Gearbox shennanigans

Hi all, couple years back the disco 2 had a brief struggle selecting gears. Then wouldn't select any gear. Took it to Bristol Transmissions- supposed to be the dogs... They charged me for a complete rebuild. 18k miles later, on the motorway there was a clunk and now 1st, 2nd (maybe 3rd) and 5th there is a whirring noise. 4th year is normal and all gears work. Anyone got any ideas as to what might have occurred? Occam's razor suggests something has come loose and is causing the noise. Any idea what the culprit is and what level of remediation is required?

Spoke to transmission creatures, they said they are happy for me to pay for them to sort it out. Neither financially viable or acceptable- expect a gearbox to last longer than 18m miles.

Thanks in hope...

Sounds like a collapsed mainshaft bearing.

Nig43 said:

Sounds like a collapsed mainshaft bearing.

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no if 4th gear still works its lay shaft thats the issue,if it still drives in the other gears but is noisy get i fixed asap,as it will be scrap soon if layshaft bearing fails completely

Correct me if I'm wrong but is'nt 4th gear direct drive thro the gearbox putting less strain on the bearings and consequently less noise.

Nig43 said:

Correct me if I'm wrong but is'nt 4th gear direct drive thro the gearbox putting less strain on the bearings and consequently less noise.

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Wocket said:

4th gear is normal

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I think you are right about this and as JM says this is how he knows it is the layshaft where the problem is. All other gears involve the power passing through the layshaft, and if the noise comes when in other gears then that is why they make a noise the 4th gear doesn't.
One day I would love to have a gear box with a perspex top on it, open to inside the cab so I could watch the gears turning as the vehicle is driven along. I have obviously rebuilt gearboxes and sennthem turning really slowly as I turn them by hand in all gears but, you know, it'd just be fun to see them going full whack!

Nig43 said:

Correct me if I'm wrong but is'nt 4th gear direct drive thro the gearbox putting less strain on the bearings and consequently less noise.

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yes there isnt a 4th gear as such its just the connecting of input shaft to mainshaft, hence no torque through the layshaft in 4th as with all other gears,your less strain is on the layshaft bearings

What I was getting at is because there is less strain on 4th gear bearing any wear is lessened (and therefore less noise). I feel its the mainshaft bearing that's the problem.

Nig43 said:

What I was getting at is because there is less strain on 4th gear bearing any wear is lessened (and therefore less noise). I feel its the mainshaft bearing that's the problem.

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I'm not going to go far with this a JM rebuilds this stuff for a living, but from my more limited knowledge of gearbox rebuilding, if the mainshaft bearing is worn than I think you would find you had noise in all gears as the mainshaft turns all the time, the mainshaft is technically two shafts, the input and the output linked together, one way of another.
In all gears except 4th, the input passes drive thru the Layshaft then back to the output shaft, so all three are turning, but the input and the output turn at different speeds, in reverse, there is yet another small shaft with the reverse idler on it ro reverse the direction of the output shaft.
So if the noise is only appearing in 1st, 2nd, 3rd and 5th, then it is either worn bearings or other problems on the lay gear, i.e the Layshaft and all its connecting gears to the mainshaft components.
But this matters little to OP who unfortunately is going to have it taken off and either swapped for a rebuilt one, rebuild it himself, which i have always found more expensive as gearbox people always charge like fu ck for the parts, or stick a secondhand one in and hope for the best.
IF it is only bearings, then option two MIGHT be quite cheap, but as soon as he has to go replacing gears or, god forbid the actual layshaft, then he is into big money.
But I'll shut up and let JM talk him thru it.

I did once have a 4 speed gearbox that whined only in fourth gear, that was an MG Metro box that came with the engine when I put it in a Mini City E to make a real sleeper. Went like sh!t off a polished shovel. Never did get around to stripping it down or anything. Sold it as was but together with the original engine and box. If they put the City E box on it it would actually have been better, I think, as the ratios might have worked better. Can't be sure, it was a while ago, I have no longer got the manuals so would have to search for the ratios and cannot be asred!

My RRC v8 Manual had a whine in all gears, and it was a ****er to select any gears..

Horrible thing..

Prefer me autos!

Nig43 said:

What I was getting at is because there is less strain on 4th gear bearing any wear is lessened (and therefore less noise). I feel its the mainshaft bearing that's the problem.

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anything is possible but youll find its the layshaft bearings

we'll probably never know!

Thanks so much guys. I appreciate the time and knowledge.