Gearbox help

[PaulAnderson]

Hi All - I hope this finds you well?

I have recently had my gearbox and overdrive rebuilt by Overdrive Repair Services.

They have done around 4 boxes and overdrives for me over the years and no issues to speak of.

The clutch is adjusted to as far as it can go.

Oil is at full and it is EP90 as recommended.

What happens is that changing down from fourth to third gives a little crunch

Changing down from third to second is nigh on impossible and when you do a nice crunch is audible.

No synchromesh on first - all good.

Overdrive goes in and out fine.

If I forget to disengage the overdrive and try first and reverse it is not a happy scenario and appears to lock up a little and judder.
I have a Triumph TR4A with a similar box and overdrive set up and this never happens.

Any thoughts on what I might do solve that lot?

Best wishes.

Paul.

[musicman]

Hello Paul , I had the same problem many years ago, it was the clutch release bearing that had worn down, no matter what adjustments we made it came down to the bearing. I hope this helps

[PaulAnderson]

Thanks. It is a new bearing. Could be the issue?

Best

[10kph]

Hi,
     I assume that you are using a moss gearbox with overdrive. Oil is shared between box and overdrive and I would say that EP90 was probably for a gearbox only. Years ago I used a moss box and overdrive in a 2.6 for road an hillclimbs. I obtained quickes shifts in using a thinner oil, infact auto transmission oil and no problems within 10 years and the car is still going 20 years further on. Give it a try or buy a more modern thin gearbox oil.
     Tony

[PaulAnderson]

I was at the Beaulieu International Autojumble and Overdrive Repair Services were there. They rebuilt the gearbox. After a lengthy conversation they felt something had not been done correctly so the box is out and with them now. We'll see if there is any improvement on its return. I have a new release bearing and the different in material is less than 1mm, so it looks like that was all OK.

[AE 501]

BE CAREFUL!

At least from the wiring and switches it should be impossible to engage reverse, if the overdrive is switched on! If you do this, you will certainly kill your overdrive. The planetary gears in overdrives are intended for rotation in just one direction! If you use reverse with overdrive, the gears will stuck and that makes the judder feeling.
So normaly you should have electric switches on top of the box wich allow overdrive engagement only in 3. and 4.

Best wishes
Chris

[James Eastwood]

My Bristol gearbox is run on 20W50, the Ace hand book specifies a 30 SAE. I also run my Sprite gearbox on 20W50. I only run EP90 in the differentials.

I tried to find the Moss gearbox spec with a quick search but could only find oils sold for Moss boxes, these were a 30 and 50 weight.

Possibly your EP90 is lubricating the synchro cones too well and the speeds are not being matched. The bigger crunch from the 3-2 shift may simply be the speed ratio difference is greater than the 4-3 shift.

Good luck, let us know how it goes.