Shift fork wear, what’s allowable

[NicholasUpton]

What is consider excessive shift fork wear, what should be the end float between the slider and fork, and the lever and cup on a rod change? Would like a copy of any BMC or rover document that states it, as all I can find is to replace it if it shows signs of excessive wear.

[cmiller]

Went out to the shop and measured some NOS units for a 3 syncro. 1-2 shift hub and fork was .008 and 3-4 shift hub with shift fork was .006.

Hopes this gives you a starting point.

Chris Miller

[Polarsilver]

on a remote type.. i measure a nos fork to nos ball end & the original clearance measures .003 thou.

[minibitz]

Absolute maximum selector fork to synchro hub clearance is 0.03". Clearance on a new fork is 0.003"-0.004".

Read this in a manual many moons ago but don't recall which one. Have always gone by this figure and it's served me well.

I'm just measuring up the forks on a 3 sync that's in the workshop due to jumping out of 1st and 2nd gear. Measured 0.90" clearance on 1/2 fork so looks like the main culprit has be found.

[Aussie Bill B]

I'm just measuring up the forks on a 3 sync that's in the workshop due to jumping out of 1st and 2nd gear. Measured 0.90" clearance on 1/2 fork so looks like the main culprit has be found.

This is a question (not a criticism): would jumping out of gear be more likely due to the springs/detent balls in the synchroniser (change-speed) hub? I've always assumed that once the gear was engaged, the selector fork wouldn't be running against the synchroniser hub at all.

[scoop]

I'm just measuring up the forks on a 3 sync that's in the workshop due to jumping out of 1st and 2nd gear. Measured 0.90" clearance on 1/2 fork so looks like the main culprit has be found.

This is a question (not a criticism): would jumping out of gear be more likely due to the springs/detent balls in the synchroniser (change-speed) hub? I've always assumed that once the gear was engaged, the selector fork wouldn't be running against the synchroniser hub at all.

Hi Bill, if there is wear in the fork it could cause it to not throw the full measure to latch in. My thought anyway!
John Smidt informed me once that often the condition/shape of the dog teeth played a big part in jumping gears, that could be the cause.
Cheers

[Peter Laidler]

I realise that we're going off at a tangent but what Scoop says and Aussie Bill alludes to is what I was taught, have seen and experienced. If jumping out of gear is the problem, it indicates that it wasn't IN gear correctly to start with. Because once it is 'latched-in' as Scoop describes it, then it's in for keeps and has to be mechanically pulled out.

[Herbert]

if it jumps out of gear i would also check the detent spring & plunger and also the selector rod.

[minibitz]

Thanks guys.

All the suggestions offered could also cause jumping out of gear. I go through and check all these as part of the assessment process to see what's good to go again and what goes in the scrap bin.

In this instance it is most definitely due to a severely worn selector fork. The wear is such that the selector is unable to throw the syncro hub across far enough for the detents to engage, so the hub just pops back into neutral when power is applied.

[Aussie Bill B]

Hi Bill, if there is wear in the fork it could cause it to not throw the full measure to latch in. My thought anyway!
John Smidt informed me once that often the condition/shape of the dog teeth played a big part in jumping gears, that could be the cause.
Cheers

I understand what you are saying about partial engagement by a worn selector fork, leading to jumping out of gear.

The original post was about a rod change box and from my very limited experience of them, the 1st/2nd fork seems to wear badly, although jumping out of gear wasn't mentioned as a problem by him.

John Smidt's comments about the condition and shape of the dog teeth is interesting: I seem to remember, when minis were common, that gear specialists often ground the dogteeth back to standard angles to 'recondition' the gear for better engagement, so that could be another issue.

[NicholasUpton]

So back to the original Question, what is BMC, Leyland, or Rovers Official review of allowable wear?

[floormanager]

When I asked the question, Spider kindly sent this to me

forks.JPG

[NicholasUpton]

When I asked the question, Spider kindly sent this to me
forks.JPG

I have also read that online, but want to know what Document that is quoted from.

[floormanager]

When I asked the question, Spider kindly sent this to me
forks.JPG

I have also read that online, but want to know what Document that is quoted from.

I've looked but could not find it. From memory, it was from an Auz workshop manual. If you contact Spider, I'm sure he can advise.

Paul

[Maddog]

Yes Spider's quote comes from page f-6 of the Australian Mini Comprehensive Workshop Manual by Leyland Australia (Part No TP832C).
ISBN for my copy of the publication (1976 edition) is 0 909703 16 7.

It is a very good reference with lots of detail about mechanical changes eg between the 3 and 4 synchro remote boxes.

[NicholasUpton]

Thanks, that’s exactly the document I was looking for