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MG TD TF 1500 - Gearbox mainshaft endplay

Happy Holidays,
Well, I solved my "Gearbox Mystery". Since I have the gearbox apart, I wanted to look at the mainshaft endplay question. This refers to the habit of early gearboxes Jumping out of 3rd gear.

Bob McCluskey's Gearbox section of his MG TD 2 Restoration article states: "shim (.050" ) between the circlip behind the 2nd gear sliding hub and the bearing guard in front of the mainshaft bearing, the aim being to limit movement of the third gear by limiting the longitudinal movement of the mainshaft." He comments that the 3rd/4th sliding hub was widened by 2mm beginning with #20026. Since my TD is before that, mine should be the narrower version. However, I have no way to verify that.

Does anyone know the width measurements of either the old or new version of the 3rd/4th sliding hub? Mine is 37.7mm wide.

The real question is: How do I know if I need the shim?

Thanks for your help,
Jim Smith TD17744
JV Smith TD17744

Jim,

To answer two your questions:

1/ The later 3RD/4TH sliding hub can be identified by the single locating ball inside the centre hole. I have measured the thickness on a spare (late model) I have it is 27.4mm not 37.7.

2/ The way to know if you need the shims is. When the box is assembled completely (except the top cover). With the box in neutral, the prongs of both 1ST/2ND and 3RD/4TH selector forks should have an equal side clearance in the groove of the sliding hubs. You need to find a method of compressing the 3 detent ball springs without the cover, I made a simple fixture to straddle the top end of the springs to keep them compressed.


John
J Scragg

Thanks John,
Mine does have the locating ball. I will remeasure and determine the difference between your measurement and mine. I will reassemble and check the clearances on the forks to sliding hubs.

Thanks for your help and I will keep everyone informed of progress.

Jim
JV Smith TD17744

Ok, I have had a chance to reassemble and evaluate the gearbox, particularly the 3rd/4th hub.

Using a jig to compress the three ball springs, the gearbox shifts solidly through all gears. I also left the layshaft in the bottom of the box to allow easier shifting.

John, my 3rd/4th hub is 25.2mm wide (I have no idea where I came up with 37.7mm). It is narrower than yours, but mine does have the locating ball. If mine is the older, narrower hub, should I replace it with the wider one?

The shifting fork is not centered in the sliding hub, but the total clearance is only about 0.3mm. The fork sits passively almost against the rear edge of the hub groove in neutral.


Attached are photos of the 3rd/4th sliding hub when in 3rd gear. Maybe this is normal but notice that the balls are just barely held in place by the gear points. Since I found a ball loose in the case, I am concerned if anyone sees a problem here.



Thanks for your help,
Jim





JV Smith TD17744

Jim,

This doesn't seem correct. Did you fit the circlip on the front end of the 3RD/4TH selector shaft?

John


J Scragg

John,
Yes, the circlip is in place. I wondered about putting a spacer behind the circlip, but if I did that, I don’t think the detent ball and spring would engage.

Jim
JV Smith TD17744

Jim,

In that case there may be a misalignment between the first motion shaft/mainshaft assembly and the gear box casing. Are the circlips on the front and centre bearings correctly located in their grooves in the main casing?

John
J Scragg

Is it possible to fit the synchro hub the wrong way round. I know it can be done on some other boxes because I have done it.It was a Reliant Robin 3 wheeler,the most frightening vehicle ever invented
Ray TF 2884
Ray Lee

Jim,

In that case there may be a misalignment between the first motion shaft/mainshaft assembly and the gear box casing. Are the circlips on the front and rear bearings correctly located in their grooves in the main casing?

John
J Scragg

John,
Here are two photos of the front and center bearings seated. They both feel and sound seated.

There is very slight endplay in the first motion shaft that I am having trouble measuring accurately.

Jim




JV Smith TD17744

John,

There are also two factors that concern me.

There is a 0.005" wobble in the front bearing. The bearing is new. It is not moving. The wobble is in the bearing itself.

The front bearing sits slightly "proud" of the case even though it seems seated.

See photos.

Jim




JV Smith TD17744

I tightened the first motion shaft nut more and there is no more endplay in the first motions shaft. So, let's remove that variable.

So, what about this wobble? It seems to me that once the splined shaft engages the clutch disc, the shaft engages the pilot bushing, and the bell housing is bolted to the engine that the wobble would be irrelevant. Is my logic sound on this?
At that point, my only concern is that the new bearing is crap and this wobble shouldn't be there at all.

Jim
JV Smith TD17744

Just as a last chapter to this story (hopefully). I measured the 3rd/4th sliding hub width and indeed, I had the earlier version. It happens that I found a later one reasonably priced. This adds the 2mm width to the sliding hub and looks much better when in 3rd. I replaced the front bearing and the wobble is almost imperceptible. All gears shift smoothly and gearbox is now buttoned back up. I am actually glad that the 3rd/4th ball bearing came out. It allowed me to double check and reevaluate my earlier work.

Thanks for everyone's help,
Jim


JV Smith TD17744

This thread was discussed between 29/12/2021 and 06/02/2022

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