Clutch gone slack, pedal goes to the floor

BOGIECLASSICCHEVY

MEMBER
2010 KIA FORTE
2.4L
4 CYL
2WD
MANUAL
84,000 MILES

Koup. Six speed manual transmission. Clutch pedal has gone slack (drops to floor with no resistance. No fluid loss. Can shift into all six gears plus reverse with engine off. (Have not tried with engine running.) Acts like clutch has failed engaged. Other than plumbing, seems main parts are master cylinder, regulator valve and slave cylinder (which is mounted internal to the bell housing). Clutch master cylinder picks up brake fluid from the brake master cylinder reservoir. Any ideas as to likely culprit and best way to troubleshoot to confirm?

8 Replies

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

Hi and thanks for using 2CarPros.com.

It sounds like you are right. Either the slave or the master cylinder has gone bad. Here are some general directions:

https://www.2carpros.com/articles/clutch-doesnt-work-sometimes-or-not-at-all

Here are the directions specific to checking the slave cylinder on your vehicle. Picture 1 correlates with these directions.

COMPONENT TESTS AND GENERAL DIAGNOSTICS
Inspection

1. Check the release cylinder bore for rust and damage.
2. Measure the release cylinder bore at three locations (bottom, middle, and top) with a cylinder gauge and replace the release cylinder assembly if the bore-to-piston clearance exceeds the limit.
Limit clearance to piston: 0.25mm (0.0098 in)
3. Check the clutch release cylinder for fluid leakage.
4. Check the clutch release cylinder boots for damage.
_________________________________________

Here are the directions for replacing the slave cylinder if you find it bad. Pictures 2 through 5 correlate with these directions.

Removal

1. Drain the brake fluid through the bleed plug(A).
2. Disconnect the clutch tube(A).
3. Remove the two clutch release cylinder mounting nuts(B-2ea).

Installation

1. Coat the clutch clevis push rod specified grease.
Specified grease: CASMOLY L9508
2. Install the release cylinder mounting nuts(B-2ea).
Tightening torque :
15 - 22Nm (150 - 220 kgf.cm, 11 - 16 lb-ft)
3. Install the clutch tube(A).
4. Refill the brake fluid.
5. Bleed the air in the clutch system.
(refer to Bleeding in Service Adjustment Procedure)

_______________________________________________

Here are the directions specific to your vehicle for checking the clutch master cylinder. Pic 6 is an exploded view of the assembly. Picture 7 is the parts legend.

Inspection

1. Check the inside of the cylinder body for rust, pitting or scoring.
2. Check the piston cup for wear or distortion.
3. Check the piston for rust, pitting or scoring.
4. Check to make sure the clutch line tube is not clogged or restricted in any way.
5. Measure the master cylinder inside diameter and the piston outside diameter with a cylinder gauge micrometer.
NOTE:
Measure the inside diameter of the master cylinder at three places (bottom, middle, and top) in a perpendicular direction.
6. If the master cylinder-to-piston clearance exceeds the limit, replace the master cylinder and/or piston assembly.
Limit: 0.15 mm (0.006 in)

______________________________________________________

Here are the directions for removing and replacing plus, they include overhaul procedures. The remaining pictures correlate with these directions.

OVERHAUL
Removal
1. Drain the brake fluid through the bleeding plug (A).
2. Remove the flexible hose (A) connected to brake reserve tank from the master cylinder.
3. Disconnect the clutch tube (B) from the master cylinder.
4. Disconnect the two ignition lock switch connectors.
5. Remove the clutch pedal mounting nuts(A-2ea) and the bracket mounting nut.
6. Disconnect the push rod from the master cylinder by removing the snap pin (A) and washer (B).
7. Remove the screws mounting the master cylinder to the clutch pedal assembly.
1. Apply the specified grease to the clutch pedal and bushings.

Chassis grease: SAE J310a, NLGI No.1
2. Install the screws or nut mounting the master cylinder to the clutch pedal assembly.
3. Apply the specified grease to the snap pin(A) and washer.

Wheel bearing grease: SAE J310, NLGI No.2
4. Connect the push rod to the clutch pedal by installing the snap pin (A) and washer (B).
5. Install the clutch pedal mounting nuts (A-2ea).

Tightening torque :
17 - 26Nm (1.7 - 2.6kgf.m, 12.3 - 18.8Ib-ft)
6. Adjust the clutch pedal within the standard value, then secure by tightening the lock nut.
Standard value
Free play (A)
6 - 13mm (0.24 - 0.51 in)
Height (B)
182.8mm (7.19 in)
7. Connect the flexible hose of the brake reserve tank to the master cylinder.
8. Connect the clutch tube(B) to the master cylinder.
9. Refill the brake fluid.
10. Bleed the air in the clutch system.(refer to Bleeding in Serve Adjustment Procedure)

Disassembly
1. Remove the piston stop ring.
2. Pull out the push rod and piston assembly.
3. Remove the reserve tank band, reserve tank cap, and reserve tank.

NOTE:
1. Use care not to damage the master cylinder body and piston assembly.
2. Do not disassemble the piston assembly.

Inspection
1. Check the inside of the cylinder body for rust, pitting or scoring.
2. Check the piston cup for wear or distortion.
3. Check the piston for rust, pitting or scoring.
4. Check to make sure the clutch line tube is not clogged or restricted in any way.
5. Measure the master cylinder inside diameter and the piston outside diameter with a cylinder gauge micrometer.

NOTE:
Measure the inside diameter of the master cylinder at three places (bottom, middle, and top) in a perpendicular direction.
6. If the master cylinder-to-piston clearance exceeds the limit, replace the master cylinder and/or piston assembly.
Limit: 0.15 mm (0.006 in)

Reassembly
1. Apply the specified fluid to the inner surface of the master cylinder body (A) and to the entire periphery of the piston assembly (B).
Specified fluid: Brake fluid DOT 3 or DOT 4
2. Install the piston assembly.
3. Install the piston snap ring.
4. Install the push rod assembly.

_____________________________________________

I hope this is helpful. Let me know if you have other questions or need help.

Take care,
Joe

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Tuesday, August 7th, 2018 AT 7:29 PM

BOGIECLASSICCHEVY

MEMBER
5 POSTS

Hey Joe. Thanks. This will be very helpful. Unfortunately my slave cylinder is of the internal type (inside the bell housing) so I figure if I am going to go that deep I might as well replace it and the clutch assembly as well while I am in there. (84,000 miles) I am not really tooled up to perform the measurements and rebuild described above. I am including a couple images that depict my configuration. I plan to start with the master cylinder since it is easiest and may solve the problem. Would you suggest I replace the regulator valve too? Not sure if that just regulates pressure or if it also acts as a check valve that could possibly be stuck. If you have any other thoughts I would appreciate hearing them. Looks like I am on my way to a complete clutch overhaul. Thanks for your time and detailed response. First time I have used you guys. Probably will not be my last. Regards, Greg

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Wednesday, August 8th, 2018 AT 7:53 AM

BOGIECLASSICCHEVY

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5 POSTS

Second showing slave cylinder set up.

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Wednesday, August 8th, 2018 AT 7:53 AM

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

Hi Greg. Honestly, I would replace the check valve at the same time. That way there's no question. If you are going to replace everything, here are the directions for removing and replacing the transmission. There are a ton of pictures that correlate with these directions. I do not know if you need them, but figured I would add them just in case. Note: When you remove the transmission, you will need to support the engine. The procedure is in the directions. Also, the directions indicate the torque specs for all components. Let me know if you need help with anything or need more information.

_________________________________

Removal

1. Remove the engine cover(A).
2. Remove the battery(A).
3. Disconnect the air duct (A).
4. After disconnecting ECU connector (A), remove the air cleaner assembly (B).
5. Remove the battery tray (A).
6. Disconnect the vehicle speed sensor connector (A), the back up lamp switch connector (B).
7. Disconnect the cable assemblies (A) after removing the clips (B) and pins (C).
8. Remove the ground (A).
9. After removing the clip(B) with clamping the concentric slave cylinder tube, disconnect the tube(A).
10. Remove the transaxle upper mounting bolts (A-2ea) and the starter motor mounting bolts (B-2ea).
11. Using the special tool(09200-38001), support the engine transaxle assembly safely.
12. Remove the insulator bracket bolts (A).
13. Remove the front wheels&tires.
14. Remove the steering joint assembly bolt.
15. Lifting up the vehicle, remove the under shield cover.
16. Drain the manual transaxle fluid after removing the transaxle drain plug(A). It can be easier when the oil filler plug(B) is removed.
17. Loosening the clamp(B), disconnect the the power steering return hose(A) and drain the power steering fluid.
18. Disconnect the power steering pressure hose(A) bolt(B).
CAUTION:
Be careful not to lose the washers.
19. Remove the lower arm ball joint assembly mounting bolts.
20. Remove the stabilizer link mounting bolt.
21. After removing a split pin and nut from the tie rod end, disconnect it.
22. Disconnect the roll stopper bracket bolts(A, B).
23. Disconnect the muffler hanger rubber (A).
24. Supporting the sub frame with a jack and the Special tool(09624-38000), remove the mounting bolts.
25. Disconnect the driveshafts(A, B) from the transaxle..
26. Remove the heat cover.
27. Remove the transaxle lower mounting bolts(A-4ea, B-2ea)
28. Lowering the jack slowly, remove the transaxle.
CAUTION:
When removing the transaxle assembly, be careful not to damage any surrounding parts or body components.
__________________________________________________________
Installation

1. Install the transaxle lower mounting bolts(A-4ea, B-2ea)

Tightening torque :
43-55Nm (4.3-5.5kgf.M, 31.1-39.8lb-ft)
2. Install the heat cover. (Refer to Exhaust Manifold in EM group)
3. Connect the driveshafts(A, B) to the transaxle.
4. Supporting the sub frame(A) with a jack and the Special tool(09624-38000), install the mounting bolts. (See SS group).

Tightening torque :
140-160Nm (14-16kgf.M, 101-118lb-ft)
5. Install the muffler hanger rubber (A).
6. Install the roll stopper bracket bolts(A, B).
Tightening torque :
50-65Nm(5-6.5kgf.M, 36.2-47.0lb-ft)
7. Connect the the power steering return hose(A) by tightening the clamp(B).
8. Install the tie rod end to the knuckle. (See ST group)
Tightening torque :
24-34Nm(2.4-3.4kgf.M, 17.4-24.6lb-ft)
9. Install the stabilizer link mounting bolt. (See SS group)
Tightening torque :100-120Nm(10-12kgf.M, 72.3-86.8lb-ft)
10. Install the lower arm ball joint assembly mounting bolts. (See SS-group)
Tightening torque :100-120Nm(10-12kgf.M, 72.3-86.8lb-ft)
11. Refill the manual transaxle fluid through the oil filler hole by removing the oil filler plug after installing the transaxle drain plug.
Tightening torque :
30-35Nm(3.0-3.5kgf.M, 21.7-25.3lb-ft)
Manual transaxle fluid :SAE 75W/85
12. Install the steering joint assembly bolt. (See ST group)
Tightening torque :
18-25Nm(1.8-2.5kgf.M, 13.0-18.1lb-ft)
13. Lifting up the vehicle, install the under shield cover.
14. Install the front wheels&tires. (See SS group)
15. Install the transaxle insulator mounting bracket bolts (A).
Tightening torque :
60-80Nm(6.0-8.0kgf.M, 43.4-57.9lb-ft)
16. Remove the special tool(09200-38001).
17. Install the transaxle upper mounting bolts (A-2ea) and the starter motor mounting bolts (B-2ea).
Tightening torque :
43-55Nm(4.3-5.5kgf.M, 31.1-39.8lb-ft)
18. Connect the power steering pressure bolt(A). (See ST group)
Tightening torque :
55-65Nm(5.5-6.5kgf.M, 39.8-47.0lb-ft)
19. Connecting the concentric slave cylinder tube(A) install the clip(B).
20. Install the ground (A).
21. Connect the cable assemblies(A) by installing the clips(B) and pins(C).
22. Connect the vehicle speed sensor connector (A), the back up lamp switch connector (B).
23. Install the battery tray (A).
24. After installing the air cleaner assembly (B), connect ECU connector (A).
25. Connect the air duct (A).
26. Install the battery(A).
27. Install the engine cover(A).
28. After completing the installation perform the following procedure;
A. Refill the all fluids.
B. Clean the battery posts and cable terminals with sandpaper and grease them to prevent corrosion before installing.

________________________________________

Let me know if this helps.

Take care,

Joe

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Wednesday, August 8th, 2018 AT 7:04 PM

BOGIECLASSICCHEVY

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5 POSTS

Thanks Joe. I will let you know how it goes. Regards, Greg

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Monday, August 13th, 2018 AT 11:15 AM

KEN L

MASTER CERTIFIED MECHANIC
47,602 POSTS

JACOBANDNICKOLAS is one of our best! please let us know what happens. this video can help as well.

https://youtu.be/6N6b5F2ChyE

Let us know what happens and please upload pictures or videos of the problem.

Cheers, Ken

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Thursday, August 16th, 2018 AT 12:12 PM

BOGIECLASSICCHEVY

MEMBER
5 POSTS

Hey guys. Sorry for the delayed response but we actually just did this job this weekend. Couple lessons learned/observations:

1. Kia parts are hard to come by. None of the local auto parts stores carried what I needed and could not even order them. We had to go directly to Kia and that required at least ten days to get them. Not the ideal environment to work with - need to make sure you have all the parts you are going to need (or think you will need) and then make sure you do not break something else in the process of completing the job.

2. You need special equipment the average DIY car guy probably will not have but you cannot live without - Engine cradle that will allow you to raise and lower the engine/transfer case combo and a transmission jack.

3. I assumed incorrectly that if the fluid reservoir had fluid between the min and max line that we had not lost any fluid. Turns out the clutch system can be empty and the fluid reservoir not show low. (This car shares brake and clutch on the same fluid reservoir.) So a simple check of adding fluid and pumping the clutch would have shown we did in fact have a slave cylinder failure. We did this but only after replacing the clutch master cylinder did not work. Dumb mistake and should have been the first thing I tried.

4. Having an internally mounted slave cylinder that when it fails commits you to this level of effort to repair seems a pretty crazy design. I assume these things are not supposed to fail at 94,000 miles and be "maintenance free" but it clearly was not so in our case. Not sure if driving/shifting technique could have a play in this premature failure or not. Pretty aggravating.

So once we knew we were going after the slave cylinder, we ordered the parts we would need: slave cylinder and since we were going that deep, the pressure plate, clutch and rear main seal. We opted not to replace the flywheel feeling pretty confident it would be okay. Fortunately it was.

We used your written instructions from above and the YouTube video and after studying our specific situation with the Forte Koup, felt confident we knew what we were getting into and needed to do. We pretty much followed everything as outlined but we were able to do the job without following a couple of the steps. Bottom-line, if it was in the way of or attached to the transfer case and would hinder its removal, we removed it. This included the need to drop the frame sub-assembly. Sorry, but we did not slow down to take any pictures. Your video of the Chevrolet clutch replacement does an excellent job though.

Took about six hours to get the transfer case out, only about five minutes to replace the failed part (insert angry face here), less than one hour to replace the rear main seal, clutch, and pressure plate, and then about five hours to put it all together again. So twelve hours for two guys who have never done this before.

No extra nuts or bolts at the end of the job and the car started right up and drove away. (Fingers still crossed).

Thanks again for the help. Would not have tried it without you.

V/r Greg

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Monday, October 15th, 2018 AT 12:41 PM

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

Welcome back, Greg. It sounds like you had a hard time of it. Even under the best conditions, it is a tough job, so with that being said, great job. Also, that you so much for your detailed post. I know it will help someone else in the future.

Please feel free to come back anytime you need something.

Cheers,
Joe

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Monday, October 15th, 2018 AT 7:02 PM