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3500-4500 RPM Vibration

Hello All,

1st - YES! I have used the search function.

2nd - Here is the description of the problem: 1987 944 N/A 115K miles

Went out this morning to go to work, car was parked outside, didn't want to start. This is pretty normal here in the early morning with the temps in the mid-teens. I got her started and running without much ado.

When I revved the car to 3500 and continue past to 4500 it vibrates the gear shifter horribly and it very noisy. Doesn't matter if I do the following: stopped, rolling, any speed, clutch engaged, clutch disengaged. I never go above 3k without the car being up to temp, FYI.

This is a brand new problem. I have not ever had this problem. Balance shaft and timing belts with rollers done at 112K.

Clutch condition is unknown, assuming original.

Based on my search results, and assuming an original clutch, I think the rubber centered disc ist Kaput!

I also thought misfire but it doesn't seem to act that way.

Thoughts?

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89' 951 Turbo S Race Car - SP-3, PT-B
87' 944 Diamond Blue Metallic - DD

"Practice does not make perfect. Perfect practice makes perfect" - Ross Bentley
Old 02-05-2013, 08:37 PM
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Blake,

Your probably right-rubber center clutch disc going bad.

Pull the starter and poke your finger in the hole and feel for small chunks of rubber. That is how I checked my '87--at about the same mileage as your '87 944 a couple of years ago. I felt the vibration increase at 3300rpm.

You could also do the disc thickness test per Clarks Garage.

With your experience, maybe a long weekend of work with the delay to wait for the FW resurface.

EDIT: First check the distributer cap and make sure the rotor is on the shaft tight.
Check the reference sensor connections at the rear of the engine. No cracks in the plastic or the wire insulation.
Make sure the coil wire is not grounding/arching to the engine or hood
Look at the spark plug wires in a dark garage to check for arching.
Just a couple more ideas about the hard starting.
Clean the battery connections--and the main negative ground on the block. Cover the TDC hole in the bell housing.

GL
J_AZ
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1988 924S, 80K ..+ 1987 924S, 150K DD (+15K est. bad odo)

Last edited by John_AZ; 02-06-2013 at 04:41 AM..
Old 02-06-2013, 04:31 AM
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If it were the rubber centered clutch, it would change when sitting still in neutral whether you had the clutch in or out.

With clutch disengaged, and in neutral, the rubber center stops spinning and is resting on the throw out bearing. It wouldn't be creating a lot of vibration. I drove for an extended period on the limp home tabs in one of my cars, while waiting for a new master brake cylinder for the other.

Because there is no difference clutch in or out, I'd be looking at your engine. Possibly engine mounts have bottomed out?

Does the engine feel like its shuttering from not producing power momentarily?
Old 02-06-2013, 09:21 AM
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Thanks for the replies.

I will look over the things you suggested. I did pull the plugs and have attached pictures. I have never been very good at analyzing plugs for some reason. I would much rather hook up a meter and check resistance or something .

What do you think about these plugs:

They are Bosch Platinum 4+ I am thinking about switching to NGKs though after reading what Nize had to say.

The engine mounts look ok but I will jack them up and look closer.

There is a bit more vibration overall then before so maybe I'll order up a new PP, FW, disc, and Throwout bearing. more money away from the race car
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89' 951 Turbo S Race Car - SP-3, PT-B
87' 944 Diamond Blue Metallic - DD

"Practice does not make perfect. Perfect practice makes perfect" - Ross Bentley
Old 02-06-2013, 11:40 AM
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I'm currently using platinum 4's by Bosch and they seem to work fine however multiple members have stated the 944 runs better and starts faster with the OEM Bosch copper plugs. My PO had NGK's in and seemed ****ty
Old 02-06-2013, 01:35 PM
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+1
Motor mounts.

If they have never been changed it's time. And if your clutch is original (rubber centered) then its time for that too.

Quote:
Originally Posted by Tervuren View Post
If it were the rubber centered clutch, it would change when sitting still in neutral whether you had the clutch in or out.

With clutch disengaged, and in neutral, the rubber center stops spinning and is resting on the throw out bearing. It wouldn't be creating a lot of vibration. I drove for an extended period on the limp home tabs in one of my cars, while waiting for a new master brake cylinder for the other.

Because there is no difference clutch in or out, I'd be looking at your engine. Possibly engine mounts have bottomed out?

Does the engine feel like its shuttering from not producing power momentarily?
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Old 02-06-2013, 03:15 PM
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I contacted the PO (love PCA member cars ) and he said that the clutch was changed to the spring centered one around 40K. I am not saying I am perfect but I don't gear grind or clutch dump so I don't think it is the clutch.

Looking at motor mounts tomorrow.

Any thoughts on the plugs? Can you see the Picture?
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89' 951 Turbo S Race Car - SP-3, PT-B
87' 944 Diamond Blue Metallic - DD

"Practice does not make perfect. Perfect practice makes perfect" - Ross Bentley
Old 02-06-2013, 04:13 PM
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Quote:
Originally Posted by Gawernator View Post
I'm currently using platinum 4's by Bosch and they seem to work fine however multiple members have stated the 944 runs better and starts faster with the OEM Bosch copper plugs. My PO had NGK's in and seemed ****ty
I use the BPR6ES NGKs in both cars--cheap and efficient. Bosch just as good

The Motronic DME ECU is programed for the resistance of the copper center electrode plugs with a single ground electrode. No gain from platinum 4's. Loss of $ in wallet.

J_AZ
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Old 02-06-2013, 04:20 PM
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+1 to Tervuren!

If the PO says he changed the mounts, go back to my original post =EDIT.

J_AZ
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Old 02-06-2013, 04:23 PM
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Quote:
Originally Posted by John_AZ View Post
I use the BPR6ES NGKs in both cars--cheap and efficient. Bosch just as good

The Motronic DME ECU is programed for the resistance of the copper center electrode plugs with a single ground electrode. No gain from platinum 4's. Loss of $ in wallet.

J_AZ
Only have them because they were selling brand new on evilbay for about the same price as copper

Your plug wear doesn't look too strange!
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Old 02-06-2013, 07:37 PM
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It may be time to re-tension your belts. Why?

You stated:
2nd - Here is the description of the problem: 1987 944 N/A 115K miles

AND, you are now 3,000 miles after the belts were done at 112K miles. Since these were new belts changed out at 112K miles, they need to be looked at again according to the factory manual (check at 2,500 miles). Then, rechecked/retentioned at 15,000 mile intervals until 45,000miles.

It could be your balance shaft belt is loose and causing the vibration.

This is just a guess, but I do hope it helps if none of the other suggestions resolve your issue.

BTW...your plugs look normal to me.

Good luck
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Old 02-06-2013, 11:26 PM
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We had this vibration issue when we bought my sons 88- 944. During the drive home the vibrations were so bad the shifter handle would climb on the shaft and fall off (the clip was missing). Yes it was that bad. A 65 mile ride at 30 mph takes foreverrrrrrr to get somewhere. I had a good idea as to the problem, when we got home we pulled the belt cover and found the balance shafts out of time.

Pull your covers and double check the balance shaft timing. Maybe the balance belt roller slipped and the belt loosened up and jumped a few teeth on the balance shafts.
Old 02-07-2013, 08:55 PM
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PS,,, Your plug wear looks very good. No dark sooty deposits, no oil, no glazing and a fine ash gray/tan coloring. Fuel mixture must be set well and no overheating. Getting around 24-26 MPG?
Old 02-07-2013, 09:01 PM
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Sometimes if you look carefully at the bell housing you can see bits of rubber coming out of the pressure plate.

any way I wouldn't take the po's word for it that the clutch had been replaced without verifying that for myself
Old 02-08-2013, 06:29 AM
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i'm surprised nobody mentioned the obvious before tibetan did. very likely the balance belt is not set on the right teeth. happens all the time.
Old 02-08-2013, 07:43 AM
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Go look at your balance shafts again. I had everything lined up fine but something came loose and it started vibrating because it was off a couple teeth. We got it lined up again, started it, and somehow that lower sprocket ended up 180 degrees the other way. Lined everything up and tightened the belt again, started it, and once again 180 degrees the other way. We did that about 4 times until everything stayed put. No idea what caused that mess but everything is fine now! (all belts and rollers were brand new btw)

Last edited by mueller944s2; 02-08-2013 at 08:55 AM..
Old 02-08-2013, 08:53 AM
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Well the OP did say the belts were recent and that the vibration was new... but a properly paranoid (sensible) 944 owner would have checked for a torn-up BS belt flopping under the belt cover and about to cause bigger problems right away.

It would not be the first time that a BS belt slipped or came apart mysteriously.
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Old 02-08-2013, 08:54 AM
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yup - far too often i've seen people look at the marks on the pulleys, and not the keyways, thinking that the orientation was right based on that. it's all about the keyways.

the balance belt is supposed to be retensioned every year. i can count on one hand though the number of people that do it. also, a number of people use inferior belts (like conti) which stretch more than others. too often they are left in there too long too. one good quick rev on a loose or stiff and hard belt, and the belt jumps. that's why we hear about this so much.

Old 02-08-2013, 09:36 AM
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