pointfivezero

Hi Rennlist;

Long time lurker, first time poster. Sorry to be needy but would really value your collective experienced opinions on an issue with my 1987 944S.

I recently purchased this car from the original owner. 82K miles and a stack of maintenance receipts. In the past year, he had installed a new clutch, power steering rack, water pump, all belts, tires, battery, exhaust and a major tune up. He advertised the car as "mechanically perfect". The car is in awesome condition (photo attached) but due to my lack of diligence, I inherited a serious vibration which is primarily manifested through the gear shift **** at between 3500 and 4000 RPM. The vibration occurs in nuetral or in gear. This vibration becomes so bad it resembles an electric shock and has me worried about losing my molars.

I have the car at a local (Bay Area) Porsche specialist shop. To date, we have tried the following:

1. New gear shift ****
2. New motor mounts
3. Adjust all belts included balance shaft
4. Remove aftermarket exhaust and test with stock exhaust

As you may have guessed, the problem persists. The mechanic's next approach is to tear apart the clutch and check the flywheel, which was lightened when the clutch was replaced. This is about a $1200 quote.

After seaching the forum, I was certain the problem was related to the balance shaft so I went back and discussed it with the mechanic. He assured me the shafts are installed correctly and set to the proper specs.

Before I embark on a $1200 fishing expedition, I would appreciate any advice from anyone who has experienced, diagnosed and solved a smiliar issue.

Thanks in advance!

Tim

Dmitry S.

Hmmm, still sounds like balance shafts to me. If the lightened flywheel gave you no problems before, it shouldn't give you any now. Where in the Bay Area are you? I'd be glad to help you out.

RedlineMan

Hey;

Gee... I'm amazed the new gearshift **** did not solve it.

Does it do this at a standstill, or when moving, or both? If it only does it while moving, I'd suspect a driveline issue, basically anything. If it does it standing still, there is an engine imbalance. It would not be the first time I saw a balance shaft improperly set. I would want to know for absolute certain that the bottom balance shaft was not 180 degrees out of phase, not just off the alignment mark. Ask them this specifically. This is fairly common.

Ask me how I know?

Serge944

Balance shafts. No doubt about it. 2 teeth off will cause major vibrations at a very limited rpm range, just like you're experiencing.

Its a very simple adjustment, which can be done in 1.5 hours, start to finish. Also, don't be hesistant to accept Dmitry's help. He's a nice guy and a very able mechanic.

YES!

pointfivezero

Thanks for the quick responses and advice.

This vibration occurs sitting in the driveway in nuetral or at speed or the street. LOL on the gear shift **** comment but the old boot was a very faded red, so it had to go anyway.

Dmitry - I live in Richmond and the car is at a shop in Pinole. I appreciate your offer. Do you have a shop in the area?

RedlineMan - I'm guessing you had a similar issue???

Thanks again. This has been a very frustrating issue.

Tim

Dmitry S.

I'm in Cupertino, and I work at a Volvo shop in Campbell, but have been wrenching on Porsches for about 3 years now. I've done the timing/balance belts on my car, and have helped out with a couple others. Next week, a couple of the 944s in the area (Santa Clara) are getting together, if you want to come down, we can try and solve your issue.

Porsche-O-Phile

Almost certainly balance shafts. Possibly 180 degrees out of alignment.

RedlineMan

Tim;

I learned the ocassional fallibility of the factory service manuals (FSM) some years back. The procedure for reinstalling the balance belt gears is WRONG.

Each gear has two keyways; one for the key on the shaft, and one for the tab on the gear faceplate. When you put them back, it says to set the gear & faceplate so that the "O" stamped on the face of the gear shows in the round window of the faceplate. The bottom gear should have the "U" visible. This is how you get the bottom gear 180 out-of-phase to the top one, creating the opposing, vibration-cancelling rotation.

Problem is there is no "U" on any gear I have ever seen . So, if you did not mark anything, and cleaned the dirt off that usually leaves "ghost tracks" of how things were oriented, you have to guess. Sometimes there is thread sealing compound slopped into the two keyways and you can tell by how the tab on the faceplate fits which keyway it was in, and therefore how it was oriented.

I cleaned everything scrupulously, so I was left to guess. I put it together with both "Os" visible (figuring an "O" would have to do since I had no "U") and it shook like a mother! There is no "U", but when things are put togehter right, the "O" on the bottom gear is partially visible in the slot where the tab on the faceplate is cut out and bent in.

This all sounds pretty convoluted, but it will make perfect sense once you see it. You REALLY have to know about this in order to be looking for it.

I hope it is the case for you, because it's an easy fix. GOOD LUCK!

Dmitry S.

The U was only on 1983 n/a models, after that they went to the stupid O system.

Stuttgart 944

I have that same problem.

Mighty Shilling

Exactly. it's DAMN easy to do the balance shafts 180 degrees off.. I had to do it 4 or 5 times before I learned that... each time wondering "WTF IS THE PROBLEM?" It'll be the lower balance shaft (passenger side)

Peckster

The mechanic is aware of the problem that frequently occurs with balance shaft timing, even with Porsche mechanics? Ask him if he knows how it can happen, if he can't describe it, bingo.

944Ecology

Yep, and the true test to see if he is worthy of working on your 944 is to ask him to show you his set of factory workshop manuals and his P9201.

If he doesn't have both of those, run away and find yourself a real 944 specialist.

Just putting a patch on your overalls that says "Porsche Specialist" does not mean that you are one.

gb

pointfivezero

First, let me say I'm grateful for the amazing response. What an informative and professional website. Thank you for taking the time to respond.

I have returned to the shop twice with information from this post. I have a tremendous amount of respect for this mechanic. He has customers from San Jose to Sacramento. He takes the time to not only explain the issue but acutally showed me the balance shaft markings on a 944 he has in his shop.

His first assumption was also the balance shafts when I described the problem. He showed me the manuals and explained how the woodruff key and tab align. My car has the "O" showing in the window on the top shaft but not on the bottom, as they should.

Nonetheless, he is going to take another look Monday. I asked him to rotate the bottom shaft 180 degrees and see how it affected the vibration. He is also going to install a new belt.

Thanks again to everyone. I will certainly report in on the progress next week. Dmitry - I hope we will meet in the near future.

Tim

Mighty Shilling

That's bizzare... He is tensioning the belts with the engine at room temperature, correct? (no less than 4 hours after running it)

It's bizzarre...this may sound dumb, but is one of the pulleys on backwards? that would make it so the O wouldn't be visible, yet still have it 180 degrees off... It REALLY sounds like a Balance shaft problem... I had the same symptoms EXACTLY with my balance shafts off...