The Stovebolt Site Forums The Shop Area Engine Shop Grinding them gears

Yesterday my '66 3 speed began grinding gears. When changing gears from 2nd to 3rd or visa-versa, the gear grinds severally. The problem only begins after the transmission has warmed up and gets worse the warmer it gets. Thinking it was the fluid, I changed it without having results. The truck has a brand new clutch, possibly needs an adjustment? Thanks in advance.

Hi
It sounds to me like the syncronizer for second and third gear is worn in the transmission. I had that problem on my 67 with a three speed.
Those transmissions aren't hard to repair.
Good luck.
Jim

have you tried shifting without the clutch like the big trucks do? if it shifts good like that it's defiantly the synchronizer

Yes, I almost always shift this way actually and it does shift very smoothly. I guess it must be the synchronizer. I have another 3 speed that I can put in but I may just want to fix this one to make sure for long life.

Not hard to repair Dell. When I was a parts man for Chevy we kept a well stocked ben of syncros mostly for the hot rodders.
I myself used to go thru a syncro every few months back in the day. Speed shifting was real hard on them!
Worst part of servicing the transmission is loading the needle bearings, but a heavy grease holds them in place while you insert the shaft.
Denny Graham
Sandwich, IL

Ok, well I think I may try to rebuild it myself even though I have never torn into a transmission before. It seems pretty simple as it is so small and light that I can pick the whole thing up easily. First of all I need help on finding parts. Where do you find the specific parts to rebuild this thing? Is there a rebuild kit that you can buy. Which one in this diagram is the syncro? Is there any other parts that will need replaced? Sorry, but I am a moddest mechanic but I learn quickly. Denny, which part/s on this diagram is the needle bearings? Thanks a lot

8, 11, in the back of the clutch gear and 35 in the
cluster gear. The syncro is 13,14 and 15 usually
found as a unit.
Not sure where you would get parts now days, it's been years since I've worked on one. You might start out with Novak.
Denny Graham
Sandwich, IL

Try adjusting the clutch first. The new disc might have worn-in a little, or more likely, the linkage has worked into a relationship that's not allowing the clutch to release all the way. There should be about 3/4" of free travel before the throwout bearing contacts the pressure plate fingers. If there's much more free travel than that, the clutch might not be releasing fully, causing the grind when shifting.
Jerry

Is there any special name for this transmission other than GM 3 speed? I am having trouble finding parts. I will have the clutch adjusted soon too. Thanks

I found this link although it wasn't much help Link The books just calls it 3-Speed Synchromesh made by Chevrolet.

They made the same transmission form 1933 to 'round 1986 with minor changes. Can't be that hard to find. Chevy 3-speed synchromesh.

It is commonly known as a SM318 and also as an early Muncie. Anaheim Gear in Anaheim, CA has a rebuilt syncro drum assy for $125. Same basic internal parts from 55-67 cars & trucks.
Fred

Speaking of three speeds, were the passenger and truck three speeds the same transmission??
Denny Graham
Sandwich, IL

The 55-67 transmissions were the same with minor differences. The gear ratios were the same except for Corvettes & some Pontiacs. Trucks & cars used different side covers and the lower mount holes were threaded on Trucks. Early cars & trucks had a longer tail shaft than the later version. The later cars also used a rear mount.
Fred

Thanks a lot for the info! I removed the 3 speed from my parts truck, it looks the same except for the bottom mount holes are not threaded and are larger and do not appear to have been drilled out, is it possible that it came off of a car? I opened the side cover and the syncro looked to be in very good shape. I noticed that each bolt on the side cover was different or had a different washer, also the rear seal was completely missing. Someone also used pieces of wire instead of clips to hold the shift rods on. I am not sure if I want to use the transmission as the clutch gear bearing retainer is cracked almost all the way around.

I'm going to toss a question into this thread, I'm not trying to hijack it.

Will internal parts swap between the plain-jane 3 speed and a Borg-Warner R-10 3 speed with an overdrive? And where can I get parts for it if I can't swap between the two?

Dellman,
It's from a car but it will work just fine in a truck. Install some longer 1/2" bolts with nuts on the truck. If everything else looks OK, use the side cover and bearing retainer from your existing trans. Install a new seal and you are good to go.

Drew, If both of the transmissions you are referring to have the 4 bolt side cover, all the transmission parts will work with the OD trans. If one of them has the 7 bolt side cover, none of the trans parts can be used in the other. Note: The only part of the trans that is B/W is the OD portion, the front half is GM.
Fred

Ok, I rebuilt the transmission with the syncro from my other transmission and installed a new bearing kit for good measures. The brass ring was slightly scuffed but otherwise looked pretty good. Now the transmission still grinds... I contacted Anaheim Gear as rfs56trk suggested (thanks a lot for that info) and they said they do sell the drum which includes the brass ring for $150 after core deposit. I am glad they sell it, they seem to be the only ones that do :S . Anyway, just updating everyone, I will let you know the results after the second rebuild. Thanks a lot.

try obsoletechevy.com for some parts, they have some in their catalog for trannys, they supposedly have NOS parts... some parts from the '40 trannys will work in the ones from the '50s, check the Master Parts Catalog if you have the GM part number.

Mike

Thanks for the info. That site seems to be down.

In the mean time while I have been waiting for my syncro, I have been driving my truck to and from work (taking it slow on the shifting). In the last two days it has began to pop out of 3rd gear. The transmission seems to only pop out when I am going at a smooth speed, not accelerating or decelerating. Now I am a little worried, since 3rd is direct drive could it still be the syncro doing this? Before the rebuilt it never popped out of gear.

The popping out may from a bad detent/spring/ball on the shifter rail/rod.

I wonder if a linkage problem may be the cause of the initial grinding?
Maybe the transmission is trying to go into first and third at the same time?

The transmission has a definite distinction of gears, the old syncro did look warn out. I really don't know though, is the detent/spring/ball hard to replace or find parts for? Oldly enough, after the rebuilt it has no problem when going from 2nd to 3rd.

Generally a worn syncro will cause it to pop out of 3rd gear but you have to look at some of the other parts also. The clutch gear could be worn where it makes contact with the syncro, the tip can also be worn where it makes contact with the pilot bearing and the pilot bearing can be worn. In addition, you could have a worn 2-3 shift fork. While you are at it check your U-joints, the input yoke and the bushing in the rear of the trans. All of these can be contributors to the problem.
Note: The parts for your trans must come from 55-67 car or truck, with the same configuration, nothing earlier or later will interchange.
Fred

Okay, thanks I will check everything again. I know that the pilot bearing is good and the 2-3 shift fork was a little worn but not too badly. I will check the rest when I pull the transmission out again. My new syncro should arrive on Monday. How about the control rods? I adjusted them as well as I could according to the manual but I don't really know how. The first and reverse control rod is loose where is connects under the hood.

Sloppy linkage can cause sloppy shifts and also hang up between gears, usually between 1st & 2nd. The transmission should stay in gear providing the rod is adjusted correctly to get it into the gear selected.
Fred