Crunch when selecting 3rd and sometimes 4th

[dixiebabes]

Its been like this since i bought the car. I believe its the syncromesh but no doubt im wrong, is this an easy fix or is it gearbox out?

Dix

[keatsie]

If its a synchro gone its box out and rebuild, personally I would bleed the clutch. The fluid gets hot due to the location of the slave, deteriorates the fluid. Start here before gearbox out.

[matt-man]

Firstly check the clutch system for any leaks as this is important.

However, you have another option before you rip the box out! Does your gear stick lift up and down? If so, the bushes in the selector might be shot. Mine wore out and it started crunching into third but after fitting these it fixed it!

Try lifting the gearstick when you shift and see if this makes a difference

[dixiebabes]

It only crunches when im driving the car hard or changing down in high revs. If im taking it easy its fine?

Dix

[keatsie]

It does sound like a worn synchro, but check the clutch system. Others may have better input..

[Number 7]

As others have said, there could be several causes. Check the master cylinder - is there evidence of fluid seepage along the pushrod to the pedal? If so, the seals are gone, and the unit needs replacing (I know some change seals, and I've done it in the past, but don't bother now). IME crunching third when going down the box is a sign of worn synchro. Only cure is a rebuild. What fluid is used in the box, has it ever been changed, how many miles has the box done etc.? The LT77 does not like rushed changes -it's an ancient box, although will last well if cared for.

[adam quantrill]

Before going for a rebuild try the Mobil 1 oil change - it's worth a try. Mine has got smoother since the changeover.

[dixiebabes]

Can the gearbox be dropped without taking the engine out. Whats the easiest way to extract the box?

Dix

[Number 7]

dixiebabes said:

Can the gearbox be dropped without taking the engine out. Whats the easiest way to extract the box?

Dix

I know it was done (twice over the years) on my 400 by the outfit that rebuilt the box, but I couldn't tell you how. I believe it is pretty fiddly though.

[dixiebabes]

Number 7 said:

I know it was done (twice over the years) on my 400 by the outfit that rebuilt the box, but I couldn't tell you how. I believe it is pretty fiddly though.

If it can be done I have the expertise available. Just need the ok so I can plan to rebuild the box and clutch next year.

Dix

[dixiebabes]

Number 7 said:

I know it was done (twice over the years) on my 400 by the outfit that rebuilt the box, but I couldn't tell you how. I believe it is pretty fiddly though.

If it can be done I have the expertise available. Just need the ok so I can plan to rebuild the box and clutch next year.

Dix

[adam quantrill]

Easiest way is engine out, I'm afraid...

[dixiebabes]

adam quantrill said:

Easiest way is engine out, I'm afraid...

Bloody hell i was afraid you were gunna say that adam

Dix

[ultimaybe]

mine would crunch a bit like this, in my case was worn selector bushes.

When the gear is selected, keep pushing on the lever (while moving, clutch not down). If it's crunching then I'd change the bushes. These are done without dropping the box, they're just a set of rubber bushes in the remote gearchange extension.

[honestjohntoo]

I urge you to read back thro' this thread and take the advice of matt-man and adam quantrill to change the remote selector assembly mounting bushes I believe there are four of them, not very clear on this diagram



and then switch your LT77 lube to MOBIL ONE or CASTROL RS

Full scary details here:

http://www.vintagemodelairplane.com/pages/Download...

None of the above requires the gearbox or engine to be removed from the car.

[dixiebabes]

I will try all of the above when i get the car back on the road cheers lads great info once again!!

Dix

[dixiebabes]

Can anyone tell me the grade the gearbox oil either on mobil 1 or castrol rs.

Dix

[honestjohntoo]

dixiebabes said:

Can anyone tell me the grade the gearbox oil either on mobil 1 or castrol rs.

If you re-read my referenced web page you would see this extract

"The box was then refilled with 5W40 "Castrol RS" (0W40 "Mobil 1" is virtually
the same and I have subsequently used both with no discernable difference)"

on page 4 of the pdf - It's not gearbox oil, BTW, just their fully synthetic engine oil, straight from the can.

Search back thro the forum for oodles of prior discussions on the same subject.

Dont forget the molyslip, either!

[dixiebabes]

Ok HonestJohn I have been on to my local motorfactors and they asked what grade oil and what is the correct spec I require? So i (as a clueless idiot) said ill ask him and ask what was the right soloution. By the way Moly must mean molyslip like it used to?

Dix

[GV]

I had my box re-built and found that it was a bit crunchy. They recomended using AT Fluid then I switched to Mobil 1 & Molyslip which improved things greatly. My box is still newish and hasn't settled in fully. But I would not rule out bleeding the clutch again, looking at the remote bushes before getting drastic by taking out the engine & box which

I have managed to do on my own! My technique for taking out the both units together is to slide the engine crane under the front wheel and not over the car's front...