Need transmission problem diagnosis..., Or best guess Options

[Dr Evil]

Thank you Cap'n. Sounds like I need to repair what I have and leave my other trans alone.
Thanks also to Dr. E. Hope I did not cause the hard feelings. I appreciate the wisdom of you both.

Jim, you are very welcome and you did nothing to start hard feelings. Thanks for sending me the email to direct me here. Anytime I can help, let me know.

[Porsche Rescue]

OK, now what? While in the process of removing the tranny I discovered there was no linkage bushing in the firewall, not even any crumbs! Figured I had found the problem. Went ahead and dropped trans as it needed a new input seal. I had already replaced the two forward bushings and had been waiting to replace rear two until I got to the seal job. With tranny on the floor I turned the mainshaft by hand in all 6 gears, very smooth, no noise. Now I'm sure it was the bushing. New seal in, new bushings in, linkage adjusted, fired it up with great confidence........noise still there!

I can select all gears with ease. The noise starts as soon as the clutch begins to engage, just like before. This time I set the e brake and began to engage clutch. A growling noise in all gears just as I begin to load the engine. Seems like the problem is not in the tranny as nothing is turning in there.

Clutch? Throwout bearing was smooth, clutch fork plastic bush was fine. I did not remove the p. plate. I had expected it to be oily and when it was dry I left it alone.
So, trans is coming out again and clutch will come out this time. Any guesses as to what I will find? Or am I looking in the wrong place?

[Dr Evil]

How it acts under hand torque is completely different from how it acts under engine tq.

It still is likely the bearing in the plate (IMG:style_emoticons/default/sad.gif)

[J P Stein]

Tore appart Jim's trans this afternoon.
The guts look great to me...even the 1st ear slider & dog teeth are nice.
Intermediate plate bearings look great.
A pic.

The noise I've heard over the phone happens under circumstances which led me to believe it was not the trans but appart it came nohow. Now I gotta put the tailshiftingsumbitch back together......that's new to me...I'm a side shifer kinda guy. (IMG:style_emoticons/default/biggrin.gif)

The groaning sound switchs on each time the trans is in gear and any load is applied.....even when the mainshaft is *not* turning....ie: trans in gear, E brake on so the wheels can't turn......clutch slipping.
Groan is less when the wheels *can* turn.... off the ground but louder when they are on the ground & the car is moving.

All ideas entertained.

[Dr Evil]

That is the problem with doing diagnosis over the internet. Are the rest of the bearings good? I assume nothing now.

[J P Stein]

Everything I can see looks very nice & turns smooth & free...including the gears on needle bearings. The ring & pinion are smooth as a baby's ass. I haven't had time to disassemble the shafts and I'm off to play with the SCCA for a 3 day weekend. I probably won't get back to it till next weekend.

Jim also brought by his clutch and it didn't look too shiney. He said the flywheel looked worse. The noise seemed to be a rotational sound but he said the clutch wasn't slipping. (IMG:style_emoticons/default/confused24.gif)

[Jax914]

pilot bearing in the flywheel?

[Porsche Rescue]

Pilot bearing feels good to the pinky finger, looks good. Main shaft smooth on bearing surface.
Planning to resurface flywheel and replace clutch. Hoping that's the problem. One theory is that the female spline in the disc is slipping, but can't duplicate with disc in a vice. No visual evidence of a clutch problem.

[Katmanken]

You sure it's not the throwout bearing???

I've had them quiet when idling and growl when engaging the clutch.

[Porsche Rescue]

TO bearing is smooth and quiet in my hand and in the car at idle, clutch in or out. In fact all is quiet until the clutch begins to make contact with the flywheel. Then "growling" noise begins and continues as long as the clutch is out, even when brake is on so that nothing is turning.

[Dr Evil]

Has your flywheel been resurfaced before? If the step was not cut accurately as well you can have clutch disk chatter. If you resurface your flywheel you will need to shim the clutch fork ball out a little.

[Katmanken]

Ok, let's think this through.

Tranny is out of gear and clutch pedal is released. At this point the clutch disk is compressed into locked engagement with the flywheel by the pressure plate. This causes the maishaft and attached gears in the tranny to spin at the same speed as the engine. The mainshaft gears spin the unengaged gears on the secondary pinion shaft without spinning the pinion shaft.

Push in the clutch and the throwout bearing engages the pressure plate. This moves the pressure plate away from the flywheel and disengages the clutch disk from the flywheel, pressure plate ,and rotating engine. At this time, the mainshaft in the tranny is disengaged from the rotating engine and can stop rotating. But one end of the stopped main shaft is rotatingly engaged with the shaft bearing in the flywheel.

Now you engage a gear and let out on the clutch and the growling noise happens. Is it ONLY when the tranny is in gear? Does it ever occur when the tranny is not in gear?

When you engage a gear and let out on the clutch, the pressure plate begins compressing the clutch disk between the rotating flywheel and the non-rotating pressure plate. At this point, the clutch disk slips to bring the non-rotating mainshaft and tranny up to engine rotation speed. Once the pressure plate is fully released, the clutch disk should be locked to the flywheel. That is, spinning with the flywheel and it shouldn't slip. In the tranny, the main shaft should be spinnining at engine speed and the engaged gears should be spinning the pinion shaft at a speed related to the selected pair of engaged gears (gears 1-5). At this point the ring gear in the differential is engaged with the pinion and should spin the axles.

I see two things, if the emergency brake is stronger than the clutch and locks the intermediate shaft so the clutch disk spins, the clutch disk and pressure plate are toast.

Next, I'd look at whatever is connected to the pinion shaft. Why? because whenever the pinion shaft is engaged to the intermediate shaft, the noise happens.

Which brings up a question- gone into the differential yet? Rings and pinions growl and whine when going, and the bearings in the differential that support the axle plates could be the culprits. Hows about the spider gears?

[Porsche Rescue]

Growling noise only when tranny in gear (any gear), no noise when out of gear, regardlees of position of clutch/p. plate. Begins as soon as disc begins to contact flywheel.
Flywheel has a deep groove at outer circumference. It will be turned and clutch replaced in the next week.
When doing the "E brake thing" I can kill the engine easily. Clutch was not slipping so as to allow the engine to rev higher.
JP's initial inspection of the differential reveals no problems. He says the condition of gears, dog teeth, especially first, are the best he has ever seen.

[Katmanken]

Well, does it growl when the clutch pedal is in and the tranny in gear?

When you select a gear, the synchros and dog teeth engage the selected gear with the pinion shaft so the pinion shaft can be driven by the selected gear. When the clutch pedal comes out, the clutch disk contacts the flywheel and begins to spin the mainshaft and the selected pair of gears, the pinion shaft, the differential, the axles and wheels. Note, this description is for a stationary car. If the rear wheels are turning, then it's a bit more complicated.

So in an unshifted position, the pinion shaft and all it drives are stationary,and it doesn't matter if the clutch disk is engaging the flywheel or not. All is quiet.

When the car is in gear AND you engage the clutch, it gets noisey. The pinion shaft becomes driven and starts to spin as well as the differential, axles and wheels.

That says the problem is either motion or load dependent. For the noise to occur, the pinion shaft has to spin and the tranny and clutch have to be transmitting torque . Two things make noise when going bad under load- gears begin to whine, and bearings begin to grumble..... I'd recheck the pinion shaft bearings, the differential bearings, and look at the pinion and ring gear for chips. They are super hard but are brittle and can chip.

I can assure you it's one or more of the items discounted in this thread.

[Porsche Rescue]

No noise when in gear with the clutch "in". Noise begins immediately on release of the clutch.
When I release clutch part way, in gear, BUT with the ebrake tightly set, clutch "slipping", almost to the point of stalling the engine, I hear the noise but wheels are not moving and I assume nothing is turning in the transmission or differential. Is that wrong?

[Katmanken]

I'm gonna put on my Patent Law and my engineering hats and look at this several different and possably contradictory ways....

When the clutch is slipping and the rear wheels are locked, the tranny drivetrain will rotate a little to take up slop- It's called called windup. Windup in this system happens through all the components from the clutch disk to the wheels.

I'd replace the flywheel bearing for sure. It's cheap and is rotating around the stopped mainshaft.

Which brings up several other points.

Have you measured the flywheel for endplay? When a system loads, things move. I'd check to see if the endplay is OK because if it's not, the flywheel/crank could move and contact things and make noise...

And, are the clutch disk and pressure plate flat? ..... I'd check that because if the clutch disk has a thicker section (lump) and/or the pressure plate has a broken spring and can't push uniformly on the clutch disk, you might get uneven slipping as the disk slips relative to the pressure plate, and then we enter the world of vibrating systems. If the clutch system isn't flat, you could be sending a rotational oscillation (ie a small oscillating clockwise and counter clockwise rotation motion) which will wind up the system and then unwind it. That would rotate some tranny and cv bearings back and forth.

If I understand correctly, when the tranny is in gear and the clutch pedal is fully released, the car should move and the growl should happen. At that point, the flywheel bushing is fixed (non rotating) relative to the main shaft, the clutch is locked relative to the flywheel and main shaft, the tranny pinion shaft and differential start to move and noise happens. At that point, the flywheel bushing and the clutch should be considered non-noise making elements and out of the picture- unless we have some slippage. Is the clutch disk burned or glazed???

I keep coming back to the pinion shaft/differential because it becomes rotatably engaged when two things happen- 1. you are in gear, and two, the engine is driving the wheels. If you look at it from the point of letting off the gas in a moving car with a gear engaged, the rear wheels load the tranny and try to spin the engine .....- wich means the pinion shaft/differential is spinning.......

[Porsche Rescue]

Noise begins with first clutch contact with flywheel (brake on or off) and continues when car moves. Car feels "restricted or bound up" when moving. I have only driven it back and forth slowly in the driveway.
No question the clutch disc and flywheel are suspect. Flywheel was apparently not turned last time disc was replaced as there is a groove around the outer circumference of the flywheel which is matched by a ridge around the outer edge of the disc. Pilot bearing looks and feels good.
My next step is to remove and resurface the flywheel and replace pilot bearing, disc and pressure plate. And then hope that all is quiet!!

[Porsche Rescue]

Here are some pics. One theory is that the center spline in the disc is turning in the disc. Unable to duplicate by hand with disc in a vise and a mainshaft in the spline. The spline does feel a bit loose in the disc however.

[Katmanken]

Looks glazed to me. The clutch disk is a two piecer design that is designed to move a little to absorb shocks when it becomes engaged. Take the 4 springs out that surround the splined hub and the splined disk should rotate relative to the other disk with the clutch material riveted to it. Put them back in, and the springs absorb shocks when engaging. Don't take the springs out please. The description was meant to be educational.

[Bleyseng]

use the 6 spring clutch disc for a early 911, yes it fits just fine and is smoother...