Stingray1967

Well guys, now that the car has been to the alignment shop, I am putting on some miles. I have about 70 down so far this season.

The transmission seems to be having an issue though. Here's the background.

Roughly 70K mile very original 67 L79 4 speed convertible taken apart in the fall of 2006 with a full blown, every nut and bolt, NCRS restoration. I think the only thing I didn't touch was the antenna mast and the ash tray.

Fast forward to last fall, and the car is complete. I had a guy here in town rebuild the M-21 (original to the car). He said the main gears were in as good of condition as he has ever seen. So all he did was a "rebuild kit". If I remember right, it was all new synchros, actuators, etc on the inside. We filled it with new fluid (not in front of my notes, so not sure which kind, but my local expert used the transmission fluid he's been using for years). It was mated up to the completely rebuild and blueprinted L79 with a new flywheel that was machined flat, and a new clutch assembly that was balanced.

Here's the problem. Until the car warms up, I can NOT get it into second gear. I have adjusted the clutch pedal action a few times on the clutch rod in the engine bay by spinning the two nuts. I wind up putting my foot through the firewall with the clutch pedal, and it just grinds when trying to go into second. I had my dad drive it, and he couldn't get it to work either. He grew up on a farm double-clutching grain trucks, and he REALLY knows how to drive a stick. He couldn't get it. It goes from 1 to 3, and 3 to 4, and all other combinations just fine. Just not 2nd.

Here's the weird part. I had the car out weekend before last, and just a couple miles down the road, I tried DOWN shifting from 4 to 3 to 2 and it went in just fine. I thought "oh good, it's fixed". I started out at the next stop light in 1st, went for 2nd, and it ground the gear like crazy.

Very sad camper here if I have to pull the driveline back apart....

Thoughts?

66jack

Sounds like that 1/2 synchro gear is not aligned...

jack

Stingray1967

I think I know the answer to this, but is that a fix that can be done by simply removing the side cover of the transmission and leaving it in place? Or do I have to drop the tranny out of the car?

Dan Hampton

Can you shift into second when the engine is not running? You said it did it when it was cold, but from your narrative it seems that it does it when warm, too. Please clarify.

There a couple of things I would look at (and this means that the trans has to come out).
There are three things, internally, that are responsible for the shift into second. First, there is internal hub that is spline to the mainshaft. That hub holds two C-springs: one for the back and one for the front. Those springs are responsible for keeping the three clutch keys in a floating position. When the slider mates with the internal hub it is those clutch keys that are sandwiched between the internal hub and the slider. The spring pressure must be equal against the bridge end of those keys; otherwise, the slider will **** when attempting to engage the clutch teeth on the gear, which will produce a grind or no shift at all. The springs must be offset between the front and the rear of the internal hub. Many people pay no attention to that when they rebuild a Muncie or a Ford Toploader, for that matter.

I am not saying that is your problem, but, in all likelihood, the grind is due to something going wrong with that assembly (internal hub, slider, springs and keys).

Now, first and second share the same hub, slider and keys with second gear. Why it doesn't do it in first is probably due to the fact that you are not down shifting into first and you certainly are not up shifting into first. Also, the problem could reside in the internal hub on the second gear side.

Stingray1967

I haven't tried to get it into second when the car is off. I'll try that and see.

It sounds like the transmission needs to come out of the car.

Tampa Jerry

While the tranny is out of the car, double check that you have the correct size T/O bearing. If you have the one for a passanger car instead of a vette, you will experience grinding. There is not enough room in the clutch linkage to adjust out for the incorrect bearing. Jerry

Dan Hampton

When the transmission is out of the car, try and shift into second gear and remove the side cover. You might be able to see the problem from viewing it from above. At least, you can try to manually move it into second, but given that you cannot do it with a shifter, you will have even less leverage doing it by hand.

I would grab the slider and see if there is any unusual play. Try and move it right to left. Use your 3/4 slider (the one closest to the input shaft) as a template to see if there is any difference betwee the two. Spin the assembly 360 degrees or more to see if there is anything visually not right. Move the slider to first and check the keys to see if they have spring tension. Moving it to first will expose everything needed to engage second gear.

I will post a pic of the synchro assembly.

Dan Hampton

This pic is of a Ford Top Loader synchro assembly but it is essentially the same, in principle, as a Muncie.

street62

I had the same problem with my 67 when the car was cold. If your clutch is adjusted correctly, then the brass rings are not slowing down the gear, to much clearance, when the trans warms up and things expand the clearance is reduced. The brass rings have a taper on the inside that matches the cone on the gear so as you shift the slider pushes the brass ring toword the gear to slow it down to the same speed as the slider so the teeth can engage. The trans has to come out.

Dan Hampton

But he only has the issue with second. If the clutch was the problem, all the gears should be grinding.

66BlkBB

Wouldn't you think it is a problem with either the Syncronizer or the "Insert" (what we used to call "dogs" in the old vernacular) that is causing the problem? Prior to companies putting syncro's into tranny's all you had to do to get into the next gear was to double clutch. He has tried this and it did not work. That means something is blocking only 2nd gear, which leads me to the Syncro or the Insert being out of position or damaged. JMT

Stingray1967

Thanks guys for all the input. I'm going to check the linkages this weekend and see if it is something simple. Kind of doubt it, based on my description of the problem and your responses.

It sucks to drop the driveline out of a 3x Top Flight car......there isn't a mark on that car anywhere.

Dan Hampton

It is, undoubtedly, in the synchro unit, as I described in an earlier post. Whether it is a "key" or a misplaced internal hub spring, it is hard to say.

SledgeHammer 2.0

Before I went pulling it out, If it works when hot and not cold, try thinning out the gear lube with a lighter weight oil.

If all the other gears work, you probably just have a bad brass ring, sometimes thinning the oil allows the ring to "grab" the cone of the gear a little better stopping it from grinding.

Definitely worth a try.

Dan Hampton

According to the OP, the unit was just rebuilt with new synchros.

SledgeHammer 2.0

Yea, I read that. Can't tell you how many transmissions I have rebuilt over the years that we have gotten bad parts right out of the box. If the inside cone of that syncro ring isn't machined just right it will give you problems.

When the car is running and the unit is spinning, oil gets thrown up into that syncro between the cone and gear. When you go to shift into that gear the movement of the syncro pushes that oil out, the brass of the syncro contacts the cone of the gear, it acts like a brake matching the speed of the output shaft to the speed of the gear. Shifting up through the gears, the syncro is spinning slower than the gear, shifting down the syncro is spinning faster than the gear, (it's early I may have that backwards), anyway if you can picture it in your mind, That syncro works as a brake two ways against that gear, one to slow it down, one to speed it up. The OP says that he can downshift no problem, but can't upshift, but also states that when it gets warm he can get it to shift. That oil that is trapped in that syncro gets thinner as it gets hotter.
That's why I suggested trying a thinner oil, before pulling the car apart.

May or may not work.... but it's worth a shot. Otherwise he will be staring at that brass ring trying to see what is machined wrong.

Dan Hampton

He needs to pull the box out and look at the second gear assembly. If the other gears shift without the need for an oil change, second shouldn't need it, either. Fix the problem the right way. He has yet to tell us if he can shift into second when the engine is not running. I would like to know that. You said it yourself: it is, undoubtedly, a bad part.

Stingray1967

Well guys, here's an update.

To someone who asked "can you get it into second when the car is off and cold", the answer there is YES.

I adjusted the clutch travel with the two nuts on the clutch rod inside the engine bay and it seems to have made the situation better. I need to start it and drive it cold again to see. There was NO free play at the top of the pedal travel. I moved the connection point of the clutch rod to the clutch cross shaft further towards the firewall.

Also, the shift linkages all appear to be tight. I looked at them with a light and a mirror yesterday, and they seem fine.

Hopefully this made the difference. I'll report back when I go to work on the car again next (probably Friday).

Wish me luck.

GCD1962

Sometimes with new syncros it might take a few hundred miles before everything works smoothly. When I bought a new Autogear M-21W it was fairly rough for the first few hundred miles. I was told it was because the syncros needed some "wearing in". Drive a few hundred miles, change the trans oil and it shoudl be O.K. I did that and it worked find - shifts like butter now.

Only other thing could be an adjustment of the shifter rod for 2nd.

larrywalk

With your comment that there was no freeplay and that moving the nuts closer to the firewall helped; the most probable cause is a misinstallation of the throwout bearing which results in a failure to completely disengage the clutch because of the leaf spring being outside the groove in the throwout bearing. This also results in the lack of free play. And, if the nuts are moved closer to the firewall to get freeplay, the clutch can't be disengaged completely. Here's a drawing of how the throwout bearing is supposed to be installed and how it can be misinstalled:



You can inspect for this as follows:
By pulling away the clutch fork's cover from the bellhousing a bit, one can inspect the installation with a small flashlight and mirror.

Unfortunately, if it is misinstalled, you will have to pull the transmission.