H42 Transmission Question

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Sep 20, 2004
Curious, what oil did you fill it with ? The statement that it doesnt grind, just wont go in and then if you clutch & rev it you can get it in desired gear is very telling. I have an sm420, syncro's in 3rd & 4th and I can downshift, just have to be in the right rpm. If it isnt grinding & just wont go in, I have a ? does it come out of current gear and wont go into lower gear , stuck in Nuet. ?, or does it not come out of current gear ? I ask because IMO if it is not coming out of gear at speed its the clutch not releasing all the way. Experts please review the pics, is the 1,2 synchro in backwards ?
Apr 21, 2005
is this H42 a early style type with a cast iron 2 piece shift tower / top plate / plates assy. ?


a later 1piece ALL Aluminum Shift Tower assy. ?

Cast iron versus aluminum was not a date change but a series change. 40 series H42 and H42 were always cast iron. 60 series and later 70 series were always aluminum. Four speed aluminum covers the shift tower was further back on aluminum covers. All H41 and H42 four speed transmission the tops were interchangeable. Does matter before or after 8/80 change or cast iron or aluminum they will work.

The H55F on the 40 series was aluminum. They were different than 60 and 70 series because the shift tower was forward like all other 40 series. While the H55F for the 60 and 70 series are still sold while the 40 series has been discontinued for a long time. 40 series with a H55F were only sold in North America from 10/82-10/84 in the BJ42 sold in Canada. Most 40 series covers that make it here are from Australia and Europe.


Aug 23, 2019
Portland, ME
Just for follow up, I drained the oil out and replaced it with an absolutely precise amount of transmission oil. Drove it a few times and it is shifting much more smoothly. Maybe it just needed to loosen up a bit after the rebuild? I don't know, but it seems to be getting better and better each time I drive it.

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