VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1933-1936 Transmission rattle

I finally got the 3 speed transmission installed in my 1936 Chevy pickup. It shifts fine. Once in a while a slight grind going into 3rd if I shift too quick. I have a rattle, or marble/ticking sound when the transmission is in neutral and the clutch is let out. It goes away as soon as the clutch pedal is pressed in. It also can be heard in 1st gear the most, less in second and just slightly in 3rd. It seems to go away the higher the engine revs. Any ideas? Thanks, Mike

When the trans is in neutral, the only things in motion are the input (clutch) shaft and the cluster gear. The input shaft
has a ball bearing where it enters the case; There is a set of
smaller needle bearings on the inside of input shaft (also
called the 'main drive gear) where it meets the output shaft
(sometimes called the (main shaft). The surface on the gear
and the mainshaft end are carefully machined for the needle
bearings to roll on, and it also serves to support the main
shaft and keep it solid under load. I suspect your noise is
coming from that area! When in third (high) gear, every thing
is locked together and turning as 9ne unit, so the noise will
dissipate. It looks like you will have to remove the trans to
check it out! What are you using for trans lube? I have a '35
Chevy, which is very similar, and I found the best lubricant
is 600W, the same as is used in Model A Fords. The other thing
could be an incorrect or missing thrust washer at the end of the cluster gear. Either way, I believe the trans will have to
come out and apart! Good luck!

I'm also using the 600 weight oil. Thanks for the explanation.

Common for the clutch fork to do that. Press against the fork with something while you hear the noise and see if it goes away.

Mike,

If you find a way to eliminate that crunch going into 3rd please let me know how you did it. I have 2 of those transmissions for my '36 PU and they both do that, even with 600 oil, once everything is hot. That crunch does not occur with the oil cold. Both of those transmissions are set up at the middle of the 0.025" - 0.035" synchronizer end play.

600 oil is not a gear lube, it is steam cylinder oil. It would be much better to use an actual gear lube and there is a gear lube more viscous than 600, but the minimum available quantity is 5 gallons for about $100. That's kind of pricey to try something out to see if it's an improvement.

Some of the amateur chemists mix stuff like STP, grease and other goo in to thicken oil.

I played some more with it today. I think its backlash or a missing tooth on a gear. It does it in reverse, 1st and second but not in 3rd. Loudest at idle with tranny in neutral and clutch pedal out. Goes away as soon as the clutch is pushed in. Its not the clutch fork. It makes a rhythmic knocking that speeds up with engine rpm and seems to get less pronounced with rpm. Seems to do it under acceleration and quiets down under a load. Not as noticeable when decelerating. I'm wondering if its worn gears since it seems more pronounced at idle and accelerating, then when its decelerating? One side of the gear teeth more worn than the other side. Its not whining, growling, or grinding that you would associate with a bad bearing.

If the noise disappears in 3rd I would think it is cluster gear or the gear on the input shaft that drives the cluster.
In either case it sounds like gearbox out to fix.
Tony

One thing you could do before removing the transmission, is
drain the gear lube as completely as you can. this is something you would have to do anyhow to remove the Tranny.
Remove the floor mat and the floor section over the trans,
and carefully remove the shifter mechanism and shift cane from the
trans. Now, with the rear wheels off the ground, and the car safely supported on stands, you can easily visually inspect
the gears for damage. Making sure the low & reverse gear is in
the neutral position, you can turn the engine over and inspect
the gears for damage or unusual wear. I would also advise taking a good at the shifter forks on the bottom of the
shifter mechanism. One fork engages with the low & reverse gear, the thinner one is for the 2nd & 3rd synchro. Chances
are great you will see the cause of you noise then. The shift
forks have been known to wear, and could contribute to the problem.

Thanks Phil, I will give that a try. Mike

I believe I found the problem. The synchronizing spring for the main drive gear is in back of the drum and not in front. I can slide the drum back to the clutch sleeve. Any way to fix this in the truck? I'm not sure how I would get in to the other side of the synchronizer drum, if that's even possible without tearing apart the transmission. Any way it slide there by its self, or is that not even possible and was put back together wrong? Thanks....

I took a better look tonight. Someone installed the spring first and locked it onto the shaft with the slots facing rearward, then installed the synchronizer drum. The should have installed the drum first and the installed the spring with the slots facing forward to lock into the fingers on the drum. As it is, the drum is just flopping around until you put it into 3rd when the clutch sleeve would push it into position and tight everything up. So instead of the clutch sleeve pushing on the spring, it was pushing directly on the drum. It all makes sense now. Only way to fix this is to take it apart, flip the spring and put it in the right position.

Transmissions are very unforgiving! They are either correct,
or very wrong! There is no gray area! I'm glad you found the problem, but there is no shortcut to success; it must come
out and apart! I wish you the best!

Thanks Phil, taking off the top cover really helped figure out what was going on inside. I'm going to take it to John at Roxbury Transmission in VT. And have him go through it.

Mike,

If the bearings and gears are good there is really nothing a "professional" transmission guy can do for you that you can't easily do for yourself. Synchronized shifting requires that the synchronizer end play be in the range of 0.025"-0.035". That's easily measured with feeler gauges or number drills. That end play is affected by the degree of wear on the brass cups in the synchronizers themselves and the width of the synchronizer "springs" that come in various widths to adjust that end play.

As you know from just buying one the synchronizers are rare and expensive and the "springs" are extinct and have been for decades.

Your 3rd gear end play will probably be excessive. Using the thinnest possible gaskets at the front and back of the transmission case will reduce that end play by bringing the main drive gear and the mainshaft closer together. Brown paper grocery store bags make excellent gasket paper and are very thin.

The only caveat is that the front bearing retainer must be in tight contact with the transmission case. I have found that occasionally the gasket surface of those bearing retainers or the recess that contacts the bearing has to be slightly faced off in my lathe to get that "perfect" fit, probably due to manufacturing tolerances of 80 years ago.

Hi Brino,
I have the manual and parts diagram. How hard is it to take apart and reassemble without the special tools that are called for in the manual. One worry is the counter shaft. It says you drive the shaft forward to drop the gears into the bottom of the case. How hard is it to reassemble? Thanks...: