Appreciate your wisdom guys and sorry for the long post I’m learning what is / is not relevant to include…

Here are the symptoms…looking for educated guesses on root cause:

Problem area - transmission, viscous coupling, front differential on a manual 2002 996 Turbo. Details:

- When in neutral, very tough to push / role the car because of medium / high resistance in the drivetrain.
- On the lift with motor off and car in neutral. If I spin one rear wheel clockwise, the opposite rear wheel spins counterclockwise with typical resistance - e.g. very easy to spin the wheel and no unusual noises - e.g. chirping / grinding; no movement occurs in the front wheels
- Easy to also rotate the front wheels with no chirping / grinding, the rear wheels don’t move
- Trying to rotate both rear wheels by hand in the same direction is very difficult
- Still on the lift with motor on and in gear, all wheels spin in the forward direction. I can “grab” a front wheel and stop it while the others continue to spin. There is no chirping or grinding noise when I do this.
- While driving the car there is always a chirping sound as long as the car is moving whether clutch in or out. The frequency of the chirping is directly tied to the speed of the car - fast at high speed and low at low speed. The noise is closer to the squealing made by cold race brake pads on steel rotors vs. a grinding noise like clutch less shifting without proper rev match.
- If the car is stopped, transmission in neutral, and clutch engaged (i.e. clutch pedal not depressed and the engine and transmission connected), the car stays put and no noises are made in the driveline.

Transmission was rebuilt by Isaac Fritsche in 2013 (lost 2nd gear at Road America) - Fairly well known Porsche Motorsport mechanic spending most of his time in Europe now - I kept standard gear ratios, stuck with helical cut gears, but upgraded synchros to Cup parts. Nothing was touched in the driveline forward of the viscous coupling. I was happy with the work - the transmission was so smooth and positive in its movement, it was clear I had no idea what good was before that.

Motor is an EVOMS GT700, with a SACHS Stage 4 “puck clutch” - I frequently tracked the car before the transmission was rebuilt - to the tune of about 3,000 track miles. You may be wondering why I did not convert the car to rear wheel drive and install a limited slip. I decided it was better to buy a purpose built race car than keep modifying this one - so returned it to street form vs. hybrid track/street. Ultimately I am not wed to an AWD or RWD solution. I’ll probably go with the most cost effective.

Thanks for your help!!!

 

The car is hard to push or roll when in neutral probably because it weighs like 3400lbs.

The behavior of the rear wheels when you spin them with a standard non-LSD rear end is normal behavior.

When you spin the front wheels the rear wheels should not move. Normal.

You should not have the car on the lift with the engine running and the transmission in gear. This abuses the viscous coupling.

The chirping if directly tied to vehicle speed and not engine speed could be a dragging brake pad. If you lightly apply the brakes does this affect the noise?

If the noise not associated with the brake hardware, with the track time the car has seen you could be looking at a bad wheel bearing, or a bad CV, rear or front.

If the chirping is tied to engine speed then suspect a bad idler roller bearing, tensioner roller bearing, even perhaps a bad water pump.

The power steering tank has a high pressure relief valve that can make a noise. I heard a squeal. A chirp could be possible I guess.

Is the power steering fluid level ok? Any signs of fluid leaking out at the front (clutch) reservoir under the panel just ahead of the driver?

Have to add I never heard this noise until the engine/drivetrain was up to temp and after rolling to a stop with the transmission in neutral and the clutch released. A dip of the clutch pedal would have the noise gone.

You have to try to determine what you can do, what you can *reasonably* do, from behind the wheel that can or can not affect the noise.

You can weave, turn in a tight circle first in one direction then the other, while off or on the brakes. You can see if putting the transmission in neutral has any effect on the noise.

 

Thanks for quick response Macster.

I initially thought dragging brake pad as well. I have not ruled it out, but have pushed it further down the list since there is not a hint of that noise when the wheels were spun manually and in gear while on the lift.

Bad wheel bearing and CV still high on the list - the front passenger cv boot is oily on the outside and will need to be addressed. Unfortunately, probably looking at an "AND" scenario vs. "OR" - I've pushed this Turbo around plenty at paddocks and it was substantially easier than it is now - my first reaction was to double check the car was in neutral because it felt like it was still in gear.

I have ruled out that chirping is due to engine speed. I ran car next to highway median in order to hear better, held car at constant velocity, and ran it in 3rd, 4th, and 5th gear. The chirp frequency was the same in all gears.

I'll check the power steering fluid levels and for leaks at the front clutch reservoir and report back.

Thanks

 

If the front (or any) CV boot is oily on the outside the CV joint itself has to be suspect.

BTW, the boot should not be "oily". The CV is packed with a heavy grease.

If indeed there is oil this could be from a brake fluid, power steering fluid leak.

The front axle flange seals on my Turbo's diff developed leaks. However I do not know if the the inner (or outer) CV boots were oiled. I never saw them. But they were not touched so probably not.