How does one adjust the stop correctly?
I would put the car up on jack stands, get it close to where I think it should be and then use an assistant outside the car telling me when the drive wheels start turning (Obviously the car is running) to dial it in. Something like that? Is there an easier way?
msterbeau said:How does one adjust the stop correctly?
I would put the car up on jack stands, get it close to where I think it should be and then use an assistant outside the car telling me when the drive wheels start turning (Obviously the car is running) to dial it in. Something like that? Is there an easier way?
Park on a slight hill in first gear with engine off. Put a block a couple of inches behind the back tire or in front of you are nose down (and a handy assistant as a failsafe if you like).
Install the stop in the car. Push down the clutch pedal. Keep adjusting the stop inward until the car rolls against the block when you push the pedal in. Done.
Most cars have unsynchronized reverse so it's pretty easy to tell the clutch engagement point in most cars by just holding the shifter in a specific spot where reverse is not engaged but the gears are touching. When the clutch starts to engage you'll feel it through the shifter as the moving gear starts to clash against the stationary one.
David S. Wallens said:
Click on either graph to open in a new window.From the top, the data cells show speed on track, throttle pedal position, engine speed, and total time gained/lost. The lower chart is just a zoomed-in version of the top one. “The zoom better shows the resolution of the throttle trace and rpm spike in that shift,” Clay explains.
“Before the first shift on the back straight–third to fourth–both drivers are approximately the same speed,” he explains. “After the first shift, the blue driver is 2 mph faster than the red immediately.”
Clay dives deeper into the data: “In this shift, red comes off throttle at 1:19.766, back on at 1:20.269–almost exactly 0.5 seconds. Blue comes off throttle at 1:19.928, back on at 1:20.269–about 0.3 seconds.”
“Note that clutch pressure would be an interesting data point also,” he continues, “and the blue driver shows the negative effects of shifting too fast: trying to jam all the actions of the sequence in.
“The ‘shift tail’ in the rpm graph shows that the driver overlapped pedals–a big no-no. The clutch pedal was already going down before the throttle pedal was fully released, although you can see in the graph that it was more of an issue of inertia than late throttle release.
“Nevertheless, this is one of the ways that shifting fast can damage the engine, clutch, or driveline–although adjustment of a proper clutch stop does make this much easier to time.
“Over the duration of the full back straight, and with no other factors in these runs, faster shifting and the increased terminal mph achieved has made the blue driver, who came onto the straight slower, a total of 0.3 seconds faster in this straight alone.
“Add the front straight and the shorter middle straight and you just put at least half a second in your pocket through proper equipment adjustment and perfecting technique.”
The most telling thing I see in graphs is the engine rpm traces. It's obvious that the quicker driver made more power thru the shift, evidence of that is in the rpm flare. The engine's rotating assy absorbed energy during the shift which is what caused the flare, then the car was able to transfer that added flare energy to the track without spinning the tires. The result was more power applied to the track over the same time period. Pedal stop adjustment may have had a hand in changing the driver's timing to create the flare, but harnessing that rpm flare without breaking traction is what made him faster.
I actually have clutch pressure data on my car, and also have a way to adjust the rate that the clutch actually engages. The main benefit of being able to adjust clutch engagement rate is the ability to reduce the intensity of energy transfer between the rotating assy and chassis, to a level that doesn't cause the tires to break traction. Most customers are using my ClutchTamer and Hitmaster clutch control devices in a drag racing setting, but some road and rally guys are also using them as more efficient alternatives to the Tilton Flow Control Valve .
Grant
In reply to wspohn :
Nice. Thanks.
Pretty sure my Focus needs some adjusting because there's no way I could shift that fast. Of course it has no clutch feel and I have no skill either, so that compounds the problem. 
Having a taller clutch stop helped daily driveability on my Mk8 GTI too. Not sure if it knocked any time off my autoX runs, but I'm confident it will help at the NCM time trial event next month.
Neither of my clutches slows me down one bit 
This approach is a bandaid on the problem that became pandemic back in the seventies when manufacturers deleted the onerous service task of checking for "free-play" and adjusting the linkage accordingly. Since that time, the $0.65 linkage return spring deletion has left us with the "self-adjusting" hydraulic clutch. You know, the one that one day just starts to slip with no warning, let alone notice that our clutch technique was resulting in excessive clutch wear. Early on the system could be reverted to the manually adjusted type with just the installation of the earlier-model's clutch return spring, but eventually the bean counters discovered they could cheapen other parts in the system and eliminate the adjustability too. When the return spring was eliminated, the disengagement point rose to the top of the pedal stroke and three-quarters of the stroke was wasted over-releasing the clutch pressure-plate, which in the versions employing a diaphragm pressure spring, caused it to be flexed "over-center," giving a distinctive hard-at-first-but-then-easier-the-further-the-pedal-was-depressed experience. The high-reving types with that kind clutch discovered their clutch pedal could stick to the floor, fully depressed, on so-called power shifts, making excess RPM an expensive likelihood. Their response was to screw a short piece of 2 x 4 to the firewall under the clutch pedal, or in the case of the BMW guys, a hockey puck! Genius innovation! Voila! No more clutch overextension. But the pedal was still sitting so high you had to raise your knee to the back of the steering wheel to initiate disengagement, no longer able to rock the left foot off the dead pedal to the clutch pedal and point your toe to perform a shift.
With all the little cost savings and manufacturing simplifications that have come about since the "early" system, the operating elements (master-to-slave volume matching by some manufacturers for the resulting long stroke self-adjusting scenario) have baked in the dumbed-down scenario to the point of making it almost impossible to revert to the manually adjusted system that would normally have been tuned to accomplish this clever work-around. Whew! If you don't believe me, check out the way the becoming-universal concentric slave cylinders operate. And their mandatory constant contact with the fingers of the spinning pressure-plate, assuring early bearing failure, as a bonus. Now it's not only failure prone, but with the slave-cylinder buried in the center of the bell-housing, amazingly expensive to repair/replace. Mustang guys are lucky. Don't want to pay for that new throwout bearing for your late-model Corvette. Racers don't care. they're always disassembling their drivetrains between events anyway, right?
I'm done. Now it's up to you guys still running interesting beasts to pressure the aftermarket to come up with off-the-shelf corrective solutions. A clutch with a nice low pedal height and a long-lived T/O bearing is a beautiful thing to drive, and not live in fear of mechanism failure. You should try it.
Bob Moore
In reply to Cactus :
Can I get a dogbox for 19.95?
In reply to Cactus :
Lessee... Effective Bimmerworld mod, plus free advice: $20
Just did Google search on dog-box transmissions: $4000-25,000, just for tranny's, add thousands more for installation.
Great if you have the money and your rules allow, but... And simpler than the clutch stop? Ha!
Uh, huh. And btw, this is Grassroots Motorsports magazine.
In reply to Cactus :
Lessee... Effective Bimmerworld mod, plus free advice: $20
Just did Google search on dog-box transmissions: $4000-25,000, just for tranny's, add thousands more for installation.
Great if you have the money and your rules allow, but... And simpler than the clutch stop? Ha!
Uh, huh. And btw, this is Grassroots Motorsports magazine.
Great article, good stuff indeed. However clutch travel can be kind of tricky to get right in my experience. My E36 M3 did not have particularly low engagement. It did already have this clutch stop. It drove great, until going to 7k rpm, then the 2-3 shift got difficult, sometimes just would not go. Bottoming out the stop, with no lock nut, helped some but not perfect. Taking the bump stop to the belt sander with significant material removed was enough to fix my 2-3 shift. Why my clutch seems to need more travel at high rpm I have no idea. Have others experienced this?
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