Transmission Mainshaft Nut

[JerryH]

The transmission of my 1976 spider has no 3rd gear. We've pulled the transmission and are attempting to disassemble it to diagnose the problem. We were able to pull the guibo centering fitting, but we can't seem to loosen the mainshaft nut (see photo)


I first want to make sure that the threads on this nut are standard (righty-tighty, lefty-loosey) threads. Do you guys have any advice on loosening this nut? It seems to be very tight and we can't generate enough leverage to loosen it.

-Jerry

[ventura ace]

Yes, standard right hand thread. I made a special 'tool' to hold the shaft still so that I could remove the nut and retorque it later. I used an old broken snow ski, but you could use a length of angle iron, or other strong wood, like a construction 2 x 4 stud. I drilled three holes to match the hole pattern of the shaft flange, and used a hole saw to cut a large hole in the middle to get access to the nut. Bolted the 'tool' to the flange, and let it but up against the floor while I put a large breaker bar / socket on the nut to get it loose.

You don't really need 3 holes to hold it from turning, 2 holes would work fine on a length of angle iron.

Alvon

[engineerted]

Jerry

Yes standard theads, and the best way to get it off is to use an impact gun, its dam near imposible with out one. Same goes for the counter shaft nut that you will find once you get the rear end cover off.

Ted

[ClarkTheShark]

stick that big guibo bolt in the triangle backwards. that will dog it off. i believe that mainshaft bolt has a little punch dent on the end you have to release with an ice pick or something. you should be able to get your partner to hold it then use your spanner and very large bar and twist her off.

[JerryH]

Well, I got it off.

The first thing I did was purchase an impact wrench. No luck--the nut wouldn't budge (but I got a new tool out of the deal ). Next I tried drilling some holes in a 2x4 to accept the guibo bolts--I ended up splitting the board in two. This nut was tight! Finally, I bolted the guibo bolts to an angle iron and I used a pipe to extend the lever arm on my 1/2" ratchet. That did it!

Now I'm deep into the transmission. It looks like the 3/4 gear fork is bent. I don't know why. I'll post some pics soon. I did see some fine brass particles mixed in with the gearbox oil--it looked like metallic paint.

Thanks to all for your guidance and ideas.

[JerryH]

Here is a photo of the bent 3/4 gear shifter fork:

And hear is a photo of the sliding sleeve (a new one is on the left and the worn one on the right--the edges on the worn one are rounded over) :

I'm officially re-assembling this transmission .

[JerryH]

...and here is a view of the 3/4 selector fork. The old fork (left) has a severe notch worn in it. The new fork is on the right.


Now I'm having trouble removing half of the old race which has been pressed on the front shaft. I spent about an hour working on this. I think I'll have a shop do it.

[beachboy]

The comparison of the two syncro sliding rings is not accurate. Those two rings are different styles, that is why the inner groove area is shaped differently. One is not worn compared to the other. If you measure them, they should be almost exactly the same in diameter. They do not wear, the brass syncro forks are what wear. It is the teeth that wear from grinding the shifter.

[ventura ace]

Jerry,
Take a close look at the teeth that engage the 4th gear synchros on your input shaft (the straight teeth, not the helical teeth). If they are rounded on the ends, you may need to replace the input shaft -- in which case you wouldn't need to try to remove the input shaft bearing race from the old one. If the teeth on your existing shaft are good, then you might be able to apply heat from a propane torch to the bearing race to help free it from the input shaft.

Alvon

[rasouth]

I had the same problem when I was rebuilding my trans. My impact was not strong enough because of the limited amount of air pressure in my tank (125psi). I ended up taking it to a local transmission shop and they popped it off within seconds. Their air pressure is a lot higher than mine was. (180psi)

[JerryH]

Guys,

Thanks for the pointers with my transmission rebuild. Ace, I studied the all the gears and they all still had a diamond shape to them (not rounded)--so I concluded that they were okay. Beachboy, the ring on 3rd was definitely rounded over--I just couldn't capture the damage well in the photo.

Here's my theory on what happened. The 3rd gear synchro wore out. Here's a photo of the worn synchro (left) and a new one (right):


Because of the worn synchro, the PO had difficulty shifting into 3rd and therefore tried to muscle it into gear--leading to the bent fork. The PO continued to run it with the bent fork and that led to the wearing of the fork and the ring.

In any case, I've replaced all the synchros, sliding rings and forks, and many of the bearings and installed new seals. It's been back in the car for a few weeks. At first the shifting was a little stiff but after about 30 miles it smoothed out and now I've got a solid 5 speed tranny.

This was a fun project. My advice to anyone thinking about doing this is--go for it. But you've got to allow some time. If you're in a hurry to get your car back on the road you're probably better off purchasing a rebuilt tranny.

-J

[SpiderJim]

To get my main shaft nut off I simply placed one of the three arms in a vice then used the breaker bar with a tube extension to loosen it. It is 108 ft pounds so bloody tight. For the other nuts that will need undoing just set the tranny into two gears per the manuel and use the angle iron or whatever to hold the tranny case.