Slipping Clutch?

[MikeSomeone]

I have a 1994 audi 90 quattro. It's a 5 speed and this is the only stick shift I have ever driven (I am new to it). When I got the car, I remember that in 2nd gear at 3000rpms the car would be at 35mph exactly. Now at same gear and rpm's it is only at 30mph. Is this a sign of the clutch slipping? It seems to have lost slight power overall.

Also, before the car driven for a couple miles shifting into 1st and 2nd is difficult without letting rpms drop below 1000. It feels almost what I would imagine is grinding gears but doesn't sound like it. And once its warmed up it shifts fine. Any ideas what could cause this? or maybe its normal, but it didnt do that when i first got. Maybe it could be the pedal needs adjusting cause its not "opening" the clutch all the way. thats all i can think of. If it is then how do you adjust the pedal?

[curtis73]

A slipping clutch will act like you have the clutch pedal halfway engaged. If you give it gas the RPMs will climb.

But a steady RPM is not a sign of a slipping clutch. When you're in gear (maybe 3rd or 4th) stab the throttle. If the RPMs flare up as if you have the clutch pedal half way down, that is a slipping clutch.

[arrowf1]

exactitude

[shorod]

For the vehicle speed versus engine speed, have you checked your tire inflation to make sure it's where it should be? The speedometer on that vintage (and earlier) vehicles is often driven off the output gear of the transmission/transaxle. But, Audi may have been early in deriving vehicle speed from the ABS wheel speed sensors, in which case tire inflation could play a part in what you describe.

As for the difficulty shifting until the vehicle warms up, that sounds like an issue with the transmission gear oil. When is the last time the transmission/transaxle gear oil was changed? If you don't know, or the answer is "never" that will likely have quite an impact on the ease of shifting. You may consider going with a synthetic to work even better at cold temps.

-Rod

[MikeSomeone]

This is great information to know. One of the rear hub bearings failed and grinded off the tip of the ABS speed sensor. I would imagine this to be the cause since you mentioned speed is derived from speed sensors. When you say it is derived from the sensor does that means that I am actually going faster than the speedometer is reading?

[MikeSomeone]

Also, the pedal seems to be grabbing higher up then it used to. As I mentioned earlier could this just be that the pedal needs to be adjusted? If so, how do I go about adjusting it? Can I do it myself/someone whos got decent mechanical skills, or would I need a professional mechanic to do it?

[shorod]

Originally Posted by MikeSomeone

This is great information to know. One of the rear hub bearings failed and grinded off the tip of the ABS speed sensor. I would imagine this to be the cause since you mentioned speed is derived from speed sensors. When you say it is derived from the sensor does that means that I am actually going faster than the speedometer is reading?

I said that some vehicles derive speed from the ABS wheel speed sensors. Often they pick a single wheel speed sensor to use for vehicle speed. Also, a wheel speed sensor will either work or it won't work. If the tip was ground down, that wouldn't cause the sensor to read slower or faster. Slower or faster than actual would depend on if your tires were over or under inflated.

-Rod

[curtis73]

Wait... it doesn't matter where the speed sensor is, it won't change when the tires are low. It will change the ACTUAL speed the car travels, but it won't change the speedometer relative to the tach.

The wheels are mechanically linked to the engine by a fixed ratio. You could put 33" truck tires on it and wouldn't change the indicated speed/RPM ratio. The actual speed of the vehicle will change, but not the ratios involving the speedo/tach. If the speedo reads 35 at 3000 RPMs before, it will always read that way unless you change a gear ratio somewhere in between the speed sensor and the engine.

There is no adjustment on your clutch. Its hydraulic, so it self-adjusts every time you depress the pedal. If you are noticing that the pedal engages higher, you have probably reached the end of its adjustment and the clutch is so worn that is slipping.

Try the suggestion I put in my first post and post your results.

[shorod]

Originally Posted by curtis73

Wait... it doesn't matter where the speed sensor is, it won't change when the tires are low. It will change the ACTUAL speed the car travels, but it won't change the speedometer relative to the tach.

Doh! That's right.

-Rod

[MikeSomeone]

Not once has the clutch up slipped the way you described it curtis, that the rpms flare up. the rpms just aren't at the same corresponding speed anymore. There's no explaination for this? It seems as though the clutch is slipping at a constant rate. Thats the only that makes sense to me, but is that possible?

[curtis73]

Its not really possible. If its slipping, then additional torque input from the engine would make it slip more.

I think its more likely that you are either A) misremembering your benchmark RPM, B) Something about the speedometer or sensors has malfunctioned, or C) something about the tach is malfunctioning. I might suggest you test the speedo on the highway between some mile markers. The tach can be checked by a shop. Many smog shops have an inductive coil that they can just lay on the engine and it will read RPMs. See if theirs matches yours.

The only way for that benchmark RPM/MPH ratio to change is either slippage (which I think we've eliminated) or a change in a gear ratio somewhere in between.... or a malfunction of one of the gauges.

[Moppie]

The speedo in my Prelude has recently starting reading 20-30kph higher than actual speed.

I have yet to figure out what is causing it, but my best guess is a failure somewhere in the unit itself, as the trip meter, and odo still work fine, and are driven from the same VSS as the speedo.

[LeSabre97mint]

Originally Posted by Moppie

The speedo in my Prelude has recently starting reading 20-30kph higher than actual speed.

I have yet to figure out what is causing it, but my best guess is a failure somewhere in the unit itself, as the trip meter, and odo still work fine, and are driven from the same VSS as the speedo.

Moppie

I looked up your car in a manual and it says that your speedo is powered by a cable. I'm thinking that the magnetic drive in the speedo head needs repair. I think the best thing to do is to pull a used one from a bone yard. I had to replace the speedo head in my 95 Windstar.

Regards

Dan

[LeSabre97mint]

Originally Posted by MikeSomeone

I have a 1994 audi 90 quattro. It's a 5 speed and this is the only stick shift I have ever driven (I am new to it). When I got the car, I remember that in 2nd gear at 3000rpms the car would be at 35mph exactly. Now at same gear and rpm's it is only at 30mph. Is this a sign of the clutch slipping? It seems to have lost slight power overall.

Also, before the car driven for a couple miles shifting into 1st and 2nd is difficult without letting rpms drop below 1000. It feels almost what I would imagine is grinding gears but doesn't sound like it. And once its warmed up it shifts fine. Any ideas what could cause this? or maybe its normal, but it didnt do that when i first got. Maybe it could be the pedal needs adjusting cause its not "opening" the clutch all the way. thats all i can think of. If it is then how do you adjust the pedal?

Mike

I would have an experienced stickshift driver drive it. There may not be a problem.

Dan

[bobss396]

You usually will get a smell from a slipping clutch or notice it going up grades. The aforementioned "20 mph and gas it in high gear" test always worked for me. You should first rule out mechanical issues before you get into gage or indicator related issues.

The clutch should engage approx 1" off the floor. Too close to the floor and it'll bind, not allowing the clutch to release. Too high up and it won't be fully engaged and could slip.

The adjustment is probably pretty easy once you know how to do it, I'm sure you can hit the reference books at the library, an invaluable source that few know about.

Also look at the condition of the linkage and or cable. Look for rusted spots which can indicate abnormal metal-to-metal wear.

Bob