SR20DET Transmission synchro life, double-clutching necessary?

[chickentendah]

Okay, so i finally started to master the "heel-n-toe" downshift technique....and boy am i excited .......i can't resist using it at every 4th-gearish corner i get

Anyways, how long are sr20det transmission synchros known to last? I single-clutch downshift a lot in daily driving street conditions i.e. cruising rpms just in the 2k zone.

And, how much does a sr20det transmission rebuild usually cost in parts + labor?

[RMiller]

They last a long time. I would never consider double-clutching for the sake of prolonging the life of my synchros. My two transmissions both worked perfect at 70k and 153k miles. You'll probably have other items wear out before you need a new trans anyway.

[s13sr20chris]

They last a long time. I would never consider double-clutching for the sake of prolonging the life of my synchros. My two transmissions both worked perfect at 70k and 153k miles. You'll probably have other items wear out before you need a new trans anyway.

this is true assuming you are easy on it. if you are rough it will shorten the life expectancy. for that matter downshifting is rough on the trans anyway. its fun to do from time to time but i would not get too carried away.

[89240]

My friend had an ACT stage 2 clutch in his SR and he drove the hell out of it for at least 4 months redlining and kicking the clutch the whole time everyday and it still to this day does not have one problem.....SR engines are just tanks!!

[RMiller]

Well the transmission is the same on the KA and the SR, and I think there's something to be said about the quality and durability of all Nissan parts. Edit: Except the bell housing, and the dust collar, those are different but whatever.

[Def]

Cheaper to swap the bellhousing to a KA transmission than rebuild your SR transmission. You should be fine without double clutching - even though it's a good thing to master.

Start working on heel and toeing - that's where it gets really hard to be smooth 100% of the time.

[chickentendah]

Thanks for the replies guys. Another question for you hardcore gearheads while we're on topic:

Does a rev-matched-single-clutch-downshift wear the synchros just as much as a normal rev-matched upshift?

[ibzbro]

this is the one and only time you need to double clutch. YOU DRIVE A CAR THAT HAS A DOGGEAR transmission. so basicly if you drive a 1960 jaguar you need to double clutch, other then that you don't need to, end of story. i don't care what you hear on the fast and the furious. you do not need to worry about wearing out your synchros, you will never drive your car that hard for that long. i would worry more about your transmission in genearl.

Thanks for the replies guys. Another question for you hardcore gearheads while we're on topic:

Does a rev-matched-single-clutch-downshift wear the synchros just as much as a normal rev-matched upshift?

[EazyBreazy]

what is double clutching...im serious. ive been involved with or participating in racing since i was 12 and never in that 11 years have i seen someone press the clutch twice..seems to me it would take twice as long to shift up and down. i dunno maybe some one can explain this to me because im seriously lost

[ibzbro]

asumming you are going from 1st to 2nd.push clutch in take out of gearlet out clutchraise rpmrev matchpush clutch input it in to secondlet clutch out

[chickentendah]

this is the one and only time you need to double clutch. YOU DRIVE A CAR THAT HAS A DOGGEAR transmission. so basicly if you drive a 1960 jaguar you need to double clutch, other then that you don't need to, end of story. i don't care what you hear on the fast and the furious. you do not need to worry about wearing out your synchros, you will never drive your car that hard for that long. i would worry more about your transmission in genearl.

that doesn't answer my question. and i already knew that double clutching isn't necessary for modern trannys. i took the F&F comment as an offense btw. i was asking a legitimate technical question to those who are more knowledgeable then me on the internals of a modern transmission. thanks for the reply, but no thanks for the attitude.

[EazyBreazy]

asumming you are going from 1st to 2nd.push clutch in take out of gearlet out clutchraise rpmrev matchpush clutch input it in to secondlet clutch out

if im ever in any performance situation raising the rpm at the end of a gear is not a very good idea..so you say at say 6300(redline for the ka) you clutch the transmission, disengage the shifter, release the clutch and then raise the rpm...to what extent do you raise the rpm. rev-limiter usually hits about 6500 or is it that you let the rev's drop so far that you have to blip the gas on the second clutching so that the engine and transmission match.....im still completely befuddled by this whole concept...it makes as much sense to me as a football bat. i dont mean to flame or anything like that i just wanna understand why anyone would ever want to clutch the transmission twice.

[chickentendah]

Btw, this is NOT a driving technique thread; I'm NOT asking you folks of when to double-clutch or not in a given driving situation.

I'm asking about syncronizer wear and tear....the knitty gritty mechanical details.....simply out of curiosity. If this offends you, please don't even bother replying with smartass comments. I'll be doing some extra reading elsewhere. Thanks for those who actually took the time to actually read what I was asking.

[ibzbro]

k. double clutching is of course going to be easier on the syncros, but it is not going to be noticeable in the life of the transmission. i don't know what you want to hear. that single clutching the transmission is bad???

[ItzGenX]

if im ever in any performance situation raising the rpm at the end of a gear is not a very good idea..so you say at say 6300(redline for the ka) you clutch the transmission, disengage the shifter, release the clutch and then raise the rpm...to what extent do you raise the rpm. rev-limiter usually hits about 6500 or is it that you let the rev's drop so far that you have to blip the gas on the second clutching so that the engine and transmission match.....im still completely befuddled by this whole concept...it makes as much sense to me as a football bat. i dont mean to flame or anything like that i just wanna understand why anyone would ever want to clutch the transmission twice.

Double clutching is actually for straight line down shifting when at a lower RPM. Try cruising at 60mph in 5th gear, and you want to throw it into third. Rather then throwing it into 3rd the normal way and letting the car nose dive then go, you can double clutch by pressing in the clutch and throwing the gear shifter into neutral, then depress the clutch. Immediately after you depress the clutch in neutral, give a quick blip to the throttle, push in the clutch, throw it in third, let go of the clutch, and nail the gas. Try it and you will understand.

[EazyBreazy]

couldnt you just rev match and not press the clutch twice just seems like a waste of time

[nismostate]

that's what i do. i don't ever double clutch. i either rev match when i down shift or heal and toe. that's all you need to do if you want to save the life of your transmission. double clutching is mainly used for trannies with no synchros.

[s13sr20chris]

chikentendah-i have no facts to back this up but i do think downshifting is harder on synchros than upshifting. this may just be something i have been told so long that i believed it. i practiced downshifting in my old accord for over a year and i will say that it got tougher to put into gear and ground a little more often. was that connected? i cant be sure. i do not downshift very often now unless i am trying to drive fast.

now, sorry to perpetuate the jacking of your thread. in certain race cars i have driven with non sychronized hewland gearboxes double clutching was absolutely neccesary on the downshift. turn one on vir's south course is a 2nd gear turn that an f2000 car comes into at the top of fourth. that means heel toe braking and downshifting(with a double clutch at every gear change) to make it into the turn properly. however, being non synchronized hewlands we could just bump out of gear with no clutch, slide to neutral, revmatch, THEN clutch, snick it into gear, and release. so there you have it. how to double clutch without the first clutch. funny when you do it right its still not a standard single clutch maneouver.

[ItzGenX]

Double clutch downshift is more for letting the transmission see how fast the engine is spinning vs the tires spinning. That is the whole point for depressing the clutch in neutral. If the transmission see's both sides, it will spin the syncro up to that speed and almost no syncro wear takes place during the downshift since the gears being mated are already going the same speed (well almost). This requires less syncro *braking/accel* to even wear it out.