VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Double clutching and grinding gears-1940

I haven`t made any meaningful post in awhile , but maybe this one might help some novice like myself with their double clutching and gear grinding on their vacumnn assisted trannys. I`ve tried to follow the instructions in the service manual with limited success. Over the last 3 years of owning this car I`ve had to double clutch to avoid clashing gears. I`ve replaced the grommets and tightened up the linkage and fooled with the linkage adjustments and it still gave me trouble shifting. I decided the syncros were shot like a lot of the trannys of that era. But the shift lever seemed a little "soft" inside so I replaced the spring in the picture and fooled around with the 2 bolted clamp above the spring....I was shocked to find that it has made a HUGE difference in the shift eliminating ALL of the grind into second and 95% of the grind into 3rd. Downshifting from 3rd to second still needs to be done at 10 MPH or less to avoid the crunch. A slow shift is necessary , no speed shifting. The spring is a 1 1/8 X 3 x .105 from Ace Hardware.....had to cut and try 3 times to get the right "feel" on the shift lever inside the car. This made my day and I hope it might help someone out there who is having the double clutching blues!

Hi David,

I have never had grinding from third back into 2nd. I have grinding if I do not double clutch when I go from first to second. Like you I have many times tried adjusting the linkage to eliminate my shift problem. My car is all apart as it is being painted but I hope to try out your suggestion next summer when I have the car back together. I wonder if you have continued working on linkage adjustments since you replaced the spring?

Thanks, for your suggestion, Mike

P.S. My transmission is not vacuum assisted. I also like how you have added additional washers to the the adjustment points to take up a lot of the slop. A picture is worth a thousand words!!!

The syncronizers "work" when shifting into or out of second or third gears.oes not work for first gear either way.

Interesting...thanks for sharing. This is the best way to learn how stuff is supposed to work.

p.s. all of my grinding sounds are due to the driver's inability to remember to come to a complete stop before shifting into first.

Kind of hard to wean the muscle memory off from 30 years of driving 5-speed sticks...

Mike ...the small linkage is "bottomed out" on the threads and and I`m wondering why? When I adjust it up off the bottom it grinds shifting out of 1st( I`m thinking hitting reverse). I tried to adjust the large rod up and the the small rod up , thinking they would move in sequence and I could get off the bottom of the adjustment on the small rod, but no luck . The only adjustment I made at the time of the spring change was moving the clamp above the spring towards the firewall about 3/32 in. and that seemed to be the best spot. So, experts and novices , any suggestions or explanation why the smaller linkage is bottomed out ? Thanks for any reply`s in advance ~D

FYI page 213 of the 41 shop manual indicates that there should be 3/4 of an inch of space in the area the large spring is positioned. The spring in the picture does not look very heavy duty!!! It appears from your picture that the distance on yours is over 3/4 of an inch. Maybe the 1940 specs were different than in 1941?

Thanks, Mike

Mike ....no, the same specs for the 40 as the 41....I`ve tried the 3/4 inch and that does`nt work ....Iv`e also gone by the book for the correct distance of the steering shaft at the steering wheel ....so, I have reached the point of trial and error and most likely have things out of kilter somewhat ....but much better than before. Thanks for checking your manual though ! appreciated ~D

Oh Mike ...I forgot to comment on the spring. It actually is VERY stiff . do you have a picture of the correct spring you can post ? Thanks ~ D

Assuming all is well with the rest of shifter's "world", I'd suspect the inter-lock lever is damaged or worn out. The lever on the outside of the side cover is often over-tightened causing damage which after time and usually even more shade tree tightening, upsets the geometry. If the alignment is not correct (the flat spot) the interlock will have trouble keeping gears in the neutral position while shifting to other gears.
Combine that with other worn internal parts shifting clash is inevitable.

B-25 ...thanks for your reply .....I guess at this point I could`nt hurt it much tightening that lever on the side of the tranny ....I`m clueless on how to do that and didn`t see that in the manual . Any instructions on that procedure ? Thanks~D

Thought it was time for a few more pictures to better explain potential problems. The first picture shows the cover of a 39-48, the second shows the back side of the cover with its two yokes mounted on the guide bar. The face of the bottom yoke which I believe is the lo-speed one shows almost no wear. The top yoke is very worn it is for second and third gears. It aligns with the clutch that holds the synchronizer rings. The next picture shows a new top yoke. The last picture is of the clutch that the two synchronizers ride in. The top edge of the clutch (the part that sticks out the most from the from the clutch) is what rides in and out of the damaged yoke shown in the second picture.

Until you take the cover off you can not tell the condition of your yokes. I see nothing that can be tightened on the two shafts sticking out of the cover. If someone would like me to take the guide bar off of the cover I will be glad to do so.


It is possible to put the cover back on and not have all the yokes aligned properly. I have been there and done that. So be extra careful to make sure the low-speed yoke is aligned with the correct gear and the very small yoke is aligned around the top ridge of the clutch.

Good luck, Mike

P.S. The damaged yoke is currently for sale on ebay for $25.00
Chevy shifter yoke shift transmission 1941 9142 1946 1947 1948 591738. The other yoke is also for sale for $42.00.

There is not all that much too it.
The lever only has one pinch bolt/nut holding it to the interlock shaft. Follow the shift rod down to the end and you'll be able to see the bolt on the other side of the lever. But tightening it won't change anything if the lever is not first in the correct orientation. Also check the other end of the lever for "slop". There's no bushing in there making it a high wear area for the lever and the shifter rod end.

Mike ....thanks for posting the pictures . I`ve never been inside this tranny and I probably won`t be anytime soon , but this all is valuable information to me and will save. Thank you! BW25....I think the pinch bolt is shown in Mikes 1st picture of the outside cover, As far as a possible adjustment I could try , would that be the correct bolt and would that possibly give me more adjustment thread on the upper end of the smaller linkage? As for correct orientation you spoke of ...not sure about that if I`m supposed to adjust forwards or backwards with the pinch bolt to give me more thread on the linkage. Maybe I`m confused ....but if I`m on the right track with this , I may tinker with it . Thanks guys for your help! ~D

Yes, the lever and the bolt are in first picture. But what we can't see is the shape of the shaft underneath the lever. The orientation of the lever and the shifter rod is by design with the transmission in neutral. Behind the "button" we can see, the round shaft is machined down into a rectangle shape. The only adjustment is the nut on the top side of the shifter rod.

While the example lever in the picture may be ok on that end, the shifter rod end is completely shot. There's not even enough metal left to install a bushing. The original hole is on the left side in the picture. The shifter rod that was attached very likely had a deep groove cut in it. Adding the two worn parts together the shifter rod would have to be shortened (the area you where concerned with) in order to work.

I have some very worn parts from our trans stored "somewhere". If I can find them I'll take some pictures. Our's was so worn out I had to replace every part in the side cover. Odd thing was, the only complaint was slipping out of first gear. After seeing the rest of the worn parts I could not believe it worked at all in any gear.

BW25....thanks for the added info. I`m starting to get the picture of the wear and tear on the metal parts from years in service. I don`t plan on removing the tranny at this time to check out the internal condition . Looking at my cover , it does`nt have the same pinch nut . It has a spring steel expander holding the shaft in the outward position . Do these need replaced ever? and why is mine different from the cover in Mikes picture? Different year tranny ? Also would adding a few more threads to the small linkage shaft make any difference since I`m bottomed out on the shaft? Thanks ~D

David,

Please post a picture of your linkage at the transmission. I have done some more work on a donor transmission so I will post more pictures to show wear areas. I could see doing a post just on the transmission cover as a prelude to diagnosing transmission problems. I am getting my body back from the paint shop tomorrow so will try to work in more posts before the weekend.

Thanks, Mike

Oh Ok. It sounds like your trans is one of those converted floor shift models. If it is go to the "project" and check out the 1939 shop manual. The linkage adjustment is well covered.

The 1939 vacuum shift parts are very different from the 1940 and up. Also the 1939 had the trans. cover on top of the case and not on the side.

....Mike ,..BW25 ,..Gene...all...here is the picture you asked for Mike . It shows the steel spring expander , no pinch bolt. so, whadoyathink?? ...there doesn't seem like much play in the shaft going into the tranny ...I may have put the expander piece backwards , but either way , it isn`t very tight . Is this a replaceable part , or what ? ~D

I think this is correct, but it is for a 48

CC.....thank you for clearing that up ....It made no sense the way it was in the picture. Still no pinch bolt on the shaft going into the tranny, so still wondering why the cover is different from Mikes picture. It is a side cover on the tranny . ~D

I think removing the cover of the transmission is a good barometer of the overall condition of the transmission. The following pictures will point out wear areas that are going to effect your overall transmission performance.

If you want to remove your cover you should follow the steps in your manual as well as thinking out what you are getting into. First drain your transmission fluid, next plan on how you will reseal the cover so have a gasket on hand or the sealer of your choice. Realize that it will not be easy to see into the transmission because of your head room in relationship to the floor of the car. For me it is easiest to use my camera for inspecting the inside condition of gears etc. As you remove the linkage inspect it for wear. An out of round ovally worn part should be repaired (weld a new washer over the the damaged area).

A lot of what you will be looking for is worn/damaged parts. When removing the cover you do not remove all of the bolts. In one of my above posts it shows the cover with two bolts still in place. They are used to attach the guide bar to the cover. Remove these two bolts only with the cover on your workbench.

Also it is easiest to remove the cover in neutral. When taking the cover off do it slowly so you can see the position of the clutch and the gear that rides on it. Below I included a diagram of the transmission so you can become familiar with the names of the parts. The cover parts will have to lineup with the clutch and gear to reinstall the cover correctly. And yes it is possible to not lineup the yokes with the clutch and gear. I have been there and done that. In the best case scenario it is always easier to work on the transmission off of the car so you more easily see how things are lining up.

Several of the following pictures show badly worn parts. Notice the interlock that the linkage is attached to and the one 2nd gear/high speed yoke. If you are looking at this degree of wear you can imagine why gears are grinding as you shift, or why a gear can slip out of position.


Diagram from Chevs of the 40's also available on line in our online parts catalog http://chevy.oldcarmanualproject.com/parts/1929_54/index.htm



This linkage is attached to the interlock. It is probably not unavailable as a NOS so repair it as I mentioned above.



The above picture and the two pictures below show a worn interlock. Another challenge to find a replacement part. Maybe another candidate for a welding repair.







The yokes in their neutral positions attached to the guide bar.



Underneath the yokes you will find a spring and 2 ball bearings. Be careful removing the yokes so you do not loose the bearings. If the yokes do not slide off with brute strength then use a brass hammer to gently remove one. Once the bearing is exposed the yokes will move easily off the guide bar.

Reinstalling the spring and the bearings requires you too have the bottom yoke in the neutral position. That position has the bearing in the middle hole of the bottom yoke. The spring will then stick up less than a 1/4 of an inch. If it sticks up more then it will be very hard to depress with the bearing on top of it. This also means that the bottom yoke is really not in the neutral position. Carefully put a 1 inch wide putty knife on top of the exposed bearing and gently push it down inside the guide bar. Next slowly scoot the yoke over on top of the bearing as you move the putty knife away from the yoke. Please be aware what might happen if you are not careful, the bearing could shoot away from the guide bar/yoke and now you have to figure out where it flew to!!!



Do not try to pull the shaft through the seal on the cover without removing all the burs off of it. Rarely do you find a shaft where someone has not taken a pipe wrench/etc and tried to shift the transmission with it. Pulling a chewed up shaft through your seal is going to damage it and cause transmission fluid to leak. Be cautious when removing the interlock to clean up its shaft before trying to get it out of the cover.



It is very important that the bolt is tight on the interlock shaft. If it is not then you can imagine the amount of play that could be in this piece. A part designed to move a 1/4 of an inch could require 3/8 of and inch or more to move a yoke.

I am sorry if this needs some editing but I only have so much unsupervised time.

Please comment so we all can better understand this component of our transmissions.

Thanks, Mike

Mike ....The information you provided and photos are above and beyond!! Thank you for this effort and the post will go in my favorites list of repair info for a later date. I can see that trying to inspect the side of the tranny would be difficult while in the car . Will wait till I can remove the tranny or pull the engine. My linkage piece does not have a pinch bolt ...The picture ins`t good , but is it welded or pressed onto the interlock? There is a small hole in the end of the linkage piece?? Before I dig into it any deeper I`m going to add a few threads to the long linkage shaft to see if one or 2 more turns on the adjustment does any good. I know that is a silly way to approach the problem , but since it is bottomed out and 1 turn the other way gets a crunch or grind , I`m curious. I`m sure some of my adjustments and settings are out of specs, so no telling what I may get. So, anyone know why the piece in the picture does`nt have a pinch bolt set up?? Is this just something someone did along the way ?? ~D

My thoughts are the lever is just an earlier design. If someone made it, they did a very good job. The other end fits in those little notches in the yokes (aka forks) near the center of the guide bar (Great Pictures! Mike)

If the adjustment procedure is the same as the 41-48, just follow it. But as a prelude check the bushing that's under the new spring you made, check the vacuum unit for leaks and if it's good, service the unit per the manual. It's much easier to work on if you remove the trans cover from the floor.

BW25....thanks for the reply.....I have removed and serviced the vac. assit unit( works as it should). Will re read the manual and see if I`ve missed anything ~D