'87 944S:Engine revs too high in 5th gear

[akaKJB]

I'm stumped on this one and I'm hoping somebody has either a better idea than I've had up to this point or an actual fix.

1987 944S 5-speed manual. Seems to run okay in lower gears but when you hit the highway and put it in 5th gear, the engine is revving way too high. It almost sounds like it's waiting for you to shift into a non-existent (for this car, anyway) 6th gear.

Anybody else ever run into & solve this problem (please, God, let someone say YES)? Other than this issue, it's about as close to a perfect daily driver 944S as you're likely to find. Astonished at how well its started and performed in the recent freeze blast. Just afraid to take it on any prolonged trips out of fear that I'm rapidly decreasing the life expectancy of my engine.

[mattdavis11]

Rubber centered clutch. Sorry to deliver the bad news, but it makes perfect sense.

[akaKJB]

It's got a fairly new clutch (replaced right before I bought it, has maybe 1k miles on it) and replaced the slave cylinder a couple of weeks ago. Are you saying that the replacement clutch itself is bad? It is shifting gears properly - it's almost like something has thrown the gear ratios off. If you don't mind, could you give me a little more detail on your answer? Much appreciated.

[ncspit80]

My 87S has always reved high. I think all the 87's had the short 5th gear. It's great for diving here in the Mt's but on the open road it always feels like you need another gear.

[rhett]

The 16V engine does have a bit more 'headroom' with regards to revs (over the 8V) but as it really doesn't start to perform until you hit about 4K, it can seem that the engine is running out of gears. I experience that too, and have to double-check sometimes to ensure I am actually in 5th .

Here are the specs direct from the owners manual for ref. It appears that the 5th ratio is pretty much the same across all 944, S and turbo models, but 1 to 4 is shared with the 951, albeit the diff ratio is different:





However, it could be that you do have a fault, so perhaps you could let us know what sort of revs you are experiencing when in 5th and at what road speeds, etc.

[emoore924]

What do you mean by "revs too high"? How many RPMs are you indicating at what speed?

[petrolhead611]

Its exactly the same mph/revs top gear ratio as the 944, looks like about 23.5mph/1000rpm whereas the 924S is just under 23

[djnolan]

Are you saying the revs vary in top gear, like the clutch is slipping? Then first make sure your clutch pedal is adjusted properly, as improper adjustment could cause the clutch to slip. If the slave was replaced, the pedal should have been checked and adjusted properly. There is a procedure for this in the Porsche manual.

If the clutch pedal is out of adjustment don't drive the car until you have it sorted out or you will risk burning out the clutch...

The clutch cannot be operated properly unless there is 0.5mm of play at the clutch pushrod. It cannot be measured and is about 3mm at the pedal pad and must be determined by feel. (I call it big toe slack)

[Volhv]

Sorry Rhett, but that first chart makes no sense... not sure where you found it.
Let me fix it. everything is just offset by one line, thus 5th is made to be reverse.



I've also added a red line on the graph, showing 5th gear in a 8V trans.
Quite different. I did not bother with the rest of the gears, since they are pretty close. I would prefer the short 5th in my 8V. The gap between 4th in 5th is HUGE!

akaKJB, wanna trade transmissions?

[djnolan]

Doesn't look right, revs to high. Owners manual says top speed is 140 for N/A, 150 for S, 160 for turbo.

[akaKJB]

Thanks to all of you for the helpful responses! After all of the internet searches, talking to other mechanics and some direct fiddling on my part with no change whatsoever, I was starting to think I has the one '87S in the world that was doing this (which, given past experiences, would be about par for the course).

I've looked over the gear ratio chart from the manual several times. If I'm reading it right, the engine should be running at 2900 - 3000 in fifth gear if you're at a normal highway cruising speed of around 70mph. Mine seems to be running at about 3500. It's getting about half the gas mileage it should (roughly 17mpg) which leads me to believe it's not meant to be run at this rpm intentionally.

The slave cylinder replacement came after my clutch pedal went straight to the floor one day thanks to leak in the slave cylinder. Tested everything after bleeding the system and that whole assembly seems to be functioning as it should.

[akaKJB]

DJNolan - No, it's not like the clutch is slipping. I shift into 5th gear at around 45mph or so where it sounds like I should but getting the car up to highway speed of 70mph causes the engine to run at around 3500 rpm, which makes the engine sound like you should be shifting into another gear. It stays at that rpm as long as you're driving at that speed, a little higher if you get it up to 90mph or higher. It just sounds like it's going to throw something if I keep driving it like this for any kind of distance.

[v2rocket_aka944]

3500 rpm isn't going to hurt anything.
How confident are you in your instrument wiring? Could the tach be off a bit? I have a turbo trans in my NA and it sees around 3000 at 80, but my axle ratio is higher than yours.

[akaKJB]

Originally Posted by v2rocket_aka944

3500 rpm isn't going to hurt anything.
How confident are you in your instrument wiring? Could the tach be off a bit? I have a turbo trans in my NA and it sees around 3000 at 80, but my axle ratio is higher than yours.

I'm reasonably confident in the wiring but God knows, it's not unusual for something in the instrument cluster to go weird by this point. I think this is the first old Porsche I've owned that has a functioning odometer. But I tend to think the tach is reading correctly because of the sound & feel of the engine. Like most people, I tend to up & down-shift based more on the feel and sound of the engine and this just sounds like it's screaming for me to shift to another gear. As someone said above, I'm checking a lot to make sure I'm actually in 5th gear. It just sounds off to me. Maybe I'm just hearing too much of the engine noise thanks to a previous owner removing the heat & sound baffling from the underside of the hood but then there's the poor fuel mileage as well.

Is it possible for some of this to be caused by a bad or mis-programmed custom performance module? I'm not even positive it has one but considering all of the part swapping for Turbo-spec parts the previous owner did to it, it wouldn't surprise me if they put one in.

[Mericet]

The source of your bad mpg is not due to the rpm the engine is turning and I do not think your clutch is slipping. 3500 at 70 sounds about right for the S and is about the same as mine.

[Jfrahm]

Sounds pretty normal. What is your wheel and tire setup?

[djnolan]

If you are hearing a lot of engine noise your shifter boot may be bad.

[rhett]

Originally Posted by Volhv

Sorry Rhett, but that first chart makes no sense... not sure where you found it.
Let me fix it. everything is just offset by one line, thus 5th is made to be reverse.

Hey, well spotted, I just cut n pasted from a scanned image of the owners manual on the net. I must admit I didn't look too hard at it, but your revised version now does make sense . I haven't looked in the original paper owners guide, but I wonder if it is a printing error?

[akaKJB]

Again, I really appreciate the assistance.

It's good to hear that I'm probably not burning out my engine but I'm kind of surprised that this seems to be a common trait of the '87 944S. I didn't think about noise coming in around the shifter boot. Maybe a combination of that and the missing heat / sound material from under the hood is combining to make the sound more noticeable. I picked up a can of what's labelled as heat & soundproofing material that looks suspiciously like that Flexseal stuff they sell on television. Anybody have any experience with this stuff?

If the noise I'm concerned about is normal for the 944S, I'm still trying to figure out the reason for the poor gas mileage. It's considerably less than what most other 944S owners I've talked to seem to be getting with theirs. I have been wondering about the exhaust system recently and hear the occasional sound that's a cross between something physically knocking against something and exhaust rattle. As far as I can tell, all of the hangars for the exhaust system are present and where they should be. The catalytic converter isn't very old but a spare one did come with the car when I bought it so if nothing else works, I can swap that out and see what happens.

[Gawernator]

Buy an inner shift boot from only944 while you're at it