FS5W71B Rebuild Thread - Tips tricks and discoveries!

[Captain Obvious]

Oh, and by the way. Just want to let you know that I do totally get it.

If you slide the synchronizer onto "the first gear" to lock it to the main shaft for 1st, and
you slide the synchro onto "the second gear" for 2nd, and
you slide the synchro onto "the third gear" for 3rd...

Then what would you call the gear that gets locked to the main shaft by the synchro when you're in fourth?

I'm gonna stop talking about it now.    

[Captain Obvious]

Sorry... I'm baaaaaaack. But this time it's actually with some useful input!

I just snipped this from the 78 FSM (MT-18). Not sure if the other years contained this info (assuming not, or you would have simply found it and not asked in the first place), but this should answer most questions about the gear tooth counts:

 

In 80 they they started messing around with the ratios, but this should hold for everything up to and including 79.

[zKars]

Well now other than the need for a set of input shaft 4th gear set, I now need a main shaft too. I took apart the last of my good close ratio 5 speeds, in fact the one I’ve had rebuilt back 2008-9 and have had in my old 73 Z until its sale, and more lately in my 510. 

It was noisy in several gears, most noticeably in 3rd and 5th, and when you’re at a stop, foot off the clutch, you get a good rattly bearing noise. Other than that it worked perfectly.

Upon disassembly, I noticed really only one problem. The forward end of the main shaft where the little needle bearing seats inside the back end of input shaft, is all scored up. And not evenly. When I put the shaft in the lathe, it seems to have about 5 thou run out. The needle bearing is quite loose on the shaft over the damaged area.

These videos show the problem.  Dang stroker torque bent the dang thing.... 

The 6 bearings look just fine, and spin silently. 

Edited February 27, 2020 by zKars

[zKars]

This transmission also has a leaking shifter shaft. The area where the shifter plugs in was always full of GL4 and causing a dribble on the floor. So I had a chance to try both my latest discoveries about removing that wedge pin to take the shifter rod out to change that little seal, AND how to remove and replace that little buried seal.

Success on both cases. The air hammer gun popped the wedge pin out in 30 milliseconds again, and this time without any heat. 

I bought a set of really long seal picks, and that’s all it took to get that little seal out. You just need to put the tip of the 90 deg pick under the seal and YANK. 

And then to put it back in, I had no choice but to spend time on the lathe making a seal pusher-in-ner thingy. What other option would there be? Guess you could whack it with a 3/4” punch tip, but what fun is that.

The specs are 13.9 OD on the seal ID part, 13mm long, then a section of 19.8 mm again 13 long. The nose guides into the hole, and the OD is just a tad smaller then the seal to push it home. The place it sits is about 1.5 times deeper than the width of the seal, so make sure it goes all the way to the bottom. 

I have no clue why the old seal leaked other than it was pretty hard and fit pretty loosely on the shaft. It was not damaged.

Oh yeah, remember to put the dang thing in the right way. Oil is in FRONT of it, so when you insert it, with the open side to the back, against the insert tool. 

 

[zKars]

And finally The o-ring on the outside end of the shifter rod body. Somewhere it was noted that it’s the same as the one on the outside of the speedo cog. That is in fact true. The groove ID is 24mm, and it’s 2mm deep, and just over 3 mm wide. The o-rings I pulled off were 24mm ID by 2.4mm cross section. And magically a 15/16 or 7/8 x 3/32 o-ring fits just fine. The cross section is nearly identical and tiny stretch from 7/8 to 24mm does not deform the ring. I tested the fit into the speedo cog hole and they all felt identical in drag and insertion ease.

 McMaster Carr has a 24.3 x 2.4mm oring too if you can’t get a Nissan one and you want a really close equivalent. 

[Zed Head]

Descriptions of how to replace those two seals are definitely an addition to the body of knowledge.  Many people over the years have commented about the puddle of oil in the shifter hole.  I've given bad advice about it in the past.  @FastWoman I'm not sure she still has her car but she had the leaky seals way back when.

[zKars]

Nobody caught my booboo on the little seal. I installed it backwards. The fluid your trying to keep out should be on the open U shaped side of the seal, you would then see the flat closed side looking down into the shifter housing. 

I had just done the front cover plate seal, which you install with the open end of the seal outward, and my head for what ever reason said “ this seal too”. Not.... 

Edited February 29, 2020 by zKars

[Zed Head]

I actually did notice that the one you took out seemed backward, in the pictures, from the one you out in.  But, I trusted your experience.

[wheee!]

Are you saying I need to be gentle on my transmission with your old stroker? [emoji1]

[zKars]

17 minutes ago, wheee! said:

Are you saying I need to be gentle on my transmission with your old stroker?

Naw, flog it. I stuck 3 different shafts in the lathe and they all say 5-7 thou run out. Should have spent more on the lathe....

[Patcon]

6 hours ago, zKars said:

Nobody caught my booboo on the little seal. I installed it backwards. The fluid your trying to keep out should be on the open U shaped side of the seal, you would then see the flat closed side looking down into the shifter housing. 

I had just done the front cover plate seal, which you install with the open end of the seal outward, and my head for what ever reason said “ this seal too”. Not.... 

I caught it but let it slide. You've done yeoman's work!

[Captain Obvious]

17 hours ago, zKars said:

I stuck 3 different shafts in the lathe and they all say 5-7 thou run out.

I was going to suggest that to you. My assumption is that the error is in the measurement method, not the shaft. And it's probably not the lathe spindle itself. The spindle is probably pretty good, I bet most of the error is coming from the chuck and the unrepeatability of the mounting of the part.

If you're just tossing the shaft into your three-jaw and tightening it down, it's not going to be centered unless you've got a fantastic three-jaw AND you get lucky (that time) when you put the part in.

If you really want to check something like that you'll have to do it between centers.