Lotus Elan

gearbox question

PostPost by: seniorchristo » Thu Dec 05, 2019 8:38 pm

There is somewhat of a loose fit between the 1st/2nd slider hub and the mainshaft. is this acceptable? Should some type of loctite be used here?
Also, what exactly holds the gears in place? Is it just the detents in the selector shafts or do the blocker bar and springs contribute to this?
Thanks
Chris :)
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PostPost by: 2cams70 » Fri Dec 06, 2019 10:12 am

They normally do show a bit of wear on the splines connecting them to the mainshaft but unless extreme it's not usually much of a concern. I wouldn't bother with any Loctite. I don't think it would hold up to the very high contact stresses in that area and will just contaminate the oil when it breaks down.

Usually the only symptoms you'll get from that kind of wear is a slight clonking sound if you are in that particular gear and rapidly pulse the throttle on and off at low speed.

What keeps the gears engaged is probably a combination of things: the selector rod detent springs, the synchro key springs and also the rake angle along the sides of the dog teeth (if you look at them carefully you will see they aren't exactly parallel to the centerline) - Is there a reason for the question?

Seeing your reverse gear was not in a very good state you'll need to check reverse on the synchro hub and also the cluster gear. Reverse is not a very important gear so you'll have to balance the cost of repair versus the extent of the damage. You must have had a badly adjusted clutch at some stage or probably more likely you or a previous owner is accidently selecting reverse instead of 4th. Check the protection lockout. It may not be operating correctly.
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PostPost by: seniorchristo » Fri Dec 06, 2019 12:19 pm

2 cams
The reason I ask what holds it in gear is because while on the bench after sliding the synchro ring into gear there is no resistance to then slide it out of gear. I don?t see how the ?synchro key springs? would have any effect. If they do then I will replace them.
Reverse on the synchro hub and cluster are in much better shape. I just dressed them up a bit.
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Chris
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PostPost by: 2cams70 » Fri Dec 06, 2019 12:40 pm

The main purpose of those key springs is to keep the dimple on the top surface of the key engaged with the corresponding recess in the outer hub sleeve. When the hub sleeve moves for gear selection it pushes the 3 keys along with it and so the keys are then able to push the synchronizing ring on to the cone surface of the gear being engaged to bring it up (or down) to speed. Once the speeds are synchronized continual movement of the outer hub sleeve will overcome the tension of the key springs allowing it to move further still and so fully engage with the coupling dogs on the gear and enable it to transmit drive.

Good to replace them if you can but far more critical to assemble them correctly and not mix them up across the different hubs as they aren't all the same! If your box is suffering from jumping out of gear they probably aren't the cause.
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PostPost by: seniorchristo » Fri Dec 06, 2019 1:30 pm

2cams
I don?t have first hand experience with using this gearbox as it?s a c/r spare box I purchased used. Based on what you?re saying and what I?m seeing, I don?t think those springs have any significant affect on holding the gear in place.
Thanks
Chris
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PostPost by: joe7 » Fri Dec 06, 2019 2:19 pm

On a c/r GB, 1st & 2nd gears & 1/2 syncro hub are held in place by the draw nut configuration securing the 1st gear bush. Torque to 25 lbs. 3rd is held in place by the 3/4 syncro hub which is retained by a snap ring at the end of the mainshaft.On the other side, both, 2nd & 3rd gears butt up to a flange on the mainshaft. Just to add, on a later model semiclose non bushed 1st gear GB, the 1/2 syncro hub is retained by a snap ring which in turn holds 2nd gear to the mainshaft flange with the draw nut configuration securing 1st . Take a look at your shop manual.
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PostPost by: joe7 » Fri Dec 06, 2019 2:27 pm

Just noticed from the picture of the syncro ring it appears to be a later/late model GB as there doesn't seem to be any cutouts for the syncro hub blocker bars. Also the ID of the gear looks like its larger than a cr GB. A few more pictures would help.
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PostPost by: seniorchristo » Fri Dec 06, 2019 2:51 pm

Joe
If you look closely you can see the cut outs in synchro ring. I?ll have to count teeth when I next get home
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PostPost by: 2cams70 » Sat Dec 07, 2019 9:53 am

joe7 wrote:On a c/r GB, 1st & 2nd gears & 1/2 syncro hub are held in place by the draw nut configuration securing the 1st gear bush. Torque to 25 lbs.


Always use some red Loctite on this nut. It's almost guaranteed to come loose otherwise. Don't just rely on the locking tab. It's probably part of the reason circlips were used instead of the nut in later gearboxes.
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