TTops

Let me start by saying I know what the drill mod is, and what it is supposed to do, and I also know that it works for a great many people. I myself have done it with so-so results, and am currently planning on buying a Tick master cylinder and calling it a day.


However, my question is what exactly goes wrong that the drill mod becomes necessary? The magazine articles and reviews from the time period for our cars (1997-2002) seem to be cracking off great acceleration times and praise the T56 transmission. I've even read a few articles that mention some hero 1/4 mile runs when power shifting, something that is impossible when our hydraulics all of a sudden need the drill mod or less restriction, and they make no mention of difficulty going into gear at WOT and high rpm. So, what happened to my clutch hydraulics between 2001 (for my car) and 2016 that have made it a requirement for me to tinker with them?

JD_AMG

This needs to be posted in the manual trans section.
Good question though. I don't think I remember anyone ever being able to successfully power shift with the car stock though. GM literally engineered it that way so you couldn't power shift and potentially break something.
Im betting it has to do with the slave cylinder and clutch springs getting more worn out over the years making it harder and harder to shift at high RPMs. Doing the drill mod or using the tick master will push more fluid making the potentially worn out parts work a little better.

blackandgold

iTrader: (2)

A brand new car with a brand new clutch, brand new trans, brand new master, brand new slave, brand new pressure plate and fresh fluids all around isn't going to experience many of the problems a car with even 20k miles will start to exhibit. I think our MC problems are just the weakest link showing it's trouble first.

Darth_V8r

iTrader: (4)

The first symptom that shows up to make one say "I think I need to drill mod" is after a high rpm shift the pedal doesn't quite return to full height. Then you go to the next shift and don't get complete disengagement. Then it starts to get to the point where it doesn't require high rpm driving to not return to full height. If you've ever had the pedal randomly only return halfway and other times come all the way up, that's screaming "drill mod me" Think of it this way - your left leg provides enough force to move the hydraulics, thereby compressing pressure plate fingers, etc. the return force from the pressure plate must overcome everything in reverse fighting a ~8x mechanical advantage. If thirty pounds from your left leg can move all that, certainly a flow restrict or can, er...., restrict flow. Likely crap builds up on the orifice from fluid breakdown.

Darth_V8r

iTrader: (4)

Like to add three if the self adjuster starts to go on the pressure plate it rede us fluid return pressure, exhibiting identical symptoms. This is why it sometimes works and other times doesn't.

Sometimes you have to do the clutch and the drill mod to restore performance

blackandgold

iTrader: (2)

I know the ls7 has a self adjusting PP, but I didn't realize the LS1 PP did.

Darth_V8r

iTrader: (4)

yup. That's why if people have pedal return issues sometimes you got to do the clutch and hydraulics to fix it. Mine was that way on two different cars

TTops

Sorry for posting in the wrong section, I'm used to thirdgen.org's layout and I'm still figuring this site out.


Everything you all have posted seems to make sense. What I'm reading is that the hydraulics themselves haven't really changed. minus some build up of gunk in the hose and cylinder. What has changed are actual mechanical parts, like the slave cylinder and springs in the pressure plate?


I work on a lot of 99-04 Mustangs, and every time I looked at their clutch mechanics, which are cable actuated, I cursed GM for giving me hydraulics with issues. Now it seems that the problems could've cropped up regardless.

chrysler kid

iTrader: (14)

Drill mod is just a feel good mod. Removing the restriction does not increase the volume of fluid being pushed into the line. Most of the time a sticky pedal is the result of contamination in the line and heat absorbed into the stainless line.

Darth_V8r

iTrader: (4)

It does nothing for when you press the pedal. The entire benefit of the mod is pedal return

1 FMF

iTrader: (1)

disengage clutch = push down on clutch pedal = clutch master cylinder pushes fluid into slave cylinder which extends into clutch fingers releasing clutch.

engage clutch = release clutch pedal = force of clutch fingers pushes back on extended slave cylinder pushing fluid back into clutch master cylinder.

the purpose of the restriction was to help ease clutch engagement for normal driving, without the restriction the engagement would be more sensitive to clutch pedal movement and speed, and make it harder for non coordinates people to drive the car.

the problem occurs when one tries to speed shift or power shift, they want the clutch disengagement to happen as fast as possible - this requires movement of clutch fluid as fast as possible. the restriction prevents that and the few hundredths of a second delay is enough to cause shifting problems, with clutch not fully disengaged the synchros and forks bear the extra force required for shifting. Have an aftermarket clutch that's beefier or twin disk then there's that much more clutch not disengaged making it worse.

the clutch hydraulics is a closed system, the pedal should always return to original height. the oem clutch master cylinder is plastic and can only take so much pressure. if fluid has not leaked out of the clutch system and you don't have a stuck slave cylinder, then it would be the clutch fingers not returning to original position - pushing slave cylinder back to original position - pushing clutch pedal back to original position.