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Transmission Shifting Question

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Raindog Avatar
Raindog Alan W
Saint Augustine, FL, USA   USA
The transmission in my 1959 100-6 shifts with no issues until I have been driving for awhile, about 1 1/2 to 2 hours, and then the shifting gets difficult. The synchros are not grinding it's just difficult to put in gear, especially 1st at full stop. Clutch adjustment seems fine.
I am running 30W non detergent, have tried MT-90 but the tranny leaked like a sieve. The car is driven in NE Florida, so the weather is hot and I have been contemplating using 40W.
Can anyone shed some light on this situation?

1955 BN-1
1959 BN-6

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panelbeat Dave C.
I don't think thicker oil will have much effect on getting into 1st when at full stop. When sitting at a light or stop sign if you put it into 3rd then 1st does it seem to go in better. Mine sometimes is also hard to put into 1st at full stop, but has been that way for years. Sometimes I find that it is just me with the clutch. Not getting it depressed far enough. Other times it is just the nature of the beast. Cogs just not lined up well enough. A slippery modern oil might help but then they leak as you said. Also real slippery oils might not help the OD to work well.

Jack T Avatar
Greensburg, PA, USA   USA
Sounds like an issue with your clutch itself or with the hydraulic system. Try replcing the fluid with a good bleed. Doesn't sound like a gearbox problem.

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Raindog Avatar
Raindog Alan W
Saint Augustine, FL, USA   USA
Thanks, I'll give that a try.

1955 BN-1
1959 BN-6

Phase2 Avatar
Phase2 Derek Snead
Augusta, GA, USA   USA
My BJ8 does the same thing. Wonder if oil additive like Z Max would help. I guess the overdrive is some type of fluid drive system, Z Max might not pair well with that. Any thoughts?

rusty1c Avatar
rusty1c Peter D
Antioch, CA, USA   USA
1961 Austin-Healey 3000 BT7 "RUBY"
1963 Chevrolet C10 "Rusty"
I've had three Healey's in my life and all were as you described. There is no synchro for first gear. I put my car into neutral when sitting at a stop light and when I try to get it into first it sometimes won't go. I now always put it into second then move it to first and I have no trouble. When you do this it seems to align the gears up a bit better and then it goes right in. After doing this for awhile it becomes a habit and I don't even think about it anymore.

thodav Avatar
thodav Thomas Davis
Owings Mills, MD, USA   USA
I suspect it’s having to do with heat and hydraulic pressure. You can’t help the heat so I’d make sure the linkage pins and holes are tight and not egged out. Linkage play reduces the stroke of the hydraulic piston and gets worse over time.

Leyburn, North Yorkshire, UK   GBR
Rusty, what you do is the correct way to engage first gear on any car with non synchro first, and many British cars were that way for a long while before all synchro was introduced. No one seems to have mentioned it, but the practice is the same to engage reverse, it stops all that gear grinding, even if it does go in! Have to say, mine is harder to engage when hot, sometimes even second will not engage at a standstill, so instead go for third then first, my personal take on it, is that the first signs of synchro wear are appearing, which I think is why third, maybe even top are successful, second will have had so much more use, and therefore wear. My BN4 had a really worn side change box, virtually no synchro left anywhere, so I now have a centre change BJ8 box, much better, but still not perfect.

Another what seems perfectly plausible explanation for difficult hot shifting is the clutch, being hydraulic there's not much outside the clutch itself that can go wrong, but when hot I can well imagine that there is some expansion of the flywheel, clutch pate and cover, and even the bell housing that will move the release bearing and the pivot point further back causing some clutch drag, and so the shifting problem. As a retired mechanical engineer, this really does seem feasible to me. As for a solution, well, I think there could be one,it seems to me that a longer stroke in the clutch master cylinder will give a better clutch disengagement. As this is unlikely to be available , then perhaps opening up the bore by a little to use an available size of seals would be the way to go, or reduce the seal size of the slave cylinder by sleeving the bore. That would be a cheap way of trying with a worn out slave cylinder. One final possibility is the gearbox main shaft expanding and becoming tighter in the bearing in the end of the crankshaft, causing drag. Maybe the most unlikely thing to believe, but in life, it's often the most unlikely that is the answer. Love to hear back if anyone, agrees, or even tries any of this!


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