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TR2/3/3A I have a doubt about the gearbox

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V

vype

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Hello everyone,
The restoration of my TR3A continues slowly but surely. The chassis will soon be on its wheels again.
I start to take care of the gearbox in parallel. It is a gearbox without OD.
I did not intend to open it but after cleaning and inspection I noticed that the input shaft had a radial clearance of about ~0.12" measured at its end.
Do you think this is OK or do I have to disassemble and change the bearing (s)?
 

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My guess is that it will be ok once you fit the box back in the bush in the end of the crankshaft will take up any slight movement in the input shaft.

Graham
 
Doesn't seem like a problem to me.

But I would still open it far enough to do some inspection, including pulling the countershaft out far enough to check the bearing surface under 1st gear. It's a known weak spot, and a whole lot easier to deal with now, than after you've put it back in the car and the car together around it. Use a dummy shaft to hold the bearings & gears in place.
 
+1. I would not rebuild for that little play on a known tranny, but these are not strong gearboxes. As a minimum I would pull it for new synchro rings, top hat bearing, countershaft bearings, mainshaft C clip, and seals. Of course, all bearings are a good idea, and even a working tranny may have minor broken parts inside.
 
Thank you all for your feedback and advice.
I am reassured but I will follow your advice and push my inspection a little more while the box is out of the car.
 
It is better to get it fixed while it is out of the car. My transmission seemed OK but when I started driving I found it would jump out of second gear on deceleration. Worked fine except for that small issue.
I found an OD transmission and had it rebuilt.

David
 
Good morning all,
After investigations I found the origin of the play of the input shaft. I thought it came from the bearing but in fact it is the internal bronze bush which is very worn (~0.02")
(part 10 on the Moss catalog).

Bague arbre d'entrée BV.jpg
So I decide to dismantle the whole gearbox to check and redo it.
The bush was replaced by a bearing on the more recent boxes and I wonder if I could not replace it by a bearing on mine. I do not know if the diameters
correspond and if the lubrication groove of the axis will not be a problem because the bearing does not have an inner ring.
What do you think about this?IMG_4500.jpg IMG_4498.jpg
 
You were right the first time. Play in the input shaft is from the large bearing. The pilot bearing, in the tail of the crank supports the nose of the input shaft and keeps the clutch disk aligned. A bush is best for this bearing unless you like to launch at 5k rpm.

The other “bush” i think you are talking about is inside the tail of the input shaft and keeps the mainshaft aligned to the input shaft. That one was later changed to a roller bearing. To switched to a roller bearing you would need a new input shaft and mainshaft. I recommend keeping the bushing, as that is not a normal failure point.
 
I'm with John, I don't think that bushing (or the later roller bearing) is supposed to be so tight to the mainshaft that it will keep the input shaft from tipping. IMO what you are seeing is the accumulated clearance in the big ball bearing that holds the input shaft to the housing. Remember, that little bearing spins pretty fast, and carries a lot of load when in 1st gear. So it can't be super tight. And any movement at the bushing will be amplified at the tip of the shaft, because it's so close to the ball bearing.

IIRC, Bob Schaller (RIP) actually recommended retrofitting a brass bush to the later gearboxes, because of problems with the roller bearing.

.020" is worn, certainly and I would replace it. But not worth trying to re-engineer the joint.

Interesting, if not necessarily relevant: According to the SPC, the factory first tried the roller bearing at TS26825 (with a corresponding change to both input shaft and mainshaft); then went back to the bushing for 11 gearboxes before doing a second change to rollers at TS27063, with yet another input shaft, mainshaft and bearing. Make of that what you will, but my take is that the first change failed in some way, and they had to go back to the old setup while they re-engineered the change.

If you do want to convert to rollers, I think you need to find the later shafts that are machined and hardened with rollers in mind. The rollers are surprisingly picky about the surfaces they run on, and getting it wrong will lead to rapid failure. The input shaft could probably be machined to accept the even later bearings that come with their own outer race, but you would still need an inner race surface, not your existing mainshaft.
 
Thank you very much for your feedback.You are right. I will change the 3 bearings of the main shaft and replace the ring in the input shaft with a new one and forget the idea of ​​replacing it with a bearing.
John your thread about the gearbox rebuild is very interesting.
It is true that it is not always obvious to know if a part is to be replaced or not and your explanations are very useful.
 
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