5 replies to this topic

[Sharks]

Hi All,

I'm new to the forum, but active on other sites a bit closer to home. Hoping the brains trust here can give me a hand with something.

To cut a long story short, we have a five speed Tran-X straight cut gearbox that is currently out of commission as it keeps chewing idler gear bearings. While working on a fix for that, I want to keep the Moke on the road, so I'm refreshing the old four speed.

However, when measuring the clearances for the baulk rings, I expected second to be in the worst condition - but this is not so. In fact, fourth is in bad shape (only 0.50mm/0.020"), and second is bloody good (1.00mm/0.040")!

Taking the fourth gear baulk ring and placing it on second reveals that actually, it's not out of spec (I get 0.90mm/0.035"). So does this mean the synchro cone on fourth is in poor shape?

Reading up on these forums, I came across some worrying comments from Spider a few years ago:

I've found in many DAM 5262 Cases a machining error (I can't explain it any other way).

For 1st, 2nd and 3rd gears, the distance between these is set by the Mainshaft on to which they are mounted, however for 4th gear, being a separate shaft, it relies on being mounted in the correct location.

What I have found on many of these late cases is that the registers machined in to the cases for the Mainshaft and the 1st Motion shaft are 0.020" too close together when compared with a great number of other gearbox cases measured, with the Mainshaft Bearing Tunnel being in error. When assembled, this puts the 1st Motion Shaft too close by 0.020" to the 3 / 4 Synchro Hub. This usually results in 3rd or 4th Gear Baulk Ring 'dragging' or indeed locking up more often than not and on some boxes - relevant here - can drag on 4th gear, or 3rd and 4th at the same time (resulting in the lock up I've mentioned)

It also results in serve overshoot of the synchro hub when selecting 4th gear to the point were the detent balls almost come out when everything is new. It will only take a bit of wear in the selector and these will come out and either lock it in 4th gear (this happened to my brother) or the balls will come completely out and you’ll have no sychromesh on 3rd or 4the gears.

I'm assuming that the "DAM 5262" casting referred to is a typo, as I can't find anything detailing the existence of a gearbox with that number.

To me, this still doesn't make complete sense as I would expect the baulk ring to wear out long before the synchro cone. That said, I know the baulk rings have been replaced in this gearbox at least once before. Additionally, the only reason I pulled this box apart to refresh it in the first place was that when it was taken out of the car, it occasionally crunched in second - we assumed baulk rings and I was going to replace the selector fork while I was in there, as that too measured out of spec. Third / fourth gears were never any trouble.

So what is the verdict? Is this casting one of the ones with this machining error, and if so, should I replace the baulk rings and put it back together again or is it only going to give me trouble? Even on fourth, our 'good' second hand baulk rings give 0.85mm/0.033"...

Thanks in advance,
Sharks.

Edited by Sharks, 01 April 2024 - 01:49 AM.

[Spider]

Hey Ash,

 

What gear set does it have ?

[Sharks]

Hi Spider,

 

It is all standard A+ gear. I have however borrowed the 1st/2nd selector fork and synchro hub outer from a pre-A+ box and can't find any reason why they shouldn't work with the A+ gearset. They're in better condition than the ones that were in it.

[Spider]

Ash, the fork should be fine, as long as it's in spec. The wear limit with these is 0.015".

 

Coming back to your gearset, sorry, I probably should have given more info what I'm looking for here. There was 3 different gearsets factory fitted in to these gearcases, those with standard unmaked teeth, those that have a single line machined across the tips of the gear teeth and those that have 2 lines. Also, what year casing is it ? If you look on the diff cap, there's a date code.

 

I'd say here you'll need to make a shim to add between the Mainshaft Bearing and the gearcase to move the location of the Mainshaft up towards the speedo housing. The gearcase really needs to be measured to determine how thick that needs to be, but I've found they need anything from 0.005 to 0.025". There appears to be an error in how they were machined.

[Sharks]

Hi Spider,

Thanks for your help.

The fork was out of spec, so even though it wasn't playing up I've swapped it over.

I wasn't aware of the differences in gearsets, sorry. This box does not have its original gearset in it, but what's there does not have any markings on the teeth. This gearset was new old stock in the early 1990s. The five speed has straight cut gears with a single marking in the middle of each tooth, so I presume I would be looking for the same thing on these helical gears, and that is not evident. The diff housing is marked 84 and 13. 13th week of 1984?

Bugger. I got excited and put the thing back together again, but sounds like I'll have to pull it all back apart to put that shim in. How exactly does one measure the box?

Edited by Sharks, 01 April 2024 - 01:11 AM.

[Spider]

84 and 13. 13th week of 1984?

Bugger. I got excited and put the thing back together again, but sounds like I'll have to pull it all back apart to put that shim in. How exactly does one measure the box?

 

Being early in this series of gearboxes, you may not have an issue, but you won't know until it's measured and you did mention that the baulk ring for top gear was quite worn, I'm sus that it have the error that I mentioned in that thread where you found that post. When you fit up all new baulk rings (and on the bad assumption they are right), after fitting the Laygear and tightening up the 1st motion shaft and Mainshaft Nuts, if there's binding between the 1st Motion Shaft and 4th Gear Baulk Ring, you can be sure the case isn't machined as it should be. 

I'll find a photo and send it to you.