Transmission Noise in 3rd Gear - F4W71A

[Dave WM]

I found a pic of what I was trying to describe in my 75/76 FSM. Its fig MT-28 on page MT-8

they show two "synchronizer hubs"

front is 3rd & 4th (move the sleeve one way to lock 3rd to the main shaft, move it the other to lock the input to the output no gears.

there is also an illustration of the 1st & 2nd "synchronizer hub". If you look carefully at the see thru side view you will see how 3rd and 4th have an offset while 2nd & 3rd look to be symetrical.

[Dave WM]

I have attempted to highlight the areas that are diff at least on the B model

[Zed Head]

57 minutes ago, AnvilZ said:

Is there a 1971 FSM floating around somewhere?

CanTech Z uploaded this 1970 FSM to the site a while ago, it describes the F4W71A.  For whatever reason the 1971 FSM is oddly formatted but it has a chapter also.  The 1971 document has the same description as 1970, so it looks to be the same transmission.  The 1970 document is a clearer copy.

https://www.classiczcars.com/files/category/11-240z/

 

[AnvilZ]

57 minutes ago, Zed Head said:

Have you checked the action  of the shift fork on the coupling sleeve, and the sleeve on the hub?  I wonder if the sleeve could get cokced on the hub as the fork pushes it over.  Like if one tine of the fork was ahead of the other.  The sleeve should lock in, or center over its final position, but maybe you're getting incomplete travel and final engagement.  You have it all torn donw now but you might find some sign on the parts.  Maybe a loose fork on the rod.  The roll pins do fail.  Ideally, you would check the action by moving the shift rods with it mostly assembled.  There are also the detent pieces in the adapter plate.  The balls, springs, and pins that set the final position of the shift rods after a gear selection.

Your description sounds like something relatively large wobbling around the shaft.  If all of the bearings and other parts seem undamaged and correct then it seems like the parts must not be correctly positioned.

Good suggestion, I did check all of the shifting mechanisms once I removed the transmission housing before disassembling everything. The coupling sleeves and selector forks were aligned and everything clicked into placed pretty smoothly. The forks were held onto the selector rods tightly by the pins. Seemed like the detent balls/springs were doing their job as well. 

I mentioned in post #31 that I might have found my issue, or one of them. The main shaft adapter plate bearing seemed like it was starting to fail once I removed it from the plate and inspected it further. I didn't really notice it when the shaft was still installed but checking the bearing itself once removed it is not rolling as smoothly as it should. Maybe under higher loads it causes excess vibration. I have a replacement on order and will replace both of the main shaft bearings when they come in. 

17 minutes ago, Zed Head said:

CanTech Z uploaded this 1970 FSM to the site a while ago, it describes the F4W71A.  For whatever reason the 1971 FSM is oddly formatted but it has a chapter also.  The 1971 document has the same description as 1970, so it looks to be the same transmission.  The 1970 document is a clearer copy.

https://www.classiczcars.com/files/category/11-240z/

 

Thanks, I will definitely check that out. Probably more helpful than the 72 FSM I have been using. 

[EuroDat]

9 hours ago, AnvilZ said:

Good suggestion, I did check all of the shifting mechanisms once I removed the transmission housing before disassembling everything. The coupling sleeves and selector forks were aligned and everything clicked into placed pretty smoothly. The forks were held onto the selector rods tightly by the pins. Seemed like the detent balls/springs were doing their job as well. 

I mentioned in post #31 that I might have found my issue, or one of them. The main shaft adapter plate bearing seemed like it was starting to fail once I removed it from the plate and inspected it further. I didn't really notice it when the shaft was still installed but checking the bearing itself once removed it is not rolling as smoothly as it should. Maybe under higher loads it causes excess vibration. I have a replacement on order and will replace both of the main shaft bearings when they come in. 

Thanks, I will definitely check that out. Probably more helpful than the 72 FSM I have been using. 

If the bearing in the adapterplate start failing, it generally is first noticable in 1st gear. 1st being the closest gear that puts sideways pressure on it. I would expect the sound to be most audible in 1st then 2nd then 3rd and 4th being a direct drive the least of the noise.

You can get noises when certain frequencies match, but 3rd gear clunking when a mainshaft centre bearing fails is one I havn't heard of before.

That is why I focussed on the third gear as the area that would cause a noise in third, but noticably less in 1st or 2nd.

[AnvilZ]

6 hours ago, EuroDat said:

If the bearing in the adapterplate start failing, it generally is first noticable in 1st gear. 1st being the closest gear that puts sideways pressure on it. I would expect the sound to be most audible in 1st then 2nd then 3rd and 4th being a direct drive the least of the noise.

You can get noises when certain frequencies match, but 3rd gear clunking when a mainshaft centre bearing fails is one I havn't heard of before.

That is why I focussed on the third gear as the area that would cause a noise in third, but noticably less in 1st or 2nd.

Interesting, based on what we have looked at so far it seems like this is the only issue from the transmission internals correct? Anything else I should check before replacing the main bearings and reassembling? Would you recommend replacing the synchro rings as well while I have it apart or leaving them alone, I know new is not always better but definitely don't want to pull the transmission again in the near future if I can help it.

[Dave WM]

if you were not having issues with sycrhonization i would tend to let it be. there are measurements that you can take to see how much wear there is (gaps) to give you some idea about how much life you have. If you decide to replace them there is a guy on youtube that does nothing but transmissions. i cant recall him but a search should find easy. He goes into great detail about what to look for as far as the brass parts are concerned.

[EuroDat]

All the ball bearings and the needle bearing between input and main shaft should be replace

I would replace all the seals regardless of how they look.

You can check the wear on the synchros by following the procedure in one of the 71B manuals. The original nissan synchros would need to be very worn before I would go after market. 

Next is to check the shifting inserts and the circlips. If you can get new circlips, them I would definately get them.

Remember what I wrote above. The pressure the circlip applies to the shifting inserts determines how much force the sleeve can apply to the synchro ring before the sleeve rides over the shifting insert and engages the gear. A weak circlip (or on the 71B it's 3 springs) will allow the gear to grind a little when going into gear.

If you can find new detent springs for the selectors, then it would be a good time to change them.

 

 

 

 

[AnvilZ]

1 hour ago, Dave WM said:

if you were not having issues with sycrhonization i would tend to let it be. 

 

40 minutes ago, EuroDat said:

You can check the wear on the synchros by following the procedure in one of the 71B manuals. The original nissan synchros would need to be very worn before I would go after market. 

 

 

 

 

 

Thanks for the tips. I am not having any issues with synchronization, so I will check them according to the manual and hopefully they are fine to continue using. I will plan to replace seals/ball bearings/detent springs/main shaft needle bearing etc. 

Maybe thinking too far ahead here but once that is done and the transmission is back in the car, assuming I am still having an issue is there a recommendation for how to isolate which part of the drivetrain it is? I had considered the idea of removing the prop shaft and running through the gears to see if there is any noise to try and narrow it down to the trans or something else. However I don't know if the same issue would occur without the load on the transmission. 

 

[Dave WM]

if its really that loud, you should try bench running it. a large drill and some rubber hose over the input shaft. I know its a long way off from actual loads and rpms, but its fun and who knows maybe something will turn up.

[AnvilZ]

On 8/1/2021 at 12:50 PM, Dave WM said:

if its really that loud, you should try bench running it. a large drill and some rubber hose over the input shaft. I know its a long way off from actual loads and rpms, but its fun and who knows maybe something will turn up.

I will give that a shot, thanks.

A few of the bearings will not be in until the end of the month. I will update the thread once they are in and I have tested the transmission. 

[AnvilZ]

@Zed Head @EuroDat @Dave WM I found another possible issue when I was digging back through all the part numbers from my engine/transmission rebuild that I was hoping someone could help clarify for me. When I started this project 2.5 years ago and had little to no knowledge of Z cars, one of the first things I ordered was this Transmission Service Kit from Z Car Source: https://zcarsource.com/transmission-service-kit-240z-260z-280z-72-78-new/ 

Mark it up to inexperience or my own stupidity at the time, but I did not look closely enough at the fact that this only works for the B type transmission. Pretty obvious based on the compatible years in the title, kind of kicking myself for that. Anyway, this kit is what is currently on the car with their clutch kit (14400103 - Clutch Kit, 260Z 280Z 280ZX 300ZX, 74- 83 Non-turbo 2+2, 81-86 Turbo - new) and flywheel (13100402 - Flywheel (Manual Transmission), 260Z 280Z 280ZX, 74-83 2+2 and Turbo - new).

From what research I have done I am a little confused on compatibility year to year but it seems like the flywheel interface is the same for all Zs 70-83. Would that mean that this flywheel will work for my 71 regardless of the description stating 74-83? Similarly for the clutch disc and pressure plate, the overall kit itself states compatibility for 72-78, while the sub kit with the disc and pressure plate says 74-83. Some other kits with a clutch disc and pressure plate say 70-74, that seems to indicate that the disc and pressure plate for a B type trans will also work for the A type? 

Hope that makes sense, just trying to determine if any or all of those components need to be replaced and if that may be contributing to my issues at all. It may be that other components in the Transmission Service Kit like the clutch fork or rubber shift boot are why it is labeled for B type only.