This one’s on my 93 MR2. 172k miles on it. It’s the naturally aspirated version.
The clutch engagement point shifts, but only when I’m backing into my garage. My driveway is short. It’s almost flat on the bottom, then rises at around 20 degrees or so for about 3 feet, then flattens out again to go into the garage. When I get to the up-hill section, the engagement point drops from its normal place, just before 50% of travel, to 2mm at most from the floor. It stays like that until I get it into the garage.
It’s hard to get it out of gear when it’s like that, so I know the clutch is not completely disengaging when I have it all the way to the floor. If I let it sit for a couple of seconds, then put it in first and roll forward slightly, the engagement point moves back to where it’s supposed to be, and stays that way. I took it on a 100 mile test drive to visit my mother on Sunday, and it behaved perfectly the whole time, including reversing on her driveway, which had me on a very slight downhill rather than up hill. Then I got it back home and as soon as the car hit the uphill on my driveway, the engage point popped back down to the floor.
It doesn’t do this when I reverse somewhere flat like the street or a parking lot, which is why I suspect it has something to do with the hill.
The clutch fluid is full, but looks a bit dirty. I’ll be changing it out in a couple of weeks (and won’t be driving it until then), but I’m kind of doubtful that dirty fluid would cause this only when reversing on a slight incline. That said, I’m not really much of an expert on hydro clutches since until now I’ve mainly worked on cable ones.
Any ideas what this could be?
I wonder if the problem might be a broken motor mount or transmission mount,
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Hm. I can see where that might cause issues. That’ll be the first thing I check when I dive under it this evening. Thanks!
open the engine cover and have a 2nd person watch the motor move as you go thru the motions. try different spots on your driveway and see if there is any motor/trans moving
Jack the rear of the car to the approximate angle of the problem hill, set the brake and check the reservoir to see if the master cylinder port is above the fluid level. The master cylinder may be catching a gulp of air.
Mounts look pretty good. A little flex off the lower one, but no more than it’s ever done in the 10 years I’ve owned it. However, @Rod Knox put me on to something. I got it out on the driveway so the angle would be exact to do some testing.
I discovered some things: First, if it’s on the hill already before the problem happens, it won’t happen. I have to transition from the flat part at the bottom to the hill, and then it happens. And I have to do it at a normal speed (probably 5mph or so), and the clutch has to be almost all the way out. If I leave the clutch farther in because I’m planning on stopping on the hill rather than in the garage, the problem does not happen.
I discovered that when the problem happens, if I take it out of gear, then release the clutch, the problem goes away the next time I use the clutch. So when the clutch problem happened, I had my SO watch the reservoir. The fluid was at the max line. It normally is just above the min line, and that’s where it dropped back down to once I put it in neutral and let out the clutch. Pushing the clutch back in again moved the fluid slightly, but not to the max line.
Line pinching off internally, maybe even caught by something flexing when I transition to the hill?
There is a flex line between the hard line from the master cylinder and the slave, down near the transmission. I wonder if the hill causes enough of an engine shift to pinch that flex line, causing the issue.
That’s what I’m starting to suspect. I’ll have to get it up on stands this weekend to have a look. I suspect I’ll be putting new engine mount bushings in and either replacing or rerouting that line. Will report back. Thanks!
Something is wrong with the clutch master cylinder. I am wondering if some foreign debris is behind the primary cup and lifts the seal to allow the fluid to bypass thus letting fluid back into the reservoir. The debris gets pushed out of the primary seal path on level ground and stays out of the way until the cylinder bore is pointed downward, i.e. car nose severely lower than rear. The displacement of the master cylinder piston would raise the reservoir level when the fluid bypasses the primary seal. I suspect that as the piston travels further into the cylinder the primary seal can reestablish requisite pressure.
BTW has the clutch master cylinder been replaced? Since you will be doing a clutch fluid flush shortly, you might as well replace the clutch master cylinder or at least do a clutch master cylinder seal kit overhaul. You might consider doing the slave cylinder also as it will probably be failing soon.
If you do find the solution to and/or the why of this problem let us know.
That’s what I’m planning. And as long as I have to remove the front engine mount to replace the slave cylinder, I’m gonna put in a poly bushing to reduce some of the flex I saw yesterday. Probably be a couple-three weeks before I can get to it as I’m pretty booked, but I’ll let you know!
hi shadowfax, been some years since this discussion, but I found it after this week experiencing this EXACT symptom(s) on my exact same car: 93 MR2 NA. I have 86k on the ticker and have owned it 23 years. Wondering what more you discovered and if you were able to resolve the problem. Thanks!
Glad you posted. I obviously forgot to update. The slave cylinder was dead. I replaced it and the master at the same time. I also as promised put a poly bushing in the front engine mount, which eliminated the engine flex. The downside is that it transmits more vibration and a little more noise to the cabin. The upside is that it feels a lot more responsive because part of the initial energy isn’t going into rotating the engine. And since this is a fair-weather only car that I hardly ever drive with the T-tops on, the noise isn’t a big deal.
The slave on the MR2 is a pain as you will discover (much like almost everything else on the car). When installed, the bleeder nipple is below the highest point in the cylinder, which means normal bleeding will leave an air bubble in the cylinder. People bleed these clutches one of two ways. Either they don’t install the slave, but hang it with wire so that the nipple is pointing up, then bolt the slave in after it’s bled, or they use a vacuum bleeder. Not the stupid Mityvac hand pump thing - a real one that hooks up to an air compressor.
I went the vacuum bleeder route because I had one anyway. If you have a compressor you can get a bleeder kit at Harbor Freight that works very well and doesn’t cost much money at all.
I was thinking that or a bolts are loose on the linkage.
Thanks! Just before I found your initial post, I had taken it to my “MR2 guy” here in Colorado. He had not heard of this either (with his extensive experience) but when checking noted my “filthy” clutch fluid. I could not recall ever changing it (not being in the car’s manual; me bad!), so he did a flush/fill using a pump method from the front of the car back to the slave. He also checked the pedal linkages and did a clutch adjustment, with the words “I have seen dirty fluid do some wierd things”. Ironically when I got home to my sloped driveway, the symptom recurred. Some days later after reading here I took it to one of my general mechanics and had him check the engine mounts, transaxle fluid and the above mentioned “flex line” (although it sure doesn’t flex; I even got under there and tried it). He declared all looked good. Since then I’ve put more than 100 miles on the car with no symptoms including my driveway. Of course all of this has focused my attention on the hydraulic system, but I also wonder about the mileage differences between yours and mine; almost 100k. Could I really need new cylinder(s)? On a related, are rebuild kits available for the internal seals, versus buying a whole new part?
Dunno without looking. I knew I needed a new slave because I saw the leak, but whether that was causing the weird-clutch-on-the-hill problem or the engine flex was, I can’t say with 100% certainty. I tend to lean toward the engine flexing. I’d inspect that front mount one more time. Mine actually looked good on initial inspection, until I got an inspection mirror real close and saw that the rubber was cracked. The crack was almost invisible from a distance.
Maybe? I mean, you can get both the master and slave cylinders from Rockauto for less than 40 bucks, so I doubt it’d be worth your time to rebuild anyway.