Hey Guys; A bit of background information before I request help. I have a 72 corvette here in Ireland and I am finding it difficult to get an expert opinion on my gearbox. I have removed my engine and gearbox to carry out an overhaul.(No major problems just some simple oil leaks and an opportunity to paint engine bay and chassis). However on occasions the gearbox would pop out of second gear when easing off the throttle. Apart from a gasket leaking on this gearbox and the occasional pop out of second gear everything appears to be fine.The only problem I can see is the slector fork for 2nd gear is slightly worn but maybe not enough to cause the problem. I believe my selector rods are adjusted correctl also.

However, as I have the gearbox removed I would like to take the opportunity to rebuild anything that needs to be done. The problem is, I have no specs/tolerances to check/measure to see if any gears are worn, play in shafts etc. Its probably very difficult to tell from the pictures below if anything is badly wrong but any feedback is greatly appreciated.

Also, I have receipts from a few years back which show the gearbox was rebuilt but I do not have specific information.

Thanks guys. Joe.

 

First off, I'm no expert, but if you've got it apart and want to tune things up it sounds like it would be wise to replace the 1st-2nd synchro. Also all the brass rings. The shift fork I would replace if I wasn't worried about the $$, some one else could give you a better idea on if that was needed. Check the input shaft bearing for wear and changing the pilot bushing while the tranny is out is a good idea.

 

It probably doesn't need a new 2nd gear but I certainly change out the stock syncro sliders with a set of Torq Loc Sliders that prevent the popping out of gear. Since second gear usually takes a beating, inspect the gear closely for signs of wear, a new one should run less than $100 if it looks like it needs to be replaced. The syncro teeth themselves are starting to look a little rounded off, not too bad, but a small parts kit comes with new ones. The fork doesn't look too bad. Make sure the shifter is adjusted as well.

 

The fork will not cause that problem, in fact, if it starts to come outta gear, you cannot hold it in. That problem, generally, is wear inside the shift collars (sliders), and also on the hubs.
Chuck

 

V8Vega: the brass rings are the synchros.
Joe:Your synchros look like they are in new condition.

Before disassembly do this. Put everything back together & install shifter.
Put alignment pin in your shifter and make sure all shift levers are adjusted properly. You may find the 1-2 shift lever out of adjustment.
If its not out of adjustment. Remove side cover of trans and check the shift fork detents on the inside of the side cover.
Do these things take more pics and report back

 

It looks good...if there are no issues then just replace the seals...unless you just want the experience.

 

I suspect a shifter throw adjustment is in order. If you push the brass rings toward their respective gear and have at least a two business card thickness separating them, they will be good to go. The brass rings act as brakes and slow/stop the gear for engagement. What can make trans. jump out of gear is when the little teeth (on the gear) that the snycro sleeve slides onto are worn at an angle or the shifter is mal-adjusted and not fully engaging the gear. From the pictures, the gear teeth look good/decent IMO but better pictures with oil removed would be better. The teeth on 4th gear look pretty chipped up though which is unusual. I tend to agree with AzMotorhead's analysis. Again, better pictures (better focus & no oil) allowing close inspection would be an aid.

 

Everyone who replied: Thanks a million, it is great to get experienced guys' point of view. I am feeling a bit better after reading your responses. Apologies about the quality of the pix, (Just had my Phone handy!) I will clean gears and take better pictures. Again, Thanks guys!!

 

I agree the slider should be replaced but, I would also replace the shift fork while it is apart.

Autogear in the USA is the place to source quality parts.

I would purchase a complete overhaul kit with bearings, gaskets, seals, and the small prts kit along with 2 torque lock synchro sliders, new shift forks, HD side cover spring and synchro hubs.

Rebuilding is pretty straight forward as called out in the GM service manual. I would make sure you pulled couter gear shaft out from the rear of transmission, and use a sealer on the front part of that shaft or get a "O" ringed one to replace the original shaft to prevent future leaks. Make sure to deburr the reverse gear set as they are usually chipped up from people not properly putting the transmission in reverse. Make sure the thrust tabs for the countergear thrust washers are bent over 90 degrees and the countergear endplay is under 0.025" and the Muncie should give you years of good service.

There are many sellers of parts on Ebay, many of these kits are inferior quality Asian sourced products buyer beware!

 

Hi, So again thanks for the replies, great information. I got a chance to give the gears a quick cleanand take some better pictures. AzMotorhead, I need to get the alignment pin for the shifter adjuster, but I believe I need to re-install the gearbox to mount the linkages? However, It is something I will need to check.
I hope the pictures are of better quality and let me know what you guys think.
Picture 1:

Picture 2:

Picture 3:

Picture 4:

Picture 5:

Picture 6:

Picture 7

Picture 8

Picture 9

 

Geeze, I hope MY tranny looks that nice! Those gears look pretty new to me.

 

Those are better pictures but I was hoping for some shots directly looking down on the small teeth that are on each gear (like picture 8 except even closer). Yours look to be okay but a couple of pictures suggested a bit of taper. IMO, you don't need any sliders/sleeves. They aren't what hold it in gear. The condition of the big teeth on the gears was never in question, they look perfectly fine to me. I'd probably replace that shift fork while I was in there. I have in the past used brass to braze/add material back on to the side of the fork. Of course you have to file it clean it back up after doing do.
Jim

 

Looks to me like there is a small chunk of metel on the countergear in your last photo. Probably a piece of reverse gear but, if transmission pops out of gear, you should tear down and check synchro hub and slider.

I would change slides for "torque lock" style as you gear dogs are a little worn, same for 3rd gear brass blocker ring, it looks like 3rd gear is getting beat. The brass blocker rings make the gears slow down for proper shifting by wedging into cone shaped part of gear. You need to check brass blocker rings by pushing them towards gear and see if they wedge before they bottom on gear.

There have been many lubrication induced synchro problems caused by running wrong gear lube in the old technology Muncie transmissions. Make sure to use the right gear lube for an older gearbox with brass blocker rings in it.

 

Solid LT1 is that the piece of metal you're referring to?
If so that is the back side of a rivet. The rivet holds the slinger on the front of the countergear. Do not remove those rivets or that slinger.

Note: If slinger or rivets are loose,after counter gear removal,they can be peened a little more to tighten them up.

Joe. I forgot if you are using the original shifter yes you do have to have it mounted in car to adjust. A Hurst Competion Plus shifter will give a much better feel. Several aftermarket suppliers offer a Hurst shifter and a handle that matches the stock look