Sticking clutch pedal write-up

**JonB** · 07-03-2007, 02:03 PM

The Problem

When driven aggressively, GM cars with manual transmissions have the problem of the clutch pedal sticking to the floor or other symptoms as a hard or soft pedal., slow to return or lazy pedal, stuck mid way pedal, or the classic its just stuck on the floor board. For anyone that has experienced any of these they know how annoying they can be. Its even more annoying trying to find the right fix for the problem. Unfortunately there is no definite answer to this problem every car is different. For some they just need to flush the fluid some the drill mod solves the problem. Others have to start replacing parts such as the clutch master or the slave cylinder.

Since this problem seems to be ever so growing in the ls1 community I have taken the time to put together a write up on the steps that should be taken to hopefully solver your problem and hopefully stop it from ever coming back.

So how do you stop my clutch pedal from sticking in the first place?

First lets start off with those that have not yet experienced this problem or have recently changed all there hydraulics and clutch. The number one most important thing is to keep your clutch fluid clean and fresh. Its cheap and easy insurance to keeping your pedal working properly. Gm recommends changing it every 100,000 miles. This is total crap I don’t think there is any fluid that should be left in your car for 100,000 miles. No one has come up with a specific time frame to change your fluid so I would leave it up to your judgment. If your fluid is black its time to change it but it should be done way before it turns black. You should try to keep your fluid clean and fresh. The harder you are on the car the more frequent it should be changed. I personally recommend a full bleeding of the system if your fluid its dirty but once kept up with you can get away with just swap out the fluid in the reservoir but every once awhile you should still do a full bleed of the system.

You clutch fluid is plain old DOT 3 brake fluid. Most run just regular DOT 3 but DOT 4 will work as well and has a higher boiling point. We all know that brake fluid boils and when it does it essentially breaks down and does not work as it should. The same goes for your clutch fluid as it is brake fluid. One must remember that the slave is located inside the bell housing. That location puts clutch fluid in a very high heat, stress situation. Also the line from the master to the slave is in very close proximity to the exhaust often even closer when you have headers. When launching or high rpm shifting the fluid temperate rises dramatically over regular driving. These situations of increased friction are sufficient to boil clutch fluid. Once the brake fluid has been boiled it will emit a gas or steam which when compressed in a hydraulic system meant for fluid it will cause a malfunction in the system aka you clutch pedal sticking or acting different than normal. Again this is why your fluid needs to stay clear and clean to keep your pedal from sticking.

For more information of keeping your fluid clean click HERE

First step to solving the sticking clutch pedal is to bleed the hydraulics.

Having clean fluid and no air in the lines is your best bet to keeping everything operating the way it should.

On to the bleeding the system

One of the more difficult things about a T56 is accessing the bleeder screw. You cannot see it without a mirror, so you must rely on feel. If you are beneath the car and you are looking at the transmission where the master cylinder line connects to the slave cylinder, reach straight upward. At the very top of the transmission you will feel a hex-shaped rod about two inches in length. That is the bleeder screw, which comes directly from the slave cylinder.

To bleed the system, you will need a 7/16th” socket, thin-walled, in ¼ drive. It would behoove you to use a few swivels and extensions. I also highly recommend taping the socket to the extension/swivel/etc. If for some reason you drop the socket, it will end up at the bottom of the bellhousing and you will have a hell of a time fishing it out.

If you plan to bleed traditionally, you will need two people. One under the car opening and tightening the bleeder screw, and another in the car operating the pedal.

If you are not squeamish about cutting into your car, you can make traditional bleeding a one man job. Underneath the car, do your best to put a dent in the transmission tunnel, straight across from the bleeder screw, with a punch. Get into the car and pull back the carpet around the pedals, and cut a small ‘access square’ so that you can also fold back the plastic, foam-lined piece beneath the carpet. Under that you will find the dent you made. With a 1” holesaw, cut a small part of the tunnel out. Now, with a 7/16” socket and a few extensions, you can reach the bleeder while being in the car! From here you can operate the pedal with your hand and use your other hand to tighten/loosen the screw. When you are done, simply put a piece of duct tape over the hole and recover with the carpet. It does not introduce any more noise into the cabinet.

Here is what the hole looks like (I had to drill mine a couple times to get it right

Different options for bleeding the system

Your best bet for learning how to bleed would be to search this forum. People have posted many different ways of removing air from the system, from using a traditional way, a Mity vac , etc. If you want to do it traditionally (whether by yourself or with help) it is very simple. The reservoir needs to be full of fluid the whole time, otherwise you will just continue to introduce more air into the system. With the bleeder closed, push the pedal to the floor. Open the bleeder (fluid and air will come out). Close the bleeder, release the pedal, bring it all the way back up. This process gets repeated until you have a firm clutch pedal. Don’t panic – it can take up to 30 minutes to get it bled correctly.

The fluid that dribbles out will end up in the bottom of the bellhousing, and it will seep out that rectangular hole in the bottom and take care of itself. If you would like, you can spray some brake cleaner into the cavity to speed the process along.

A thank you goes out to keliente from ls1tech for the clutch bleeding section. So might recognize it for the manual trans faq thread. I borrowed it from her so thank you keliente.

I’ve changed my fluid but I still have a sticking clutch pedal.

The next step if it already hasn’t been done is the drill mod.

What is the drill mod?

To sum it up, basically GM didn’t think things through all the way when selecting the hydraulic lines for your T56. The steel braided line that plugs into the master cylinder has a tiny, tiny hole in it, which causes unnecessary restriction. During a quick, high-rpm shift, fluid cannot get where it needs to go fast enough, so basically it will feel like you are shifting without a clutch. It may be difficult or impossible to shift into 2nd or 3rd, and you may have some problems with the pedal itself.

When performing the drill mod, you remove the master cylinder, separate the line from the cylinder, and drill it out. To visit a site with full information and pictures, click HERE . It will be listed under the Transmission section, along with the adjustable master cylinder install (although you can do the drill mod without changing the master).

Another good idea when doing the drill mod is to wrap your hydraulic line with some kind of heat reflective tape.

I’ve changed the fluid and did the drill mod my pedal still sticks.

Next step is to replace your clutch master cylinder.

You can use the same site as the drill mod for an install write up. They used a McLeod adjustable master. Through my research the stock GM 01+ master is the best. Most that have tried adjustable masters end up switching back to stock. There is nothing wrong with an adjustable master but for many it can be tricky especially if you do not know how to properly adjust one. For all you 98 to 00 people it is recommended that you upgrade to the 01+ hydraulics. Although there have been no test done the general idea is that if you fluid in your master turns black rather quickly after flushing it your master is shot. Like I said there is no proof to this statement but it seems to be an ever more popular belief. Most masters come bench bleed and full of fluid. This does not mean you don’t have to bleed the system once it’s all put together. It is recommended that if you do the drill mod on the new line that you bench bleed the master. For a write-up on how to replace the master click HERE

**JonB** · 07-03-2007, 02:04 PM

I’ve changed fluid did the drill mod and my master and the pedal still sticks.

Next it’s time to replace your slave cylinder.

At this point you have tried everything to avoid this. This is the hardest and most expensive part. Unfortunately to get to the slave the whole tranny has to be lowered down. At this point it’s also a good idea to replace the whole clutch assembly, since you’re already in there. For a write up on removing tranny/clutch slave click HERE

To sum everything up.

It is very important to keep your fluid clean.

First step is to bleed the system it is important to have clean fluid and no air in the system.

Second step is the do the drill mod.

Third step is to replace the master cylinder.

Fourth step is to replace the slave cylinder.

Fifth step is to replace the clutch assembly(usually done at the same time as the slave cylinder).

**Danger731** · 07-03-2007, 02:08 PM

Sweet write up !

**JonB** · 07-03-2007, 02:13 PM

Thank you. I really hope maybe we can get this to be a sticky.

**mikeaford** · 07-08-2007, 03:34 PM

Used this today did a one person flush job - my hole looks all jacked up but the fluid looked black as can be and started giving me issues shifting yesterday (hot as hades and stuck in traffic). I hope this cures my blues as I've previously replaced the entire hydraulic system myself - and THAT SUCKED! Thanks for the awesome write up I'd never been able to do it myself without this!!!

**9t8z28** · 07-08-2007, 06:17 PM

Yeah, this needs to be a sticky! I haven't had many problems w/ mine, but I am sure I will!

**JonB** · 07-08-2007, 07:22 PM

Originally Posted by mikeaford

Used this today did a one person flush job - my hole looks all jacked up but the fluid looked black as can be and started giving me issues shifting yesterday (hot as hades and stuck in traffic). I hope this cures my blues as I've previously replaced the entire hydraulic system myself - and THAT SUCKED! Thanks for the awesome write up I'd never been able to do it myself without this!!!

Not a problem, that why I decided to do the write up. There was alot and I mean alot of threads being started about sticking clutch pedals and how to flush/bleed there hydrolics. I did it to hopefully help everyone out.

**GatorSS** · 07-11-2007, 12:06 PM

Nice write-up. This is one area that is severely overlooked...or not even considered at all...until problems arise.

**mikeaford** · 07-11-2007, 04:50 PM

Originally Posted by JonB

Not a problem, that why I decided to do the write up. There was alot and I mean alot of threads being started about sticking clutch pedals and how to flush/bleed there hydrolics. I did it to hopefully help everyone out.

Well this sucks I replaced the master cylinder after bleeding it 2 times still didn't work now looking into a new clutch since I have to already replace the slave for now the transmission sits in front of the car waiting for new bones.

**Hot Rod SS** · 07-12-2007, 01:25 AM

My clutch is slipping pretty bad, especially if I get on it hard in first and second gear and I can smell it burn. I just ordered a new clutch yesterday. Should I go ahead and replace the slave cylinder while I'm in there? The only time I've had issues with the pedal was when I was coming out of the hole really aggressive, roasting the tires in first, and when I shifted to second the pedal "half stuck" or was a "soft, lazy pedal". Is that normal with a worn out clutch, or could it be a slave cylinder problem?

**JonB** · 07-13-2007, 07:58 PM

Originally Posted by Hot Rod SS

My clutch is slipping pretty bad, especially if I get on it hard in first and second gear and I can smell it burn. I just ordered a new clutch yesterday. Should I go ahead and replace the slave cylinder while I'm in there? The only time I've had issues with the pedal was when I was coming out of the hole really aggressive, roasting the tires in first, and when I shifted to second the pedal "half stuck" or was a "soft, lazy pedal". Is that normal with a worn out clutch, or could it be a slave cylinder problem?

Its a good idea to go ahead and replace the slave if you are going in there to replace the clutch. Its better to do it while you have it apart than to not do it and have to go back in. As the write up says it very important to keep your fluid fresh and clean.

**mikeaford** · 07-14-2007, 08:39 AM

Originally Posted by JonB

Its a good idea to go ahead and replace the slave if you are going in there to replace the clutch. Its better to do it while you have it apart than to not do it and have to go back in. As the write up says it very important to keep your fluid fresh and clean.

I decided friday I was just going to replace my slave cylinder the clutch really isn't slipping and only time I smell it "burn" is after about EXTREME MPH driving which believe me isn't that often. All it's costing me is a day of "suckiness" since I do my own labor and got a lift. clutch has approximately 43K miles on it so I'll drive it till it goes. In the meantime I'll try to save for a nice clutch.

**JonB** · 07-15-2007, 08:55 PM

We've got some new info as of 7/14/07 gm acknowledges degraded clutch fluid causes pedal woes.

Originally Posted by Ken Fichtner;1561070929
Document ID# 1982105

Subject: Intermittent Spongy Clutch Pedal Sticking To The Floor During Hard Acceleration And High RPM Shifts - keywords contaminate fluid hydraulic #PIP4145 - (06/04/2007)

Models: 2005-2007 Chevrolet Corvette, Corvette Z06 Equipped with a Tremec 6-speed Transmission RPO MM6, MZ6

--------------------------------------------------------------------------------

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
Some customers may comment about an intermittent spongy clutch pedal feel or clutch pedal sticking to the floor. This may be aggravated by aggressive driving and high clutch operating temperatures. Higher than expected levels of water in the clutch fluid greater than 2% may cause the clutch fluid to boil. The presence of water in the fluid lowers the boiling point significantly; when these conditions are present the driver may lose customary clutch pedal feel and performance.

Recommendation/Instructions:
If the above condition is intermittent flush the hydraulic system using DOT 4 fluid part number 88958860 (88901244 in Canada), prior to replacement of any mechanical or hydraulic components.

To eliminate the opportunity for moisture to enter the clutch hydraulic system.

The clutch fluid level inspection should be a VISUAL inspection only. Look through the transparent reservoir and observe the fluid level. Avoid removing the cap. Do not remove the cap just to top-off clutch fluid. Leave the system closed and sealed. During PDI inspection or routine servicing the cap should not be opened for just an inspection.
DOT 4 clutch fluid has a 2 week shelf life. Do not use fluid if container opening date is unknown or older than 2 weeks. Do not mix or re-use old fluid. Current service information already covers the issue of reuse.
To provide the best clutch operation, it is recommended that the owner change the clutch fluid every 2 calendar years. Please flush and replace the clutch fluid with P/N 88958860 (88901244 in Canada) or equivalent DOT 4.
The current service information and owners manual will be updated to reflect this information.

Note: If the concern is not intermittent, inspect clutch hydraulic system for leaks and repair as necessary after repairs are completed flush system with DOT 4 fluid part number 88958860 (88901244 in Canada).

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

**t-rock** · 07-18-2007, 04:05 PM

man that was some great info guys keep up the good work! im gonna check my fluid and bleed it this weekend thats the only time i get to tinker with it.

**Eagle** · 07-22-2007, 08:17 AM

I ran my car with the 150HP shot for the first time yesterday and the pedal went half height on me. Now its off to the garage to bleed it out and hope it gets better... Oh ya, and my fluid wasn't pretty in the reservoir either... nice and black. And I completely agree, ignored until its a problem! Time to pay the piper for me, off to the garage I go.

Excellent write up! Deserves Sticky!

-Eagle

**mikeaford** · 07-22-2007, 02:46 PM

Originally Posted by mikeaford

I decided friday I was just going to replace my slave cylinder the clutch really isn't slipping and only time I smell it "burn" is after about EXTREME MPH driving which believe me isn't that often. All it's costing me is a day of "suckiness" since I do my own labor and got a lift. clutch has approximately 43K miles on it so I'll drive it till it goes. In the meantime I'll try to save for a nice clutch.

Ok bought the LS7 clutch and am going to have the fidenza flywheel surfaced while I was at the shop picked me up some long tube headers as well. Going to just "do it right".

**t-rock** · 07-22-2007, 03:02 PM

thats what im talkin about.i just bought my 2nd 02 ta and havnt made the
1st payment or tags yet so that will come in time so ill get 02 sims and gut my cats till i save up for headers.

**JonB** · 08-05-2007, 06:10 PM

To the top

**LS1Formula01** · 08-07-2007, 07:27 AM

Sticky!

**Blackout01** · 08-07-2007, 09:51 AM

If I bought a new clutch master cylinder would I still have to perform the drill mod? I plan on buying an adjustable one. I also need a new slave cylinder now or very very soon. So should I just buy a clutch kit too? master/slave and clutch kit?