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3/11/00 -- Now here's a project that's taking quite a bit more time than I had anticipated. In corresponding with the Spitfire@autox.team.net list members, a kind-hearted fellow named John Smith contacted me and offered to swap me a Mk3 gearbox cover in even trade for the Mk2 gearbox cover fitted to my car.
The previous owner installed a Mk2 transmission at some point, which is fine, since all the round-tail Spitfires used the same gearbox. Beginning in 1967 with the Mk3, however, the cover for the gearbox changed to incorporate a switch that activates reverse back-up lights -- a new feature unavailable until the Mk3's were introduced. When the PO dropped in the new gearbox, for some reason he didn't keep the Mk3 cover and jury-rigged a toggle switch that he installed on the dash to manually operate the back-up lights. Pain in the you-know-what. Making matters worse, when the car arrived, one of the brake lights didn't work, one of the tail lights didn't work, the front left turn signal didn't work, the front parking lights didn't work -- and neither did those toggle-switched backup lights.
Anyway, John of Cincinnati, Ohio said that he had a Mk3 gearbox cover and switch that he would gladly swap me for my Mk2 cover since he had no use for it anyway. I gladly accepted his offer and set out to make the swap. By this time, I had fixed all the lights on the car (most were ground related problems or dirty contacts) except for the parking lights and license plate lamp. It turns out that the parking light bulbs were missing entirely. I cleaned up their corroded sockets, gave 'em a shot of WD-40, created a new spring for one of the positive leads that lost its spring (or it simply rusted away) and was back in business. I was anxious to have working back-up lights again.
Once the original transmission pressboard cover was removed, I made sure that the transmission was in neutral, removed the four bolts that held the gearshift extension in place and removed it. Then, I removed the bolts that held the transmission cover in place, removed the cover and attempted to reinstall the new cover. My worst fear was realized, in that it isn't just a simple matter of taking one cover off and bolting another one on. Well, maybe it is for someone who knows what they're doing -- and by the time I finally get through this, I hope to count myself among them!
On the right side of the gearbox, there's a little arm that sticks up and has a little nub on it. (It appears on the top in the photo at left). This is the reverse lever. The gearbox top has three rails inside. They control the shifting forks which move the gears around. The rail closest to the reverse lever has a little square hole cut into it, that the reverse lever is supposed to fit into.
Note: For your reference, the transmission is in first gear in this photo. The reverse gear can be seen in the upper right corner area. The lever is pushed forward (left in photo)m which keeps the reverse gear towards the back of the gearbox and out of the way. With the new cover on, the reverse lever is closer to straight up and down (or back slightly from the photo), which causes the reverse gear to come in contact with first, thereby locking things up.
I discovered that this is not such an easy thing for an amatuer like myself to do. Once I thought I finally had it, however, I discovered that I was wrong. Here's what the new gearbox cover looked like before I reattached the shifting linkage. The three round spots on the front correspond with the position of the three rails inside. Right above them, you can easily see the back-up switch.
Once I had the shifting linkage back on, I ran through the gears with the clutch in and motor off. Imagine my stupor when I finally got my car down off the stands the other day, put it in first -- and nothing happened! First gear was (and continues to be at this writing) locked up tight as a drum. It's like placing an automatic transmission in "park".
The crazy thing is, all the other gears work perfectly: 2nd, 3rd, 4th and reverse. I've consulted with some of the brightest list members out there -- John Smith, Andy Mace and Joe Curry. The consensus seems to be that somehow, first and reverse are being engaged at the same time, thereby locking the mainshaft. This evening, Bill Kelly sent me an outstanding explanation of what he thinks might be going on that's very worthy of a reprint:
Jeff,
There really is only 1 plausible problem with your gearbox, and it's not
the 1st/2nd selector. It's that dang Reverse.
Spitfire/Herald 3-Syncro Gearbox 101
(hope I'm not being too pedantic - I've always found it easier to fix
something when I know how it's supposed to work)
The input shaft is in constant mesh with the layshaft, that single cast
cluster underneath. 2nd and 3rd are also in constant mesh with the
layshaft. They ride on bushings over the mainshaft. When the engine is
turning and the clutch is engaged, the laygear, 3 and 2 are all turning,
at various rates.
The front end of the mainshaft rides in a bearing inside the input shaft
- the 2 shafts are free to turn at different speeds. Gear selection for
2, 3 and 4 all work the same way. The selector fork moves the selector
hub so it engages the dog teeth on the gear you're selecting (for 4th,
it's the dog gear on the end of the input shaft). The hub rides on
splines on the mainshaft. Whichever gear is selected is locked to the
mainshaft through the hub and its splines.
Not so 1st and reverse. 1st gear _is_ the 1/2 hub. It is NOT normally in
mesh with the laygear. Notice the straight cut teeth on the hub, and on
the rearmost swell of the laygear, and on the reverse idler gear. All
three can be slid into mesh with one another in various combinations.
Actually, only 2 combinations are valid. for 1st gear, the 1/2 hub
slides toward the rear of the box, bringing it in mesh with the laygear.
This is a forward motion arrangement - like 2, 3 and 4, the gear driving
the mainshaft is in mesh with the laygear.
For reverse, the reverse idler slides forward so it is in mesh with both
the laygear and the 1/2 hub. The laygear drives the idler, which then
drives the 1/2 hub. Bingo - back you go.
Now what would happen if the reverse idler were in _constant_ mesh with
the laygear? In N, 2, 3 and 4 it would just spin away quietly on its
shaft, like 2 and 3 do when they're not selected. But in 1, look out!
You've got the 1/2 hub in mesh with the laygear, which normally wants to
drive the car forward, and you've got the reverse idler in contact with
both the laygear and the 1/2 hub, which is the recipe for going
backwards. It can't do both!
My best guess is the reverse idler isn't being tucked all the way back
in its hole when you put the lid on. The little nub on the lever that
moves the reverse gear is probably slipping behind the actuator in the
top cover, instead of slipping into the slot in the actuator as it
should. Press this lever all the way forward, and verify that the
reverse gear is clear of the laygear. Then put the top on. You should
have 1st gear back. Caution - that reverse idler will slip forward on
its own if you're not careful. Something to do with the weighting of the
lever.
There are 2 more possibilites. Both involve serious (not hard to fix!)
flaws in the top cover assembly. I consider them both very unlikely.
Write back if you can't get the top cover on after following my
suggestion, or if you get it on but the box still locks up.
I think you'll agree that this is an excellent explanation of how the gearbox works for the layman. Another thing that Bill mentioned in a subsequent e-mail is that the reverse lever needs to be pushed fully forward (thereby disengaging reverse fully), before refitting the gearbox cover. To date, I have been unable to accomplish this, but I'll try again tomorrow. Bill said:
The normal position of the reverse lever, when reverse is not selected, IS all the way forward. The idler gear should be all the way back in its pocket when you put the cover on in neutral. If you can't get the lid on with the lever all the way forward, then your top cover assembly has a problem. Which wouldn't be too surprising...
3/12/00 -- Well, I tried again today. No good. Oddly enough, I was able to get first gear to work without the cover being bolted down, but as soon as I tried to secure it, I lost first gear again. In order to get the bolts lined up with the holes, I had to pull the cover slightly reward, no more than 1/16th of an inch. This was enough, however, to pull the reverse gear up just far enough to interfere with first again.
This evening, another list member posted that he's had the same trouble when he tried to swap the gearbox covers on his two '66 MkII Spitfires. First locks up. I'm guessing it has something to do with wear, but who knows?
John let me know that he's sending a different Mk3 cover, along with my original Mk2 cover, so hopefully, by the end of this week, I'll be back on the road with all gears working -- with or without backup lights. We'll just have to wait and see.
3/13/00 -- I don't even have the new replacement cover from John yet, but thanks to some investigative work by Joe Curry, the problem is solved and the mystery unraveled at last!
While most of you won't have occasion to replace or swap your gearbox cover independently of your entire gearbox like I've done, here's something new to learn regardless. All round-tail Spitfires ('62-'70) used the same 3-rail gearbox, where first gear is non-synchromesh (you can't shift into first while the car is moving). One rail controls the 1st/2nd selector fork; another rail controls 3rd/4th and the third rail engages reverse. In 1967, the reverse switch was added for the Mk3 gearbox cover. In 1971 when the MkIV was introduced, the gearbox was still the three-rail variety, but some internal changes were made in the gearbox and cover, that aren't obvious to the untrained eye. The MkIVs and newer all had full-synchro transmissions, so you could shift into first while the car was in motion. Later Spitfires, like the 1500, converted to a single rail gearbox cover, which is easier to differentiate from the Mk3's and MkIV's.
The covers for full-synchro versus non-synchro gearboxes are subtley different, but since both the Mk3 and MkIV covers have the back-up switch provision and are both three rails, you have to know the difference.
The most important change is that the notch position of the reverse actuator on the third rail in the cover is pushed forward 1/4" on the earlier gearboxes (all round-tail models), which tucks the larger reverse gear that's used in the '62-'70 non-synchro Spitfire boxes back farther into the corner -- and out of the way of first gear.
This difference is NOT noted in any of my parts catalogs, but here's a telltale "marker" to look for to differentiate an earlier Mk3 non synchro gearbox cover from a later MkIV full-synchro three rail gearbox cover: The full synchro cover has a spacer washer on the reverse rail, whereas the earlier non-synchro Spitfire reverse rails do not. That, and the 1/4" spacing difference in the notch position on the reverse actuator, which is mounted to the reverse rail on the cover. The spacing difference of the notch in the actuator was enough to cause reverse to move forward and come in contact with first whenever I engaged first gear.
By the end of the week, I should be able to get out of "park" and back into first
gear! If I was less patient and was faced with having to buy a complete new cover, I would likely engage the services of my die grinder and simply cut a new notch in the actuator that moves it up 1/4". But fortunately, that won't be necessary, now.
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