Year: 1931
Location: SO CAL

Re: Dropping out of 4th

Post by Bob C » March 15th, 2018, 11:22 am

The 4-speed transmission parts were used into the early 50's which may help expand your search.
Jumping out of gear could also be caused by worn bearings especially the one in the input shaft that the
main shaft fits into, 7120 in the picture.

AAtrans.jpg (157.28 KiB) Viewed 1140 times

Posts: 36
Joined: May 29th, 2013, 6:05 pm
Body Type: 89A
Model Year: 1929

Re: Dropping out of 4th

Post by Ulysses6 » March 15th, 2018, 4:20 pm

BB7120-A bearing transmission main shaft pilot

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Posts: 303
Joined: April 20th, 2003, 7:09 pm
Model Year: 1931
Location: Orwigsburg, PA

Re: Dropping out of 4th

Post by tiredtruckrestorer » March 20th, 2018, 6:26 pm

Make sure the spacing washer (part #7063) is on the front of the mainshaft too. Often these get forgotten or lost. The Model A three speed didn't use one of these so some rebuilders don't realize that one belongs there. Without this washer the mainshaft can move back and forth too much helping to disconnect the fourth gear from the input shaft. Also a bad pilot bearing in the flywheel or a worn input shaft that fits into this bearing can cause the shaft to wobble enough to spit the fourth gear out of contact with the input shaft. If the flywheel housing wasn't dial indicated when it was installed to the engine block to see if everything was true, it too could be the problem that caused unusual wear from running out of line.

Keith Ernst

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