Help me to rebuild my transmission

September 1, 2018 | By Staff


I have a 1960 Corvette that has been in the family for many years, and it is generally in very good shape except it pops out of gear at times and the transmission is getting noisy, so I think it is going to need some work soon. I am pretty handy, but have never rebuilt a transmission. Is this something I can do at home or should I farm it out? And if I can do it at home, what should I look for?


Whether your skills and experience are up to the task of rebuilding your T10 is something you will have to determine for yourself. Are you mechanically inclined? Are you orderly and patient? Can you follow instructions from a manual and understand the terminology that is involved? If so, I would say “yes” you can rebuild the transmission. But if you are a novice, I would suggest you at least get an experienced friend to help and guide you.

Here’s now to troubleshoot your classic Corvette gearbox, and for other readers checking out standard American-made standard transmissions, the same general tips hold true. In Ralph’s case it sounds like his transmission is well worn and that the shifting detents or synchronizers need replacing, and also that least one bearing is failing.

In the case of Ralph’s Vette we are talking about a Borg Warner T10, which remained Corvette’s standard four-speed until 1963 when General Motors replaced it with the tougher Muncie. Old-time racers will tell you that the Muncie could take more abuse, but that the T10 was quicker and smoother to shift. This had to do with the fact that the T10 came with narrower, lighter gears that had a better tooth pitch for quick shifting.

But the problem now is, all Corvettes equipped with T10 fourspeeds are over 50 years old, and many of their trannies most likely have suffered abuse and neglect in their long service. Also, often as not, most old standard transmissions have gone for years with the same tired old gear oil in them, along with the accompanying corrosive moisture.

In fact, if your early Vette or other contemporary classic has done a lot of miles, it may be about time to refresh its transmission too. This is especially true if you are going to push the car hard in the future. And what redblooded Auto Restorer reader isn’t tempted to push his car now and then? So if your old T10 or other standard gearbox is getting tired, making ominous noises or jumping out of gear, here’s how to check it out:

To begin with, drain the transmission and have a look at the old gear oil. Most likely it will be black and dirty, but if it smells burned, or there are metal shavings or bits of old gear teeth in it, you definitely have problems that will require a rebuild.

Next, take the box out of the car, and give it a good cleaning and inspection. Always clean the gear case completely of muck, filth and grease before removing the side cover. The reason for this is you don’t want grit getting into the transmission bearings and damaging them. Disconnect the shifter linkage and remove the side cover, and then check the bottom of the gear case for metal particles and shavings.

Look over the gears for chipped teeth, wear, and bluing or discoloration from excess heat. Also check for pitting. Slightly chipped gear teeth can be cleaned up with a knife-sharpening stone in a pinch, but since the transmission is going to have to come apart for that anyway, if the gears are pretty chipped up it would be better to replace them as well as the bearings while you are at it.

Check the shifting detents in the side cover of the transmission. Are they worn and rounded, thus making shifts sloppy and allowing the transmission to pop out of gear? If so, replace them. Next check the small balls that ride on the detents for galling and pitting. And also check the springs in the side cover. Hand shifting by using the levers on the outside of the cover should take a bit of effort and the detents should shift crisply.

Remove the front bearing retainer and look at the big bearing in front. Are the ball bearings pitted, galled or discolored? Are they loose and sloppy in their cage? If so, that bearing needs to be replaced—and most likely, so do others in the transmission. Also take a look at the end of the tail shaft. If it is leaking, the seal will need renewing.

Have a look at the synchro ring dog clutch teeth. Are they rounded off or broken? If so they need to be replaced. Check out the slider sleeve. Is its collar thin and knife-edged? If so it needs to be replaced because someone has been driving around with their hand resting on the shift lever—a bad habit—and the collar has worn it too thin. Move the cluster gear assembly forward and back. If you can move it more than .025”, the thrust washers need to be replaced.

These tiny annular grooves must be sharp for the synchronizers to work.
These tiny annular grooves must be sharp for the synchronizers to work.

Handle needle bearings with care because if you drop them on the floor you will be skating around on them. If they are pitted or discolored replace them.
Handle needle bearings with care because if you drop them on the floor you will be skating around on them. If they are pitted or discolored replace them.

Look at the splines on the clutch and output shafts. Are they twisted? Twisted splines indicate real abuse and can cause major shifting problems. Often, twisting a shaft also bends it, and a bent shaft can bash a driveline apart if the deformity is severe. At the very least the transmission will not stay in gear.

Almost all of the above symptoms indicate a rebuild of the gearbox in order to be safe and prudent. Whether you do it yourself or have a professional handle it should depend on your experience as a mechanic and your willingness to be methodical and patient and follow the shop manual’s instructions.

Four-speed gearboxes are complex, but they are less difficult to build than engines. With a good shop manual the job isn’t beyond most hobbyist restorers. It is just that they have many small components that can go zinging off and become lost if you are not careful.

And then if you consequently take your transmission in a basket to an expert, he may charge you more just for figuring out what you have done and what you have lost. If you do decide to tackle the job yourself and need parts, or just want to find a good transmission rebuilder, try:

Dave Waugh Remanufacturing

11965 Rivera Rd. Santa Fe Springs, CA 90670