When I shift from first to second the first few minutes that my car is running, I get nice smooth shifts. Once the car is all warmed up, I grind when I make the same shift (using the same technique). I've read about the synchronizing gears getting worn, but I don't get why it's smooth when it's cold. I'm going to read up on double clutching and work on that technique as well.
Your transmission appears to work best with cold THICK fluid.
The gear lube can make a huge difference in syncro operation. Syncros need some thickness/body to the lube to keep the syncro gears spinning for the engagement into the next gear. If the lube is too thin or too thick, the speed of the syncro gears will not stay in a close enough match to the speed of the next gear you are selecting, and you will get a grind. Wear will exaggerate this problem but since it works well when cold, a fluid change may work in your case.
Even in my modern cars I've experimented with fluid specs and brands and the difference in syncro operation can be very significant even though the fluids are not terribly different.
In your case, just putting fresh fluid in might be a good start if you have no history of the current fluid. If you do some searches, I recall Gene recommending synthetic 85W140 or similar. I'm going from memory on this so do some searches.
1938 Canadian Pontiac Business Coupe (aka a 1938 Chevy Coupe with Pontiac shaped front sheet metal - almost all Chevy!) 1975 4-speed L82 Vette
I can find tons of reference on what type of fluid to use and how much, but I can't find any process. This is my transmission. I assume I drain from the on that is bright (flash) and fill via the other port? How do I accomplish this? Seems awkard for a funnel. I've never taken my carpet out, but I believe there is access there. Can I do this under the car? Do I just full to the level the port allows, or am I missing something altogether?
Your syncronizers are weak. With the cold thick grease it helps to slow down the gears. Try filling with stright #140 gear oil. Holds 1 1/2 pints so buy a quart.
Scott The lower plug (shiney 1) is the drain, put a wide mouthed tin under it (up close) and undo the plug any oil will come out at a angle. The other plug is the filler plug, the easy method is with a hose and pump until oil runs out the hole. Tony
Per shifting without grinding: My grind is with the thick fluid mentioned above, but rather than double clutching I just count to 5 with the clutch pedal down, that gives my synchronizer gear enough time to slow things down (I don't double clutch). I also live in a town of 40,000 where 99% of the roads are under 45 MPH, and I don't care if I am slowing someone down. I also have never had any grinding when shifting from 2nd to 3rd.
With lubrication I go with the manufacturers recommendation as stated by Gene. Overfilling the transmission just leads to more transmission leakage either out the front of the transmission onto the clutch/pressure plate or back into the rear axle. Get enough oil there and you better have good rear seals or your brakes will be contaminated.
Loss of transmission fluid usually means the drive shaft seal is leaking passing the fluid to the rear axle. The rear axle also has a recommended amount of oil by the manufacturer (3 1/2 pints). Draining it and measuring the amount of oil will tell you how bad the front driveshaft seal is leaking.
For further discussion on this topic do a SEARCH of old POSTS using the terms +transmission +grind and even try using a DISPLAY NAME like Mike Buller or another poster that you might want to know his opinion, like Chev Nut, or try the terms +transmission +fluid. Always remember the + (plus) symbol before the terms you want to SEARCH.
An update on my grinding. The thicker fluid seems to delay my grinding (it starts about 20 minutes into a trip, not 5 or 10). I've been asking around at my mechanic and old-school transmission shops about it, not getting many good answers. I see that Co40s has a rebuilt transmission for $600. This almost seems like a no-brainer to me. I presume that Co40s would be selling a well rebuilt product.
My shop manual says that I need to remove the floor mat but makes no mention of the seat. I presume that's accurate.
I guess labor on removing, reinstalling, and adjusting the linkage is whatever I can get. Any guesses on what would be a fair range??
And...is there anything else I should have done while they are down there (for example adjust my steering wheel mast so I can get my horn working right)?
From my dealership experiance years ago the problem is most likely to the in the syncronizer drum. Was common back then onmodels with vacuum shaft. The vacuum assist forced the gear change and was harder on the syncornizer rings. Double clutching will solve the problem.
I normally do not recommend today's "higher technology" lubricants for these older vehicles. It really is a waste of money.
In your case, I do suggest you consider experimenting with something like Redline's MT-90 fluid. It has a friction modifier in that that might help your synchronizer problem. The key point is that the friction modifier works regardless of the actual viscosity of the fluid. Redline MT-90
The fact that your car shifts with the gear lube colder and thicker indicates that the synchronizer drum is not completely worn out. I have improved synchronizer operation in multiple newer transmissions (up to 40 years old) using this lube. You can get it through Amazon. Plus the viscosity is more consistent over the temperature range. In our climate it shifts much better in the cold winters.
It's worth the $20 to experiment rather than start with a $600 transmission. Plus I really wonder what that rebuilt transmission has for synchronizer hubs. Based on all the posts I have seen it is very difficult to find NOS hubs. Most people end up choosing the best of the used ones they can find.
I agree with Gene that you can get the transmission out without removing the seat. However, I tend to favor removing it just to give this old body more room to work and avoid getting dirt and grease on the seat.
Thanks Gene. So...when my car was redone (probably had 76k miles on it)...they probably didn't do anything more than clean the transmission out. It likely wasn't worn enough to merit a full rebuild and I think my dad was happy to have a running car and didn't really care. It was probably driven less than 1000 miles after restoration before I got it.
Rusty...I'll try that fluid, I guess it doesn't hurt.
I'm not keen on spending $600 on a rebuilt unit. I'd be pretty dang upset if it shifted poorly.
A Wednesday night update. No rebuilt transmissions at Co40s. Rusty...no improvement. 1st to 2nd grinding starts immediately. Gene, I'm still not good at double clutching.
I did notice something tonight. In order to get to my house I have to go up a slight hill then down a hill to get to my uphill driveway. I go up the first hill in first gear and then push the clutch to the floor and coast to the base of my driveway. I noticed gear noise even with the clutch pedal to the floor. I slid from 1st gear to neutral and the gear noise much went away. I tested this on a few stops and starts and confirmed it. Do I need to mess with the clutch adjustment....guessing I have too much free play?
Drat. I thought for sure I had found my smoking gun, or at least a good contributor. I don't get it though. That means 1st gear is still slightly engaged (if it goes away when I shift to neutral). Or is that slight engagement what helps the synchronizers do their thing?
I thought about it some more and now I get it. The gears are engaged with the output/rear end so they're going to make noise regardless of what the clutch is doing.
When I initially had problems with the synchros in my 38, I discovered that bringing up the idle using the throttle eased the problem with the first to second shift. That is sort of the same thing that happens when double clutching.
My 1951 1 Ton is now on the road! My 38 Master 4 Door is also now on the road .
When I initially had problems with the synchros in my 38, I discovered that bringing up the idle using the throttle eased the problem with the first to second shift. That is sort of the same thing that happens when double clutching.
Will try that. I was looking at my idle while I was out yesterday....bringing up idle just a hair made my mirror jiggle a little less.
As I mentioned above I have accomplished the same results as "double Clutching" by merely leaving my clutch depressed and releasing it after counting to 5 or an even a higher or lower number depending on the condition of the synchronizers.
You have probably noticed that at a stoplight when you push the clutch in, you have to wait to put the car in first gear or it will grind. That is normal due to the unsynchronized first gear. When you push the clutch in, the clutch disc, input gear, countershaft, and all the gears must spin down to a stop before their speed "matches" the output shaft, (which is not turning when the car is not moving). Thick oil will drag and help it all spin down faster.
However, if you "touch" second or third gear before you try to go into first, you don't have to wait. In that case, it doesn't matter if your oil is thick or thin. The synchronizers are essentially brakes. Most people use second but either works. For this test I am going to suggest you use third, because the condition of your second gear synchronizer is in question.
If you can't "touch" gears on a car with vacuum shift (can you?), going all the way into the gear and then right back out would accomplish the same thing.
Try it. With the car stopped and idling, push in the clutch, touch third, and immediately go into first. It will probably slide right in. What you have done is used the third gear synchronizer to stop all the rotating stuff (clutch disc, gears, etc.) that you would normally have to wait for.
Now do it again, with the car stopped and idling, push in the clutch and hold it, touch third gear (to stop all the rotating stuff), and wait a few seconds. Then, (clutch pedal is still held down), try to put it in first gear. If it grinds this time, but did not last time, a dragging clutch has most likely spun the gears in the transmission back up to the speed they turn at idle.
If the clutch drags, you are going to have shifting problems no matter what shape the synchronizers are in. It is worth eliminating the clutch as a cause.
P.S. For what it's worth, I second Rusty 37 Master's recommendation to try Redline MT-90 (or some other real synchromesh oil). Modern gear oil is much slipperier than gear oil of the 40s, and it does everything in it's power to keep your synchronizers from working. Remember, a synchronizer is a brake! If the brake can't stop the gears, you are gonna have a bad time. That is why synchromesh oils exist, and why they are common today.
Bloo....I had no grinding in either of the 3rd to 1st scenarios you laid out. The MT-90 fluid isn't helping my situation. I think my 2nd gear synchro is totally gone. Sitting in my driveway with the car in neutral, clutch out...I push the clutch in and counted to 5 and put it into 2nd. No grind. Counted to 4, just a tiny grind. Anything less than 3....grind-city. That supports Mike's slow shift suggestion, but I'm into the car for $0, so I'm willing to spend some $ to make it better.
I've watched these videos
and
This did wonders in demystifying the transmission for me. The one thing I don't get is how to remove/replace the brass synchros that you can get from Chevy of the 40s. I'm thinking of heading to Hershey....will I find the synchro drum assembly there (part number 605020)...or are all the rebuilders hoarding those?
I like and use MT-90 in a couple newer transmissions but since you've found the shifting somewhat tolerable when cold with thicker fluid, maybe you should just try something thicker, even a GL5 like a 75w140 or maybe a thick Lucas treatment? Might work well enough to give you another summer to think about and source parts.
1938 Canadian Pontiac Business Coupe (aka a 1938 Chevy Coupe with Pontiac shaped front sheet metal - almost all Chevy!) 1975 4-speed L82 Vette
There was a posting by one of our members in Germany, about a year ago, regarding those replacement synchro rings. He glued his in place and I don't know if he has it on the road yet.
My 1951 1 Ton is now on the road! My 38 Master 4 Door is also now on the road .
There was a posting by one of our members in Germany, about a year ago, regarding those replacement synchro rings. He glued his in place and I don't know if he has it on the road yet.
I kind of remember reading about gluing in and just don't get it. That's why I'm asking.
I was not aware that you could get new synchronizer rings for that transmission. That is good news!
I know it is extra work but I would go that route rather than take a chance on a used drum assembly. The rings are retained in the drum by snap rings. Check page 203 of your shop manual.
Rusty, Everything I've read is that the brass part wears. In Fig 8 on page 203....it's not the part in his right hand. The brass part is the one that stays in the drum. That's not held in by a snap ring. https://www.chevsofthe40s.com/detail/6248/Chevrolet_Synchro_Brass_Ring_Press_In.html I spoke to a VCCA guy named Marvin in Canada who replaced the brass rings on his. He said there were three indentations on the brass ring that is used to pin the new ring into the drum. He said he also used red Loctite. He very kindly offered to install the new brass rings on my drum if I sent to him.
For now, I put 140w back in and it's back to giving me 20mins worth of smooth shifting. I'm picking up a pair of transmission in Hershey next week. I'll see what those are like inside and take a stab at rebuilding with the best parts of the two. I'll also be on the lookout for drums (part # 605020) at Hershey.
