Hi All, I know this is a stock car question, but thought the knowledge base here might be able to help. I have a 49 Merc two door in my care that is a very low miles original car, has the stock 3 speed column manual. Its done a genuine 75,000 miles. I have just done a clutch and gearbox strip and rebuild, and have a persistant problem that wasnt cured by this work, and wondered if it is a common problem and if there is a cure. The box itself was in great condition, and the only issue it had internally was that the spacer behind the second gear was missing, allowing too much freeplay in the synchro sleeve, which in turn damaged the synchros. these were replaced and I machined a spacer to give the required 15 thou clearance, and the box now changes very well, but when you decelerate to a stop in second gear, at about 10 MPH it drops out of second gear. it doesnt do it under load, or when you decelerate from a high speed in second ,only when coasting to slow down. the linkages are all good, new bushes in them, and its adjusted to get full throw into second. I thought the detent spring might be too short, so pulled it out to check, and it is right, stretched it a bit longer to provide a more positive stop and still no better. Is this problem common? would a new sychro sleeve ***embly have a positive effect on holding the gear in? The br*** synchros I used were macs ones, which ARE rubbish (they were supplied by the owner) but in this case they seem to be working fine, and the problem has not changed at all from before the gearbox rebuild. I have built about a dozen early ford three speeds, side and top loaders, so im familiar with them, but cant get my head around what is causing this on such a low miles, and overall 'like new' gearbox. any help appreciated!!
Sounds like it is just "floating" out of gear, possibly the wrong gear lube in the trans? That is what I am thinking, I did one years ago and used a thinner lube in it and it did that, so I would think possible if you did one now with say the correct viscosity however using something like Royal Purple it may act like a thinner viscosity lube, also the column its self at the bottom where it shifts, these areas were originally pretty gummed up with heavy grease, this would have added some resistance, in our new age of over restoring sometimes we forget things like this does make a difference in the way things on these old cars work. Just some thoughts from someone that has had a bunch of mercs, take it for what you will, I am no mechanic just some ideas....Jim
Thanks Jim , good suggestions! I have run 80/140 and T 250 which is a modern version of the old 600w oil Recommended for banjo diffs , so I don't think it's thin lubricant. The linkages are lubed up, as they should be, I'm sure the cars didn't rely on gummed up linkages to hold second gear when new! This car is very low miles so it's not ac***ulated wear on a bunch of parts as you'd expect in a high mileage car.. Posted from the TJJ App for iPhone & iPad
If this is a standard (non-overdrive) trans, check your front and rear ball bearing snap rings. Look for something thicker than what is on the OD of the front bearing. The rear snap ring is actually fitted in the front of the tailhousing, but you might find something thicker. The idea is to minimize the end play of the two shafts that surround seond gear. The other thing is to check the wear on the internal splines of the synchro sleeve. Replace if you see shiney wear spots on the ends of the splines. You mentioned placing a shim behind second gear...Ford never used one at this location on these trannies. If you have 15 thou clearance behind 2nd gear, you have too much. It should be about 4-8 thousandths. Probably better to replace the mainshaft. Hope this helps...... Mac VP
Thanks Mac, I ***umed the washer was missing because there was a huge amount of play ( abput 70 thou!)which was allowing the synchros to slip off the three square tabs and damaging the corners of the slots in the br*** synchros. This washer or spacer is there on the earlier 3 speeds, ( the one you use to set the second gear end play )so I ***umed it was missing. Is it possible the second gear or mainshaft is THAT worn on a low miles box where everything else is like brand new? I doubt it, but anything is possible I guess.. Posted from the TJJ App for iPhone & iPad
from my past experience I'll bet you need a new 2nd gear too, look at the teeth where the synchro collar slides over. teeth are probably worn from running loose and coming out of gear.
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