Hi I need some advice on whether to replace the first gear on the layshaft on my spare gearbox before I swap it into the car. My 66 3 litre has done at least 150k miles and the gearbox is pretty shot. No synchro in second, noisy input shaft bearing and lots of other rumbles. Fortunately the car came with a spare gearbox that seems to be in good condition other than two teerh are chipped on the first gear on the layshaft. There is no damage to the tooth profile as far as I can see. I think that if the gearbox was in a car it would be unlikely that the damage would be apparent. If I don't need to strip the box down I don't want to but also don't want to replace the box twice. This damage is likely to have been done with one rough change into first while the car was moving.
What at I am most interested in is anyone's experience when opening up a gearbox and what these gears usually look like in a used box. If a few chips are normal then I will fit as is. If not then I will fit a replacement gear.
Hi Martin. I have never rebuilt a Rover gearbox, but have rebuilt a couple of MGTD boxes where new parts are often not available, so the best used parts get reused. Here's a picture of the first gear and layshaft on my current box which works quite nicely without any problems at all. So I think 1st gear can be very tolerant of a few chips as long as no teeth are broken off and missing.
The spare gearbox job is a bit of a fill in, I made a start due to the car being off the road waiting for a pair of rear suspension mounts from Wadhams that are lost in transit and a locally sourced one that seems also to have gone astray. Having said that I think it will be a much nicer drive without the gearbox issues.
I had a look at the gears when in mesh using a mirror this morning and the damage is not in the contact area once first gear is engaged. It would probably be ok but I think having slept on it that I will fit a new gear. As you say if new parts are not available then you are stuck with repair or reuse but this gear is available. The chips may create a stress raiser and the gear might fail in the future.
The picture of the cluster gear looks very much like the one in the Moss box of my '62 E Type. Mine had the first gear chipped quite badly and I had to replace it, not too hard to do I thought. I just have to keep remembering that there are NO syncros on first gear of any kind when I'm driving it, just like the Rover.
Thought I would post an update. The spare gearbox has a new first gear. The damage probably wouldn't have been apparent if the gearbox was in the car but once dismantled was a lot worse than I could see with the top off. I lucked in with the rest of the box though. All the bearings, syncros and bushes are as new. The only thing needed was to make a new distance piece for the layshaft. The clearance was 13 thou so 8 over top tolerance. Fortunately I had a bit of hollow bar to make a new one 10 thou longer. So the box is all reassembled on the bench with a magnet installed in the drain plug. Next weekend I'll swap them over. Cheers Martin
Final update I hope on my gearbox. Over the past two weekends I have swapped in the overhauled gearbox, fitted a new rear crankshaft oil seal, rear engine mounts and given the front half of the car's underneath a clean and touch up. i haven't investigated the old gearbox but the synchro detent springs were among the scrap metal that came out with the old oil. My flywheel had a few hot spots with surface cracks that machined out with a skim to minimum thickness. I found my rear driveshaft had seized universals front and rear which pointed to a reason for the rear end vibration the car has had since I bought it. I ordered a sump gasket, a pair of universals and some other bits from Wadhams however being down this part of the world the ordering process can be a bit slow. To get the car back on the road I decided to cut a sump gasket from some 1.6mm sheet. The old universals freed up with a soak in kerosine so I pulled one apart to see if a repack with new grease might be an interim fix. The first pair of cups put paid to this plan though as the trunions were really bad. I want to go on the club run this weekend so I repacked and reassembled the joint with a view to reassembly for the weekend and pulling the shaft out again when the new universals arrive. So prior to refitting the floor, I went for a test drive to make sure the overdrive was working properly and to have a listen to the gearbox. All was well other than a surprising amount of noise from what look like perfect gears and bearings. A more positive finding was that even with what I would call completely toasted universals in the rear driveshaft, no vibration at all. Interesting given what I have read re the tricky setup required to get rid of this rear end rumble. I just bolted the centre bearing carrier into place with no attempt to set the height as it will be comming out again in a couple of weeks. Anyway, with the floor and carpets in what a nice smooth drive. Quite a different experience with 90% of the drive line lash gone and with the floor and carpets in, very quiet! Well worth the effort as now I don't need to double declutch to change down or try to time my change up into second to avoid a graunch. Hopefully no more oil stain on the driveway either. Cheers Martin
Last Edit: Sept 29, 2019 8:09:14 GMT by 3litrekiwi
I am sure I have written this before, but my experience with installing new Hardy-Spicer UJs is that the end caps need shimming (behind the circlips) to centralise the UJ, otherwise the propshaft will run out of true. Maybe no vibration initially, but quicker wear on the UJs. I do quite high mileage in all of my Rovers, so this becomes significant.
The shimming is easier to do after a thousand miles or so, when the new UJ has loosened up a but and you can feel the play by vigorous yanking on the propshaft.