HZJ78 - Transmission rebuild (2 Viewers)

[Joss]

Hi guys - great forum and have been a non member reader for a long time!

Just wanted to share an experience with anyone else with an HZJ78 in the event that it may save them some serious $!

i have a 2000 HZJ78 troop carrier as below (i live in new zealand), with about 260kms, has a rough life but its a beast:

A while back i lost the ability to get the truck into 4th gear (i.e straight through), upon checking the gearbox oil (R151F) for the first time in 6 months, sure enough the drainage plug was covered in metal so i knew it was bad news. More concerning was the fact that there was no oil in the gearbox, so i figured it must have all moved across to the transfer case (although the gaskets were holding up well). Pulled the filler plug on the transfer case and out came all the gearbox oil!

Initially from researching on the forum i guessed that the seal between the two must have failed which i understand to be a fairly common problem on these and on Land Rover Defenders, so i decided to fill the gearbox oil up,drain the t case and see how far i could drive the thing before inevitably replacing it.

I ended up doing over 3,000 kms by checking the gearbox oil level periodically, and moving oil from the t case back to the g box manually, it didnt move over that fast so this wasnt as painful as it sounds. The problem with continuing to do this was the s***ty metal filing filled oil from the gearbox was coming through the t case and i was keen not to screw the t case too.

Few weeks back, removed the transfer case and g box with a view to replacing the gearbox and turns out that what had happened was the bearing on the input shaft to the transfer case had completely collapsed and was allowing oil to move between the two. Looking in the gearbox it is completely buggered due to running with no oil for a period of time. Therefore the g box required a full (and pretty expensive) rebuild as all bearings and gears had lost the nice surface from running dry. The transfer case needed only a replaced bearing and one gear. Total cost for parts and labour just over NZD3,000.

Couple of things i wish i had done differently: checked the gearbox oil level much more regularly, had a good old listen to the bearings under the truck periodically (probably could have heard that collapsed bearing on the t case if i'd paid more attention).

Has anyone else had a similair thing happen? Anything i should have done differently!

Also, i find it pretty amazing the truck just kept going until i decided to rebuild the g box and t case given the state of the insides! It was still driving very strong without 4 th gear for a lot of kms and over some pretty challenging terrain.

Cheers guys and great forum! From NZ....

 

[coldtaco]

when people notice this one can connect a hose between the gear box filler and the transfer filler, that way the oil can migrate back into the transmission. But a new rebuild is better

 

[ca18sean]

I added the transfer case / gearbox hose. Seems to be a common issue. Pretty easy to do and it works well!

 

[roscoFJ73]

The bypass hose only works if the oil is migrating uphill, that's when the oil in the t/case is getting into the gearbox. Then it can run downhill back to the t/case via the hose.
If the gearbox is emptying into the t/case(which is lower than the g/box) it can not run uphill back into the gearbox.
But the hose is still a good idea.

I haven't heard of this happening on a R151F, always seemed to be a H55F

 

[ca18sean]

You're right, I misread what his was doing. Mine was draining the TC and overfilling the gearbox, eventually leaking gear oil out past the front input shaft seal. Once I added the hose and set the levels correctly my leak went away. I will need a clutch eventually, when I do that I'll fix all the seals. I'll probably leave the hose on there as I can't see any downside to it.

 

[Joss]

Yea I definitely considered the hose, and given that the filler plugs of the transfer case and the gearbox I think that the pressure in the transfer case of an additional two litres of oil would have been enough for it to move back across.

Ca18sean - I’m shocked your oils moved uphill from the transfer case to your gearbox!?

I would guess that a leak out towards the front of your bell housing was probably caused by a knackered rear main seal, definitely something worth replacing either way once you have your gearbox out..

 

[Joss]

Roscofj73 - all good points, amd the only reason this was happening on this r151f was due to that bearing collapsing on the front of the transfer case.

Given I will have a completely re built r151f and transfer case (throwing a new heavy duty clutch too), have any of you guys got any idea on the life of the rebuild? Have yours held up well?

I’d be hopping for 250,000 kms, is that realistic?

 

[ca18sean]

Yea I definitely considered the hose, and given that the filler plugs of the transfer case and the gearbox I think that the pressure in the transfer case of an additional two litres of oil would have been enough for it to move back across.

Ca18sean - I’m shocked your oils moved uphill from the transfer case to your gearbox!?

I would guess that a leak out towards the front of your bell housing was probably caused by a knackered rear main seal, definitely something worth replacing either way once you have your gearbox out..

Common H55 problem. That's the only way the external hose would work is if it forced the oil "uphill" while driving and the hose allows it to drain back down. I guess the TC gets hot and pressurizes itself, forcing the oil up to the transmission. The leak out the front is probably input shaft seal. It was leaking gear oil, not motor oil. As long as the fluid is at the correct level it doesn't leak, but when I had an extra 2 or 3 liters in the gearbox it seeped past.

 

[roscoFJ73]

I’d be hopping for 250,000 kms, is that realistic?

On single driver vehicles, the R151F holds up ok,you should get more than that. There was an upgrade for the main shaft, making it 2 piece instead of 3 pieces.