High gear clutch slippage

[69Cobra]

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.

[Stewart Way]

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.

[Jeff Lee]

I'm pretty sure the question has been answered.

[Stewart Way]

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.

[goinbroke2]

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.

[goinbroke2]

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

[Jeff Lee]

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!

[Stewart Way]

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.

[eddie c]

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

[Jeff Lee]

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.