T35 gearbox noises.

[george sutton]

 My gearbox no.2355 (1947 ?) makes a horrible harsh grinding kind of whine ,only when i change down.and run in a lower gear, very embarrasing as you pass people.   consulting' spannerama', and the like, i have worked on the final drive as the most likely cause, three times. new sealed bearing, re shimming several times but no joy ! but now i 've noticed that as i withdraw the clutch it stops, untill engaged again. That tells me ,that as the m/c is free wheeling , the final drive (always rotating) is not the cause ?.    would i be right then to suspect internal bearings ,or worse ? Today i checked the shock absorber on the final drive as per Eddies most recent advice, seems ok though.    OK, if its the worst news ,give it to me, i'm quite battle hardened to this B-----  bike by now. Denis .S.

[eddie]

Denis,
          If the whine is only present with the gearbox under load in the indirect gears, the cause will most likely be wear on the teeth of the input shaft and the mating gear on the layshaft, or possibly, the bearings at the front of the 'box. The mainshaft bearing has loose 1/4" rollers that seldom give much trouble unless water has found it's way in there - in which case the tracks will be pitted, giving rise to rough running. The layshaft bearing is a normal ballrace.
        The 2 gears and bearings mentioned are only under load in the indirect gears - in top, the drive is straight through the box - with the gears idling.
                                 Regards,
                                        Eddie.

[george sutton]

Thanks again Eddie, couple of months back when i looked in the box though the selecter opening ,gears and shaft seemed ok..  so it looks like managing for summer ,and a strip down for the winter. IS there any proper strip out procedure i can copy offline, or just rely on my experience ? Denis.S


Quote of previous post removed - Dave, 6th June 2010

[ChrisS]

Denis,
I have a Mk3 which I have had over 20 years and it  has always had a noisy gearbox. I have been into it a couple of times over the years but did not cure it. Originally I thought that the bevel gears were the cause and coupled with a worn rear mainshaft bearing (LJ1) that looked very likely. I carefully set up the backlash in the final drive and expected it to be OK when the box was fitted, however it continued to be noisy. I recently stripped it again and the bevels gears and LJ1 were OK but the sleeve pinion bearing( input shaft) was badly worn, surprisingly the rest of the parts were in very reasonable condition, certainly no wear on the gears
 This sleeve pinion bearing in a Mk1 ( and my Mk3 which was very early) has 36 1/4 by 1/4 rollers arranged in two rows with a thrust washer between. Of course this bearing is not available off the shelf the inner being the sleeve pinion, so its a judgement call on reassembly as to the acceptability of the clearance in this bearing. I believe you can get the outer race for the sleeve pinion bearing from club spares and may be possible to get oversize rollers. You can also substitute the 1/4 by 1/2 rollers if you can get them.
The Mk1 box may also have main shaft sleeve pinion bush which is fixed in the sleeve pinion, later boxes had the bush fixed on the shaft. Plate 16 in the spare part book shows the later arrangement with a relieving groove in the main shaft to allow the oil to return from the space in the sleeve pinion. The earlier ones had a helical groove in the main shaft to provide a path for the lubrication.

ChrisS
 

[george sutton]

ChrisS
 thank you very much criss for that very usfull information, strange it is though , my 1948 mk3 i owned in 1950, never had a noise problem. Regards Denis.


[remove quote of previous message. 06Jun10, -Doug, Site Moderator]