High gear clutch slippage

[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!

[Jeff Lee]

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.

[Mark Madison]

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 .

[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