gearbox-a long story

[mrsjhmog]

The brakes ( front discs ) on my '57 Tourer would seize up on anything more than a short trip. The last time this happened I was about 200 yards from home, so pushed on, revving high in first gear and slipping the clutch to get into the garage...
Then could not disengage first gear, despite every manoeuvre I could think of. So dropped the gearbox and found that the first/second gear synchronizer hub had come apart with ball bearings and springs out. Why had this happened? The 1st. gear fork had moved too far because the plunger had loosened, as a result of someone repairing a defect ( around the head of the bolt ) in the casing with a "metal weld" substance which had finally failed. Gear box had been purchased from a dealer in California as "reconditioned", many years ago.

Not knowing how to repair this, I looked for a replacement rib case casing. Found one from a '71 Midget that was being sold for parts locally. Swapped over all the good bits and put in a (stronger?) 1098 clutch fork and release bearing to replace the 948 ones ( which had worked OK in the original rib case ) since it has a diaphragm clutch. Also new mechanical clutch linkage parts; and appropriate residual valves in the brake lines-seemed to solve the brake problem.
Drove it last week. Clutch was a little "fierce", -as is mentioned re. diaphragm clutches- and there was a loud mechanical clattering in 2nd. and 3rd. just after changing gear.
So dropped the box again and find that there is evidence of interference between the outer part of the clutch cover and the inside of the bell housing ( see photo ) and also that the release bearing is only engaging on the outer part of its circumference.
Is this evidence of a worn front gearbox bearing? Or do the Minor and Spridget rib case boxes have different bell housing thicknesses? ( Mowog Mb 326 and Mowog MB 505 46L respectively ) they don't seem to be different.
Planning to replace the 1098 clutch release arm ( realize the engagement arc is not correct for that clutch ) with that from the Midget, with the Midget front cover, and a hydraulic clutch and roller bearing, since I believe a 1098 clutch cover will not fit the adapted flywheel.[frame][/frame]
Any thoughts? ( LHD 1275cc )

[les]

I'd use the standard gearbox components for a '57 car, it sounds like you are mixing to many different parts together. Also swap the clutch for an original spring type, much smoother. If you're using a 1275 unit then again use the standard 1098 box with all its associated parts or better still the midget 1275 box.

[philthehill]

Did you change the engine rear plate from the thin plate type to the thick forged plate type when you changed the gearbox from the 948cc to the 1275cc gearbox?

[mrsjhmog]

Thank you for your ideas, Les and Philthehill.
The original for the '57 was a 948 and smooth case. This gave v. little power at 5000' altitude here in Denver, Colorado. Thus the 1275 unit. It has the thicker back plate and the flywheel was machined and drilled for the diaphragm clutch-the 1098 clutch cover bolts won't now match the holes in the flywheel.
On reflection, the marks on the gearbox cover were probably there when the replacement box came out of the Midget ( the car was pretty far gone and this project has taken about 2 years...), so I'm thinking my problem is the wrong fork and release bearing and also a worn front gearbox bearing ( the front end of the 1st. motion shaft wiggles back and forth about 1/4 inch ).
Will let you know if this sorts it out--in a few months![frame][/frame][frame][/frame][frame][/frame][frame][/frame]

[philthehill]

Unless the first motion shaft is supported in the rear of the crankshaft it will move / wiggle that 1/4".
I notice that your clutch release arm is not central relative to its mount and the hole in the bell housing and that a spacer has been fitted between the mount and the arm.

[mrsjhmog]

Phil, the clutch release fork and spacer you are referring to are 1098 items on a 1098 front gearbox cover. After checking the part nos. of the internals of both boxes this afternoon I've found that both are from later model sprite/midgets, so , yes, the clutch fork, e.t.c. are incorrect. I thought the original box was for a 1098.
After dismantling the box I've just removed from the car I finally found what I think is the problem-see photo. The 1st. motion or input shaft was sliding forward a little and the nut was shaving metal off the inside of the cover. Obviously need thicker shim(s) inserted and probably new bearing.
In the absence of Plastigage to estimate the thickness needed, do you think chewing gum might work, removing it to measure its thickness??[frame][/frame]

[mrsjhmog]

Also, Phil, the input shaft is supported by a needle bearing in the back of the engine. The 1/4 inch play I was referring to is when the gearbox was out of the car, if that helps.

[philthehill]

I would suggest that you should use the correct front cover for the gearbox being used.
Then you would not require to adapt or space the release arm. I am interested in how the release arm is supported in the front cover as there is normally no room to insert a spacer especially of the thickness currently being used. A front on photo of the release arm mount would not go amiss.
You should be able to determine the shims required by feeling the fore and aft movement of the first motion shaft.
Just build up the shims until all for and aft play is eliminated.
As I said above when the engine and gearbox are separated it is normal for the first motion shaft to wiggle somewhat and of course the lack of shims will not help.
You will need to clean the inside of the gearbox to remove all the metal grindings/shavings.