Gearbox

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Gearbox

Postby lschwendeman » Tue Jul 07, 2009 12:23 pm

Just finished a gearbox rebuild on my 70"s Midget. The box needed new syncros, 2nd and 3rd gear. The rebuild was straight forward until all was reinstalled and road tested. It will not stay in 3rd gear. I can hold it in, but under acceleration or if the shift lever is not held it will pop out.

I can not fully engage 3rd gear. 1st, 2dn, and 4th, work ok.

All gears engaged ok on the bench test.

Could this be a result of replacing 3rd gear?

I know I have to pull it back out, does anyone have a suggestion on what to look for when I get the side cover back off?
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Re: Gearbox

Postby admin » Tue Jul 07, 2009 1:22 pm

There are little detent balls and springs for each gear cluster. Check those to be sure a) they're there and b) the springs are still functioning. Next up are all the shift forks themselves (they can wear and not have a full travel--i.e. because they're worn the gear won't get pushed "all the way home" by the shift fork).

From your symptoms, this is what I suspect--you didn't mention whether you replaced the shift forks?

Check all those little springs and balls and plugs...I've seen boxes where the little springs had broken and weren't putting any force at all on the plunger or ball that helps locate things.

Good news is the Spridget gearbox is pretty straightforward--you can get at everything (just read along with the manual).

Maybe some photos would help once you've got it out?
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Re: Gearbox

Postby Charlie Tolman » Wed Jul 08, 2009 12:07 am

I had a similar problem with a factory close-ratio transmission.
The problem was a worn 3rd-4th synchro hub, and possibly worn small teeth on third gear that engaged into the synchro hub.

Charlie Tolman
H/P 40 (Retired)

P.S.: This transmission used standard internal parts, except for the cluster gear and gears one, two, and three ( different gear ratios, when compared to a standard transmission ).
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Re: Gearbox

Postby lschwendeman » Wed Jul 08, 2009 9:51 am

Thanks for the advice guys.
I should add that the gearbox shifted (stayed in each gear) before I took it apart. The rebuild was done because regardless of gear selected it would grind. Downshifting could only be accomplished by double clutching.
When I got the box apart the syncro rings were worn out along with the 2nd and 3rd gear syncro cones.
I got the rebuild kit (bearings, gaskets, lay gear shaft, ect) along with the gears and reassembled.
I keep thinking that the main shaft (3rd motion) rear bearing position is suspect.
When I first installed the rear bearing I pressed it all the way to the shoulder. When I installed the main shaft the gears did not line up with the lay shaft. Also the main shaft did not appear to fit all the way into the input shaft (1st motion).
I took the main shaft out and brought the bearing up a bit, reinstalled and the gears seem to line up better.
Does anyone know the correct procedure for installing the rear bearing on the main shaft?
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Re: Gearbox

Postby admin » Wed Jul 08, 2009 2:12 pm

Hmmm...as I recall (and it's been a while since I was elbow-deep in a gearbox) the bearings should all be seated to full depth. If things don't seem to be lining up, then I suspect that's the issue.

Do you still have the old bearings? Perhaps measuring the old/new would be of benefit to verify they all have identical dimensions.

Haven't really had too many problems with Spridget gearboxes over the years (knock on wood). When will you have the box out, so that we can take a peek at the guts?
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Re: Gearbox

Postby Charlie Tolman » Thu Jul 09, 2009 12:01 am

If the transmission is jumping out of gear, the shop manual lists:
Broken changespeed fork rod spring.
Excessively worn fork rod groove.
Worn coupling dogs.
Fork rod securing screw loose.

In my note, above, the 3rd - 4th synchro hub was worn.

I replaced a main shaft, after it became bent (don't ask). I seem to remember fabricating a thin shim (washer), about 0.020" to 0.030" to fit on the main shaft, to align the gears. My notes are in disarray, but I think that it was placed on the shaft inside the transmission, ahead of the splined end of the shaft, against a shoulder on the shaft. I am not completely confident that this was the location, but wherever it was placed, it did help in the gear alignment and/or end float.

Charlie T.
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Re: Gearbox

Postby Asolepius » Tue Sep 22, 2009 4:00 am

I only just saw this thread, and it reminded me of my 1098 gearbox saga - see my post of 5th Jan 09 at viewtopic.php?f=14&t=3573&start=15. Watch out for incorrect 3rd motion shaft bearing dimension.
Les Rose, Salisbury, UK
1959 Sprite, owned since 1978
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Re: Gearbox

Postby admin » Tue Sep 22, 2009 8:24 am

At some point I'd like to get together from all our post some "hints and tips" for different projects...kind of a "best of SpriteSpot"...not quite sure how to do it though, but this is a good example--lots of great gearbox info, but it's scattered among a few different posts.

Hmmm....
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