FYI- Proper shifting of the NSX

[ATERPAK]

I just came across this service bulletin from Acura concerning the proper way to shift the NSX, RSX, TL's and TSX's.

They say:

Regardless of what's comonly thought, skip shifting is punishing to an M/T. Those flicks of the gearshift from 2nd to 5th gear or from 3rd to 5th gear can speed up synchro wear, leading to some nasty gear grinding over time. To avoid problems, and to prolong the M/T's service life, we advise you to shift through the gears in sequence and don't speed or power shift.

Well any thoughts on this?

 

[CDX_NSX]

I'm no expert, but here's my $0.01 (not quite worth $0.02).

As I understand it, the sychromesh comes into play both on the upshift and downshift. The larger the gap in gearing, the more shaft speed the synchos need to compensate for. With a 3 - 5 upshift, theres a larger RPM gap than would be with a 4 - 5 shift, and therefore the synchros have to work harder to match the shaft speeds. This is the same on downshifts.

I double-declutch on the downshifts to save the synchros somewhat, but don't on the upshift (just never got into the habit.) However, I think that if you double-clutch on the upshift, you should be OK with skipping gears.

 

[Modernceo]

As long as you rpm match the gear your going into, how can it be that harsh on the transmission ? Ie, going from 3rd into 2nd to fly around a corner and then power out of it ?

 

[CDX_NSX]

As long as you rpm match the gear your going into, how can it be that harsh on the transmission ? Ie, going from 3rd into 2nd to fly around a corner and then power out of it ?

Well, the reason why we are able to do single-clutch downshifts in most modern cars is because of the syncromesh. Before the introduction of syncros, shifting required double-clutching (I believe that some trucks still require double-(de)clutching). The wear is on the syncromesh. Quite simply, the more we use it, the more it wears. By double-clutch/declutching, you reduce the use and therefore the wear on the syncros.

 

[NSXVURGIN]

What is double clutching/ declutching?

I sometimes down shift 5-3 to get up into VTEC on the Highway, but I've never shifted 1-3 or 3-5....or 2-4 what purpose would this serve anyways?

 

[brahtw8]

Short shifting is a matter of convenience. Sometimes you take it to redline in 2nd and then want to cruise at a more relaxed pace.

The technical bulletin is correct, but the wear can be avoided through rev matching. Synchros wear when they have to compensate for the RPM difference between the road speed and the gear selected. If you do this yourself with the throttle, there is no additional wear from short shifting.

Double clutching is part of the process known as Heel and Toe Double Clutch downshifting. Basically, when you downshift you press in the clutch, shift to neutral, let go of the clutch, blip the throttle to match the road speed/RPM of the new lower gear, press in the clutch, engage the gear, and you are done.

Heel and toe describes the act of using your toe on the brake and your heel on the gas to do this while you are braking. On modern cars, the pedal layout is such that heel and toe is actually toe and toe, with the left side of the foot used for the brake and the right for the gas.

 

[Hiroshima]

The S2000 guys say the Woodwork says not to skip gears as it speeds synchro wear. Makes sense that it applies to our cars as well. They just talked about this same thing a few weeks ago.

 

[CDX_NSX]

Another penny in the pot. Just to be clear, I believe that a simple rev match without double-declutching doesn't do much other than smooth the feel of the shift. To benefit the syncros, the transmission should be put into neutral and the clutch let out before rev matching. This is where you save wear on the synchromesh.

 

[netfreak]

Another penny in the pot. Just to be clear, I believe that a simple rev match without double-declutching doesn't do much other than smooth the feel of the shift. To benefit the syncros, the transmission should be put into neutral and the clutch let out before rev matching. This is where you save wear on the synchromesh.

correct. If the clutch is not released in neutral while downshifting, rev matching serves no purpose. Double clutching is a good skill to learn and very easy once you get the hang of it. With a short throw shifter it's easy enough to double clutch as quickly as someone who simply rev matches. This leads to prolonged synchro life and a weird look from your passenger.

 

[Larry Bastanza]

Rev matching does nothing to minimize syncro wear. All it does in bring the engine speed close or equal to the mainshaft speed which has been set by the syncro when the selected gear is engaged(syncro has already done it's job). This technique will minimize clutch wear only, and also allow a smoother transition as the engine is re-engaged to the drive wheels.

HTH,
LarryB

 

[OLDE GUY]

Rev matching does nothing to minimize syncro wear.
HTH,
LarryB

So Larry, does the "service bulletin" comment in the top post make sense to you - that skipping gears (going up i.e. 3-->5) is harmful? Thanks,,,Bill

 

[Dave Hardy]

If the clutch is not released in neutral while downshifting, rev matching serves no purpose.

Not quite. It doesn't minimize wear on the synchros, but it does still serve the purpose of not upsetting the car while downshifting and braking for a turn.

 

[Larry Bastanza]

Yes, I do agree with the post above, a few folks here have stated why, if you skip gears the differential speed of the two shafts are further apart, so the syncro will work harder. If skipping gears is habitual, then I am sure if you compare two transmissions over time, the one skipping gears will be more worn out.

For those who responded about the double clutching, does this technique mean disengage clutch, go to neutral, engage clutch, blip throttle, disengage clutch, shift into gear?

If so, then you are bringing up the mainshaft speed, which thoeretically will bring the shafts in the trans closer together in speed in the case of a downshift only.

Make sense??

Thanks,
LarryB

 

[timothyaw]

If you're redlining in 3rd and then shift to 5th, wouldn't that be ok because the speeds would be pretty close?

 

[CDX_NSX]

For those who responded about the double clutching, does this technique mean disengage clutch, go to neutral, engage clutch, blip throttle, disengage clutch, shift into gear?

If so, then you are bringing up the mainshaft speed, which thoeretically will bring the shafts in the trans closer together in speed in the case of a downshift only.

Make sense??

Thanks,
LarryB

The Blip is done on downshifts only. On upshifts, you skip the blip. As mentioned above, I don't do it on the upshift just coz I'm lazy.

 

[CDX_NSX]

If you're redlining in 3rd and then shift to 5th, wouldn't that be ok because the speeds would be pretty close?

No. It should actually be further apart. The higher the gear the lower the RPM at a given speed, so the higher the RPM at the lower gear, the greated the difference would be....... I think.

 

[DRZZZ]

OK, so I'm driving down a wide open road from a stop. I floor it in 1st, then briefly into 2nd. But now I'm going 60 in a 50, and don't want a ticket. So Acura says it's better to shift into 3rd for a second, then 4th, then 5th, and NOT go 2-5. This seems like I'll burn out my clutch sooner now

For the record, my DSM turbo trans was unharmed for 120,000 miles doing the 2-5 shifts, but I know experiments where n=1 don't mean a whole lot in the big scheme of things. :wink:

Dave

 

[DutchBlackNsx]

I think this whole thing is a bit over the top.

It depends on another factor, which is (i think) even more important then the shifting from 2nd to 5th.
That factor is the speed of which the next gear is selected.

I'm sure that a very spirited shift from 2nd to 3rd is putting more strain on your synchro's, then a very moderate/slow 2nd to 5th.

When then transmision would be unselected for a few moments (aka neutral), the revs of the primary shaft will drop, and when selecting 5th gear, the synchro would not have to do a lot.

If you ever turned the primary shaft of a gearbox by hand, you know that it will drop in revs quiet well..

When shifting down, its a complete different story.


Mich

 

[OLDE GUY]

For the record, my DSM turbo trans was unharmed for 120,000 miles doing the 2-5 shifts, but I know experiments where n=1 don't mean a whole lot in the big scheme of things. Dave

I can advance N to 5 by adding that I have frequently skipped gears going up, most often 3-->5 or 2-->4, in my cars for decades without having a problem with synchros or clutches.

'92 Honda Accord to 65,000 miles
'96 Honda Accord to 105,000 miles
'82 Porsche 928S to 103,000 miles: high torque V8, so frequently 1-->3-->5
'88 Porsche 944Turbo to 67,000 miles: new owner says 80K and no problems

The 928S had 7 or 8 track weekends on it and the 944 T had 25+ weekends. I have never had to replace synchros or clutches. But I don't make these shifts FAST. As DutchBlackNSX said if you do it slowly and give the primary shaft time to wind down, I think it isn't too harmful. Also each time you skip a gear you save one useage of the synchros and the clutch. It may even out on the synchros and saves the clutch.

 

[SilverStone05]

Well, in order to drive ANY manual car smoothly, you have wait for the right rpm to engage the clutch during upshifts anyway. If you know your car well enough, this isn't too tough. As far as skip shifting, you're gonna be okay as long as you know what your engine is turning at-at a respective MPH/RPM/Gear and make sure you engage your clutch at that spot. Huge gaps like 2nd to 6th are tough to estimate/remember, though.

Anytime you upshift and you feel a shudder and the tach instantly drops (you engaged the clutch too quickly) or instantly rises (you engaged too late), you've made a boo boo and that wears on your synchros.

I've made an art of this and I know all my shift points. I've got it so precise that I even adjust for RPM drops when the air is on, and when its off. (When the A/C compressor is on, the revs drop quicker) Ha, when I had my Z I remember more than one person telling me that I could drive that car better than anyone they knew. :wink:

This phenomenon is one of the main reasons I sold my IS300. The flywheel was SO heavy on that car, that I'd seriously have to wait a couple seconds between upshifts so the revs could fall to the optimal "sweet spot" that would engage the next gear without a nice shudder. Oh that was so irritating.

Practicing this "rev matching" (and I dare call it rev matching because many attribute that phrase to double clutch downshifting) will not only save you a bit of wear on your clutch, but it will also keep your synchros happy.:biggrin:

 

[AndyH]

Regardless of what's comonly thought, skip shifting is punishing to an M/T.
Well any thoughts on this?

Then how come Vette have their gear skip from 1-4 as a standard thing?

 

[NSXDreamer2]

Then how come Vette have their gear skip from 1-4 as a standard thing?

Because many other parts will fail before the synchro:biggrin:

Since their engine had so much useable torque, this 1-4 shift will yeild better mileage rating.... That will allow GM made few more silverado and some other big gas guzlling SUV.

 

[Deltron Zero]

my favorite line from fast and the furious (after the drag race) - "granny shiftin. not double clutchin like you should." hilarious!

 

[02#154]

Because many other parts will fail before the synchro:biggrin:

Since their engine had so much useable torque, this 1-4 shift will yeild better mileage rating.... That will allow GM made few more silverado and some other big gas guzlling SUV.

It's true that the purpose of the 1-4 shift on the Corvette was to increase fuel mileage but would GM design that into the car if they knew it would cause pre-mature wear on the synchros? That said, what other motivation would Honda have to send out the bulletin if it weren't true?

J

 

[OLDE GUY]

That said, what other motivation would Honda have to send out the bulletin if it weren't true? J

I do think that it is true but, for drivers who shift smoothly (and not too fast), there is minimal additional wear - based on my two Honda Accords, etc. as noted above. I don't think that Honda has an ulterior motive.

But I could be wrong since my experience was NOT with the NSX transmission. Perhaps the issue is NSX trany specific. However I continue to occasionally skip gears.