The Stovebolt Site Forums The Shop Area Driveline transmission dropping out of 3rd

Since I've had the 1950 chevy truck, the tranny has been dropping out of third into neutral. I had the tranny rebuilt by an experience mechanic who's rebuilt hundreds of transmission. So I think his work is good. I reinstalled the tranny, adjusted and readjusted and verified the shifter linkage was set up properly as per manual. Grommets at the shifter arm levers were also replaced and it will shift quite well on all gears. Yet it still drops out of 3rd. The "shifter swivel lever" for the 3rd gear slides on a post/shaft and there's quite a bit of play 1/2" or so. It does not slide off because there's a retainer clip at the end of the post/shaft. Should there be a spacer or a spring to reduce the swivel lever from moving that much? Does anyone have pictures? I'm at lost as to why it's still dropping out of 3rd gear and sure wouldn't want to remove the tranny once again if the problem is somewhere else. Dan

popping out of 3rd is a common problem with these transmissions, invariably the syncro - did the rebuilder replace the syncros, or maybe just seals and bearings? not clear what or where this "shifter swivel lever" is, do you mean the forks in the box on the column?

Bill

I am not clear what you are referring to when you say "shifter swivel lever".
I do know that if everything is in good shape and it still jumps out of third gear than it is an alignment issue.
To remedy this you need to shim between the bellhousing and trans case. This puts the input and main shafts in alignment so the synchronizer drum is not walked off the third gear teeth. It is described in some of the shop manuals.

Bill, I know you are a smart guy so I ask this in the nicest way, and I know the answer.
How is the synchro effecting a transmission jumping out of gear.
It is just that some of these myths drive me nuts.

not smart, and not always right, just years of experience of these trucks - replacing the syncro does fix it, maybe wear? maybe the shimming compensates for wear? would be odd that so many of the old 3 speeds start popping out of 3rd after years of use because the case mis-aligned itself .... but yes, the manual does suggest a variety of causes and remedies worth checking

Bill

Saying it is a bad synchro is not explaining it correctly.
Synchros have nothing to do with keeping a gear in place, only to bring the two gears up to the same speed for engagement.
Where the confusion comes in is that the synchro drum, which contains both second and third synchros, becomes worn on the teeth that engage for second and or third gear. The teeth can become shortened from the leading edge being ground off from a bad synchro, or they can become worn at a taper from trans misalignment. Both will cause a transmission to jump out of gear.

The side post or bolt is mounted on the transmission housing. On it is the swivel bracket that joins the lower linkage from the transmission lever and the upper linkage from the control box lever. This swivel bracket slides lateraly about 1/2" on this post. Is this normal should it be that loose, should there be a spacer??

The syncro was replaced. The manual says shim between clutch housing and transmission. The tranny mounts flush with the clucth housing why would I want shim it and if I did what am I trying to align it to?

When I had my 3-speed rebuilt ('52), I mentioned to the rebuilder that dropping out of third was a common complaint with these transmissions. He was aware of the issue and had a fix. I can't fully remember what the fix was (but I think I mentioned it in an old post...try searching for it). Basically, a notch or grove was machined all around the cluster gear. This notch retained the gears in mesh until the clutch was released and load removed. I was worried it would make the transmission feel notchy, but he assured me it would be imperceptible.

I seem to remember he said the problem was due to the minimal engagement of the gears and wear of the cluster gear due to weak synchros, etc.

The process of shimming requires installing a main drive gear with a dial indicator attached that indicates in the rear bearing bore.
Then shims of varying thickness are installed between the trans and bellhousing to change the angle of the trans so the front and rear shafts are inline.
Over time the bellhousings warp putting the trans out of alignment making the Main drive gear and main shaft run at a slight angle to each other. This angle will walk the synchro drum off the main drive gear.

I had the same problem which went away by replacing tired out bellhousing to frame mounts.

A worn pilot bearing could also cause it.

Other than engine and transmission movement causing the linkage to pull it out of gear. The other common thing that was kind of covered is the splines wearing at a slight angle, I have seen that happen in big road ranger transmissions. The fix it to replace the parts that have the worn splines, shift collars etc.

The old 3 speeds did commonly jump out of gear with the synchro system they used. Worn shift forks also contributed to this. Borg Warner and later the GMC Saginaw had a much better system. But if the rebuilder was experienced, I would think that he replaced the synchro as well as the shift forks. I would strongly suggest pursuing what Cletis suggested. Either you have a worn pilot bearing and it is not uncommon for there to be no pilot bearing. It is not very common, but too much runout on the clutch housing can cause any transmission to jump out of gear. We check the runout every time we remove a transmission. As far as splines wearing at an angle, that is not common in Fuller transmissions. I have been running Eaton/Fuller transmissions for 45 years. I usually have from 10 to 20 trucks. I have never seen splines wear at an angle. If it were common, I'm quite sure I would have seen it.

The angle is not some drastic to the eye type of deal. It is what caused the roadranger I fixed to have to be held in gear by the driver. I was much younger then and had talked to an old time truck gear shop guy that sold us the parts that he knew by hearing the symtoms would need replacing, hes the one that said that was going to be the problem. And not the last time I've seen the problem on manual transmissions. Torque load causes axial pressure to force the splines out of engagement when an ever so slight angle is worn into the surface of the shift splines, it takes lots of years of loading to do it, along with some metal in the oil.

My three speed top loader is popping out of third as well. Yes, the pilot bushing is worn and will be replaced. Motor mounts were soft so they are getting replaced. Here is my worry; with the shifter cover removed from the top of the trans, the input shaft and the tail shaft when I push up or down on them buckle a bit. Is this normal or is something worn inside? And if worn, where do I get those old parts?

There should be almost no up and down movement.
If the pilot bushing in the crank is bad then you will get movement.
Bad front or rear bearings could also give you some movement.
Parts for these are on ebay all the time. If you have problems finding parts or need special advice PM me.
I know a number of tricks to make these 3 speeds work better.
You may want to check out my blog for one tip.
My blog link

For those of you who have not seen how the teeth for 3rd gear wear at a taper, here are some pictures from a 1940 I just rebuilt. LINK