LT77 gearbox crunch with fast gear changes

[KKson]

So the SEAC is now back on its wheels and I've given it two quick squirts up the road. When I first went out, taking it nice and steady, the gear changes are smooth, progressive and no issues. If I spank it however with fast changes then the box crunches a little in every forward gear. If I slow the change down, to allow synchros to align then no problem. Today I have checked the clutch, flushed and bled the hydraulics, so I don't think it's a dragging clutch issue.

The box previously was running normal ATF. I've flushed the box and replaced with the very expensive Difflock Evolution 1, which is considerably thinner than the original ATF. Could the thinner oil be causing the issue? Of course, prior to purchase I couldn't check as the car had been laid up so all I had was a crawl around a farm yard in it.

I'm tempted to drop the expensive oil and try something thicker out of curiosity. Thanks.

[phillpot]

I was advised that Castrol SMS or SMX are good in the LT77 ?


Now appears to be called "Syntrans" ....... clicky

[adam quantrill]

Might be worn synchros.

A dragging clutch is most noticeable when putting it into reverse - it will crunch and grate quite a lot.

It's worth trying another oil change as you know I'm a fan of the Mobil 1 0W40 + moly.

If it's too thin it will be worse when hot, so spank it when cold and see.

[KKson]

Thanks Adam. Got your mixture in my old 350i and current 390SE and both work great. Given the fact that the "crunch" when rushing the gear change is with every gear change it makes me suspicious. From stationary no issues selecting 1st or reverse.

[Lesliehedley]

Keith, I've got the Difflock evolution 1 oil in my gearbox. When I changed the oil from whatever it was to the Difflock there was a noticeable improvement in the gearchange quality, so that may not be your problem. It could be the remote bushes are shot. When my remote bushes started to wear the first indication I had was what sounded like synchro noises but turned out to be the remote catching the propshaft on changes. If you can move the gear lever vertically by more than a few mms it could be your problem.

Edited by Lesliehedley on Friday 8th May 23:42

[gmw9666]

Got the Difflock stuff in my rebuilt box. Can’t comment as Ive still not driven it lol

[KKson]

Lesliehedley said:

Keith, I've got the Difflock evolution 1 oil in my gearbox. When I changed the oil from whatever it was to the Difflock there was a noticeable improvement in the gearchange quality, so that may not be your problem. It could be the remote bushes are shot. When my remote bushes started to wear the first indication I had was what sounded like synchro noises but turned out to be the remote catching the propshaft on changes. If you can move the gear lever vertically by more than a few mms it could be your problem.

Edited by Lesliehedley on Friday 8th May 23:42

Thanks Leslie. Just checked the gear knob movement and if I try and lift it, there's a good 20mm of slack movement so hopefully that is the issue. Cheers.

[adam quantrill]

Oh yeah, that will be it, fix that first and all should be well.

[LLantrisant]

difflock is also my first choice ....and it really helps to improve gearchange..you feel it instantly after change,but you should run quite a few miles until it really develops its complete "power"