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2006 Mustang GT Manual Wont Shift When Warmed Up

I have a 2006 Mustang GT with a manual transmission. The car shifts fine when cold, then gets more and more difficult until it will no longer shift. This is over the span of 20 minutes or so. I had a full clutch kit intalled approximately 5,000 miles ago and had the brake fluid replaced. That said, I figured it had to be the clutch master cylinder. Replaced that and vacuum bled it through the reservior- the clutch is quite firm, so I’m thinking it’s fully bled out.

Problem still occuring. Could it be the clutch again? Maybe a premature slave failure? I really only use this as a Sunday cruiser and don’t drive it hard at all.

Yeah, I’d be looking at the slave cylinder… I think. I’m not really sure - because you say it gets difficult to shift, but don’t say how it gets difficult. The clutch won’t let out? It grinds going into gear? The shift lever itself is stiff? What?

THanks. To add, it will grind. I’ll have to press the clutch further and further, then it will no longer be sufficient to disengage the clutch, at which point it will grind or ultimately just not go into gear at all. I haven’t pushed it that hard as I’m not too keen to grind the gears.

If I had to sum it up, it feels like as my car warms up, I get less and less throw from the clutch untill the throw is completenly insufficient to get into 1st/2nd. It will go into higher gears with some difficulty, once warm.

Carry a bottle of water in the vehicle.

The next time it becomes difficult to shift, stop the vehicle, open the hood, and pour the bottle of water over the clutch master cylinder.

If doing this allows shifting of the gears, the new master cylinder is being effected by under-hood heat and is leaking internally.



Hey Tester. Thanks. The problem existed before the master cyclinder replacement as well. I replaced the master cylinder becasue I thought the heat may be affecting it. Is it possible that the heat has affected both?

Pouring water over it will confirm it.


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Yes, absolutely heat affects both. The master and the slave get very hot as there isn’t a lot of airflow in that area. The same for the hose that connects the slave. If you haven’t changed the clutch hose to the slave, do that because it sounds like you have already changed everything else.

Yeah- that’s what has me confused here. I’m going to see if it’s being heat-affected. If that’s the case, I’ll probably try to insulate the area. The engine isn’t running hot and the bay doesn’t feel any hotter. The only other change I can think of is that I switched to DOT 4 at some point, but I think that was well in advance of all this.

To add, by both, I meant the old and new master cylinder, not master and slave.

Since you said a “clutch kit” was installed, that should include the slave cylinder as well as the clutch disk and pressure plate. Since you have to pull the transmission to replace the slave, change the clutch hose first and see if that solves it. I think it will.

(1) A clutch, slave and pilot bearing were installed
(2) Hard to shift problem appeared
(3) Clutch master was replaced
(4) Hard to shift problem remains

The line just clips into the master, then outside the bell housing, correct?

I believe that is correct. Oddly enough the hose is not listed on RockAuto but there are braided stainless hose upgrades from a number of sources.

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I generally find that when a problem appears right after a maintenance action, its either a faulty part installed or a mistake by the installer. I think your new clutch is going to need to come out and be inspected.

Yeah, I’ve had that in the back of my mind. The clutch kit install set me back a nice little chunk of change. Not looking forward to paying for another one so soon afterwards. I normally do most work myself, but am not too keen on being under a sports car for four to five hours. Suppose I should have…

Explain again how you bled the air out of the clutch hydraulics after the most recent clutch MC install. On my Corolla there’s a bleed nipple on the slave. I push on the clutch pedal while alternately tightening and loosening the bleed nipple, using a clear hose on the bleed nipple, until no air bubbles are seen. Is that how you did it?

It doesn’t mean another kit is needed. Possibly just the throwout bearing/slave combo wasn’t installed correctly but I’d try the hose first

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This year s197 doesn’t have a bleeder valve. You need to fit a brake bleeder over the hydraulic reservoir and pressurize to 20mb, then brake the vacuum. Pump the clutcha few times. Repeat until clutch is firm.

Here’s what I’m seeing for that procedure

Tighten all bleed screws to 70 inch lb, place clutch pedal in full upright position, fill reservoir, place 15-20 inch hg vacuum on reservoir, hold vacuum for 1 minute, then quickly relieve vacuum, refill if necessary, install cap, depress and release pedal 15 times. Repeat steps above two more times if it doesn’t work the first time.

Is that what you did? Note that there’s no pressurization involved, only placing a vacuum. The reason I ask is b/c the symptom sounds like the clutch hydraulic system hasn’t been fully bled of air yet. The whole scheme seems sort of sketchy to me anyway. Is there an actual bleed nipple on the slave? If so, you may need to disassemble things to that point and bleed the normal way, could work.

My experience has shown that if there’s air in a hydraulic system, be it in a brake or clutch system, there will be a soft pedal from the get-go.

And not be dependent on temperature.