Sreadon

Hi,

First of all sorry for the mistakes, I'm from France, english is not my main language.

I'm the owner of a 2007's Mustang GT/CS with 75.000 miles on it and although I like my car the transmission is getting on my nerves. My clutch (Spec stage 1) is 6000 miles old, so is the slave cylinder and the tranny's oil. Sometimes gears are switching perfectly like butter, even at low speeds, but most of the time, when the motor is cold or when cruising (ie, shifting below 3K RPM) I can't sift into gears correctly, it's really hard but no grinding, it feels like the clutch is not fully disengaged. If I'm going hard on it, I can shift easier into gear, that's the exact contrary of maning threads I've seen.

I know that on our cars the brake fluid is used by both the brakes and the transmission, and my brake fluid has never been replaced (should have been when replacing the slave cylinder, no?) looking at it's color (black), I'm going to replace it as soon as possible, but I doubt it'll improve shiftings and it can't be bad for the car. I also know those Tremec TR-3650 are not that reliable but the fact is sometime it goes into gear like butter several times, so I don't think it's a synchros problem, am I wrong?

Any ideas? I can go with a rebuild kit but as I'm in France parts are expensive to get here (imported vehicle, not sold in the EU ) unfortunately so I'd like to be sure before buying anything...

Thanks
Steven

Dino Dino Bambino

I don't think there's anything wrong with the tranny itself, plus the TR3650 is pretty tough and not easy to break unless you beat on it.
If the clutch/brake fluid has degraded as it seems in your case, depressing the clutch pedal may not generate sufficient hydraulic pressure to disengage the clutch. There may also be tiny air bubbles in the system that further aggravate the problem. Therefore changing the fluid and properly bleeding the system would be a very good idea.

Sreadon

Okay thanks.

I don't think my gearbox has been beaten, I'm the 3rd owner, I don't know about the one who kept it from 0 to 40K miles but the one before me was a guy who was afraid of the speed and just wanted to hear the V8's sound.

Yes I don't think it has ever been replaced since 2007 looking at the invoices I have with the car (and the color of it...), so I'll ask some mecanics to do it for me. Any advices on the fluid to use? I know I have to use DOT4 one so I was thinking about the Motul's RBF600 but If I can let the mecanic to choose, that's good too.

Dino Dino Bambino

Check the owner's manual for the recommended type of brake fluid. If I remember correctly, I think it's DOT3.

Sreadon

I've brought the car to a garage, unfortunately they did had the right tools for that so he advised me another mechanic, I'll call them asap.

The problem is getting worse, I can't even change gears correctly when the car is running... Even though he was not able to change the brake fluid, he looked at the car and showed me that even with the clutch pedal down, the car was still trying to move, that's a proof that the clutch is not fully disengaging so I guess I'm one the right way.

Anyways, as you said, he highly recommended me to change the brake fluid before anything else so that's what I'll do.

I'll post here when I have news.

Derf00

Yuh, check the brake fluid and check what oil is in the transmission. Some take auto tranny fluid, some take actual gear oil. If you're using gear oil, perhaps a lower viscosity will help or if it's auto fluid, check the condition.

danzcool

Either there is air in the hydraulic line, or the throwout bearing (slave cylinder) has gone bad. There was a trick to getting the pressure up... it was parking on a hill with the front of the car pointed either up or down (I don't remember which) and then pressing the clutch pedal repeatedly before going out anywhere.

Dino Dino Bambino

Hopefully that'll help but I fear that Danzcool may be right about the slave cylinder going bad. A bad clutch master cylinder is also possible.

Sreadon

I think the oil is fine as the problem "suddently" started, but I'll change it again if needed. I've read that the best oil for the manual tranny is the MOTORCRAFT MERCON ATF, is it right?

I hope it's not the slave cylinder that is going bad... it's only 6.000 miles old, so as the clutch (Spec stage 1). On the other side, the clutch's master cylinder is the factory one, so it's 10 years old and have 75.000 miles. I've read that there is a plastic part that often broke on this thing, the one who connects to the clutch's pedal, I'll check if this part is not on her way to the death, may be that's "just" that. I also read that I could check if my master cylinder was working correctly by pressing the clutch pedal down and asking another person to check if the brake / clutch fluid was moving in the reservoir, is it a good way to check?

Yeah, there is so many parts that could do those symptoms that I don't really even know where to start but tomorrow I'll call the other garage to ask them if there have the right tool for the brake's fluid change.

Sreadon

I couldn't wait tomorrow to check so I went to see what I could check on the car, and here are some videos and tests I've made.

1. Clutch pedal with Clutch Master Cylinder: Sorry for the poor video quality but it's not easy to get in there while the car is parked without damaging the doors You can here that squeezy sound, never noticed it before but my car is pretty loud so maybe it's there since a lot of time.

2. Brakes fluid reservoir: I've tried to record the reservoir's level while pressing the clutch all the way down slowly. It's moving but I would say to 1-2mm, I think it's normal, am I right?

3. I pressed 5-6 times the brakes, I could here a little "pump" sound (like if air was leaking) then the pedal became hard as fu*k, I think it's normal as it became normal right after I started the car.

4. I tried to change gears with the engine off, it changed without problem (feels notchy -Hurst shifter hereeee- but changed pretty easily).

5. I started the engine, I was able to change gears without problem (almost as if the engine was off) during approximatively 15-20 seconds, after this delay the gears started to be "impossible" to change again.