Gear[crunch crunch]box

[bitwrx]

Right, recently (2k miles) did a gearbox build with all new bearings, new MiniSpares straight cut gears and genuine baulk rings.

Changing down into second often results in a nasty crunch, but it does go in. It only really happens when I'm out for a spin (usually on the tight section on the hill towards Crediton from Tiv, just after the Fisherman's cot ), not when just pootling.

I'm going to have to take it apart and see what's up, but I'd like to know what to expect. I just wondered what any of you think about it...

My thoughts, for what they are worth are...

-Wrong endfloat somewhere resulting in premature wear of the baulk ring (not enough endfloat), or insufficient baulk ring engagement (too much). Where though? 3rd motion shaft bearing is the only one I can think of. Possible?
-Manufacturing error. Either in the gear kit or the baulk rings. Anyone heard of this before?
-Put the dog on the 3rd motion shaft the wrong way round. Can this be done? Would it work if I'd done this?
-Lack of mechanical sympathy. Yes it only happens when during spirited driving, I shouldn't be able to force brand new synchros should I? It never happened with the old box so why now?

I'm going for the endfloat one, or some other assembly related cock up. It was my first one after-all. Sweepstake starts here. Winner gets a fiver.

[guru_1071]

a fiver eh?




-Wrong endfloat somewhere resulting in premature wear of the baulk ring (not enough endfloat), or insufficient baulk ring engagement (too much). Where though? 3rd motion shaft bearing is the only one I can think of. Possible?

possible yes, did you measure the endfloat at both ends?, you can adjust it at both ends with shims at the third motions end and a selectable circlip at the other. when you built the box did you ensure that there was as little possible drag?, many people just 'throw' the box together and nip the nuts up. a correctly built box will have a mainshaft that will turn by hand and not drag the gears round. when using new gears and bulks you have to account for the baulks knocking their top coating off (which they are designed to do) and settling down on to the gears.

i would guess with you box that the bulks where too tight (the fact that its second suggests that the third motion was shimmed too tight as it forces second further into the bualk cone) as you have used it its knocked the bualk ring (and probably the coating on second) out, which has opened the clearance up, which has allowed the syncro teeth to start catching, which is the noise you can hear.

id guess that the gear, the baulk and the 1st/2nd syncro hub are now knackered as it doesnt take a lot of abuse to damage the syncro teeth beyond use.

its commen when building boxes to have to dry build it a couple of times and swop and change the new baulks around to get the correct clerances between the gear and the baulk, even when its right on paper i often find i still have to shuffle the bualks around before im happy with how the box has assembled. this is before you are overcomming the problems with streched cases etc


-Manufacturing error. Either in the gear kit or the baulk rings. Anyone heard of this before

doubtful, if your using gen bulkrings and a new kit

-Put the dog on the 3rd motion shaft the wrong way round. Can this be done? Would it work if I'd done this?

impossible to build it if you do this

-Lack of mechanical sympathy. Yes it only happens when during spirited driving, I shouldn't be able to force brand new synchros should I? It never happened with the old box so why now?

its very easy to overcome the syncro, think of the leverage at the top end of the gearlever

I'm going for the endfloat one, or some other assembly related cock up. It was my first one after-all. Sweepstake starts here. Winner gets a fiver

good luck

[bitwrx]

guru_1071 said:

id guess that the gear, the baulk and the 1st/2nd syncro hub are now knackered as it doesnt take a lot of abuse to damage the syncro teeth beyond use.

Bugger.

I'll let you know how I get on.

[rww]

I had a very similiar experience some time ago. Centre mainshaft bearing collapsed and, after some time and use, I had to strip it all down. Replaced all the usual suspects and put it back in the car. Then I found second difficult to engage without a graunch and,if I remember correctly, reverse was also a problem(non-synchro). The first/second selector forks had worn too wide and didn't push the baulk rings hard enough before the synchro hubs were pushed home. So if you are stripping it down again, replace at least the first/second selector fork and if you can afford it also the third /fourth.And to be certain, check everything else for obvious wear but by the sound of it you have replaced all the key elements already. Best of luck, it will be worth it.

[guru_1071]

you can 'size' worn selectors by nipping the ends in a vice to match the outer tracks. its a bit of a dirty trick and doesnt work on really worn ones, but offers a very economic option over replacing them.

even the new ones normally need some sizing to be the right size

[jammy_basturd]

It has been known recently for the genuine baulk rings to be ever so slightly too wide. Have a look at the gaps between the synchro and the gear as you strip the box down.

[guru_1071]

jammy_basturd said:

It has been known recently for the genuine baulk rings to be ever so slightly too wide. Have a look at the gaps between the synchro and the gear as you strip the box down.

ive not seen gen bualks that are physically too wide (though anything can happen with resourced rover stuff), its normally the taper of the cone part thats suspect in cheaper baulks - which in turn makes the whole ring sit too far or too near on the cone of the gear. you can spot this by sitting the baulk on the cone of the gear and measuring the gap with a set of go-no-go guages, of course the trick is knowing to much to allow for bedding in.

once the box has run and damaged the gear coating and the baulk ring the resultant gap is only going to tell you what it is now, not what it was when the box was assembled.

i have had to get cheaper baulks faced down to suit new s/c stuff as they where stood so far off the gears (they where that bad the box would lock solid as the pinion nut was tighted), the customer wouldnt pay 80 quid for a set of gen baulk rings..............

[jammy_basturd]

Ah ok, it was a while ago when I read up about a guy that was having problems with gear engagement using brand new Gen. baulk rings. What you say about the taper surface makes sense though. Worthwhile checking.