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Dropping out of 4th

Posted: March 15th, 2018, 9:21 am
by motorclubaa
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

Re: Dropping out of 4th

Posted: March 15th, 2018, 11:22 am
by Bob C
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 986 times

Re: Dropping out of 4th

Posted: March 15th, 2018, 4:20 pm
by Ulysses6
BB7120-A bearing transmission main shaft pilot

Re: Dropping out of 4th

Posted: March 20th, 2018, 6:26 pm
by tiredtruckrestorer
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