Tranmission gear noise magically solved

[zKars]

Over the past two-three years my 82-83 ZX trans in my 73, rebuilt about 10 years ago with new bearings and syncros, has been making more and more gear whine noise. Not all the time, but specifically in 3rd and 5th. Most noticable on the highway. In forth it's mostly not there, but move to 3rd or 5th and it got noticably louder.

During the last trip to the coast, a rising, whining noise when downshifting started to get worse too. Specifically as you pushed the gearshift into the next lower gear prior to letting the clutch out. Going into 3rd was the worst, but other gears were starting this racket too.. oh well, I'm thinking, time for some work again.

Couple weekend's ago, I had the console out (unrelated project), and somehow I decided it was time to try yet another "improvement" of changing my gearshift knob style. I've always wanted to try a "T" type handle, so out came the shift lever from the tranny.

Well guess what I found. A damaged plastic pin bushing, on the right side.kinda crushed. Still there, but not in good shape. I did notice my shifter was SLIGHTLY sloppier than before, but not enough to make me go looking.

Well, I proceed with my T shifter mod, (fodder for yet another post), replace that bad pin bushing and put it all back together.

Natch, I had to take it for a drive to try out the shifter feel. Off I go merrily banging gears with a big grin on my face. It wasn't until I was bombing down the local freeway did a lightbulb finally go off and I says to myself, "Hey! where the hell did that gear whine go? The trans is totally silent!!!!

So what changed? Well two things. The bushing of course, but also the length, shape and mass of the shifter rod. Apparently the noises that the trans makes ALL THE TIME was getting transmitted to the shifter rod with that bad bushing. Now with a good set of plastic bushings and a different rod shape and reasonant frequency, the thing is now quiet.

Who'da thunk it? Anybody change their pin bushings to some solid metal ones notice any increase in tranny noise after doing that?

Edited October 6, 2015 by zKars

[rcb280z]

I don't have the metal ones in place but at least you were successful at getting rid of the noise. I assumed that was my problem but after replacing the bushings including the one at the bottom of the shift lever I still have the noise. But it is only when in 3rd and 5th gear. I have no idea what's causing the noise in mine. Glad you fixed yours.

[zKars]

Velly Intellesting....

Same 3/5 noise, but not solved with bushing replacement. Hmmmm. Apparently you need a T shifter too!

How about the bushings in the rear trans mount? Did you install the poly ones from the Energy suspension kit? Back to stock rubber!

Edited October 6, 2015 by zKars

[Captain Obvious]

A couple thoughts...

 

First, If the Z transmission is like others I've been into, you're less likely to hear any gear whine in fourth gear because it's a straight shot through the gearbox without going through any of the counter-gearing. Because of that, none of of the internal gears are actually under any load. They're just along for a no-load spin in the oil. All of the power goes in the input end, straight through a locked up main shaft, and then out the output end.

 

Second, I've noticed that a LOT of transmission noise is transmitted through the shift knob design. I've messed with a couple different knob designs and I've found the quietest versions are solid, heavy, and have all parts either completely firmly mounted, or shock mounted in some sort of elastomeric adhesive (fancy words for "RTV").

 

Third, I made shifter bushings out of Delrin. Doesn't add anything to the discussion, but just because I can. They turned out awesome:

 

 

[zKars]

That does help explain why 3/5 is noisier than 4.

My new T shifter is easily twice as heavy as the original shifter now that it has a fat solid SS bar welded on top of what's left of the old shifter shaft, so your increased mass = reduced noise observation makes sense and partly explains why Rob's noise is still there. I really like the ability to solidly push and pull that T-shifter. And all that cold steel under my hand feels really good. Bit chilly now that mornings are at the freezing point around here.

Make me some delrin bushings' wood'ja?

Edited October 6, 2015 by zKars

[Zed Head]

You should take a look at the shifters that come with the 300ZX transmissions.  Heavy upper lever and knob with a thick rubber sleeve between the top lever and the short arm that goes in to the transmission and does the work.  I assume that the mass and the rubber damp vibration and probably also take up some of the shock when shifting.  It's a different mechanism attaching the lever to the striking rods (71C type transmission) but you can see that they put some extra thought into the lever itself.

 

I have a 1980 transmission in my car with a 1978 5 speed shifter and knob and factory nylon bushings, in good shape, and I don't get any noticeable whine.  And it's a quiet car, exhaust system and otherwise.  Not gloating, just a factoid for reference.

Edited October 6, 2015 by Zed Head

[Chickenman]

It is amazing how a simple change in a gear shift knob weight or materiel can amplify or dampen transmission noise. I have a very nice cylindrical shaped Billet aluminum shift knob on my 5 speed. Perfect length and feel, but at certain speeds it will " sing " like a SOB. Touch one finger to the shift knob and the " singing " goes away.

 

PO had a cheezy imitation Wood knob on car. Looked ugly and felt weird, but it was quiet....

 

Heavy weighted shift knobs are big in German cars such as Audi and BMW. They act as a Mass Damper.

Edited October 6, 2015 by Chickenman

[zKars]

Alrighty then, its settled. Who would like a big icy cold shiny piece of stainless steel welded to the top of their gear shift lever? Only trick is mounting it to the tranny and getting it through the three shift boots.... It can be done.

I have all sorts of internal transmission shafts that can easily be turned in serious shift T knobs..... This one is 5/8 diameter and 4.5 long.

[grannyknot]

Jim, my 83 ZX 5spd was "singing" as well, I rebuilt transmission but nothing changed then finally I noticed the wooden knob was loose just a bit. It turned out the threaded insert in the knob had over sized threads and was buzzing against the shift lever, a bit of plumbers teflon tape took up the slop and I stuffed some dense foam to fill up the hollow inside the knob that is under the 5spd badge.

Now all is quiet, it was a wonderful moment, I had chased that noise for a year and half.

Glad to hear you found the fix too.

Chris

[Chickenman]

My aluminum knob has a plastic thread insert that is held in place with a long central screw. It gradually became undone over time and buzzing slowly became worse and worse. Drove me nuts!! Threaded insert had locating splines, so knob didn't feel loose. Finally figured it out when shift knob came off in my hand.... DOH!!!

 

BTW, metal shift knobs get DANGED hot in the middle of summer. I throw a spare baseball cap over mine when I park the car.

[Captain Obvious]

T-handle looks great, but somehow the thought of grabbing ahold of two pounds of sub-zero stainless steel on a frigid Canadian winter morning just doesn't do it for me. Sounds too much like a tongue on the flagpole.  To each his own though.

 

Make me some delrin bushings' wood'ja?

 

I certainly owe you! I can cut them a tiny bit tight and you can lap to perfect fit? Shoot me a PM.

[takayuki]

I can't comment on the transmission noise issue, however followed this modification from atlanticz after my plastic bushings got destroyed after a mechanic took it for a test drive during my out of province inspection.

 

http://atlanticz.ca/zclub/techtips/shifterbushing/index.html

 

Worked out good.. $9 from my local parts store.