Series 3 occasionally jumps out of 3rd gear

Hi I'm a new member here, I'm just in the process of buying a Series 3.

It has a few minor problems, one being that it can jump out of 3rd gear when slowing down for junctions.

Does anyone have any idea what may be causing this, and how could it be sorted?

EDIT - MORE INFO: It's a 1972 SWB, 2.25 Diesel engine with no overdrive on the gearbox.

Thanks for any info.

could be wear in mainshaft assembly especially bush much more than 8 thou endfloat causes gear to jump out ,weak springs or worn dog teeth on 3rd 4th synchro unit ,both would require box removing from vehicle

Thanks for the quick reply.

Does it mean that the box will require a complete rebuild to sort it?

Well, that depends. If it is any one of the above or even all of the above that is wrong with the box, then no, if that fixes the problem. If by "rebuild" you mean take cogs and stuff out, then yes. If you mean replacing lots of the parts, then possibly not. I would personally strip it out and have a good look at it regardless - I learnt the hard way on that one.
If it is the syncro, go for a genuine syncro, or at least a non genuine syncro but fit genuine springs on it (just my own findings on that one, others might say otherwise)

Could also be a dodgy selector fork?

sounds like a syncro problem

I had this on my 72 S3 SWB. I replaced the detent springs and balls and problem has gone. Pennies to fix, and you will probably find you only need to change the springs. This would mean that you don't even need to take the top of the gbox.

J

Thanks for the replies.

It seems that protractor's suggestion will be the first thing to look at.

The Series 3 arrives on wednesday. I will have a few months to look at it as I cannot get insurance at a sensible price until I'm 21 in March.

Which panel do I need to remove to get to the threded plugs that hold the detent balls and springs in place?

Also, where can I buy the springs and balls?

Thanks for any info.

I did mine when the gearbox was out. I would think you need to remove the tunnel to get access.

I got the parts from LR series. I think these are them... 3649 SELECTOR SPRING | shop | www.lrseries.com | L. R. Series

Thanks for that protactor.

I searched for this on here and someone reccomended fitting the spring that is used for reverse gear in place of all the springs. This is because it is apparently stronger. Is there any truth to this theory?

I have heard that. But it certainly fixed my jump from third on overrun, and is as originally specified. Get genuine if you have any concerns. *shrug* I just fitted the relevant spring at the time.

good luck!

Give it a good check over when you replace the springs. Sometimes the ball (which is what actually stops the selector rod moving) can get jammed in the drilling so that its is not pressing properly against the selector rod and holding it in place.

Its not that much more effort to take the selector cover off and check its all looking correct, and perhaps give it a clean out as well. If you do,
be careful that the balls don't drop into the box

I thought I would resurrect this thread as I can easily get at the gearbox once my bulkhead is off.

Is it worth stripping the box down to replace the bearings? The seals need doing, but the manual says they can be done without disassembling the whole box.

Also, I still need to sort out the jumping out of gear issue.

If the bearings are quiet then do they need replacing?
What seal can be replaced without removing the box? Possibly the rear but it would be hard to a good job. But the front ones definitely need box removed.

The manual says that the seals can be replaced with the box removed, but without needing to actually disassemble the box. The can be removed from the outside of the box.

Webley1991 said:

The manual says that the seals can be replaced with the box removed, but without needing to actually disassemble the box. The can be removed from the outside of the box.

Click to expand...

Ah ok I misread. Thought you meant without removing the box from vehicle. Although I still think the front cover needs to come off for the layshaft seal. But once you've gone to all the effort of removing the box, seems like a good idea to take it apart to me.