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928 transmission swap out

 
Old 02-07-2011, 10:35 AM
  #16  
WallyP

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If the transmission is still in and the car is still running, you can check the torque tube bearings vs. the throwout bearing very easily.

Start the car and spin the torque tube at moderately high speed. Quickly push the clutch to the floor and listen to the noise. If it matches the coast-down of the driveshaft, it is the tube bearings or transmission bearing. If it stops well before the driveshaft stops, it is throwout or pilot bearing.
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Old 02-07-2011, 01:37 PM
  #17  
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Thanks all. great information. its funny, ive done this a few times, but always as a part of a much greater process. (like stripping a chassis) I cant remember a thing.

anyway, Wally, that is interesting. makes sense. this is because when you lift off the moderate throttle, and push in the clutch, the engine speed and then that part of the release bearing, slows down quickly, while the torque tube continues to spin? is that the theory? if so, yes, that is what is happening. another test might be keep the rpm at 3000 and then dont lift the gas, so that the engine and release bearing are spinning at 3000rpm and push the clutch in and the torque tube and the noise will fall off slowly, right?
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Old 02-07-2011, 02:06 PM
  #18  
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another thing it does (the noise) , is that when you reve the engine up to say 3000rpm with the clutch depressed, and then let the clutch out, its a pretty hard clanking acceleration along with the whirrling noise.
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Old 02-07-2011, 02:12 PM
  #19  
Rob Edwards
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Didn't you break something in the transmission? Couldn't the noise produced whenever the TT shaft is spinning be the remainder of the input shaft flange doing additional damage to the TT splines, or 5 th gear, or ????

Stop hypothesizing and take it apart and inspect everything.
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Old 02-07-2011, 04:40 PM
  #20  
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If the bearing is that shot in the TT, you will hear it even if you spin it by hand.
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Old 02-07-2011, 04:44 PM
  #21  
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+1, its pretty much unmistakable sound, especially with no insulation in the car. Press in the clutch and you can hear it spin to a stop.

I was forced to install a less-than-perfect one in that picture above....logic was I'd rather wait to afford the Constantine bearings than rebuild with normal parts, even if it meant a re-do. And had to get it rolling, so couldn't risk breaking the carriers on a rebuild.

Last edited by Landseer; 02-07-2011 at 05:20 PM.
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Old 02-07-2011, 06:44 PM
  #22  
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It does that. it makes a racket, and then when the clutch is pressed in, it spins to a stop. but, its all connected right up to the short shaft , going through the release bearing and clutch discs. im having a hard time thinking about how the release bearing would make a different noise, or stop any sooner than the torque tube. push the clutch in, and the shaft in the release bearing still spins down tied in with the torque tube. there must be two bearings in the release bearing, because one is always spinning with the engine running, because thats how it is held by the clutch arm.

I want to be really sure its the torque tube, because if its the release bearing or just the transmission, it will save me a ton of work and expense to not have to change the torque tube and release bearing.

as it stands now, it makes a racket in idle. gets worse at high rpm and the sound entirely goes away with the clutch pressed in, and it coasts down slowly, matching the torque tube rotation. I wish I could hear a release bearing problem noise, then I would know for sure.


Originally Posted by Landseer View Post
+1, its pretty much unmistakable sound, especially with no insulation in the car. Press in the clutch and you can hear it spin to a stop.

I was forced to install a less-than-perfect one in that picture above....logic was I'd rather wait to afford the Constantine bearings than rebuild with normal parts, even if it meant a re-do. And had to get it rolling, so couldn't risk breaking the carriers on a rebuild.
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Old 02-07-2011, 06:51 PM
  #23  
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You've got a dual disk clutch in there, right? If so, whether the release bearing is toast or not is kind of academic right now, as new ones are NLA (unless Roger has finished his work on sourcing a replacement). Dunno whether Mark A. has any good used ones on the shelf right now.

Perfect excuse to leave it alone.....
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Old 02-07-2011, 06:59 PM
  #24  
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When I push in the clutch, release bearing isn't noticed as it spins-up ( its only got 20K miles) but TT is noticed as it spins down.


Another way, just release the sleeves and spin it by hand, as mentioned above.
Very easy to hear / feel the TT bearings.
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Old 02-07-2011, 07:17 PM
  #25  
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you cant release the coupling in the tranmission, as it has to be physically moved back.

when the clutch is let out, the noise instantly happens, and spins down in a second or so when the clutch is pushed in. I dont see where the throwout bearing noise would be any different or show itself any differently than the torque tube bearings.

by the way, it was making quite a bit of racket , before the tranmission broke. now whether it was the input shaft bearngs at the tranmission, I dont know. in neutral, there is no noises, so its probabaly a stripped 5th gear.



Originally Posted by Landseer View Post
When I push in the clutch, release bearing isn't noticed as it spins-up ( its only got 20K miles) but TT is noticed as it spins down.


Another way, just release the sleeves and spin it by hand, as mentioned above.
Very easy to hear / feel the TT bearings.
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Old 02-07-2011, 07:18 PM
  #26  
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nothing is broken outside of the transmission.

Originally Posted by Rob Edwards View Post
Didn't you break something in the transmission? Couldn't the noise produced whenever the TT shaft is spinning be the remainder of the input shaft flange doing additional damage to the TT splines, or 5 th gear, or ????

Stop hypothesizing and take it apart and inspect everything.
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Old 02-07-2011, 08:15 PM
  #27  
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Mark, the throwout bearing spins only with clutch pressed, doesn't it on the 928?

The TT spins when the throwout bearing should be stationary.
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Old 02-07-2011, 09:08 PM
  #28  
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Here's my 928 thinking for the day, not sure if I've ever seen it presented like this, (and I'm not sure this is all 100% right.....)

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Old 02-08-2011, 12:19 AM
  #29  
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Damn
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Old 02-08-2011, 12:52 AM
  #30  
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It's not hard to undo the 4 TT bolts with the clutch in. All you need is the right length extension. I think I used a 3/8" sears ratchet with a 1" extension and regular socket and it fit on the bolt and the wrench was just past the guide tube mount on the bellhousing.

Dan
'91 928GT S/C 475hp/460lb.ft
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