A type Overdrive & gearbox crunch graunch

[Stags Antlers]

Can anybody explain this:

ive got a MOD which has had an overhauled gearbox and an overhauled A type overdrive overdrive.
with the overdrive switched in when in 3rd gear and i then change up to 4 gear the gearbox always crunchs/graunchs its gears, but with overdrive out changing from 3 to 4th is smooth. Although the gearbox has been overhauled and synchros are unbeatable on downchanges i note that changing 2nd to 3rd (with the overdrive out )at low engine revs you can feel the gear cogs engaging / like its close to graunching also it very occosationally jumps out of third when coasting on zero throttle particualrly down long descents

Any ideas - its like the instant change of the A overdrive is beating the gearbox up sychros???

[Stagdad]

Dont know but mine does the same.

Cheers Steve

[cosmicwheels]

Hi. mine was the same on 3rd to 2nd on a recon box but just clearing after 3000 miles, and have to take out o/d between 3rd and top, John

[Firept]

Hi.
I did have the same problems on mine very notchy changes "up" especially when cold. Cut a long story short I had a manual Merc 190e many years ago very low mileage as it had been a mayoral car and the local council had "looked after" it this had the same problems. So I thought check the G/box oil and it was full of good clean gear oil so that meant the gearbox duf then .... no. It was the fact that the gear oil should have been TQF fluid according to the Merc manual so in with the TQF and it was a completely different car smooth changes, quiet, great.
Now to the Stag same problems disregard the manual and filled it with TQF I think if you go to Buckeye triumph web site in the states there is an article on using TQF with over drives worth reading.
Any how done over 1000 miles so far no problems runs cool the gear leaver and housing never get warm and the O/D engages with ease. Now its up to you but dont blame me if you try it and the gear box disintegrates, Also had a Volvo with the rear transaxle this also used TQF fluid.

Paul.

[GDPR]

The Rover LT77 gearbox started its life on EP90, and was soon on TQF due to oil pump shaft failures when the oil was cold.

I have never tried the Stag box on TQF, but cant see any reason why it shouldn't be fine - assuming the overdrive oil pump isn't heavily worn...

I reckon the synchro baulk rings might even like it.....

[Mike Stevens]

When changing gear from O/D 3rd up to 4th, there will be a bit in the middle when the O/D inhibitor switch will switch off and the O/D will start to go back to direct drive. Then when you go up into 4th, the inhibitor switch will re-engage again and so will the O/D. This will then change the speed of the main gearbox output shaft - just as you are trying to engage 4th. I reckon all this could confuse the synchro.

What I usually do is switch out the O/D when going from O/D 3rd to direct top. This seems to give the (old, well-worn) gearbox and O/D time to recover and stabilise.

A newly rebuilt O/D could well engage faster than a worn out one too...

Just some thoughts!

Cheers,
Mike.