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Old 09-23-2013, 08:17 AM   #1
krackerjack1951
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Default 49 merc jumping out of second gear??

i presume second gear and matching slider is the main problem..seems to jump out hard under load..can manually hold it in gear with out problem..TIA for reply
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Old 09-23-2013, 08:31 AM   #2
Ralph Moore
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Default Re: 49 merc jumping out of second gear??

If you pull the cover I'm sure your problem will be more obvious.
But it sounds like your on the right track.
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Old 09-23-2013, 10:38 AM   #3
rotorwrench
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Default Re: 49 merc jumping out of second gear??

They usually have excesssive countershaft cluster movement in the case. Worn shift detents, worn mainshaft bearings, and synchro problems can also aid in loss of synchro mesh.

Last edited by rotorwrench; 09-24-2013 at 08:06 AM.
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Old 09-24-2013, 07:58 AM   #4
Bobs32
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Default Re: 49 merc jumping out of second gear??

Saw this a while back
http://www.btc-bci.com/~billben/gearpop.htm

Hi everyone. i`m pretty sure my 35 ford has the original 3 speed manual transmission. It runs great except it will sometimes jump out of second gear while accelerating. The stick will just jump to the neutral position. Does anyone know what a common cause for this problem might be?

Bill M: 7/24/2000 - 1/1/1900 6:03:41 PM
RE: transmission problem
Transmissions
paul....its the high and second gear synchromesh is worn either the blocking gears or the hub insert are worn out
32tom: 7/25/2000 - 1/1/1900 6:41:45 AM
RE: transmission problem
Transmissions
I had a problem with the shifter forks once. put a different top on the trans and the problem went away
rumble seat: 7/25/2000 - 1/1/1900 1:57:41 PM
RE: transmission problem
Transmissions
Paul: Jumping out of second gear: Too much end play in the main shaft, worn main drive gear bearing, worn mainshaft rear bearing, worn bearing inside the main drive gear, sprung transmision shifting forks, worn shift rails in the trans top, worn locator pin in the trans top, weak shift rail springs, worn synchro hub assembly, worn synchro teeth on second gear, worn gear teeth on second gear, worn gear teeth on second gear in the cluster.... or any combination of any of the above!
When you`re in second gear and let off does the gear shift lever move about an inch towards neutral?
If so, I`d look at the end play in the main shaft as well as the synchro hub assembly. Also look at synchro teeth on the second gear. Look at the two sides of the teeth. Notice there are 3 teeth in a row that are shiny. And exactly 180 degrees on the other side of the gear are another 3 teeth that are also shiny. These are what the gear is constantly working against. Grind the three synchro teeth off both sides using a bench grinder or whatever you have. You don`t have to be too fussy... just grind them off the best you can. Now the second gear has to work against new synchro teeth and will stay in gear a lot better. This is done to a lot of truck gears from the factory so it`s nothing really new. I have done it to both of my cars. Just my thoughts... rumble seat.
Ron: 10/03/2001
I find that the cases stretch over time. Measuring the distance between the snap rings on an assembled main shaft and adding .010' and cutting the case to this dimension is a good starting point for any rebuild. I cut this on the rear surface in a mill. Hope this helps, Ron
JD: 10/03/2001
Steel shims (pinion shims were "handy") between the main shaft shoulder and rear bearing, unless you have a mill(?). Once upon a time there were selective washers behind second gear. Ball syncros will allow gentle spring stretching, and there is almost no limit of pressure that will prevent shifting,(test with shift lever, not fingers) and the ball "pocket" in the shift ring can be deepend slightly with a Dremel grinder (gently!) The bush clearence on second gear can be quite huge with no problem---"if" the end play is kept close. Usually it's the front bearing or the needle roller in the input. I have seen detents so worn they won't hold in any gear.
From Brian, NZ (2/24/04)
The synchro hub & drum assy on up to '38 models and the separate synchro ring '39-54 type, all rely on other factors in the box to facilitate an ideal working environment.
Wear factors on the synchro teeth of 2nd & input shaft gears.
" " " " 2nd gear bush & end thrust areas.
" " " " front & rear ball bearing housing holes.
" " " " mainshaft snout & bearing.
" " " " spigot shaft end [& the bush or bearing].
A Quick fix for Steve's '40, if there is such a thing, and you are lucky, would be to replace 2nd gear & the synchro drum [or assy] & detents & springs & eliminate any 2nd gear & mainshaft end-float.
If a box has been jumping out of 2nd gear for any time, the synchro teeth [NOT the synchro rings], on 2nd gear & the corresponding splines in the synchro drum end up with a tapered wear pattern, replacement is the only cure.
With good hydraulic brakes there is no need to change down before a corner.. change down as you go through is better when there is little or no load on the box or engine. As the great Aussie Bathurst driving champion [Peter Brock], says on TV.... "GEARS are for GO.....BRAKES are for SLOW"
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