Hard shifting restriction fix! for M6s
Thread Starter
Registered User
Joined: Jun 2002
Posts: 502
From: Miami, FL USA
Hard shifting restriction fix! for M6s
I got this from www.ls1camaron.net
Read then give me your input on this. It's a little more than what I want to do on my own, but I will take somewhere to have it done. How much labor cost should I pay for something like this? I've had a lot of manuals and I have to agree that I don't feel the lurch feel this mod refers to in my 98. Now someone else may think different and tell me something else or that I won't notice much after doing this. So read on and post up your opinions and facts.
Drill Modification
This modification is for M6 cars. It seems that GM has put restrictors in the master cylinder hydraulic lines so that non-enthusiasts would be able to drive the car without the clutch engaging too fast and causing the car to lurch forward. With the restriction in place, it slows the clutch so much that you can easily burn the clutch while shifting hard, common on the 2nd to 3rd shift. Unfortunately if you're going for performance you want the clutch to engage quickly! This mod removes that restriction completely, allowing your clutch to function to it's full potential.
1. Undo the line from the slave by sliding the nylon ring in toward the
slave and remove any necessary heat shields to free up the line.
2. Remove the under-dash to gain access to the clutch inside the car.
3. Unbolt the U-bolt nuts inside the car as well as the clip at the end
of the rod to the clutch pedal.
4. Remove the U-bolt. This is a little tricky to do because of the clip
thats on it to the inside...if you can get to it and remove it great
otherwise start tht nuts onto the bolt and beat it to
submission...errr... i mean until it comes out. Take the retaining clip
and throw it as far as you can, as you will never use or want to see it
again.
5. Fiddle with the assembly to get it out of the car. Takes some time
but it will come out, i think i fed mine out under the brake booster on
the engine side.
6. Push out the roll pin and remove the line.
7. Insert the drill bit of your choice - the magazines say that 1/8 will
fit but this WILL drill some of the fitting also, I used 7/64 which
slides past the fitting to the restrictor. It's good to have an idea
where the restrictor is in the line before you go nuts with the drill.
It should be about an inch in just past the compression sleeve for the
fitting. The restrictor is about 1/4 inch long and very soft so it
doesn't take much to drill it out use slow speeds to reduce the amount of
metal shavings.
8. Re-install the modified line.
** an assistant is very helpful from here on **
9. Connect the old slave from above and put the slave in a vice so it
won't over extend. Bench bleed and Flush out any metal that is left in
the line. I bled mine until the fluid that came out was clean and metal
free... about 3-4 M/C cups full.
10. Re-install the M/C. Very helpful to have someone else to assist you
here, took me about 1.5-2 hours alone just to re-install and put the car
back together.
Drill Mod FAQ:
Q: Where is the slave cylinder located?
A: If you are facing the engine bay it's just down and right of the brake booster, it's actually in the tranny, well, between the clutch pressure plate and the tranny actually.
Q: Step 1 mentions removing the line going to the slave cylinder, but I see a few lines. Which is which?
A: On the outside of the bell housing you'll see 2 things sticking out. The top line is a bleeder, and the bottom is the line you want to disconnect. The line comes apart by pushing the plastic sleeve back and it will release it.
Q: Where is the master cylinder located?
A: Up on the firewall, it looks like a small brake reservoir. Know where you put brake fluid in? If you're standing over the driver's fender and you look a little closer to you you'll see another reservoir there for the master cylinder, it's lower and closer to the outside. It has a line that runs down behind some heat shields to the tranny/bell housing/slave cylinder.
Q: On step 2 you mention removing the "Under-dash." What is that?
A: The plastic that is under the dash and above the pedals. (The root of all evil.)
Q: How is the master cylinder attached to the firewall?
A: The clutch mc is held in by a U-shaped bolt. 1 bolt thru both holes, like on a rearend.
Q: How does one do a bench-bleed?
A: After you drill the line you have to flush it out to get all the metal out of it. You could use a hose, but I never liked the idea of mixing oil and water, plus brake fluid is dirt cheap. So, to do the bench bleed you'll need to support the reservoir above the master cylinder and let the line hang lower than both. At the end of the line there's a little "check ball" inside that you will need to jam open with a nail or something. Fill the reservoir and push on the mc rod until it pukes out clean fluid from the line.
Q: Do I need to worry about getting air in the system?
A: Not if you bleed it before you reconnect to the slave
Read then give me your input on this. It's a little more than what I want to do on my own, but I will take somewhere to have it done. How much labor cost should I pay for something like this? I've had a lot of manuals and I have to agree that I don't feel the lurch feel this mod refers to in my 98. Now someone else may think different and tell me something else or that I won't notice much after doing this. So read on and post up your opinions and facts.
Drill Modification
This modification is for M6 cars. It seems that GM has put restrictors in the master cylinder hydraulic lines so that non-enthusiasts would be able to drive the car without the clutch engaging too fast and causing the car to lurch forward. With the restriction in place, it slows the clutch so much that you can easily burn the clutch while shifting hard, common on the 2nd to 3rd shift. Unfortunately if you're going for performance you want the clutch to engage quickly! This mod removes that restriction completely, allowing your clutch to function to it's full potential.
1. Undo the line from the slave by sliding the nylon ring in toward the
slave and remove any necessary heat shields to free up the line.
2. Remove the under-dash to gain access to the clutch inside the car.
3. Unbolt the U-bolt nuts inside the car as well as the clip at the end
of the rod to the clutch pedal.
4. Remove the U-bolt. This is a little tricky to do because of the clip
thats on it to the inside...if you can get to it and remove it great
otherwise start tht nuts onto the bolt and beat it to
submission...errr... i mean until it comes out. Take the retaining clip
and throw it as far as you can, as you will never use or want to see it
again.
5. Fiddle with the assembly to get it out of the car. Takes some time
but it will come out, i think i fed mine out under the brake booster on
the engine side.
6. Push out the roll pin and remove the line.
7. Insert the drill bit of your choice - the magazines say that 1/8 will
fit but this WILL drill some of the fitting also, I used 7/64 which
slides past the fitting to the restrictor. It's good to have an idea
where the restrictor is in the line before you go nuts with the drill.
It should be about an inch in just past the compression sleeve for the
fitting. The restrictor is about 1/4 inch long and very soft so it
doesn't take much to drill it out use slow speeds to reduce the amount of
metal shavings.
8. Re-install the modified line.
** an assistant is very helpful from here on **
9. Connect the old slave from above and put the slave in a vice so it
won't over extend. Bench bleed and Flush out any metal that is left in
the line. I bled mine until the fluid that came out was clean and metal
free... about 3-4 M/C cups full.
10. Re-install the M/C. Very helpful to have someone else to assist you
here, took me about 1.5-2 hours alone just to re-install and put the car
back together.
Drill Mod FAQ:
Q: Where is the slave cylinder located?
A: If you are facing the engine bay it's just down and right of the brake booster, it's actually in the tranny, well, between the clutch pressure plate and the tranny actually.
Q: Step 1 mentions removing the line going to the slave cylinder, but I see a few lines. Which is which?
A: On the outside of the bell housing you'll see 2 things sticking out. The top line is a bleeder, and the bottom is the line you want to disconnect. The line comes apart by pushing the plastic sleeve back and it will release it.
Q: Where is the master cylinder located?
A: Up on the firewall, it looks like a small brake reservoir. Know where you put brake fluid in? If you're standing over the driver's fender and you look a little closer to you you'll see another reservoir there for the master cylinder, it's lower and closer to the outside. It has a line that runs down behind some heat shields to the tranny/bell housing/slave cylinder.
Q: On step 2 you mention removing the "Under-dash." What is that?
A: The plastic that is under the dash and above the pedals. (The root of all evil.)
Q: How is the master cylinder attached to the firewall?
A: The clutch mc is held in by a U-shaped bolt. 1 bolt thru both holes, like on a rearend.
Q: How does one do a bench-bleed?
A: After you drill the line you have to flush it out to get all the metal out of it. You could use a hose, but I never liked the idea of mixing oil and water, plus brake fluid is dirt cheap. So, to do the bench bleed you'll need to support the reservoir above the master cylinder and let the line hang lower than both. At the end of the line there's a little "check ball" inside that you will need to jam open with a nail or something. Fill the reservoir and push on the mc rod until it pukes out clean fluid from the line.
Q: Do I need to worry about getting air in the system?
A: Not if you bleed it before you reconnect to the slave
Last edited by therealmagyver; Nov 10, 2002 at 10:19 AM.
Registered User
Joined: Feb 2000
Posts: 607
From: Casselberry FL USA
I think this mod has been around for almost a year now. Cartek does it for you in their adjustable master, and McLeod recommends doing so in the dox for their adjustable master.
There's another install document for it here...
Install University Drill Mod
My shifting is much smoother now with the McLeod adjustable & drilled line than it was with the stock master & line, especially on fast shifts. I've heard that there's also concern about additional shock to the rear-end with this mod, but since I only use street tires I don't lose any sleep.
$0.02
There's another install document for it here...
Install University Drill Mod
My shifting is much smoother now with the McLeod adjustable & drilled line than it was with the stock master & line, especially on fast shifts. I've heard that there's also concern about additional shock to the rear-end with this mod, but since I only use street tires I don't lose any sleep.
$0.02
Thread Starter
Registered User
Joined: Jun 2002
Posts: 502
From: Miami, FL USA
Oh. Thanks for the additional link. I got my car about a month and joined this board a week or so before that....well at least visited the board before I got the car. I am disappointed GM did something like this. We don't by z28's especially manuals so we can't drive hard or shift hard. Well I have to find a mechanic who will do this for me. I actually have one. He's been working on GMs for 30 years...dam I'm lucky and he doesn't over charge. On weekends a lot of dudes just be hanging out at his shop helping him on projects for his personal cars and cars he has in for work for customers. It's funny cuz 2 doors over is a Mustang shop. Those guys are crazy. I would never leave my ford with them if I had one. They spin out customer's tires all day!Wit no remorse!
Registered User
Joined: Oct 2001
Posts: 765
From: Henderson, NV
Yeah, this came out about a year ago in GMHP, They said it also reduces the shock on the drivetrain since it eases the release of the clutch rather then slam it. It's an easy mod to do though. Took about an hour to do.
Registered User
Joined: May 2000
Posts: 49
From: Largo, FL
I did the drill mod on my 98 T/A and it made the clutch pedal harder to push in and really made the clutch feel like it grabbed better. I could really hit the gears hard. So much so that it felt like you could break the rear end with some real sticky tires. I always felt the LS1 clutch felt a little mushy and the drill mod made it feel better or normal.
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