1960 Vette 3 speed manual transmission issue

[Alan #44172]

My 1960 vette has the origninal 283 CID engine with a single 4 barrel carb and three speed manual transmission. For the past two seasons I have had the transmission repaired by different transmission shops specializing in classic car transmission repair. The problem is still not fixed. Here are the details:
1. Shifting from 1st to 2nd and occassionally 2nd to 3rd you must pause for a second or two or you will grind gears. You can eliminate the grinding if you double clutch which works well, but should not be necessary.
2. On occassion, while just cruising along, not accelerating or decelerating, the transmission pops out of 3rd gear. No particular speed or condition, just randomly.

All the parts inside the transmission have been replaced, except for the syncro assembly.

Question: Does this problem sound like a syncro issue? Where can I purchase one, NOS and maybe not NOS?

[Jack H.]

Re: 1960 Vette 3 speed manual transmission issue

Those are CLASSIC symptoms of worn synchro gears! I'm amazed that anyone worked on your transmission without replacing the synchros... It's Tranny 101 to replace them once the labor has been spent to R&R the 'box' itself!

[Mike McKown]

Re: 1960 Vette 3 speed manual transmission issue

Synchro is either worn or the snap ring that holds the hub has been knocked off due to hard shifting. Used to be very common back when these transmissions were common.

It may also involve the rebuilder leaving out the needle bearings on the mainshaft/input shaft. Long shot.

I'd find another shop.

[Joe L.]

Re: 1960 Vette 3 speed manual transmission issue

Alan-----

1) Worn/damaged synchronizer assembly;

2) Worn or damaged syncro rings (brass);

3) Worn or damaged synchro teeth on gears (these are the "small teeth" on the gears and NOT the main teeth.

If it's (3), above, that's real problem. That pretty much means that you need a new gear or gears. Some guys are able to "re-point" worn teeth but the problem is that it usually does not include re-hardening. Without re-hardening of the case-hardened teeth, their life will be short.

The synchronizer assembly that you're looking for is GM #3774720. It's long-since GM discontinued but NOS examples may be around. The last available synchro ring was GM #3845039. It's also discontinued now, but there may be some around.

I would also think that parts for these transmissions would be available in the aftermarket. However, I do not know of a specific source. Call someone like Ed Hartnett or Larry Fischer. Both will likley be at Carlisle if you're going.

[Michael H.]

Re: 1960 Vette 3 speed manual transmission issue

Alan,

The replaceable brass rings that others have mentioned do not exist in a 3 speed transmission of this vintage. There were no separate brass rings. The clutch cone and brass ring were actually part of the syncro hub assembly and the brass was not serviced separately. The entire drum assembly had to be replaced.

Also, the system of engaging the sycro hub to the gear was completely different than that of later 3 and all 4 speed transmissions of the era. The teeth that the hub slides over were an inch long, not the short 3/16" teeth that would be in a more conventional design. For this reason, it's not likely that the problem is with the 2nd speed gear or the main drive gear.

Mike McKown's post was correct when he suggested replacing the syncro drum assembly. This was/is a very common problem and will produce the exact problem you describe. I don't know of a source for this drum assembly but I would think that someone has these available.

One more thing that can cause the problem that you describe is a clutch that is not releasing completely. This would cause the grind when shifting from one gear to another. To test for this condition, with the car stopped and the engine running, place the transmission into either 2nd or high gear to stop the clutch from rotating, then slowly shift into 1st gear. If the transmission shifts into 1st gear without a grind, it's likely the clutch is releasing completely and not draging. If, however, there is a grind, you may need to readjust the clutch to insure complete disengagement. I'm leaning more toward the syncronizer drum assembly as the source of your problem though.

I think Jack and Joe were thinking about later 3 speeds or 4 speeds when they suggested replacing the brass syc rings. These old 3 speeds are quite unique. Hopefully, someone can supply information on a currently available syc drum assy.

There are several other items that can cause a transmission to pop out of gear but I think I'd start with the syc drum. However, while the unit is out of the car, be sure to check the condition of the pilot bushing in the end of the crank shaft. Poor transmission alignment or a bad pilot bushing can cause the problem you describe.

[Terry B.]

Re: 1960 Vette 3 speed manual transmission issue

There is a GM #3774720 unit on Ebay now. Ebay number 300011447001 to close in 17 hours.

[Jack H.]

Yep, I missed the 3-Spd component!!! *NM*

[Joe L.]

Re: 1960 Vette 3 speed manual transmission issue

Terry-----

This is the correct one for your transmission. It looks like the seller wants a significant price for it, though, since it's already over $200 and it hasn't met reserve.

[Mike McKown]

Re: 1960 Vette 3 speed manual transmission issue

The synchro units can be found in any pass car/1/2 ton Chevy three speed from '55-'64. For that matter, you can interchange the '55-'57 pass car or 2nd design '55-'62 truck transimssion into your car by simply using your extension housing on the junkyard transmission so you can mount your shift linkage. Pickups went to a short tailshaft in '63, I think.

Gear ratios are the same unless you have the close ratior box in your car.

But your probably don't want to do that.

[Allen W.]

Re: 1960 Vette 3 speed manual transmission issue

I bought such a sycro assembly a year or so ago from a transmission supply jobber in Washington state. I'm at work and don't have the name. It may have been something like Valley Gear. Call up, give credit car part comes. No problem for something this old. They know their stuff. I think it cost me $200. Was a NOS part in an old box.

Allen