Sequential Transmissions
 

I've searched, but couldn't find much about sequential transmissions for 944's, so I have 4 simple questions: why are they so expensive? Does anyone make an affordable sequential transmission for the 944? Why are they so noisy? Why do they require frequent rebuilds? I think it would be pretty bad ass to have a sequential transmission in my car...

A sequential trans is like a motorcycle trans., it shifts linearly.
I have seen a website that shows sequential transaxles for the racing Porsches. Never seen one for a 944 pr 968, although they are similar in design.
I would imagine they require frequent rebuilds due to their application, which is normally racing.

Forget that, I want a PDK!

i installed one into my ls7 944 it's a quaife 6 speed sequential .
they do not make them for the 944's for what i paid for the gear box you can go buy your self 2 944's or a mint 968 .
they are designed for racing if you think you will be driving it on the street for get it ! that would be total hell .
once your moving the clutch is not used at all just leave your foot in it and pull up into the next gear .
down gearing is a little deferent but the same thing very little rev matching is ever needed .
this past weekend i was working on the paddle shifters for the car .

hey requaire far less maintenance that your standered type of road trans .
just keep the oil changed in them .

they are loud because they have what are called straight cut gears in them . the gears in your street trans has the gears cut on a angle . but by doing so you can't shift with out using a clutch . this is becaus eyou need to releace the pressure from the gears for them to disingage and ingage into the next gear .

the are costly for many reasons . the 1st is they are hand built gear boxes . then your picking the gearing you want from 1st to 6th final drive too your having custom build you a gear box there is nothing off the shelf about them .

Are they really that bad on the street? Not having to rev match when I downshift seems like a godsend to me. If I didn't use it for racing, would it last longer? Are they deafeningly loud or do they just make an annoying noise? Pulling/pushing a lever to shift instead of having to move it in a complex pattern seems awesome to me.

false

the helical gears of a standard transmission do not engage and disengage when the shifter is moved, or the clutch is used. the helical gears always remain in contact for all gears at all times. the shifter connects and disconnects the syncros, not the gears themselves.

and false that straight cut gears are required or necessary in a sequential transmission. depending on the type of sequential transmission, the straight cut parts are the dogs for the gear. again, this is what is actually being engaged when shifting, not the gears for power transfer.

Lol he just told you, not only do they have huge drawback for street use but for the price of one of those sesquential tranny you could buy yourself a couple off 944s plus a 968.Very few peoples here will be able to afford such a tranny for a street driven car,it wouldn't make any sense .:eek:

Complex pattern? Come on dude it's not even a six-speed :)

This is what straight-cut gears sound like: Straight Cut Gears - YouTube

You'd be a damn fool to run them on the street.

they are not in any way good for the street !!!
if you looked at the link on youtube you will have about a 10th of how loud they really are .
the harmonics in the fiberglass helmets make it worse the cabon fiber ones are just a little better but thats pretty much all you hear .
the exhaust is the other thing the noise out of the LS7 with the pipes running down the spot were the right side floor was is the other thing .
after a 2 hour stint your ears are ringing then by the time you all finished with the 24 hour event your ears will ring for the next two days .
it will be good when i finish the paddle shifters holding 12 " wide front tires with one hand as your shifting beats the crap out of you .

the noise your hearing is coming from the way the gears are cut (straight ) and meshing together .
my sports racer does the same thing it too has a 6 speed sequential gear box in it .
gear boxes differ just like LSD's do there are many types of both and they all have there own sound to them . I changed out the wedge lock in my sports racer to a triple lock you still hear the whine of the gears but now you also hear the diff more too .
now don't get me wrong ! i never stated that all sequentail gear boxes have straight cut gears . but the whine you hear like in the video is just about the same whine you hear in my cars they are coming from the gears and diff .

it's not just the cost of the gearboxes thats the bad part because all and all they are only about 9 to 12 K it's all the other crap that you have to also buy and do .

I'm sure I could afford one if I pick up a few people's shifts at work :D

I was just kidding. I couldn't think of a better way to compare the push/pull shifting of a sequential transmission to the way you have to move the lever around on a manual.

Damn, that hurts my ears! If motorcycle transmissions are sequential, why don't they whine like that? My old Hodaka Road Toad and CRF150 didn't make any funky noises.

What else would I need to buy? I'm assuming I need the shift linkage.

Actually, it's perfectly possible to shift a transmission with helical gears without using a clutch. You simply have to rev-match near-perfectly. However, the synchros and blocker rings make it exceptionally difficult and place great strain on the shift forks, so it is not recommended. This is because the synchro mechanism actually incorporates a blocker to physically prevent the dog teeth from engaging unless their speeds are synchronized. However, there are lots of non-synchro transmissions with helical cut gears (OTR semis and motorcycles come readily to mind) where shifting without a clutch is the regular mode of operation even with helical gears.

Synchros do not "connect" or "disconnect." They merely provide an amount of friction force to allow the dog teeth to engage smoothly. The synchros themselves have absolutely nothing whatsoever to do with coupling the gears to their respective shafts; all the synchros do is smooth the engagement of the dog teeth. Most synchro systems also employ some form of blocker to prevent contact between the dog teeth until the synchros have done their job and matched the rotational speeds.

On a general note, helical-cut gears are physically stronger than straight-cut gears as well as quieter. The benefit of straight-cut gears is that they allow "crash box" transmissions (transmissions where the shifting is done by engaging the gears themselves and not by engaging and disengaging dog teeth) and they are cheaper and easier to manufacture. When dealing with a racing transmission that is less likely to be expected to last 200,000+ miles and where the ability to use custom-cut ratios for different tracks is important, straight-cut gears have an advantage.

You still have to rev-match on a downshift with a sequential transmission unless you want to jerk the ever-loving ***** out of the car when you re-engage the clutch. Rev-matching is NOT the same as double-clutching; rev-matching means that you bring the engine close to the right RPM before re-engaging the clutch after a shift has been completed. This is necessary for smooth driving regardless of whether you have a sequential gearbox or a standard H-pattern box. While a sequential gearbox will eliminate double clutching between gears, it will NOT remove the need to rev-match to make a smooth downshift (any motorcycle rider can tell you this).

I meant downshift rev matching, not double clutching. I'm not exactly a pro at rev matching for downshifts. I can get it close enough that I don't have to drag the clutch to make it smooth or have the car lurch like crazy, but it's not as smooth as I would like. I guess a sequential transmission wont solve this problem :(

I don't know why, but I really feel like I have a knack for this naturally. When I first heard of it on this forum I drove and tried it a couple times, after a handful of tries I was landing the correct RPM almost every time. Now it seems almost effortless :eek:

Price for sequential transaxle transmissions start at about $25k. They measure longevity between rebuilds in hours, not miles. They represent a great advantage on the track but there would be less than a handful of people on the planet that could realistically even consider running one in a 944/951. Most of these cars are owned by young US students who don't have anywhere near the $$ to explore this level of customisation. Remember, it's not just the cost of purchasing the gearbox, you have to cut the car up a lot and custom fit it. Then there's custom axles, CVs and probably a fuel cell. You'd be over $30k before you blinked....sad to say.

Something like this could probably be adapted to work with the 968 trans with enough time and money..

http://www.sqsracing.com/produkt/354:449:sqs-e-sqs-g-audi-quattro-01e

The 968s gearbox is basically the same as an 01E and many parts are interchangeable.

My old Hodaka Road Toad and CRF150 didn't make any funky noises.



Oooh, Hodaka, haven't heard that name in a number of years. Had a Hodaka Combat Wombat, back in the, cough, '70s. Just the name alone scared off little kids. The tranny was made of glass though.

you are correct, i only use sychro because its basically the same part. the synchros engage, mate up, and then the dogs match up slip together and transfer the torque.

the reason why your not getting the whine out of most motorcycle gear boxes is just in the desing of them . yes they too have straight cut gears .
i my younger days i raced motorcycles for many years . you do not rev match to down gear many motorcycles . you can and do at times and the same goes for sequential gear boxes in cars .
what i have been doing now is installing a little computer in the car that is for the the trans .
what it does is as you go and change gears it dropps the voltage on the motor to still keep it running but drops it fast enough and for long enough to change gears at any time with out ever needing the clutch but just to get going and to come to a full stop .

because this gear box was designed to work a deferent way and we took it and turned it around and flipped it up side down .we had to have the internals reworked for the fill and drain plus , oil cooler feed and return lines and just to keep it properly lubed .
so there was another 3K FOR THAT .

then there is the tork tube and drive shaft . that needed to be totaly custom built we took two belhousings one for the LS7 motor and one from a 996 and then after doing the fab work we needed to do send it out and have a drive shaft built for mateing the two together .
there was another 3200 dollars for that in parts and labor and that does not include our labor .

then the half shafts . i'm using a 996 rear suspension front also . so to keep the track of the car the same as the 944 the half shafts have to be built for the lenght needed .
so i'm there any way i just had them install bigger and better CV's also .
add in another 1900 dollars for that .

then the car is a tube chassis car with all carbon and fiberglass body panels .
add in the cost of all the materails to get the gear box in the car and working .
my guess would be about 1200 dollars .

then the paddle shifters and the computer and gauge for the trans it tells you what gear your in and the oil temp of the trans gear oil .
there is 9K into that right now .
because the computers are deferent for the one with the stick on the floor to the one i need for the paddle shifters i maybe able to sell it ? and get some money back .

now with out the computer to drop the motor power just a little you still don't have to rev match to down gear all you do is lift your foot off the gas for a split second on each down gear and never on any up gears .

Wrong.

My 2007 Harley XL1200R use helical cut gears. Harley's 6-speed transmissions on its big twin motorcycles are also helical cut, constant-mesh units.

Most motorcycle sequential units are, in fact, helical constant-mesh units with dog-teeth engagement. They are non-synchro, but they are absolutely not straight cut.

I never had any problems with my transmission, but I never did any racing with it.
I can do it just fine with my VW, but for some reason I can't do it with my 944. Rev matching is essential with I downshift into third since the synchronizer is fried and it'll grind like crazy if I don't get the RPM's right, but I just can't do it for some reason :mad:
Damn, for 25k it doesn't even seem worth it.
Wow that sounds crazy!

i used it in the general turms !
i can only state about the ones i have seen .
like in my F1000 CAR using a gsx-r 1000 motor
or like in the motorcyecles i used to race like the R1 , gsx-r ,
then all the ones that when i was younger helping out in my brothers motorcycle dealer like the ZX and so on .
then when i started racing in the GNCC 1st with husky the for KTM they too all had straight cut gears in the gear box .
so do all motorcycles have them well no a hand full don't just like the all don't have them in all sequential gear boxes .
but again most do !
then again you really should not include a motorcycle that still uses air to cool it's cylinder heads and has no fuel injection . i would think at some point just bringing the heads up to date with some water jackets around the heads may take the out dated early 1970 design into the 2000's .
but you really still can't count a motor that they had to give to porsche to work out the bugs in the cylender heads . the jokes when i was at porsche AG about that were to funny .

because i'm no gear box expert and never clam to be one ! i can only tell you what i was told right from my friend tommy at quaife and that is the whine your hearing is coming from the gears in the gear box they are making that noise from the way they are meshing together don't worry about it the gear box is fine . i would have to say it is because it has done 3 24 hour event and still is holding up good along with the one in my sports racer that is 6 years old now and too shifts just fine .

i did race a car in a vintage event with a car that had a M22 rock crusher in it this was some years ago and it was not sequential and you needed a clutch to shift . i don't think it had straight cut gears but the noise coming from the trans was bad . on my out lap i called into the pits to ask about it . the reply was it's fine run it !
i was told that it's called a rockcrusher because that what it sounds like when you shift it .

i do not own a transmission shop i own a race car chassis ,fabrication shop a high end body shop for ferrari's lambo's and cars like that and also a custom paint and airbrush shop .

so do the gear boxes i have in my race cars whine yes ! is it because it's from the way the straight cut gears are meshing ? from what i was told yes !
part of the reason for that is also because they are solid mounted to the chassis along with the motors so ever bit of noise gets amplified from the motor and trans and goes thru the hole car .

Actually, Harley has had EFI available on the Big Twins since 1996. And EFI has been standard on every bike across Harley's entire range since 2007. Also, Porsche worked on the VROD's engine, not the engine in the Sportster nor the engine in the Big Twins. Porsche supplied absolutely zero design work for the air-cooled HD engines. The Revolution engine in the VROD is water-cooled, EFI, and was a clean-sheet design. This is just a suggestion, but it might be worth your time to do even the tiniest bit of research before replying next time.

But since you seem to have an irrational dislike of Harleys let's look at other manufacturers. Honda uses a mix of helical-cut and straight-cut gears in the Goldwing with a sequential transmission, as it did with the Valkyrie. Triumph uses helical-cut gears in the transmission for the Rocket III.

The simple fact is that modern cruiser motorcycle sequential transmissions use helical-cut gears, both for noise reduction purposes and for strength due to the high torque loads at low RPM. Helical-cut gears are stronger and quieter and it's completely possible to build a sequential gearbox using helical-cut gears no matter how much you try to wiggle out of that fact. The continued use of straight-cut gears in low-torque bikes (and yes, even a 600cc super-sport is "low torque") is largely a cost-saving maneuver because the greater strength of helical-cut gears is not needed.

Straight-cut gears are often used in custom racing applications chiefly because they are cheaper and easier to produce which outweighs the disadvantage in strength. Straight-cut gears also do not create the same sort of side-loading on the transmission shafts (helical-cut gears will naturally want to "walk" laterally and, by doing so, they impose greater thrust loads on the transmission shaft bearings than do straight-cut gears), which is a benefit because it allows the shafts and bearings in a transmission to be lighter, something which is important for racing.

Straight-cut gears whine, and you're right that they do so because of the way the gear teeth come into contact with one-another. No-one has contested that part of what you've said. However, your ancillary assertion that you cannot have helical-cut gears with a sequential transmission was patently ridiculous and you also made the absurd claim that you cannot perform a clutchless shift with helical-cut gears (OTR semi drives do exactly that a couple hundred times a day).

Bottom line: Straight-cut gears whine like a banshee when subject to any significant amount of torque. They are quiet enough in sportbikes and smaller bikes because the torque loads are typically small (even supersport engines in motorcycles have relatively little torque and instead make their power by revving to 15,000+ RPM) and because the amount of ambient noise on a motorcycle tends to drown out the gear whine. The use of helical-cut gears is spreading even in motorcycles, however, and there is nothing in the design of helical-cut gears themselves that would prevent their use in a sequential transmission nor is there anything that would prevent the ability to perform a clutchless shift. The difficulty of a clutchless shift in modern automotive transmissions is due to the design of the synchros, not to the type of gears used.

Great discussion, I learned some things reading this thread. Good stuff.

The other day I was watching an in car video of Sean Edwards racing a GT cup car (997) on the Nordschleife with a picture-in-picture view of him driving with a sequential trans (or Porsche's version, I do not know post 1989 911s very well).

I have to admit, the gear noise drowns out everything else, but I love the sound. But then it was not reverberating in my helmet at high volume.

Search youtube for it. Racemedia.tv

Jeff

Here it is.

Porsche 997 GT3 Cup Sean Edwards Onboard VLN 5.Lauf 2011 Nürburgring Nordschleife - YouTube

Rev matching alone will never prevent grinding. To prevent grinding with a dead synchro, you have to double-clutch.

The process you should be using:

(1) Clutch pedal down
(2) Gear lever out of 4th and into neutral
(3) Clutch pedal released ("up")
(4) Blip throttle to appropriate RPM to speed up the input shaft
(5) Clutch pedal down
(5) Gear lever into 3rd
(6) Clutch pedal released ("up") again smoothly with RPM close to where it would be for the speed you're at in 3rd

I used to have a 1953 Dodge M37 (military powerwagon essentially) and all shifts using first and second gears required double clutching. First and second were non-syncromesh. Later trucks did have all 4 gears with syncro.

You sort of get used to it and ot becomes fairly natural with time.

"How did they live back then"

i never stated about any model HD that porsche had to hel[ out HD on !
this is just to funny !

just like i did not state that you could in no way have a helical cut gear in a sequential gear box but the simple fact the most are not helical cut gears is just that a fact !

the simple fact that a side cut ( helicut gear ) is not as loud is the reason why they use them for say turing bikes and in some street cars .

now this is right from my engineering friend at quaife . they use a straight cut gear because the there strainght . the teeth have more mating surface on the flat part of the teeth .
i tried to up load the photo from tommy at quaife but can't seam to from my email .
like quaife stated it has nothing to do with the cost it only has to to with strainght .
so last night i pulled the lower case off the little under powered hayabusa that we are installing into a car for a customer . it's real funny how that motor too has straight cut gears . even though they (bike manurfactors ) only use straight cut gears on the little under powered bikes . like on very motorcycle that i have ever seen that gets raced and was built for racing . like the gsx-r , r1 , busa , zx , .

as a racer for 35 plus years not that has raced for two car manfactures and own and race a 962 , two classed in GT1 948's ,spec 944 , ITS 944 , hill climb 944, F1000 , sport racer aka lmp2 , itb golf , and a DSR car .
the reasons why your rev matching is not to over load the drive line on your down shifts and also unbalance the car . you should use you brakes only to slow a car for speed . by just dropping down into the next lower gear with out bring up the rev's to macth the road speed will put undo stress on the cars clutch 1st then it goes thru the rest of the drive line on your car .
then when it comes to the balanceing of your car your doing that on every part of a track with your car on all 4 of it's wheels . this is why smooth is fast !
as a race instructor i always press upon my students to be smooth in your driving inputs . when your not thinking your going fast you most likely are going fast .
again balancing the car and being smooth doing so is fast . so by not rev matching you are up setting the balance of the car .
i should make it clear that i'm talking in the general terms !
i do not rev match all that often my D-sports car or the two with the quaife sequential gear boxes as there is no real need to do so .

you see i just took it for granted before that we were talking about race cars and the gear boxes they use . but in typical forum style you always have to have some one that has never raced a car with a sequential gear box or i would bet never even drove a car with one telling you just what you said is totaly wrong and then want to get into a debate about it .
as for me i will always listen to a engineer to what and why they do what they do and for the reasons they do so .

because of the types of cars we work on in my body shop i get to drive many cars with paddle shifters . they really suck on the street ! there all very jerky at low speeds and tend to get confused . many do not want to down gear untill they want to even if you keep clicking the paddle to do so .

so the bottom line is still the same sequential gear boxes tend to totally suck for street driving !

Given that I had mentioned the Sportster and you specifically mentioned air-cooled HD engines, it's a basic convention of the English Language that you were intending to reference the air-cooled Sportster engine when you made your comment about Porsche's design help. It's not my fault if you are unable to communicate clearly.

Really?

Seems to me that you did say that you can't have a sequential gearbox with helical gears. I've never heard of a true sequential gearbox that didn't allow clutchless shifting after all.

And that still doesn't change the fact that this is wrong. You absolutely can shift without a clutch in transmissions with helical-cut gears, even in non-sequential gearboxes. The pieces that make clutchless shifting difficult on street transmissions are the synchronizers and the baulk rings, NOT the type of gears used. If you built a fully-synchronized gearbox with straight-cut gears, it would be just as difficult to shift without a clutch as the typical helical-cut street gearboxes.

Your "engineering buddy" is wrong.

The noise of straight-cut gears is because the gear teeth "crash" into full engagement and this places significantly more strain on the gear teeth. With helical-cut gears, the engagement is gradual across the surface of the teeth which reduces or eliminates the sudden "crashing together" of the mating surfaces. This is why helical-cut gears are quieter, but it's also why there is much less strain on the individual gear teeth.

Additionally, helical-cut gears tend to have more teeth engaged at any given time because of the helical shape of the cuts. This further distributes the load and reduces the stresses experiences by any single gear tooth.

Given the same diametral pitch and construction materials, a helical-cut gear will always be stronger than a spur gear because the helical cut gear will have a larger surface area in contact with the driving gear. As mentioned earlier, helical-cut gears create lateral thrust, however, and some energy is "wasted" because of this. In addition to the greater thrust loads on transmission shaft bearings, this also generates extra heat (bad in racing) and increases the amount of energy "lost" between the engine and the wheels (also bad in racing). Now, you can alter the diametral pitch or build the spur gears out of stronger material to compensate, but all else being equal, helical-cut gears are stronger.

You seem to fail to understand what I've said.

(1) Straight-cut gears are typically used in racing, for the reasons I've outlined in previous posts. Simply saying "the racing transmissions I've seen have had straight cut gears" does not in any way contradict what I've said.

(2) There is a difference between "low torque" and "underpowered." A ZX6R, stock, makes about 130 horsepower, that's pretty powerful. However, it only makes 52 ft-lbs of torque at the crank. For comparison, my "low-power" Sportster makes 77 ft-lbs of torque at the crank. Even though the Harley has less than half the horsepower of the ZX6R, it is putting 50% MORE torque load on the transmission, which is the true load factor. Motorcycle racing engines tend to have low torque and high horsepower.

Given that this is the internet and anyone can claim anything, let's say that I'm skeptical and leave it at that.

This has never once been in dispute.

so you your self just assumed some thing ( about the HD's ) .
i also assumed the being of the post was just about racing sequential gear boxes . that is because that is what i'm around so it's the 1st thing i think of when it comes to cars .
if the post was about motorcycles then it's some thing totally deferent .
but for all that matters there is such a low percentage of cars with them and they are totaly useless they are not worth talking about .

what i should say is it's not the gear in it's self that is stringer because it's a striaght cut but the GEAR BOX it's self that is stronger .
there is more mating serface to the helical gear in it's self but it's in the total design of the GEAR BOX it's self that is the down side to them .
the have to be built bigger and stronger to handle the thurst loads of the gears them selfs .
then as many know with a many street trans synchros are notorious for failing .
helical geared transmissions that i know have synchros .
we all know the helical gear in it's self is strong but the system is weak . this is why us people that race will change out the weak and heavy helical geared transmissions for the stronger and lighter sequential gear boxes with the straight cut gears . most are like the ones i my cars are 1/3 lighter that the halical type gear boxes .
the reason you see so many up grade kits for car transmissions that go to striaght cut gears for cars like VW/audis , acura / honda , toyotas and so many other cars is for just that an up grade .
a gear is much stronger than a synchro that is the 1st plus
the next is you do not need a chutch to do your gear changes 2nd plus .
the gear box is lighter 3rd plus
the gear BOX it's self is a stronger unit making them more durable 4th plus .

the down sides are
they are loud
they are clunky
you can not get lazy in your shifting .

the simple fact that all racers that want an up grade for there transmissions go to a straight cut sequential box is just that a fact .

i was just talking i a general term when i did state than all gear boxes have straight cut gears .
no not every one but most all do in the car racing world .

my D-sports car with a mild build gsx-r 1000 motor dynoed it 163 HP and 92 TORKS .
my F1000 car never put on a dyno but the guess is much more than that .

a 2009 XR1200 HD torque is 73 FT LBS . WITH 90 HP got the spec on line
a 2009 busa 99.6 FTLBS torks and 162 HP got thw specs in on line .

but this being a car forum and not a motorcycle forum the gear boxes are not the same and not in any way what was asked about .
so the person that did the posting wanted to know about cars not bikes .
so some are thinking about motorcycles and taking a comment stated and thought it would be a good idea to at them into a mix with all the cars too .

now getting back to talking about cars only and leaving other forms of transportion out .

I give up. I'm tired of wading through your brutalization of the English language just to point out what's obvious to everyone else.

The points I've made are correct. Helical-cut gears are stronger, but they produce thrust loads on the transmission shafts which causes problems in racing applications. Helical-cut gears are used in many street sequential transmissions and helical-cut gears do NOT in any way preclude the ability to shift without a clutch.

I'm confident that my points have been made and that a neutral third party can easily see which of us understands the engineering principles in play.