Outer Limits 4x4 Board

Does anyone know if double-clutching, particularly uphills is harmful to my hilux 5-speed? Both off-road and on-road? I've been told by a few people it can chew out your synchros inside the box.
I can't see how reducing the friction load on the clutch by matching the revs can cause damage. Can anyone help on this one??

Cheers,
Bart

If you don't need to - why do it
Yes I've heard it can actually wear out the syncros faster....& once they're worn you'll need to

The whole idea of double clutching on down shifts is to bring the speed of the lower gear up to the current gear speed. This was the ONLY method of shifting before synchros, and takes a bit of practice. It reduces the synchro wear, and prevents "crunch" on a worn out box

On an upshift, the lower gear slows down to match the next gear (which is effectively stationary)

Roktruk wrote:The whole idea of double clutching on down shifts is to bring the speed of the lower gear up to the current gear speed.
This was the ONLY method of shifting before synchros, and takes a bit of practice.

Agree, agreed & agreed

Roktruk wrote:prevents "crunch" on a worn out box. On an upshift, the lower gear slows down to match the next gear (which is effectively stationary)

Agreed & Agreed.

Roktruk wrote:It reduces the synchro wear

Disagree. But double clutching you are in effect making the syncros themsleves work more not less....

If the suncros are rooted or there aren't syncros - then by ALL means double shuffle....but if the syncros are working fine - just shift normal....(unless doing BIG down shifts)....

I only ever use the clutch to take off. Just match revs and change. No crunch No wear.

Apparently in the land cruiser 75 series owners manual it says not 2 double clutch.

Thanks heaps for all the great info guys,
My gearbox only seems to be making crunching noises when
I downshift when the car is cold (usually from 3rd to 2nd gear).
Other than that it's OK.

So from what I have read here, I'll just double-clutch it when its cold, or
if a quick or big up-shift is required. That way I should get the most
life out of this gearbox before replacement.

One other question, how does that lucas oil-stabilizor go in 4WD gearboxs
and transfers? can anyone reccomend a good gear oil additive??

Cheers,
Bart

Hey Bart,
now that you have said that it only happens when the car is cold it is possible that your gearbox oil is a touch too thick.
I once had a case with a car gearbox, we might have been replacing the clutch or something i cant remember what we were doing actually but we changed the oil in the gearbox and filled it up with whatever the car makers specs were. We are talkin about a gearbox in good nick with no syncros probs here to. Anyway when we filled it up and took it for a drive it would hardly go into second gear. We turned around drained it out put a thinner oil in it and it was micky mouse.
This could be something you could try as it is now winter and when your car is cold the oil in the gearbox is at its thickest.
Try some thinner oil and let us know.
just a thought,
kynan

Also i would like wooders to explain in a bit more detail why he thinks double clutching wears the syncros out faster?
You agree that double clutching was the only way to downshift in the old days without crunching. So from this, one could say that by double clutching you are efectively doing what the syncros were put in the gearbox to do in the firstplace and that is, to syncronise the two gears that are about to mesh in the completion of a gear change.
So, if by double clutching you have got these two gears spinning at the same speed there is no wor for the syncros to do.
Therefore i believe that by double clutching you would reduce wear on the syncros, this is ofcourse assuming you double cluth properly and dont over rev the enginebetween changes.
I'll be happy to read your reply just make sure you try and explain it .
kynan

Toyo Truck wrote:I downshift when the car is cold (usually from 3rd to 2nd gear).
Other than that it's OK.

Hello Bart, I'm just going through the same dramas with my Feroza. Bought it back in January and knew the gearbox was a bit worn, but apart from a bit of noise it was fine. Now the weather's colder it's grating on second to third downchange, and sometimes on the up change too :mad: .

I put some Castrol VMX80 gearbox oil into it and that's made it a bit better. It's designed for worn boxes that have coldshift problems. http://www.castrol.com.au/products/pdf/ ... X%2080.pdf It's still not perfect though, so the next step is a 50/50 mix with Dexron III auto trans fluid. A lot of manufacturers recommed that mix for gearbox shift problems.

If that doesn't fix it I'll use my old favourite of Mobil 1 engine oil . I used this for about four years in my old Charade when it had similar problems. It fixed it and didn't seem to have any adverse effects on the gearbox. I'm sure someone is sure to point out the problems with this fix, but it worked for me!

G'Day

Might give the gear oil change a go. That VMX80 sounds the goods.
A change is about due anyway, especially the transfer case oil.
It wouldn't hurt.

I'll let you know if there is any improvement on the problem.

Regards,
Bart

I've just done the 50/50 mix with the Dexron III and VMX80. Discovered it's near on impossible when lying on your back under a Feroza to get the gearbox drain plug back in quickly after draining half the old oil (oil running down arm, unable to get plug to start in thread-very messy )

So far it seems a lot better again. Will have to wait until a cold morning to see just much more improved it is.