R380 5th gear rattle

[Ryhoon]

Hi all. just driving home last night when i started to hear a significant rattle
from the gearbox. only in 5th and probably the noisiest when i'm on or off
the power.
So whats the bad news?!
Ta. Ryan

[Psimpson7]

With it only apparently affecting 5th (although it would be interesting to know if its quiet in reverse), it points to an issue with the layshaft.

Rearmost bearing/oil pump failure maybe? or the stake nut has come loose!

I would start by draining the oil and having a look at it if you are sure its inside the box.....

[justinc]

Also check the rear support bearings for the layshaft and mainshaft, worse case is they can fail and you lose teeth from gears:(


jc

[Ryhoon]

So is there any problem with still driving around but not using 5th gear. I dont want to potentially cause any more damage though.

[Psimpson7]

Yes, you can do more damage. The oil pump is driven off the back of the layshaft and will not enjoy itself if there are any issues with the bearing in front of it.

Also if a bearing has failed it is likely to have dropped a lot of debris into the box which could get caught up etc etc.

Personally I would drive it home carefully and then have a look.

[Ryhoon]

Thanks. Yep got it home and it hasn't moved since. The sound is what I would call notchy. Maybe more gear oriented. Maybe lost a tooth off 5th? What other gears are driven off the layshaft? Also can the gearbox be removed without removing the transfer?
Your advice is much appreciated.

[TeamFA]

As somebody who's also replaced their layshaft, and hence knowing a little bit more about the design of the 'box, I would be going with layshaft bearings as well.

5th and reverse gear run off the weak end of the layshaft... did you have an opportunity to see how it was in reverse? It might very well do the same thing.

Either way, it's gearbox off to have a look. I don't know if it can be done with leaving the TC intact... somebody more knowledgeable will be along shortly.

[justinc]

Yes you can take box out as a unit, although you can rebuild 5th gear and all rear bearings, replace oil pump etc with the trans in the vehicle. Remove transfer case off the rear of transmission, then extension housing and 5th gear and associated bearings etc etc are all revealed

JC

[Ryhoon]

Ok. I went out to check reverse and I could hear the knocking straight away without putting it in gear. Same noise in reverse and in 1st as well. Wasn't willing to push my luck from there.

[Psimpson7]

Unfortunately it sounds layshaft related then.

I rebuilt my r380 and documented it in detail in the build thread on my 90 which can be found in a link in my signature if you are keen to give it a go yourself

I broke the layshaft in mine.

[TeamFA]

Yes you can take box out as a unit, although you can rebuild 5th gear and all rear bearings, replace oil pump etc with the trans in the vehicle. Remove transfer case off the rear of transmission, then extension housing and 5th gear and associated bearings etc etc are all revealed

JC

Never thought of that... I suppose you could do most of the gearbox that way...

[Psimpson7]

While it is probably possible I think it would be very hard to do this and not get leaks. When you unbolt the extension housing it is the same bolts that go through the centre plate to the main housing.

I think that in removing the extension housing you would almost certainly disturb the sealant between the main case and the centre plate. as now they wouldn't be held together other than by the internals.

I would think that unless you knew exactly what you were doing you would end up with oil leaks.

[justinc]

no the trans requires removal from vehicle for a rebuild as end floats etc need to be measured etc on a bench, not possible when attached to engine:o:D.

Pete, we have done many 5th gear repairs this way, the factory sealant is quite strong, careful removal of the ext housing ensures the plate doesn't detach from the case, and after the ext case is removed i bolt the plate to the case again with a couple of dummy bolts while working on it.

no leaks yet:).

jc

[Ryhoon]

Got the box out yesterday and 5th gear on the layshaft looks like a bad boxer. Missing several teeth. All ready picked up a replacement box and should be back on the road this week which is good cause its my daily driver. Thanks everyone for your advice.

[TeamFA]

Good news.

Not especially relevant as you have a new 'box, but was there any other damage evident? Any play in the layshaft indicating worn bearings? Oil pump intact in the end of the extension housing?

Was the choice to go for a new box driven by the need to get it back on the road ASAP?

Cheers!

[Ryhoon]

We didn't really check to much but the gear that is on the main shaft was a bit marked up.
The new box was to try to get me back on the road asap. If I wasn't so busy with work I may have got it rebuilt. The guys at modern motors at dungog helped me out by coming in on saturday so I could do the exchange.