High gear clutch slippage
 

Coming back from a test session a couple of years ago, a very experienced person commented that he couldnt understand why a 4 speed car would go thru the first 3 gears without clutch slippage and then slip in 4th. I said it was because the car makes more power in 4th than in the first 3 gears. He allowed as how that was the stupidest thing he had heard, the engine doesn't know what gear its.
My feeling is like on a dyno. The slower you bring the engine up at WOT the more power it makes. An engine at 1000rpm/sec test rate will not have as high a HP number as an engine tested at 600 or 300 rpm/sec. I have never seen it done but I would think the highest HP would ne seen at a steady state test. So in 4th gear the engine sees its slowest accel rate due to various resistances and therefore makes the most power.
True or false?
I bring this up because he make the same statement yesterday and I just let it go.

Re: High gear clutch slippage
 

I don't know about the dyno thing but in my opinion when you go to high gear the clutch has more of a load on it than being in low gear. The less gear reduction the more stress on the clutch. For example if you have a 3.25 first gear ratio and a 1.94 second gear and you dump the clutch in first gear the clutch is almost out of the equation as far as load or slippage. If you dump the clutch in second gear you will slip the clutch because its seeing more load. At least that's my view on it.

Re: High gear clutch slippage
 

X2 , when I was racing the firebird last year the same thing happened to me. Not enough counter weight, or not enough base pressure.

Re: High gear clutch slippage
 

Nothing to do with engine hp.
It's resistance.
In lower gears there is gear multiplecation and less resistance on the input shaft of the tranny.

Same reason an old 6cyl pick up will go up a hill in 3rd without slippage but in 4th it breaks free. The engine isn't making anymore power, it's just reaching the coefficient of friction. Steep enough hill and it will slip in third too.

It's been well documented that slower rpm/second will increase hp on a dyno because of less torque loss to rotational forces. In other words, it's not eating so much torque to actually spin up the rotating assembly. (big blocks more effected than small blocks)
And while I agree with you, I don't think this is the case here for slippage. Not saying it can't be, I just don't think the clutch is adjusted to just the fine edge, where a couple lb'ft gained by the slower rpm increase would effect it. The only increase in torque would be from the difference of rotational speeds of 3rd and 4th.

I would say the clutch needs to be tuned to stop the slippage. (actually it does regardless, but it's because the resistance applied in 4th is more than the clutch can accomodate)

Where are the clutch guru's? They will be able to explain must more concise than I.

Re: High gear clutch slippage
 

First, I know you can adjust the clutch to stop the slippage in 4th. That wasn't the question, why it slips was. Maybe you guys are right. If you are using the clutch to shift or have a stocker type cluchless, where the engine is unloaded for an instant the load drops out the bottom (as would HP)so my theory may be flawed unless the slippage happens well after the gear change when the engine is climbing. If it happens at the change, it sounds like it could be the difference in resistance due to ratio changes, rolling resistance and aero effects.

But if you make a 1-2 gear change and the clutch has enough friction to hold it why doesn't it have enough friction to hold it on the 3-4 change. Same power applied to the clutch disc and same clamping force on the pressure plate. Goes back to my original theory. If you put more resistance to the engine being able to RPM it will produce more power and overcome the CofF of the clutch. Don't see how the same amount of power will overcome the Cof F in 3-4 shift and not the 1-2 or 2-3.

Here is my thoughts. You have a clutch set that will slip at 600hp. On your 1-2 change because the engine is allowed to climb at whatever rate it produces 550hp max. Then at the 2-3 change it climbs slower and makes 580hp. On the 3-4 change due to all the reasons we have stated the rate is slower yet and it goes above 600. Now you have slippage. Those numbers are likely larger than the differences would be in real life but you see my theory.

Again, my theory is only that and could be swiss cheese.

Re: High gear clutch slippage
 

This falls back on the high school theory of "work".....if you put a load on a rope with a block and tackle pulley arrangement (say first gear) and then you(the engine) pull on the rope it is fairly easy to move the load ( the vehicle) .....but if you eliminate all the pulleys (high gear) it removes the mechanical advantage you had putting the full load of what you are trying to move on you (the engine) so it has to "work harder"....

An engine won't produce it's full power until it needs to, so even at full throttle maximum torque won't be achieved until the engine sees a full load where it is required to do the most "work"....most dyno rooms used by the OEM's in the old days where called "load cells" because that is the only way to get a true measure of an engines power....

So to answer your question it is because the engine has to work harder in 4th gear than it does in 1st,2nd, or 3rd is the reason for the clutch slippage....



D L Rambo....

Re: High gear clutch slippage
 

DL
Thats kind of what I was saying. It made more power due to loading but then I did a google of 4th gear clutch slippage and found a writeup under worldphaco.net. At first I thought this kind of shot my theory that the engine makes more power(works harder) in 4th or at least that that is the cause of the slippage. But this writeup uses the theory of CEP (constant engine power) which is not real world. The writer talks about when you accelerate but doing it with constant power. Without additional power how do you accelerate? Not sure his calculations are valid in the real world.

Re: High gear clutch slippage
 

You are assuming the same RPM drop on each gear change. It is not. Look at your friends transmission gear ratio's. Determine the percentage of RPM drop in every gear. Then you will be able to see why there is such a difference going into 4th as opposed to going to 2nd.

Re: High gear clutch slippage
 

Correct. The gear ratio percentage drop is going to have a lot to do with this as well as rpm's. For example if you have a 1.50 3rd vs a 1.20 3rd gear. The 1.50 3rd gear is going to put a lot more stress on the clutch when going into high gear vs the 1.20 3rd gear. Therefor you are going to have to put extreme amounts of base and/or counterweights to keep from driving through the clutch with the 1.50 3rd and this is going to have you chasing your tail on the starting line to find a balance for the starting line and high gear. Hope this helps.

Re: High gear clutch slippage
 

Lets back up. First. we were not testing a clutch car, we were just talking in the toter on the way back from running an automatic. The man who asked the ? has run gassers, SS, NHRA and IHRA Pro Stock over a 50 year span. We know how to adjust a clutch (sort of, we think). If it slips going into high gear we know what to do to stop it. The question was what causes it. Is it more HP, more torque, more resistance at the higher MPH or a combination of them?
With the up hill example, pulling it into high gear drops the rpm putting more torque and likely less hp on the input shaft.
If you look at 3rd vs 4th ratios a closer ratio will get you a higher 4th gear rpm at the change for more hp but less torque at the shift. But the closer ratio gets you a higher MPH at the gear change for more of the resistances. The 1.50 vs 1.20 3rd gear ratio example talks about the added "stress" on the 1.50 vs 1.20 ratio. Where does this come from. The engine. It seems to me that since the clutch is between the engine and trans that any change in ratios causing more "stress" has to happen by the engine producing more power since thats the only thing making power.
DL Rambos pulley example would seem to show that as the resistance increases for what ever reason the power transmitted increases. Get rid of the mechanical advantage of a pulley or gear reduction, it takes more power.
All good thoughts. Thanks and keep them coming.

Re: High gear clutch slippage
 

I'm pretty sure the question has been answered.

Re: High gear clutch slippage
 

Jeff
Yes, 2 or 3 times but which one is right, or are the all right?. Being a Mech Engr I like a little proof and not just theory. Somewhere there has to be a test or paper or something to add fact to this. I am going to Kaase Racing next week for lunch. They have or had a dyno that ran thru a clutch and lenco. I'm going to check to see if when they simulated a run if they varied the rate of accel in each gear as it happens on the track and if they did what happened to the HP numbers.
If you think of it, next time you talk to you clutch buddy at Advanced (I think) would you check and see what he thinks. He likely has more experience and knowledge than the rest of us combined.
Right now I lean toward a combination of all the answers given so far and not just one.
If you use your example of the 3 to 4 ratio, on a tranny with 2.47-1.77-1.33-1.00 the 2-3 and 3-4 drop is the same, do you think the slip would then happen in 3 as well as 4? No proof needed, just your thoughts. You do have more experience at this than I do for sure.

Re: High gear clutch slippage
 

Stewart, in my example of driving an old truck up a hill;
In 3rd I could floor it all the way up the hill from about 1800 to about 4000 with no slippage.
In 4th I would slowly roll on the throttle and it would pull to about 2500 or so and then slip. This was repeatable as I'd back off and get lock up then add throttle until it slipped.

I'll stick with increased resistance since we're not talking blowing through the clutch on a gear change but after full lock up, then getting slippage.

DL Rambo nailed it.

Re: High gear clutch slippage
 

This reminds me of the 67 falcon I had. 170 6cyl 3 on the tree. Was limited to about 60mph because the clutch would slip after that. At the end I had to back up the driveway cause reverse was geared lower than first! LOL! Great times for a 16 year old!
Put on a 200 head and carb from 300 truck, thrush muffler...whooee, I was stylin'! LOL!


Oops, sorry for the deflection down memory lane, hehehe

Re: High gear clutch slippage
 

Had the same experience in a 64 Rambler American with 3 on the tree. Only slipped in 3rd. Would bark 2nd but had to be gentle in 3rd. Not sure if it was turning or dragging the tire on the 1-2 change though.
I'll be in your neck of the woods in July-August. Meductic, NB. What part of NS are you in. Got a cousin in Wolfville, NS.
Back to the topic. Looks like were saying that without the mechanical advantage of the gear reduction, that in high gear the engine makes more power and overpowers the clutch? Will post what, if anything, I learn on my visit to Kasses shop next week.

Re: High gear clutch slippage
 

Sorry that I joined this discussion late in the game,but my thought is that
Mr. Rambo's explaination of the block and tackle was an excellent one.
Another example, that I think could be used, is a 10 speed bike,there are much lighter loads in the lower gears and in hi gear or 10th there is considerable load on the engine or in this case your legs.If there was a clutch in that system,I believe you would see slippage in the 9 to 10 shift before seeing it in any other gear. Something that I dont think was mentioned, was how much would the e/t improve
if the clutch didnt slip in the 3 to 4 shift ? A number of years ago, I changed the clutch and pressure plate on a friends 68 Pontiac Firebird stocker that was slipping the clutch in its high gear shift.. Much to our surprise we saw no improvement in e/t with the new
non slipping clutch. ed

Re: High gear clutch slippage
 

Besides the mechanical issue of changing gears due to ratio, the clutch will slip more or less dependent upon the time spent between gears. A racer that uses the clutch to shift, no matter how blindingly fast he may think he is, requires a completely different clutch tune that a racer that does not use a clutch to shift. On top of that, the transmission (clutch or clutch assisted by design) choice affects slippage even if the clutch is not used to shift gears.
All of these issues can be tuned with the proper clutch. That includes not only the basics like base pressure and counterweight, but also lever design and friction materials used. The Sportsman Single 10" I have used in the past and the Sportsman Dual 7" I am going to use in the very near future has heat shields made from specific alloys not found on competitors components. The clutch disks employed on these, while not a trade secrete by design (like the heat shields), are specific to the application by material and density.
Finally, a racer that has had his clutch friction materials "rebuilt" by resurfacing instead of having friction materials replaced with new components will not see the same results by rebuilding vs. replacement parts. The reason is rebuilding by cutting surfaces lessens the thickness of the materials and their ability to absorb heat and as a result the clutches friction materials service life can be severely shortened. The thinner the parts, the quicker they will warp. The quicker they warp, the quicker you reduce the plate loads to unacceptable levels. This causes the racer to run excessive base and / or counterweight in an attempt to overcome the slippage. In the end, this is just a band-aide and performance (and more importantly; consistency) is impacted greatly.
So Stewart, there are many factors to consider. Hope this helps.

Re: High gear clutch slippage
 

So replacement of heat sheilds is normal with a $900.00 clutch rebuild. mark Madison

Re: High gear clutch slippage
 

Had a PM from a regular poster on here and he hit on a point not yet mentioned. Power strikes on the crank. As Jeff pointed out the drop is less on the 3-4 shift than the 2-3 shift. So the initial rpm after the gear change is higher resulting in more power strikes for the same time period and at a higher HP (RPM)level so more force is applied at the 3-4 shift than any other shift.
Jeff
When is the "very near furure"? Don't think I'll be out this year in my car. I went against the trend and made a couple realtors happy. Bought a house on 4 acres with a 3000' shop.
Still own the other house and equiping the shop so not much spending on the Cuda. Putting the old house on the market in a couple weeks. Will take a beating but got a deal on the new one so we don't care. You selling anything out there?

Re: High gear clutch slippage
 

Yes, I`ve had several McLeod Soft Loks rebuilt by both McLeod as well as Tim Hyatt, and each time new heat shields were installed on the flywheels and pressure rings. Usually by the time the clutch needs a rebuild, the heat shields are getting blue hot spots, irregular surfaces, and the outer edges that don`t see disc contact are curling up.I would have to think that any money saved by grinding the old heat shields would be offset by a very rapid re-occurance of warpage. New heat shields are a must.

Re: High gear clutch slippage
 

When Rob rebuilds a clutch for about $900 it's new heat shields & disk. I hear others saying that's too much so they go elsewhere and somebody takes a grinder to the surfaces and sometimes to the disk or possibly a cast off from a fuel team or maybe even a new disk. Ask, don't assume.

Use this common gear spread:
3.19
1.95
1.40
1.00

Shift all gears at 7,000 RPM
1-2 shift = 38.87 % drop = 2,721 drop = 4,280 RPM
2-3 shift = 28.21% drop = 1,975 drop = 5,025 RPM
3-4 shift = 28.57% drop = 2,000 drop = 5,000 RPM

Not sure if that helps...

I had one of my best years ever last year and I'm already ahead of 1st quarter of last year. Since I made the decision to go back in Stock, i've been pushing all parties involved. Just found out the other day the wheels I had made are not right so Monday I'm having another pair made, it will be 2 weeks. Hopefully my new custom bell housing will be done this week. Cam just received last week. Heads are done except final cut to CC spec. Short block just needs rings & bearings to assemble.
My goal is engine dyno within 3 weeks. New floors in car & fix chassis issues within 1 weeks after that. Garrett Monde is building me a new set of headers. I want everything within 90% of track readiness by end of April.
I'm changing all fuel lines, a data logger and a few other things that need to get done. Test / tune summer (aargh!), NHRA event in the fall.

Re: High gear clutch slippage
 

"When Rob rebuilds a clutch for about $900 it's new heat shields & disk. I hear others saying that's too much so they go elsewhere and somebody takes a grinder to the surfaces and sometimes to the disk or possibly a cast off from a fuel team or maybe even a new disk. Ask, don't assume."

Just got my Soft-Lok back from McLeod. They replaced both heat shields, 3 levers and pivot hardware, supplied a new disc, cleaned, repainted, re-certified and set it up for me. New studs in the flywheel and supplied a plastic aliignment tool. It looks like new and the cost was $550.00. Same as a buddy of mine had done a couple months back. I was very suprised at the work and price.

Re: High gear clutch slippage
 

Then why did my dual 7 came back without this being done? I had to complain to Rob to get this done ,After paying the $900.00 to rebuild the clutch . I paid to have it fixed the first time and didn't question the price. I just wanted it fixed. . No song and dance just fix it. Rob did as I asked and replaced the heat sheilds, the second time around. But, there should have not been a second time around.

Any body want to buy a Jerico and Advanced 7 and a clutch program from Mike Sullivan for the Dual 7? E mail me at mark_madison @sbcglobal.net And I will provide all prices and product info.

Mark Madison

Re: High gear clutch slippage
 

You need to ask Rob. There's usually more to the story...
Regarding the price of a McLeod rebuild, the parts are not the same, therefore there is a different price. No different than any other component of your race car! If your happy with your McLeod clutch and service, I would not suggest changing anything. Happy shifting!

Re: High gear clutch slippage
 

LOL...and the rest of the story is...launching a 4-speed car in THIRD gear will ruin the clutch EVERY time! The brand new parts that WERE put in will warp like a krinkle cut fry immediately when you launce in 3rd. If you can't find first the first, second, or even third time to the track, it is time to sell the parts and put an automatic in the car. Sorry it did not work out for you and there are always racers looking for a deal in race transmissions and clutches.

Re: High gear clutch slippage
 

Rob might have you fooled with whatever B.S he spun regarding this issue, I'm Not. The fact is I paid $925.64 for a clutch rebuild and the clutch came back to me with warped heat shields. So warped that when Mike Sullivan disassembled the unit to weight the leavers and check the spring rates to configure a clutch program, he sent the unit back to me and said the clutch needed to go back to Rob to have the heat shields fixed they where not flat! After I complained Rob replaced the flywheel shield and chucked the clutch side in a lathe and cut.it. So much for not grinding these parts flat. If you would like I can run up to my trailer and retrieve the warped heat shield and post pictures for all to see.

In this thread you state that a clutch rebuild from Rob is $900.00 and replacing heat shields is a normal part of a clutch rebuild . The question that has not been answered is why where mine not? I hope Rob made a photo copy of the check for $925.64 because thats the last of my money he will ever see. Now jump back on the phone and see if you two can put a positive spin on this .

Re: High gear clutch slippage
 

That's right I screwed up ,I killed the clutch . sent it to Rob to Fix and he tried to screw me . plain and simple

Re: High gear clutch slippage
 

OLD post, I know, but I had to throw my thoughts out there
- Mechanical advantage
in 1-3 gear the engine/clutch has mech advantage on the output, in 4th there is NO mech advantage, therefore as other have posted the clutch "sees" the MOST load of the run.