Rev but no power?


I recently had a problem with my Mitsubishi GTO 1992 Non Turbo MANUAL Japanese import.
When I was revving it would simply rev and the car would hardly move. I had the whole clutch changed and the slave cylinder. This fixed the most of it but now, a couple of days later, when my car gets warm it happens again, particularly in high gears.

If the clutch and slave cylinder have been changed, what can it be?


Did you replace the clutch master cylinder as well? I always replace the clutch cylinder and slave cylinder as a pair to avoid problems like this.

+1 to missileman. Master and slave cylinders should always be changed together. If the seals in one are failing, the other is not far behind.

However, the master & slave cylinders only allow the clutch to be disengaged. In your case, you clearly have clutch slippage. That’s the opposite.

When you had the “whole clutch changed”, did that include the pressure plate assembly and the release bearing? Either of these being bad could prevent proper clutch plate engagement.

Was the flywheel surface inspected? If the surface is glazed, it should be machined (or at least burnished) to provide a proper frictional surface. Glazing is not uncommon for a flywheel that’s used at length with a badly slipping clutch before changing the clutch.

Post back with the answers. We do care.

I’m going to lean away from the MC or SC simply because they’re mostly involved in disengaging the clutch. So problems there are more often about having general trouble actuating the clutch and changing gears.

I’d be leaning more toward something like mountainbike’s question of the flywheel. Or related things. Was the rear main seal replaced when the clutch was done? A small leak there could show itself as slipping more after the car has been driven a while. A problem with the new pressure plate is also a possibility.

My mechanic says he cannot push the fork in, does this mean it is the master cylinder? He says it is but I want to be sure before I pay out £200 for the part. Would this cause the clutch to slip when hot?

To answer that question I need to know exactly what happens when he pushes the pedal.

If the pedal will not push in at all, even with the hydraulic line disconnected, and the linkage is good, than the master cylinder is somehow jammed.

If the pedal pushes in, but the fork never moves, it’s the master cylinder leaking internally past its piston seal.

If the pedal won’t push in, but WILL with the hydraulic line disconnected, it’s either the release bearing or the pressure plate assembly.

A bad master cylinder will NOT allow slippage UNLESS the piston is somehow hung up and preventing the pressure plate assembly from clamping the clutch plate onto the flywheel.

Post back with details.

hmmm … what if the mechanic opened the bleed screw on the slave cylinder, then will the clutch fork move freely?

My mechanic is away for the weekend so all I can tell you for now is this:

  • The clutch works fine until I’ve drove around 7-10 miles, then it starts getting hot and it starts slipping.
  • He has removed the hydraulic line and rerouted the existing metal line to the slave cylinder and the problem still persists.
  • The clutch at first is excellent until it warms up.
  • The system has been fully bled.
  • When I drove it away from him removing the hydraulic lines, the clutch pedal actually stayed on the ground, but then worked fine again until it warmed up.

I understand that if the pedal stayed on the floor then it is a sign it is the master, but would that be what’s causing all of the slipping?

Any help appreciated!

It’s possible you have more than one problem. At least in any manual xmssion car I’ve driven, the clutch pedal would never stay all the way to the floor unless there was a very serious hydraulic or clutch linkage problem. For one thing, there is usually a fairly big spring attached to the clutch pedal that you can see just by looking down there with a flashlight, that pulls the pedal off the floor. It may also be that the clutch disk and or flywheel has got something slippery on the mating surfaces. Not an infrequent problem with replacement clutch jobs, especially if done by a clutch-inexperienced mechanic who forgets to make sure the surfaces are spotlessly clean before reassembly. Also sometimes $$ have been skimped by not replacing seals while the transmission is out. First thing though is to understand why the clutch pedal did not return from the floor when you drove away after the mechanic re-routed the hydraulic lines.

George, you got me on the bleed screw thing. A tip of the hat to you.

I’m inclined t think that the clutch pedal not returning up properly is definitely related to the slipping… but not necessarily the cause. It sounds like it’s operating as if you’re still pressing on the pedal. In my mind, that would override the thought of there being a frictional problem between the clutch plate and the flywheel or pressure plate surface.

Since you originally said “I had the whole clutch changed and the slave cylinder” but did not include the master cylinder in the statement, and since your mechanic has already said the master cylinder is at fault, you might want to let him change it and see what happens. IMHO slave and master cylinders should always be changed as a set anyway. If one is bad, the other is on its way out. The only other possibilities really are a problem with the fork, the release bearing, or the pressure plate assembly.

Okay guys I’ll tell him about the bleed screw and I will get the master changed and let you know what happens. Problem is the master cylinder for this car has to be imported from Japan and costs £210, no second hand ones are around, but oh well! Thanks very much for your advice, I appreciate it!