bigoilburner20
Full Access Member
ok so in a pinch do it like that but use the clutch in a light duty ok got it thanks
Is a SMF bad for transmission?
- Thread starter vegas39
- Start date
I'v said it before, and I'll say it again.
As long as there is no grinding going on there is no increase in wear or problems with the transmission! Bottom line no grind no problemo...grind and consider it toast..
If you are not familiar with the clutchless shift of light duty or any transmission I don't recommend it at all. I've done this for years and years and years with many transmissions, from old cars to newer ones and trucks too.
Ya I've ground a couple now and then but bottom line takes practice and willingness to blow up a trans..
Float em n Go guys...
JM2CW
Al
As long as there is no grinding going on there is no increase in wear or problems with the transmission! Bottom line no grind no problemo...grind and consider it toast..
If you are not familiar with the clutchless shift of light duty or any transmission I don't recommend it at all. I've done this for years and years and years with many transmissions, from old cars to newer ones and trucks too.
Ya I've ground a couple now and then but bottom line takes practice and willingness to blow up a trans..
Float em n Go guys...
JM2CW
Al
Someone who I trust, and who knows the ZF S5-42 inside and out (has easily put over a million miles on ZF-backed IDI trucks, and has rebuilt more than one of them), has made it very clear to me that it is not a good idea. Even if you're not grinding gears, you're still putting considerable wear on the syncros (which ar enot the strongest in the world), and are shortening the life of the syncros considerably...and those syncros aren't cheap. I can float a ZF or a T-19 smoothly, but I won't do it except in an emergency...IMHO better safe than sorry.
If you drove these pickups with the zf or the 4 speeds just like a big non-synchronized trucks, it would actually cause less wear on the zf. By that I mean;
In a big truck, when upshifting, you push in on the clutch and pull the lever out of gear, and then put light pressure on the lever till it goes into the next gear by itself. Or you can double clutch it. Either way, if you do this with a zf, it will be less wear on the tranny, since you are using the synchronizers LESS. If you drive the zf by just pulling the lever out and forcing it into the next gear like you normally would(you can't do this on a big truck) you are causing more wear on the synchronizers. It's designed for this, but it does cause them to work harder.
In a big truck when downshifting, you push in on the clutch and pull the lever out, let the clutch out, goose the throttle to bring the revs up, and then push on the clutch while putting light pressure on the lever till it goes into the lower gear. If you double clutched the zf and goosed the throttle when downshifting,, it would cause a lot less wear on the synchronizers.
In other words, if you drove the zf like it didn't have synchronizers, they would last a lot longer.
In a big truck, when upshifting, you push in on the clutch and pull the lever out of gear, and then put light pressure on the lever till it goes into the next gear by itself. Or you can double clutch it. Either way, if you do this with a zf, it will be less wear on the tranny, since you are using the synchronizers LESS. If you drive the zf by just pulling the lever out and forcing it into the next gear like you normally would(you can't do this on a big truck) you are causing more wear on the synchronizers. It's designed for this, but it does cause them to work harder.
In a big truck when downshifting, you push in on the clutch and pull the lever out, let the clutch out, goose the throttle to bring the revs up, and then push on the clutch while putting light pressure on the lever till it goes into the lower gear. If you double clutched the zf and goosed the throttle when downshifting,, it would cause a lot less wear on the synchronizers.
In other words, if you drove the zf like it didn't have synchronizers, they would last a lot longer.
vegas39
Full Access Member
I read an old DMF, SMF thread here this morning between RLDSL and a few others and although not crazy about the results I'll get from a SMF, I do feel better about changing over to it.
I was not aware that the DMF was such a trouble item . I do like to occasionally tow a heavy load but on top of that, I tend to be very heavy footed at times and with this turbo and pump turned up hot, I don't think a new DMF would last too long!
I was not aware that the DMF was such a trouble item . I do like to occasionally tow a heavy load but on top of that, I tend to be very heavy footed at times and with this turbo and pump turned up hot, I don't think a new DMF would last too long!
jaluhn83
Full Access Member
The Lucky mod fuses the two halves of a dual-mass flywheel together and makes it into a single-mass flywheel. So, if having an SMF really will ruin a transmission, a Lucky'ed DMF would have the same problem.
I haven't disassembled my ZF, but I've been running a LuK SMF for about 50K miles and haven't had a single problem. That doesn't mean that a problem won't crop up down the road, but that's been my experience to date
I would strongly advise against the lucky mod - if anything is going to cause problems this is it. The stock DMF uses a unsprung clutch disc (cause springs are in the flywheel) - eliminate the flywheel springs and you now have no shock adsorbion / decoupling between the motor & trans. That's far far worse than a SMF.
Got 50+k miles on a Luk SMF setup with no evident problems or issues. Had a old worn s42 trans for almost all of that with no issues & no real noise and now I have a almost new reman s47 trans with no rollover noise issues either. I had an s42 with a DMF for a bit in another truck and both the trannies I've had with the SMF sounded and shifted exactly the same as the DMF.
firehawk
Full Access Member
SMF does not cause damage or wear to the transmission. The dual is used for noise reduction. Some cars came with DMF or SMF for the same motor, but different applications. Heck, on one of my street cars, I have a single with a solid clutch disc, and it had no transmission wear when I opened it up for inspection after nearly 100k miles on that setup.
SparkandFire
We're drinking beer
Many of the parts in the ZF transmission are "interference fit" meaning they rely on a very tight friction fit. This interference fit is intentional as the case on the ZF is aluminum whereas the gears and shafts are steel, and they both expand and contract at different rates. The very tight tolerance when cold allows the gears to remain in tolerance when the transmission heats up and expands.
This being said, I would imagine that transmissions that are ran hotter will tend to have have looser mesh fit on the gears. The farther a helical gear gets from the pinion the less surface area the load is able to be distributed on. Also you have to consider that the farther away from centerline of the gear you get, the more leverage exerts pressure on the gear tooth. Add in the strong combustion pulses from the engine, and you've got all the makings for fretting and razor-edging on the gears.
This all leads me to think that the SMF is probably FINE for 95% of us who use our trucks between 50% and 75% of their designed working envelope. For the 5% of us who haul extremely loaded (%100 of the rating of the drivetrain components) it makes sense that the transmission will heat up and have looser tolerances, and as such more gear wear.
I have a DMF that is on it's way out. Most likely a SMF will replace it. If I get another 100k miles out of the ZF in my truck, that will mean that I will have put 350k miles on it. In my humble opinion a transmission rebuild at 350k miles is more than acceptable.
This being said, I would imagine that transmissions that are ran hotter will tend to have have looser mesh fit on the gears. The farther a helical gear gets from the pinion the less surface area the load is able to be distributed on. Also you have to consider that the farther away from centerline of the gear you get, the more leverage exerts pressure on the gear tooth. Add in the strong combustion pulses from the engine, and you've got all the makings for fretting and razor-edging on the gears.
This all leads me to think that the SMF is probably FINE for 95% of us who use our trucks between 50% and 75% of their designed working envelope. For the 5% of us who haul extremely loaded (%100 of the rating of the drivetrain components) it makes sense that the transmission will heat up and have looser tolerances, and as such more gear wear.
I have a DMF that is on it's way out. Most likely a SMF will replace it. If I get another 100k miles out of the ZF in my truck, that will mean that I will have put 350k miles on it. In my humble opinion a transmission rebuild at 350k miles is more than acceptable.
freebird01
Post Turtle!
towcat had posted pics awhile back of a high mileage high use trans with a SMF out of one of his roll backs i believe....TOWCAT!!!
i've been staying out of this fray due to too many "navel contemplaters".
On the trans shop side of the business, I've been seeing ZF's in service running single mass flywheels up to 10 years now. two experiences do stand out.
one. if there was no engine/drivetrain vibration issue before the SMF install, and one is present after the install, you have a imbalanced SMF or improperly drilled SMF. either way, the trans and clutch must come back out to replace the flywheel. You guessed it, me being the shop, won't be eating the labor. You will.
two. After 7-10 years for service, depending on how much low speed driving you do, the input shaft gear and the countershaft meshing with the input shaft is worn to a knife-point at the end of the gear. I have pictures. Don't know which computer it is stored in though. will take more on the next trans job. the rollover noise you hear is the brinelling effect on the gears slowly wearing away the gear faces. you should see the look of a customer's face when they get hit with the additional parts cost bill.
I still run DMF's in my trucks. I don't discourage others from having SMF's put in but will I recommend it? nope.
it's your truck, you do what you damn well feel like doing to it as long as you pay the bill when it comes due.
yup. it's that simple.
On the trans shop side of the business, I've been seeing ZF's in service running single mass flywheels up to 10 years now. two experiences do stand out.
one. if there was no engine/drivetrain vibration issue before the SMF install, and one is present after the install, you have a imbalanced SMF or improperly drilled SMF. either way, the trans and clutch must come back out to replace the flywheel. You guessed it, me being the shop, won't be eating the labor. You will.
two. After 7-10 years for service, depending on how much low speed driving you do, the input shaft gear and the countershaft meshing with the input shaft is worn to a knife-point at the end of the gear. I have pictures. Don't know which computer it is stored in though. will take more on the next trans job. the rollover noise you hear is the brinelling effect on the gears slowly wearing away the gear faces. you should see the look of a customer's face when they get hit with the additional parts cost bill.
I still run DMF's in my trucks. I don't discourage others from having SMF's put in but will I recommend it? nope.
it's your truck, you do what you damn well feel like doing to it as long as you pay the bill when it comes due.
yup. it's that simple.
that was a customer's truck with the blown up SMF disc. not mime.
one more thing. F450 towtrucks are hauling 15-19k/lbs between two axles. that is way more than most of you will ever see in your trucks.
NO_SPRK
User & Abuser
just because you can doesnt mean you should 
if you're not hitting any of the big "O's", you're not making good money.just because you can doesnt mean you should
NO_SPRK
User & Abuser
if you're not hitting any of the big "O's", you're not making good money.
my bad, i was a page back and didnt hit the quote button. i was replying about shifting a synchro trans without a clutch
oh ok.
i can post a pic of the syncro I have on my desk for others to see what they shouldn't do that on a regular basis.
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