Occasional gear clunk!?

[JakeM]

From what I've read of your thread I can see you are very handy with a spanner, but how about some fresh eyes on it? If you can find someone knowledgeable you can trust? Is there any one on here?

 

[Shayne]

That's just it i'm not experienced with 4 wheel mechanics for 4 years my trucks have been teaching me as and when things go wrong . The mot garage blamed the steering rack which was just dumb but then i had to change the rack bushes to keep them happy A garage can only do what im doing , its a process of elimination and if i was paying by the hour the truck would likely owe me 10 grand by now and still be no better than it is .

I have a plan i just need to get to it .

 

[Beau]

Just a random though, have any of you tried double clutching when changing gears?

 

[Shayne]

No need for double clutching Beau a feel for rpm can eliminate the clunk very easily but if i wanted to drive like a fairy i would buy a hairdressers car .

 

[JakeM]

Found this. The guy shortens a stretched transfer box chain. He makes it look easy. If only....

 

[Shayne]

Your a star Oak shortening the chain is not difficult i used to do the same with pushbike chains as a kid using nothing but a hammer and nail . Where the vid helps me is i thought the cogs would drop unsupported when the box was opened which would leave the chain slack anyway . It seems not so worth a look when it stops raining maybe .

 

[Beau]

Excellent find Oak! Looking into this...

 

[Shayne]

Wherefore art thou BobMurphy

 

[BobMurphy]

Wherefore art thou BobMurphy

You rang ??

Well . . . . Locking the Centre Diff locks the input shaft to the output shaft that drives the rear propshaft, as well as locking the Differential's outer drum (Anulus) to those shafts.

The drive is now straight through to the rear propshaft.

This means that the drive to the front propshaft, via the Hi-Vo chain, has to rotate with the Anulus as its Planet Gears are trying to run on two different tracks - the outer having many more teeth than the inner - and the Planet Carrier therefore locks-up.

This would indicate that the 'clunk' is coming from the Centre Differential and the drive to the propshafts, though its more likely to be coming from the front propshaft as it has the chain drive. There may be play in the differential owing to the needle rollers in the Planet Gears being worn giving slack in the mechanism but I would think a bit of slack in the chain is the most likely culprit.

I think there is always going to be some slack in the transmission as there are a great many bits in the process. With the Centre Differential 'open' the front and rear propshafts are in opposition - turn one and the other tries to turn backwards. It is only the fact that all four wheels are on the ground and therefore providing equal resistance to rotation that allows the whole differential to turn as one. When engaging drive, all this has to "tighten up" and taking up the slack produces noise.

I wouldn't be too concerned unless the chain drive is skipping on the sprocket teeth, giving a really loud 'clunk' and a momentary loss of drive.

I have a Transfer Box in the workshop at the moment that is doing that. I haven't started stripping it yet but it will be interesting to see what's wrong as it isn't very long ago that I put a new chain in and replaced all the bearings. I don't know what the owner has been doing to it but it has been used fairly hard off road in the Pentland Hills as his wife's family are Hill Farmers.

On that one the chain still skips with the Centre Diff locked . . . So your problem isn't that .

Bob.

 

[Shayne]

Been driving my clunker this week and i'm growing more and more convinced its the rear axle moving . I couldn't shift the trailing arms and panhard rod last time i looked a couple of thousand miles ago but i'm going to change the bushes when time allows before i do anything else to the truck .

I don't weigh a couple of tonne so maybe i can't find no play because i'm a weakling .

 

[Shayne]

It does , but if i compare our descriptions my problems some more advanced than yours ie, if it does turn out to the rear axle bushes they should have been changed years ago .

I changed them on my other truck because it somehow felt unbalanced at speed , nothing major i think most would assume they were going to fast on that motorway curve but gut instinct told me it was rear wheel steer , something much easier to pick up on in a swb i suppose , and now it feels planted no matter how daft i get .

With trucks as old as ours it should be on the to do list anyway .

I will use Whiteline rubber bushes as i have (perhaps wrongly) linked the superpro poly ones to broken mounts but i most certainly cannot justify the why of it ?

 

[Shayne]

These trucks are strong mate , they will go 95% of places a standard 80 will go with half the maintenance an 80 requires so don't be disheartened , it can be fixed we just don't know yet how

but we will given time