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Jumping out of 2nd

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Joined: Sat Feb 13, 2016 6:15 pm

Jumping out of 2nd

Post by martinj » Fri Mar 22, 2019 5:34 pm

My Dart jumps out of 2nd occasionally, usually on the overrun. I have taken the top off the box and tried to set up the selector rod detent springs as described in the workshop manual but can't get anywhere near the loads quoted.

My box had no shims between the plugs and the springs but the plugs were screwed well down the holes. Unfortunately I didn't do the spring balance check before dismantling but I don't think it was much sloppier than my measurements below. Having fitted it back together the greatest release load I can achieve is about 10lbs on 1st/2nd and 8lbs on 3rd/4th. If I screw the plug down any further the spring bottoms out so the ball can't move out of the notch in the selector rod. I am using the spring balance on the threaded section for the knob, about 5" above the gear lever's pivot point. My springs are about 1mm shorter than the specified free length and from a quick squeeze seem to be of similar strength to each other.

I haven't touched the reverse selector as the plug seems to have been sealed and it ain't broke......


Has anyone tried this procedure and achieved the specified loads?
Are the specified loads necessary, they do seem a bit hefty and I would prefer not to need to make changing gear a weight training exercise?
Do I just need new/stronger springs, or could there be something else causing my slipping out of gear problem?

Thanks in anticipation

Dart Gearbox Workshop Manual Extract.png

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Vortex O'Plinth
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Location: Gloucestershire

Re: Jumping out of 2nd

Post by Vortex O'Plinth » Fri Mar 22, 2019 7:42 pm

Another possibility is worn dog teeth on the synchro cup and synchro sleeve. Over time the synchro tapers wear and engagement of the cup and sleeve results in clashes between the dogs which in turn wears those to the point where they will no longer hold stable engagement. To inspect these properly the gearbox needs to be stripped down.

Usually very light detent forces are required from the selector springs to maintain engagement.

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Ian Slade
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Location: Akrotiri Cyprus

Re: Jumping out of 2nd

Post by Ian Slade » Sat Mar 23, 2019 7:28 am

Just change the brass synchro ring this is a known problem on many 50/60's boxes, TR2-3 will fit, I believe the 2-3 and 4 rings are the same.
Owner since the 70's, Genghis is slightly to my left.

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Re: Jumping out of 2nd

Post by tjt77 » Tue Mar 26, 2019 1:51 am

Jumping out of 2nd with age is almost always due to wear on the actual synchro hub and is often combined with wear on the shims that take up the lash in the laygear to prevent fore and aft movement of said gear cluster.. there are no known short cuts to resolve this, other than a full gearbox stripdown and inspection for worn parts.. minimally you will need a new 2nd synchro cone and 2nd gear synchro hub..(this issue is commonly caused by wear on the actual hub, rather than the synchro ring itself...although worn teeth on the brass ring where it locks into the hub are often part of the issue) aways wise to replace the first motion shaft bearing too as its runs constantly and hence tends to wear faster than 'other' bearings in the box.. Yes.. triumph TR2-3 bits fit.. its basically the same box with different casing..

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Re: Jumping out of 2nd

Post by daimlersteve » Tue Mar 26, 2019 2:54 am

1st motion shaft and constant mesh gear are not the same as tr and must be changed as a pair. different ratio. The flanged bush can break apart and cause end float problems associated with 2nd gear problems.


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Re: Jumping out of 2nd

Post by martinj » Tue Mar 26, 2019 9:28 pm

Many thanks for all the helpful replies. We had some glorious weather down here in Cornwall this afternoon so had an afternoon tootling around the lanes clocking up about 60 miles.

I had screwed the detents down as far as I dared, 1/4 turn at a time until the ball would not get out of the way of the selector rod then back half a turn to allow a bit for expansion as it all warms up. Such were the roads and particularly the gradients encountered this afternoon that I spent a fair while in second and had no problems when either under power or on full over-run. It did slip out about a dozen times when either trickling along in traffic or sometimes on the transition from power on to over-run at the top of a hill. It is irritating but I feel that I can live with it for this summer and will get the gearbox stripped and rebuilt next winter. Another issue that I noticed was that when changing into 2nd the lever would go past the centre of the detent notch and I think it would stop when the stop screw came up against the front of the casing. Does this point to the flanged bush that Steve mentioned allowing the 2nd gear (95) to move too far forwards so the sleeve doesn't engage fully?

A rebuild is a bit above my competency grade so I will have to pay someone to do it. A quick Google search reveals at least half a dozen transmission specialists between Exeter and Falmouth that would be reasonably local to me. I haven't discussed the problem with any of them yet but is it a job that any such business should be able to undertake or do I need to look further afield?

I take it no-one has ever tried to adjust the selector detents so that it takes 34lb on the lever to get in or out of 1st and 2nd.

As much for my education as anything else can I please check that my understanding of the parts mentioned is correct. I have attached Plate 11 from the parts list below, will refer to the numbers thereon and include the description from the parts list.

Synchro Cup 98 Synchronising Cup for 2nd Speed Gear - I'm pretty confident I have got this one right!

Synchro Sleeve 99 1st speed gear sleeve

Brass Synchro Ring 98 for 2nd, 90 for 3rd and 4th Synchronising Cups as above, they all share the same part no so your belief seems valid.

Synchro Hub 99 1st speed gear sleeve

Shims 109 front Thrust Washer, available in various thicknesses, 110 rear Thrust Washer for Countershaft

First Motion Shaft Bearing 69 Bearing for primary shaft

Flanged Bush 96 Bush in 2nd speed gear

Thanks again
Dart Gearbox Parts Diagram.png

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