Sunday, March 31, 2013

Tranny Rebuild

One of the very odd problems with this car was the transmission.  It's a 4-speed with an electrically controlled overdrive - another standard feature unique to the '71 142E - and the 4th gear clashes when engaged.  It's not uncommon for a car with 350k miles to have a worn synchro ring or two (they are the clutch-like things that bring the gears to the same speed before engaging so you don't get a clash), but it's almost always 2nd or 3rd gear since they get the most shifts.  I've never heard of a 4th gear synchro failing.  So, apart came the transmission to see what's up.

Here's the whole assembly on the bench.  The red part is the transmission, and the alloy part is the Laycock overdrive unit.  The first step is to separate the two main parts.

Transmission and Overdrive together
Next,  the guts of the transmission are removed leaving just the case.  The overdrive is fine and records show it was recently rebuilt so I'm not going to touch it.


Gutted transmission case

Transmission entrails
Oh look, there's the problem.  There is nothing more satisfying than finding a clear cause of a problem, and this was one of the more satisfying.  The 4th gear synchro was cracked!  As a result, when pressed against the mating cone, rather than acting as a clutch and bringing the two parts to the same speed, the ring just splayed out and did nothing.  Problem solved with one $40 part.

Cracked synchro ring
While the box was apart I checked the various bearings and found the input shaft bearing was a little worn so I replaced it and the needle bearings where it rides on the main shaft.  The counter shaft thrust washers were also worn a bit more than I'd like so I went ahead and replaced them as well.  Then back together it all went along with a nice new clutch fork boot and clutch release bearing.

Transmission and overdrive reassembled and ready to go back in the car




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