I'm about 400 miles away from home getting ready to drive this '67 1800 back with me. I put on some known-good carbs which fixed the poor running condition. I fixed the rumbly driveline (transmission mount broke). I fixed the lack of OD (wire off and 1/2 quart low on oil). Before I topped off the oil, It would do this wicked noisy jump out of third gear. Now third is OK but it won't stay in 4th, any little blip of the throttle and it pops out of gear. It's not really noisy otherwise. The car has been doing this for a while and the PO's solution was to keep his hand on the shifter in 4th.

I've got another unknown condition D-type M41 in the trunk. I don't want to change it out here. The trip is almost all highway miles for which I'd like to use a large orange bungee cord tied to the passenger seat to assure that I remain in fourth gear. So does anyone know what is worn out in there and whether that worn out part is likely to lunch my transmission somewhere in the middle of the Navajo reservation?

Thanks!

Bob in AZ.

Bringin' home another one, eh Bob? Cool... I'll assume the price was right?

One thing that I don't see as having been mentioned... bad transmission mount causing the shift lever itself to foul its hole in the tunnel... Just pull off that rubber boot and see if it looks like it may not be fully engaging. For that matter, the rubber boot could be getting in the way.

(EDIT)... I see that you replaced the tranny mount already... but maybe it's still sitting low for some reason...

If that doesn't look to be the problem, I'd go with the orange bungee to getcha home... If worse comes to worse, you could always bypass the 4th gear sensor switch so you can run the overdrive in 3rd...

Good luck... be sure ot post some pics when you get 'er home!

-Matt
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-Matt '70 145s, '65 1800s, '66 122s wagon, others inc. '53 XK120 FHC

One more possibility is worn ends on the shifting fork. These ends are replaceable but I couldn't tell you where to find them. I replaced the 3-4 fork in my box and it's been working perfectly for years. Good luck on the trip home.
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Roy Olson

Phil described the possibilities well. I would pull the shifter (unscrew the big nut holding it onto the tranny) and see what the bushing looks like. If it is OK then you are probably getting into gear but it is not staying. You can drive it like that, but may create some wear on the the shift fork by keeping pressure on it. Since you have to go into it anyway I would be tempted to run with it. The only alternative is to pull the tranny, and if you have a complete breakdown you will have to do that anyway, so not much to lose by trying to run with it.

If the bushing is bad around the shifter you might want to look for a replacement before making the trip. Hate to have you damage the internal components because of a bad external component!

1) Nylon bushing at base of shift lever crumbled, meaning you never get full engagement of 4th gear.

2) Missing/stuck ballbearing at the forward end of the 3rd/4th selector rod.

3) Worn parts in 3rd/4th synchro assembly.

Missing ball or weak spring would make selection of 3rd or 4th pretty indistinct (doesn't "click" into gear, although much of the "click" is the dogs engaging the gears) and shifter would feel like it wanted to slip.
Bad bush on tranny cover (for lever) would make all gears pretty difficult to get good engagement (and you may bash hand on dash if really bad).
Ditto for bush on bottom of lever.
Worn dogs/retaining spring on the output shaft on which both 3rd and 4th ride is a likely culprit. Freshening the tranny (once you are home) is the only fix for that.

Ugh, I'm explaining this poorly.

Until then, holding the gear lever by the PO would have worn the selector and fork much more than the amount of wear it will get on the way home. Draining the oil and inspecting the bung plug for filings will give you an indication of level of wear. Suspect you will find lots of brass in there from the syncro cones as well.

No loud rumblys means you likely have a good rebuild project, especially if no issues with 1/2 (most common gears to lunch) as the layshaft is probably OK.

Popping the cover off the "spare" will at least let you take a look at what you have there. Take tools and oil for the possibility of a roadside swap if all goes "bang." Shouldn't, as the boxes are pretty darn robust.

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Mike!