Series III reverse gear problem

[abeljt]

I have recently rebuilt a Series 3 suffix B gearbox, with needle bearings reverse gear, all bearings were replaced, rev gear, bearing and shaft, 1st/2nd synchro, mainshaft bushings. Everything is fine otherwise, but reverse gear keeps disengaging once it starts to take up any load. If i try to hold it in with my hand it still kicks out with a heavy crunch.

On repairing the box I notice that the reverse gears keeps biting on 1st/2nd synchro gear, and there are visible signs of contact with these 2 gears as chucks of each are missing.

A guy advised me once to replace the rev gear needle bearing with a bushing specially made in a machine shop.... this did work but the bushing did not last long and the rev gear starting bouncing out again.

Any suggestions anyone????

 

[oneandtwo]

All the replacement s3 reverse gear idlers on the market have a little known problem in that they are machined incorrectly and will throw out of engagement in reverse when under any load. (Apparently there is only one company who makes them and they are all wrong)

The solution is to purchase a gear from R Whitehouse gearboxes - they have identified the problem with the pattern gears and machine them to rectify the problem. They did one for me last year and it works perfectly. They won’t let on what the problem is with the gears btw!

[abeljt]

yes I think that is the problem.... thanks for the feedback

[Peaklander]

I had this very problem on my S3. I knew it was jumping out of reverse so when I re-built the gearbox I changed the reverse idler gear. On re-fitting and once the vehicle was on the road it jumped out again. This was under just slight load like reversing up an incline.

I eventually realised that it was the reverse selector that was warn. In my inexperience I hadn't noticed the shiny semi-circular wear on the selector. The wear thinned the metal by a couple of mm and that was enough to not push the idler gear back far enough into mesh.

A new selector (and an easy job to do), fixed the problem although I don't know why the original had warn down.

[abeljt]

I believe the gears are not manufactured properly so the tiniest wear anywhere throws it off. I will try replacing the selector fork as I have not yet done this. Thanks 

[Snagger]

I have seen this a few times on aged boxes where the idler shaft had worn a taper, becoming conical on one side.  That caused the torque from the lay shaft to create a thrust force, pushing the idler gear along the shaft.  A new shaft and idler bearing was the cure.

[abeljt]

well i did put in a new shaft, idler bearing and gear.... no luck there. I changed the shifter, maybe its a little better but still popping out.

Today i bought a used box, suffix D its in pretty good shape. Scrap it, clean it out, replaced the reverse shaft and it is pretty worn, hoping to have done by tomorrow, will post an update then.

[abeljt]

ok guys... the box i purchased works fine...... finally able to reverse again! However I believe I overlooked something in my rebuild that Snagger sort of brought to my attention.

I reused an old 1/2 synchro from another box.... this was not new as the reverse gear i installed..... maybe this could of resulted in my problem. This synchro gear is hard to source in my country and I am thinking now that the meshing of the new reverse gear on the old synchro gear maybe was just not compatible.

I can actually feel the difference in engagement with this gearbox in reverse without yet even driving it. It goes in and is much more snug and firm.

Anyways thanks for all the feedback, it was really useful.

[Snagger]

If the teeth mesh correctly from idler to synchro, then theoretically there shouldn't be a problem,  even if different suffix parts are used (I suspect they may actually have a different tooth count or size, affecting the mesh, but really don't know).  Since the reverse gear teeth are straight cut (which is why they're noisy), there should be no thrust force to push the idler gear one way or another.  So, it suggests a wear pattern on the teeth of the replacement synchro or the lay shaft, perhaps caused by the worn idler shaft and bearing letting the idler run skewed and limiting the tooth mesh to  one edge of the teeth on the bigger gears.  That would create a thrust force with the new, flat teeth on the straight running idler.  I can't think of any other reason, other than perhaps fitting the wrong springs int he detents: there are two spring types - to are the lighter gauge and are for the forward gears, the heavy gauge spring is for reverse.  It's is quite common for people to fit the heavy spring under the brass cap (which is 1st/2nd) and the two light springs under the steel L-plates as that is more intuitive.

[Amer]

please can help me i have same problem in revere gear knowing i had changed all part internal gearbox and the problem exists