FS5W71B 280zx transmisson rebuild

[Zed Head]

Could you have cocked a bearing when installing?  Maybe try the test with the front cover removed.  Then you'll only really be using the adapter plate bearings, assuming that the front bearings aren't rubbing on something.  Which you'll be able to see.  Could also be a problem in the front cover.  The nose can get bent or damaged.

Edited October 30, 2017 by Zed Head

[Dave WM]

Tried it with the front cover off no effect, with the bellhousing off I get a considerable vibration in both the output shaft and countershaft. Hard to keep everything aligned.

I was pretty careful with bearing install.

 

Edited October 30, 2017 by Dave WM

[Zed Head]

You should have made mention of the video.  Would have looked sooner.  Sounds terrible!

I would use input, output, and counter- as the shaft designations.  One possibility that might be possible is some sort of problem at the interface between the input shaft and the output shaft.  The "direct drive" fourth gear path.  Also, could it be possible that one of your coupling sleeves is partially engaged?  Maybe a problem with a shift fork.  Or maybe one of the inserts inside a coupling sleeve is out of place, maybe missing a spring or something.  Spitballing...

[Zed Head]

I think I might have a new clue for you.  It's one of those things we don't really think about, like getting the wrong collar for the throwout bearing.  The engine is actually involved in locating the input shaft, through the pilot bushing in the crankshaft.  Without that locating and support function the input shaft can **** and wobble inside its bearing.  There's really nothing keeping its axis parallel to the other shafts without it.  I remember thinking about that when I took a transmission apart years ago.  The shaft is short and the power is transmitted through the coupling sleeve to the output shaft.   But there's not a whole lot supporting it.  It really looks all loose and disjointed when you ponder it.

In short, your drill drive test procedure, while brilliant, may be flawed.

[Dave WM]

I was concerned about using the drill as well, not knowing if that was valid test, but the second trans using the same setup had no hint of the noise. Not shown but I tried moving the coupling around (move drill while spinning pull push up down etc.) to see if I could influence the sound, no joy. On my next try I am going to try it with the rear housing still on vs just the plate in the vice. The rear housing has the rear bearings mounts for both the shafts (output and counter) fixed so that should help stabilize the shafts forward from the adapter plate. Then I will spin it again. Don't know if it will give any insights, but at least I can look more closely at the action and maybe see something, like a coupling sleeve/fork etc...

I was very careful about the synchro assemblies, but will look carefull at them as well, at least as well as you can with them installed. Fork movement transmitted to the shift rods sounds like a possibility. I am trying to think of what could transmit so much sound into the bell housing.

[Dave WM]

link to quiet transmission.

 

[Dave WM]

more progress.

I pulled the bell off leaving the rear ext housing on, this makes for a much more stable platform to observe. What I found as an issue with 3rd gear

there is a gear part and an engagement teeth part and a separation of about .3mm all the way around by design. the engagement part is what the cone that grabs the brass ring is part of. I assume its a pressed together assy. there is a clear wobble here, the .3 varies around by as much as .1 mm (have to measure more but it is obvious. I will have to time it with the sound but I think it relates. this may account for the seemingly moving sound when attempting to clock to the main or counter.

what I think I am hearing it a slight grabbing of the brass ring as the cone wobbles. maybe my setup clearance it too tight but the wobble is not present on gear 2 which seem to have the same separation of gear and engagement teeth part. The gap there is constant. the good news is I think I can remove the 3rd gear pretty easy, just pull the counter shaft front bearing, clip and gear, along with the input shaft, then a clip/washer/syncro to get to the 3 gear. perhaps when I pressed on the hub for that 3/4 syncro I pressed to hard. this is where all that yak about different thickness c clips come into play.

I modified my spin process to just use a manual socket to adapt to the front input shaft, eliminates the drill noise and I can precisely see the gaps mentioned.

re measured, the gap in the gear to engagement teeth is .7mm to .3mm so total variance of .4 mm as it wobbles. I double checked the end play about .008 which is pretty much right in the middle of the end gap clearance.

My plan to isolate this gear as the issue will be to remove it, and see if the noise goes away.

 

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Edited October 31, 2017 by Dave WM

[EuroDat]

I listened to the noise in your video. It doesn't sound good at all. I can understand your concern about moving forward with this transmission.

The wobble on the 3rd/4th synchro hub is not normal. That hub, and the 5th/reverse hub can be mounted the wrong direction, but that wouldn't create a wobble. Might be one of the springs out of place.

Just curious, have you tried your turning test with it in 3rd or 4th gear? If that hub is causing your problem, I would expect you should notice some kind of difference in noise.

You are going about it the right way, if thats any comfort. Doing one thing at a time will help identify the cause. Better than stripping the tranny down and trying to identify what was making the noise.

[Dave WM]

I did try it. when in 3rd gear it was the worst. Its not the syncro hub but the actual gear, there is a split between the helical gear teeth and the dogs that  engage the syncro hub, that is where the wobble takes place. will post up a video to better demo later. So far I have pulled the front bearings, the counter shaft gear and the input shaft/4th gear. All I have left to do is pull the 3/4 syncro, the pin and fork that holds it and I should be able to get the 3rd gear out. I know its a lot of work, but I will then reassemble with no 3rd and try it all again (bellhousing on and all). "nuke it from orbit its the only way to know for sure".

If that is the problem, I am hoping ZH can come to the rescue again, If not I will see about a new 3 from japan, hard to find and I hope I can find the right one. It may sound silly but I really really want to figure this out, regardless of cost, even though I have one that maybe fine. I guess its just my nature.

if the noise is still there after all that, well I hate so say it but may be forced to throw in the towel, geez I hate that.

Edited October 31, 2017 by Dave WM

[Dave WM]

got to use my new tool. when pulling that counter shaft gear, I have a 20 ton 2 jaw puller and it needed it. I think removed the 1st time when the CS was completely out, and used the press to get it out. Since I did not disassemble it this time I had to pull the gear with the shaft installed. my wimply 3 jaw big puller seemed like it was reaching its safe limit (just did not like the feel of it). So out comes the big boy, must weigh 20 lbs easy, any way it and my 36" cresent wrench to turn it made quick work of pulling the gear

Edited October 31, 2017 by Dave WM

[Zed Head]

I can't remember what 3rd gear looks like but I'm sure it's in the bucket. Let me know.  Post a picture.

Looking at the structure of the gear it wouldn't be surprising if it was a press-fit two-piece assembly.  People say the whole gear needs replacing if the synchro is damaged, but maybe not.  Maybe you can press it back together.  If not, take it apart just to see what the innards look like.

[Dave WM]

just about got it back together sans 3rd gear. left the needle bearing on. so as long as I don't try to shift into 3rd I should be able to run it and see if the noise is gone.

I am going to have to remove the rear housing to press that big counter shaft back on so will not get it done today but should be able to assemble all by COB tomorrow.

Will post up a pic of 3rd soon. It does appear to be a press fit. Of course all this goes to the question of how could this be the problem as I cant see how it could have been  bad from day one, but frankly I am out of options so may as well mess with it and see.

IF it does prove to be the problem you can bet I will see if I can "straighten" it with the press, don't want to defore the cone so not sure how I would do it. Plus I am sure there is a real chance of shattering it. The issue is its such a small deviation that I would need to apply pressure to the high side, that seems like a recipe for disaster but not sure what else to do. Hope ZH can locate as a plan B if this goes wrong. Clearly I am not going to do any thing to the gear unless the noise is gone (and therefore cause by 3rd). I suppose the other parts could be a factor like the shift fork, but the noise going in sync with the high side of the gap on the gear makes me want to believe this could be it.