Gearbox Woes

[JJC]

Any gearbox experts out there? Following an unsatisfactory noise in first gear I've removed the box and got it on the bench. The input shaft has significant sideways play. You can wobble it around it's axis by a couple of mm. Looking at the other two boxes on my garage floor, one which I think has done a million miles also has play, but the other, which I was told has only done very few miles has very little play at all. The end float on second and third gears looks alright. I also noticed that the oil thrower is eccentric (which it shouldn't be) and has a nick in one place as though it's been clunked by something. Any thoughts as to (i) is this play the likely cause of the noise (ii) is it the main bearing or the needle bearing between the two shafts? I know long range diagnosis is virtually impossible but possibly someone has experienced this already.

[Don Elliott]

There is a pilot bushing in the rear of the crankshaft that supports the front end of the input shaft and keeps it central. That is, if the pilot bushing is not worn. I suggest that you remove the clutch plate and the flywheel, then replace the pilot bushing with a new one. But first, soak it in oil overnight to allow oil to soak into the pores of the new bronze bushing.

[Colin Fairhurst]

Hi, In my opinion excessive sideways play at the tip of the input shaft indicates wear in the main input shaft bearing and probably also in the bearing between the input and output shafts. Two millimetres sideways play at the tip of the input shaft is not excessive.

If you find that there is wear in the spigot bush, you should not need to remove the flywheel to replace it.An old trick is to fill the bush with grease, then find a metal rod which when the end is covered with a piece of cloth is a good fit in the bush, then drive this into the bush and the hydraulic effect will pop the old bush out.

However, I do not think that any of this has got to do with a noise that only occurs in first gear.It can depend on the type of noise and the type of gear box. The three synchro' box is vulnerable to having a tooth nocked off the layshaft Ist gear producing a rythmic tap tap or nock nock when crawling along in first gear.On the other hand, since this is a straight cut gear it will always make a noise similar to reverse gear.

Regards, Colin.

[JJC]

It's now all apart and there's nothing obviously bad so I reckon it's the bush in the first motion shaft. Do you know the dimensions so I can find out if it's worn?

[Colin Fairhurst]

It's now all apart and there's nothing obviously bad so I reckon it's the bush in the first motion shaft. Do you know the dimensions so I can find out if it's worn?

 

 

Hi, I do not know the dimensions of the bush. As I understand it there are three types of bearing used on these gearboxes. One is a floating type bush, ie rotates inside the first motion shaft as well as around the output shaft, and the other is a press-fit bush into the first motion shaft and the third is the later needle-roller bearing. Either way I think you should be able to judge the extent of wear by fitting both shafts together and seeing how much sideways movement there is.

If anybody can say whether or not these bushes are inter-changeable I would appreciate it myself since it is something I may have to deal with in the future.

Hope this helps.

Regards, Colin.

 

ps. I still do not think this has much to do with a noise in first gear. Perhaps you could describe the noise.

Its a pity that none of the real experts have responded.

Edited May 6, 2008 by Colin Fairhurst