Engine/Transmission (1998.5 - 2002) Issue 38 "Clutch Life"

[RJOL]

In issue 38, I read, with interest, the article by Andy Pyfer (South Bend Clutch) on pg. 140. Two things really stuck out.



First: He recommends starting out in first gear, whether or not your towing a load (para 3 pg. 140). I've got a 5 speed with a 4:10 rear end. I've usually start out in 2nd gear, unless I'm towing, or on a steep hill. Starting out in 1st, with a 4:10, is like starting out in "granny gear. " Your up to full revs and only going about 5 MPH.



Second: He recommends not down shifting (para 9 pg. 140). I don't downshift at high speed, or downshift to a gear that will rev the engine way up, but I do downshift to aid in slowing the Ram down for turns and some stops.



This was an interesting article and causes one to ponder their driving habits. I wonder if anyone else has other ideas about this article, or the two specific areas I mentioned above. I'd be willing to bet that there are many of us doing these two things on a daily bases...

 

[NVR FNSH]

I'll have an idea when I get issue #38... .



Brian

 

[PSL53]

I'm not trying to start trouble ( I've heard some haven't gotten it yet), but TDR #38 is a great issue with a number of excellent articles.

out

Peter

 

[Midnite]

Originally posted by RJOL

Second: He recommends not down shifting (para 9 pg. 140). I don't downshift at high speed, or downshift to a gear that will rev the engine way up, but I do downshift to aid in slowing the Ram down for turns and some stops.

I don't understand that recommendation at all. Unfortunately I *still* don't have issue 38 yet, so I don't know what context the above was written in. However, I routinely downshift in every manual I've driven or have ever owned, and it never caused any problems whatsoever.



I should point out though, that when I downshift I tap the throttle to bring the RPMs up to about where they'll be after the clutch engages. Not doing that would of course cause much more cluch wear.



Mike

 

[PSL53]

I down shift also, no sense in having a manual and not downshifting. The article says brakes are a lot cheaper than clutches. remember the article is for extending clutch life and i'm sure that downshifting won't extend the life, but hay, not driving the truck at all will really prolong clutch life.

out

Peter

 

[Gary - K7GLD]

Everyone's entitled to their own opinion - and everyone has one...



BUT, *I* personally find it pretty pointless to use 1st gear for starts on my 6-speed - I don't slip the clutch excessively by any means, normally simply let the truck idle away from a stop in 2nd - and I personally feel any SLIGHT additional wear from dong so is offset by ELIMINATING one shift completely...

 

[JTroiano]

I read the article and it is all true. I will still down shift, but some people say that will not cause it to wear. Think about that. It slips when starting it also slips when down shifting, what is wear? Two surfaces rubbing together? You maybe have not had any problems down shifting but I bet if you never did it your clutch would last a lot longer.

Jon T

 

[BigBadDodge]

RJOL: sounds like we have the same driving habits I too start in second, and down shift. don't know how that is going to work with the Mitchells pulling clutch though



BBD

 

[Midnite]

Originally posted by JTroiano

... but some people say that will not cause it to wear. Think about that. It slips when starting it also slips when down shifting, what is wear? Two surfaces rubbing together? You maybe have not had any problems down shifting but I bet if you never did it your clutch would last a lot longer.

Jon T

JTroiano, sure--if you downshift and just dump the clutch, of course the clutch will wear much more! That's kind of a no-brainer. The "two surfaces rubbing together" will not need to rub if you bring the RPMs up to the appropriate speed with throttle before you let out the clutch in the lower gear. To illustrate this, here's the way I do it:



1. clutch in

2. shift

3. throttle

4. clutch out



Clutchless shifting is almost the same thing (at least in synchronized transmissions. I've never driven a big rig, so I don't know if that's any different). No grinding if you get the RPMs right.



Mike

 

[JTroiano]

Mike I agree that it won't wear as much as starting, thats why I'm going to keep down shifting. Your example is close but you need to let the clutch out before you rev. the engine to match gear speed. When you have the clutch pressed in and give it the go pedal you really aren't getting the gears up to speed because they aren't connected to the engine. Thats why they call it double clutching. It may speed them up a little because of the slight friction of the throw out bearing and the pilot bearing. I think the article is just the extremes and it all make sense but it is not practical for everybody. One example is starting out in first with a truck that has 4:10's and stock tires. It would probably be good for me because of the tires and gearing I have.

Jon T

 

[Pit Bull]

I think what Peter wrote is all true. Plus it is very hard to write something that is better demonstrated. The question is will we do it??? I think the objective of the article was to get us to think about what your doing when you are shifting your truck. I start out in 1st on a steep hill even empty. I start out in 2nd on level ground or down hill when empty. I down shift but like some of you have already mentioned I bring the RPM's up to match the gear. Talked with some other TDR members about the clutches in our 6 speed trucks and based on that discussion and the way I drive my truck (if I don't bomb it) then my clutch will live a long and happy life. I bet there are some members out there not following Peters advise at all, so they can wear out the stock clutch and tell their wife they have to buy a new one from Peter You know who you are :-laf

 

[Gary - K7GLD]

I think most of us are missing the basic intent and point of that article - whach was NOT aimed at the clutch surface - but at the SHOCK ABSORBING springs near the hub of the ckitch disk - which the author pointed out, COULD be overstressed by the torque of the Cummins when shifted or even operated low in the RPM range due to torque spikes placed upon those springs.



Note that the supplied illustrations were about SPRINGS and related hardware when discussing starting in low gear and downshifting - not clutch surfaces!



Naturally, the stress upon those springs MIGHT be greater, depending of exact method of clutch engagement, IF a user starts out in a higher than recommended gear, and essentially "pops" the clutch - forcing those springs to compress more/longer that they are designed for... That also applies to other clutch hardware when downshifting, which forces some critical parts to operate in REVERSE of their design direction at greater force than intended...



It's NOT so much about clutch surfaces, as it is about springs and related hardware!

 

[esommer2500]

I normally shift without the clutch going up between 3 and 4, and then between 4 and 5. Downshift without the clutch between 5 and 4, and bump 4th out without the clutch while braking. I normally start in 2nd on flat or downhill, and really only use 1st when towing or starting up a steep hill. I found the article interesting, but don't think that I will take the advise given. I would like to think that my personal driving habits are pretty conservative on clutch wear of both clutch surface as well as the springs. Only time will tell.



Eric

 

[rkressg]

I always downshift, it is just a habit. I learned to always use engine braking to slow down and use the service brakes as little as possible. Yes, brake linings cost much less and are easier to install than a clutch assembly, but if you extensively use the service brakes and no engine braking, I guarantee you one time you will push on the peddle one day and she isn’t going to stop.



I got 60,000 miles out of the stock clutch on my truck. When I changed it, the disk was barely worn. It thought it was slipping because of my modifications, but that was only part of it. The main reason for slipping was the rear main seal (on the engine) let go and it covered my clutch disk with Rotella T . If it was not for an oil leak and if I drove sensibly, I could have easily driven that disk for 60,000 more miles.



The stop pins in the flex plate did show some ware from the springs bottoming out, but they showed a lot more wear on the forward direction than that of the reverse hits (this is normal ware from starting under load). There was significantly more wear on fingers of the pressure plate and the throw-out bearing surface from a hydraulic slave constantly applying some pressure which I would be more worried about then wearing those pins out.



I truly agree with Gary - KJ6Q on the subject of wear on the components of the flex plate, but it takes some serious abuse to damage those pins. The only vehicles that I have seen with those stop pins worn to a dangerous (failure) point were in vehicles that were clearly abused, i. e. : dropping the clutch, overloaded, or extensive lugging.



Just burp the throttle and try to line up the RPM's with the next gear when down shifting and try not to dump your foot off the clutch, as shocking the driveline tends to break stuff. If you know how to drive and do it sensibly, chances are you will not put enough miles on the driveline to wear out the clutch. Just out of curiosity, how many stock trucks get 150,000+ miles out of the stock assembly and how many people will actually put 150,000 miles on these trucks? Personally, I know I will, but not everyone drives 50,000 miles a year or keeps a vehicle that long.

 

[Mschevey]

I agree that I want my service brakes as cool as possible. Down shifting to use engine braking is the only way to know that the service brakes will be ready in an emergancy.



I think the most wear to the clutch parts is from people who lug the engine at very low RPM's. They see the big rigs do it and have heard the saying "its a diesel, let it lug that is what the low end torque is for". Unfortunetly whis saying does not apply to the newer and smaller diesels.



Mike

 

[Pit Bull]

What RPM do you guys consider lugging? I know that depends on what your hauling or towing. But lets say an empty truck. I never get below 1200 RPM's and the engine does not sound like it is lugging. What is your RPM with an empty truck?

 

[DEZLPWR]

I think below 1500 is lugging.....

 

[Pit Bull]

I thought below 1100 or 1200 was lugging since you had 90% of your torque at around 1200 RPM's

 

[rkressg]

I would consider lugging when I am operating the engine below the torque band. You can just develop a feel for when the motor is lugging. When in doubt, downshift. The little extra cost for using more fuel is cheaper than broken components.

 

[DEZLPWR]

This article also says that exhaust brakes are tough on clutches as well..... That was the first time that I have heard that. I love my Pacbrake!Oo. Oo.