5-sp Transmission Questions and Discussion

[JKelly]

When driving along in fairly low RPM in a higher gear, I'll give the car some gas and a vibration resonates from the transmission that sounds like an accelerating F350 diesel truck. Is this considered "chatter" or is this some other vibration (selector rods..etc..)? It doesn't always make a noise, but sometimes depending on RPM and gear selection.
- Question: What is "Chatter"?

I was reading on the back of a Red Line Synthetic 75W90 Gear Oil bottle and it says:
"The extreme slipperiness of this lubricant helps prevent limited-slip chatter and reduces differential temperatures 10ºF-70ºF in heavy-duty use. Supplemental friction modifier additive is usually not required for limited-slip differentials, but can be used if chatter occurs. Red Line 75W90 is used for high-speed and high torque conventional and racing applications. This product is not designed for use in most manual transmissions, since the extreme slipperiness may cause gear clash."
According to the bottle label, the 928 transmission does not fall into the "most manual transmissions" category. In our transmissions, the differential and the transmission use the same lubrication.
- Question: How does the "slipperiness" affect shifting?

As I understand it, quite a few people use a mix of "slip" and "non-slip (NS)" gear oil to help syncro grip because the slipperiness required for proper LSD operation is too slippery for proper syncro operation. There really seems to be a contradiction in having the transmission and the LSD sharing the same gear oil.
- Question: Am I just not understanding something correctly, or is this another example of Porsche "over-engineering" to the point where the exact specification of oil has to be used which is near impossible to get "exact"?

[JKelly]

Guess I'll have this discussion with myself................

Originally Posted by JKelly

- Question: What is "Chatter"?

Maybe what I am hearing is referred to as "gear growl". (?)

- Question: How does the "slipperiness" affect shifting?

I don't know, but I just spent $50 on 5 quarts of Redline 75w-90 and ordered 2 more quarts of Redline 75w-90NS to experiment with. I am getting notchy 2nd gear shifts with an occasional grind. I have read multiple times that dino oil can create a stiff shifting symptom when the transmission is cold and the synthetic is not as bad; so I would like to stay with synthetic. The previous oil was entirely Redline 75w-90 with no NS added and has been in there for 4+years. Searching through the forums here, it seems like Redline has by far the best recommendation. Royal Purple seems to be highly thought of too. There are both some good and bad experiences from using Mobil 1 and Swepco, even though Swepco is highly recommended for 911's.

- Question: Am I just not understanding something correctly, or is this another example of Porsche "over-engineering" to the point where the exact specification of oil has to be used which is near impossible to get "exact"?

Probably an example of good ol' Porsche engineering to the point where a slight bit of wear or out-of-spec tolerance is intolerable; specs of the oil included.

[JKelly]

Having a list that identifies and attempts to troubleshoot problems which can occur with the clutch system and/or transmission and some of the potential causes would be helpful. Anybody care to add to it:

- Sloppy shifter: Front shift rod ball cup bushing, Rear shift rod coupler bushings, Weak shifter springs, Broken R-1st spring in transmission,
- Cricket noises (chirping): Throw-out bearing, Pilot bearing,
- Clutch slipping: Clutch disks,
- Rattles: Ball cup bushing on clutch fork,
- No Shift: Front shift rod ball cup bushing,
- Clutch drag: "T" adjusters on Intermediate plate,
- Soft Clutch: Air in slave cylinder,
- Notchiness:
- Grinding:
- Difficult up-shifts: Bad syncros,
- Difficult down-shifts:
- Popping out of gear:
- Chatter:
- Shuddering: Torque tube,

[Mike Frye]

Hey John,

I don't mean to interrupt here , but you said

It doesn't always make a noise, but sometimes depending on RPM and gear selection.

Is it always in the same gear, and/or at the same RPMs? If so, which and where?

Not sure I can help here, but I thought this might further isolate the problem.


I'd break down two of your item further to warm and cold
- Notchiness (when cold): gear oil? (try synth, new, different brand/blend)
- Grinding (when cold): gear oil? (try synth, new, different brand/blend)
- Notchiness (when warm):
- Grinding (when warm):

[jyoon]

worn shift bands/shift selectors will cause same problems as worn synchros.

[ZEUS+]

It would be helpful to know what the rpm, mph and gear is when this happens. Did this start after the fluid change ? Chatter from lsd happens when turning.

[JKelly]

Originally Posted by NJSharkFan

Is it always in the same gear, and/or at the same RPMs? If so, which and where?

Originally Posted by ZEUS+

It would be helpful to know what the rpm, mph and gear is when this happens.

It is usually in second and maybe third at low rpm (around 1500?) while trying to accelerate rapidly. I'll have to pay closer attention. It sounds exactly like a diesel transmission does when it is accelerating at low rpm.......kind-of like a rattling grinding noise. It's been occasionally doing this for the last 5 years without getting any worse or any better.

Originally Posted by ZEUS+

Did this start after the fluid change ? Chatter from lsd happens when turning.

I don't remember...., but maybe. I changed the fluid soon after purchasing the car and never thought that maybe the fluid was causing it or allowing it to happen. I currently drained the transmission/differential and am now waiting on some new stuff to arrive. We'll see if that makes a difference.

Thanks for the clarification of "chatter". The sound is not chatter then.

[JKelly]

Does anyone know if this is a normal amount of metallic residue buildup on the transmission drain plug? This is after 5 years and 20,000 miles. It is like a fine powder that is magnetized into spikes.

[Mike Frye]

John,

Dude, you're gonna hate me, but what are you doing in second trying to rapidly accellerate at 1500? Isn't that like shifting out of first at like 20mph? You can do it, but not if you're in a hurry.

My car hates that too, but if you run it up a bit then let the clutch out it likes it much better.

The owner's manual specifically says not to 'lug' the engine at low rpms. I think this is what they mean.

On the filings, I dunno, I've only done one of these and one or two other kinds of cars. It looks about like what mine had, but I have no idea how long it had been since the previous change.

[Charley B]

On the filings, run them through your thumb and index finger and if it's all powdery and no larger pieces, you're probably OK.
On the deiseling sound while accelerating at lower rpm's, are you sure your not hearing pre-ignition?

[jon928se]

They all do that sir!

Well not exactly but both my 88 SE and my 90GT and Paul (Ukkid35) '87 make that same chattering sound when accelerating at 1000 - 1500 rpm in say 2nd or 3rd gear. For some reason not in 4th or 5th and in 1st maybe it does who knows. We always thought it was cams but there's a simple answer. keep the revs over 5000 always LOL

[AO]

You haven't said where the noise is coming from. Is it coming from the front of the car, middle, or rear? All three of which are possible. If it's front, you may be experiencing pre-ignition becasue you're lugging the engine (BTW, this is not good for the car). If it's in the middle, it could be the clutch, or the TT that's casuing the sound. If it's the rear, then it's most likely a trans issue.

[JKelly]

Originally Posted by NJSharkFan

John,
Dude, you're gonna hate me, but what are you doing in second trying to rapidly accellerate at 1500? Isn't that like shifting out of first at like 20mph? You can do it, but not if you're in a hurry.
My car hates that too, but if you run it up a bit then let the clutch out it likes it much better.
The owner's manual specifically says not to 'lug' the engine at low rpms. I think this is what they mean.
On the filings, I dunno, I've only done one of these and one or two other kinds of cars. It looks about like what mine had, but I have no idea how long it had been since the previous change.

The 1500 is a guess, but I will start to pay much closer attention. If you run first gear up to 2000 or so and then switch gears when the idiot light comes on, that is about the area I am talking about (I think).

Originally Posted by Charley B

On the filings, run them through your thumb and index finger and if it's all powdery and no larger pieces, you're probably OK.
On the deiseling sound while accelerating at lower rpm's, are you sure your not hearing pre-ignition?

The filings are powdery.
The diesel sound is coming from the rear.

Originally Posted by jon928se

They all do that sir!
Well not exactly but both my 88 SE and my 90GT and Paul (Ukkid35) '87 make that same chattering sound when accelerating at 1000 - 1500 rpm in say 2nd or 3rd gear. For some reason not in 4th or 5th and in 1st maybe it does who knows. We always thought it was cams but there's a simple answer. keep the revs over 5000 always LOL

I wondered if anyone else ever experienced it. Your description sounds right. I was looking through the corvette forums and came across a statement from GM about the C6 vette:
"Manual Transmission Gear Growl Noise
When starting off slowly, customers may notice a slight gear rattle or growl coming from the transmission. This is a result of clearance between the gears, shifters and shift rails. This is a normal condition and does not require repairs."

This may be what I'm hearing. I am interested to see if a fill of fresh gear oil has an effect (synthetic). If it doesn't, then I'll try a dino oil next time. What kind of gear oil do you use?

Originally Posted by Andrew Olson

You haven't said where the noise is coming from.

It's from the rear.

[SteveG]

Steve Cattaeneo is the gear (head) guru here. I believe that applies to both manual and AT. Checks in periodically, you may want to try a PM.

That looks like a lot of filings, but if powdery I guess OK. I changed oil at 89K and less than half what you show, also very fine material. FYI, With rear suspended turn one wheel by hand fore and aft; mine seemed to have a lot of play in the box, but I was told this is normal. Still suspended as part of the change I flushed with 1/2 oil and 1/2 risolene and ran it through the gears at about 1000 RPMs. No LSD. It chattered, but w/o friction on either wheel, I was told this is same symptom and normal. HTH

[Shane]

My 5speed with out limited slip makes the same noises as yours. Always with low rpms, and light acceleration. It is more noticable when going around a corner. I also have redline in my tranny.

My 5speed with limited slip doesn't do this, it instead gets wheel hop on heavy acceleration. I have no idea what this transmission has for gear oil.