[IDEngineer]

Took the Evora GT on a mixed errand run today and discovered something about that 1st/2nd gear "growling" sound. I suspect it may come from the synchros and not the gears themselves. The reason is that the sound goes away, or at least gets a lot quieter, if I move the shift stalk to neutral. If I put it back into gear the sound comes back, and pulling it back out of gear makes the sound go away again. 100% repeatable. All while holding the clutch in/disengaged so there's no load on the transmission (car was coasting at slow speed).

Maybe this is common knowledge but I've read a lot of posts on this on various Lotus forums and never found anyone else mentioning this. If I'm interpreting this wrong, please correct me!

 

[Dr.Hess]

I don't think that would be the syncros. More like gear-gear interface, or one of the shafts moving. When in neutral, one shaft isn't going to be moving, or have a load on it.

 

[Frohst]

All the below is from the other transverse manuals I've dealt with. It is my understanding vast majority of modern manuals work this way. There are, of course, exceptions. Probably mostly from the early days of the horseless carriage XD.

Clutch separates engine from trans - not trans from wheels.

So if your clutched in and rolling at 5mph in 1st - trans is still spinning at 5mph in 1st speeds with the 1st gearset engaged.
Likewise for 2nd.

The synchros are only directly coming into play as you shift into a gear.

So in the above, clutched in, rolling at 5mph in first, shift to 2nd.
Your synchros are taking the hit of changing the trans speed from the 1st to 2nd ratio.

If you wanted to avoid that hit on your synchros, you'd shift to neutral, clutch out, spin the engine to spin the trans to 2nd gear rpm for you speed, clutch in, shift to second. (Oh and ofc ensure the engine itself is also spinning at that proper rpm at that time while you are clutched in)
With the trans prematched to the spin speed for 2nd the synchro has no rpm change to take up. Good luck getting this spin speed at the shift any closer than the natural spin down during an upshift would get you.
I ain't got the talent nor time for that so I let synchros do what they are designed to do.

*Fine point for the specificialists:
The synchro is engaged when your in gear - it's just locked up at that point to match the gear sped you are in.

 

[Frohst]

If you've never been inside a tranny they look cool. (Okay maybe I just like gears)

(This is el b series Honda gearset, not Evora)

Synchros are the goldy bronze bits.
Shifting slides the collars next to them over them, and the black gear but just across. This locks the synchro and gear together to spin at the same speed.

In neutral, non of the synchros are locked up, so the gears are free to spin at w/e speed they want.
In fact, one gear of ever pair in the set is locked so all the gears are always spinning. It's just they aren't locked up to the shaft until a gear is picked.

Shifting pushes the synchros towards the gear so the cone bit (hidden by stuff) acts like a friction clutch to get the speeds the same before the lock up collar can get all the way over.

 

[IDEngineer]

Clutch separates engine from trans - not trans from wheels.

Yep, knew that, sorry if I suggested otherwise. I do know how synchros work, and that the transmission's output shaft spins anytime the driven wheels do (clutch disconnects engine from transmission).

Since I hear the sound when moving the gearshift lever out of neutral and into a gear, this should engage first the frictional interface, and then the dog teeth, of the synchros as they match the shaft speeds - and the sound occurs. Returning the gearshift back to neutral disengages the synchros - and the sound goes away. I suppose it could be the main gears themselves but I think I could hear the sound before the gearshift lever was fully into 1st or 2nd, which would mean the synchros were spinning up but the main gears might not be engaged yet. I'll investigate next time I drive the Lotus.

Hopefully tomorrow, I'm a bachelor for a week and while I'm really focused on work I'm somehow finding a reason every day to run some sort of work-related errand. No, seriously. I promise.

 

[brgelise]

Please play your stereo louder so we don't have to read more OCD issues

 

[IDEngineer]

Please play your stereo louder so we don't have to read more OCD issues

Apologies if this sounds OCD, I'm just trying to learn as much as I can about this car. I'm not saying anything needs to be done about the transmission, I know this transmission is naturally growly in the low gears, I just like to know what's going on.

As for the radio, it very seldom even gets turned on. I play music or news in my other cars almost all the time, but in the Lotus I'm immersed in the driving experience and the radio is just a distraction. I'm at ~6500 miles now and I bet the radio hasn't been on a total of ten minutes that whole time, even on long road trips. As Enzo said, the engine is music enough (or something like that). I never understood that until I owned a Lotus.

 

[David Craig]

If you've never been inside a tranny they look cool. (Okay maybe I just like gears)

View attachment 1320957
(This is el b series Honda gearset, not Evora)

Synchros are the goldy bronze bits.
Shifting slides the collars next to them over them, and the black gear but just across. This locks the synchro and gear together to spin at the same speed.

In neutral, non of the synchros are locked up, so the gears are free to spin at w/e speed they want.
In fact, one gear of ever pair in the set is locked so all the gears are always spinning. It's just they aren't locked up to the shaft until a gear is picked.

Shifting pushes the synchros towards the gear so the cone bit (hidden by stuff) acts like a friction clutch to get the speeds the same before the lock up collar can get all the way over.

That does look cool!

 

[exigegus]

What you cannot see in the assembled gear set is the hubs. The shifter forks move the hub, which is permanently splined to the shaft which is running at output shaft speed. The hub pushes the synchro which has dogs that mate with the inside of the gear, which as mentioned, is always spinning, at input shaft speed. It also has a cone which matches the cone on the face of the gear. As the hub pushes the cones mate and the synchro spins the gear, and consequently the input shaft up to a speed approximating the speed of the hub and consequently the output shaft. When those speeds are very nearly equal, the dogs on the synchro slide into the splines inside the hub and the dogs in the gear follow, boom, you are in gear.
This is a long roundabout way of saying that it would be pretty hard for synchros to have lost motion and the ability to make noise when they are engaged in gear. Out of gear, maybe?
I am going to guess either iffy gear mesh which only makes noise when there is torque going through it, iffy spline geometry which my experience with machine tools tells me usually manifests as a knock

I am going with gear mesh.
Aren't several of the gears Lotus only?
Probably not the same as the originals.
THey use helical gears for noise, so you always have more than one tooth engaged at a time you do not hear the 'click click' of every tooth engaging with every other tooth, which with increased rpm becomes a growl. The downside is they create side load which does not happen in straight gears.
There is no doubt some formula with angle of tooth/side load/ strength/noise

 

[IDEngineer]

It is my understanding (which could easily be wrong!) that the Evora uses a Toyota transmission which was originally designed for diesel applications. I've heard it's from their E series transmissions but don't know for sure. Since diesels engines are noisy anyway, the tribal lore says they didn't bother making it quiet. That may include using straight gears for strength, since helicals give up some strength and simplicity of manufacture in trade for quieter and smoother operation. As you say, I believe Lotus swaps some of the gears but the basic transmission is still a Toyota product intended for diesel environments, and unless they're replacing ALL of them, their gear swaps would have to also use straight gears to be compatible with the OEM's remaining in the transmission.

Your point that "pretty hard for synchros to... make noise when they are engaged in gear" is a good one. Since the noise doesn't go away after full gear engagement, it can't be the synchros. I'll play with it some more later today.

 

[agentdr8]

I've heard it's from their E series transmissions but don't know for sure.

EA60, which is the Toyota version of the Aisin BG6. Used in diesel Toyota passenger cars such as the Auris 2.0 D-4D. A turbodiesel 4-cylinder, with a max torque of around 300 nm, or 221 ft/lb. The Evora GT puts out 430 nm of torque, so it would seem Lotus is confident that the EA60 is built well enough to handle that excess over the vehicle it came out of.

The Standard transmission is a direct Toyota unit, with no change in gears. The Sport or CR (close-ratio) gearbox which was made standard on all Evoras > MY12 IIRC, has different gears for 3-6. And unsurprisingly, when someone encounters an issue with the gearbox, it always seems to be gears 3-5 or 3-6 (the ones Lotus "touched"). Allegedly Lotus has addressed whatever issues they had early on with the CR boxes, so nothing past MY12 should be spinning gears off their splines.

 

[exigegus]

I just searched back, the 1st and 2nd are the same normal/sport at least on the older Evoras

Also saw a note that the TOyota trans is their version of the Aisin BG6
Seems to be more info around on that gearbox

^^beat me to it....

 

[IDEngineer]

Great data, thanks! I knew I'd heard an "E" series number for the tranny but couldn't remember the specifics.

when someone encounters an issue with the gearbox, it always seems to be gears 3-5 or 3-6 (the ones Lotus "touched")

No surprise there. As much as I respect Lotus, it's very difficult to replicate the experience gleaned from producing tens or hundreds of thousands of something. Start tweaking things in a proven design and you're likely to learn "Oh, that's why they did it that way...."

 

[Slobdog]

I notice at a stop or maybe rolling slowly going from neutral to 1st there is always a distinctive 'THUNK'. It reminds me a bit of a motorcycle sequential where going to first involves a similar lighter pitched 'thunk' 🤷‍♂️ I like it actually assuming it's not a bad thing.

 

[imthewalruz]

Yeah I also have the thunk into first from neutral (interestingly it just thunks once; if you clutch in and out and then do it again right away, no thunk on the second time). It's more of a shudder in the car than a sound.

I haven't noticed particularly loud gear noise but I do usually listen to a podcast or music.

 

[zthang]

I've also heard that it can be attributed to the usual chatter you would get with a single mass flywheel? Either way, i've got around 10k miles on my '17 400 and the 1st/2nd gear chatter has not changed. I almost kind of like it now...more noises = more racecar

 

[Slobdog]

Agreed zthang

 

[mark123]

I looked into this a while back and confirmed the lower gears are cut straighter, which increases noise.

 

[Dr.Hess]

My friend, Billzilla, would race 4AG powered cars with T50 transmissions. Besides swapping the gears around to make a closer ratio gearbox at the cost of a totally different shift pattern, one of his tricks was to get some gear making wizard to make him gear sets with straighter cuts. Yeah, noise was up, but they're stronger and they transfer power more efficiently than more helical cut gears, because the helical cut gears are trying to push everything apart instead of just transfer the torque rotationally. This slightly better power transfer efficiency would put him just slightly faster in a close spec race. His web site is Bill Sherwoods Home Page . Looks to not have been updated in years, but it is a very good read. Last I heard, he was flying 747 for Oz something airlines, or some PG based airlines. I forget.

 

[Cbd automotive]

That does look cool!

This is why I love rebuilding manual transmissions, they are pure, simple logic. K.i.s.s personified. Automatics are logical, but in a very convoluted manner, lots of check balls and oil passage ways in the valve body that get confusing. Beauty (and strength) in simplicity.
On a side note I think aisin and Dana make all of toyotas manual transmissions, they rarely mess up, it's common for a company that makes a one off gear set or the like to have issues at first (the comment about the lotus cr gear set). I've put many cr gear sets in for people and often heard, this is the good second generation set, or hope these are as strong as originals. It's hard to get a new set that has the testing and engineering that the first set would have with Dana or aisin s engineering and scrutinizing and then toyotas scrutinizing.