Holding my 3-speed in 3rd gear or pops out
 

Have been just holding third down for a couple years now. No trouble other than it progressively getting worse. Use to go 65 before would pop out, now soon as I put it in 3rd (around 35mph) when accelerating. Had reman'd tranny 6 years ago. I have been told it's just my drive shaft (bearings). I have checked my springs and forks and shifters, and all seems in order. I took it to Aamco today for free inspection, and we'll see what they say. But I am hoping that I can fix it without dropping tranny.

update-
I took it to Aamco today and he straight told me the problem was IN the tranny. And swore that I had to pay 400 bucks for him to look at it. This is not the first tranny ppl I have taken it to. Transmission mechanics are a shame. I will NEVER have anybody else do work on my tranny again (after owning a 99 Mazda and rebuilding it twice), lol.

One person on other thread said:
I am not familiar with this, but I assume it is either like that, detention, bearings, OR the 2/3rd gear is worn. Any help on this would be great!

Re: Holding my 3-speed in 3rd gear or pops out
 

it's a 3-on-the-tree Muncie 219 or 319 from what I remember. 4-bolt on side.

Re: Holding my 3-speed in 3rd gear or pops out
 

re. transmission mechanics: One thing to remember is that most of the cost is labor these days. A good transmission mechanic can diagnose the problem or problems fairly quickly. If you can do the removal and reinstallation yourself by renting the tools needed you save a couple of hours or more of labor.

I had a car once that used to pop out of gear but mine turned out to be a bad motor mount. It would pop as the engine lifted with the torque of the drive shaft. Only way I found it was by lifting the motor with a jack.

Re: Holding my 3-speed in 3rd gear or pops out
 

well, I would gladly do the work, but I live downtown, and park in the street. The fine would equal out the labor, lol. I was quoted 4.5 hours labor to pull it apart and rebuild. My problem was that it already has been rebuilt and I don't understand how it should be internal when Aamco "rebuilds them for life". So I am really hoping to not have to pay anyone else to "diagnose" a problem. Every mechanic I have talked to tries to get me to pay them to pull the tranny and let them dismantle it. I have been down that road and rebuilt a tranny twice. So I am looking for insight into something I can fix (even temporarily) that I can work on here in the street and not worry too much about cost. Otherwise, my truck is for sale and I will just let the next owner worry about it.

Re: Holding my 3-speed in 3rd gear or pops out
 

SM 319 is an over drive 3 speed tranny, You should have and SM 318. Popping out of third is most likely cuased by the 2nd/third shift fork being worn or the 2nd third syncro slider being bad or the input shaft bearing being bad. Could be all three. But it does have to come apart to find out.

$400 should get you a complete rebuild provided the broken parts are available and not major components.

Re: Holding my 3-speed in 3rd gear or pops out
 

Thanks, that sounds right, SM 318 :chevy:.

Not the fork, I've check it out, pulled off side casing (4-bolts). I don't think the syncro is the case, there's no syncro on first, but I have read threads that explain that issue, pops out when letting OFF the gas. Mine pops out from vibration during acceleration, so I'm still leaning towards bearings. Is input the same as drive shaft? I originally thought that it was the 2/3rd gear being worn, but I don't know if it's the syncro.

Can I fix input bearings without tear down? Thanks!

Re: Holding my 3-speed in 3rd gear or pops out
 

Have you tried adjusting the linkage? When I got my 70 I had to hold it in reverse because the adjustment was way off.

http://67-72chevytrucks.com/vboard/s...d.php?t=215307

Re: Holding my 3-speed in 3rd gear or pops out
 

yeah, I've adjusted it, it was a little tighter, but then threw off my 2nd, so I put it back, IMO best place for it, but I don't think that's an issue. Thanks.

Re: Holding my 3-speed in 3rd gear or pops out
 

I have had this problem before.

When did it begin? After the rebuild 6 years ago?

The replacement input shaft bearing on one of the three speed muncie transmissions is not made as thick as the original bearing that came in the transmission. I went through hell and back trying to figure this out.

The new replacement bearing is roughly .040" thinner than the original bearing. This causes alot of play or slop in the gears and will cause it to jump out of third if you joggle the accelerator or if it vibrates just right. If you hold the shift lever you should be able to feel the backlash in the gears as you slowly get on and off the gas.

I corrected this problem with arbor shims from grainger. I bought a 10 pack and only used two. If you think this is your problem i can send you two shims for free. It is not hard to remove and shim the bearing, you just have to get the tranny out. there is someone out there that takes these new bearing and welds a shim on it then mills it down to the correct thickness, but he wants $60 for that bearing.

Hope this helps. PM me if you have any more questions.

Re: Holding my 3-speed in 3rd gear or pops out
 

I am dealing with a similar situation now.. Started with popping out of third gear last year but recently I get hellacious vibration between 50 and 70 MPH.. When I back off the throttle (decrease load on trans) the vibration lessens but when I hit the accelerator again, the vibration happens.. I'm thinking front bearing, carrier bearing, bad synchros.. Time for a rebuild. I do have an SM-319 with overdrive here, condition unknown, but I can clean it up and try it without the OD connected and see what happens.. Gotta get Old Jim ready for the holiday season..

Re: Holding my 3-speed in 3rd gear or pops out
 

I have rebuilt a bunch of those GM stick shift trans....It has been a long time since I have been into your style trans. That said,I will have to say....if it shifts with no gear clash, I would bet that you have a problem with end play in the main shaft. That can come from worn bearings , or needs shims. when you talk about the vibrations, on/off the throttle....I would guess bearings (input or rear). On your style trans, what I broke, was the low/rev slider gear;) This was many yrs ago, & I went int Saginaws& Muncies after that. If I tore one up,it was usually the input bearing that let go 1st! If I pull one down, for a fresh clutch / & hat...that trans will get a new front bearing;) Longhorn

Re: Holding my 3-speed in 3rd gear or pops out
 

I can remember one such transmission that had been run like that with it slipping out of gear for so long that the gear teeth were actually worn with a taper to them.