Mako 928

OK this has been a very long road for me. After the torque tube let go on a track day back in November I had been chasing down a non shifting transmission and subsequently a bad vibration at 4K RPM.

Here is the series of events.

1. Replaced the TT bearings with Constantines Super Bearings ( removed the clutch to access the two top bolts to the TT/ bell housing) Upon reinstallation of TT/ clutch it would not shift into 1st or reverse. H-adjusters "looked" good and since I had no problems before TT replacement I looked at the rear shift coupler as a issue and adjusted it with somewhat sucess.

2. Pulled clutch and found worn friction discs/ pressure plate. Replaced all clutch components except the intermediate plate and had flywheel resurfaced.

3. Still would not shift properly and now I had a bad vibration at 4K RPM. Again adjusted the H- adjusters on the IMP and had minimal success.

4. Replaced the motor mounts as they were well below the crossmember and the "hooked" adjusters had a large gap. Engine would not rock back and forth when I revved the motor. Transmission mounts good.

5. Vibration still the same and shifting getting worse to the point that it would barely shift at all.

6. Replaced the intermediate plate and it shifted perfectly but vibration still there. I found the two bottom bolts to the TT/ bell housing had backed off. This must be the cause of the vibration.

7. Vibration still there. Pull clutch again and inspect.
I found a section in the WSM section 30 page 19 item f. that states "Pressure plate and intermediate plate are also marked with dots of white paint ( residual of unbalanced/heavy side) which are mounted offset 180 degrees (opposite). This must be considered when replacing one or both parts.
Bill Ball had also noted that in section 30 page 12 that at the bottom of the page it states " Parts in table marked with a "X" ( Flywheel, Intermediate Plate and Pressure Plate) were balanced together in manufacturing and must therefore be marked prior to removing for installation in same position later.

When I inspected the clutch pack I had the " white" dots on the IMP and pressure plate together not 180 degrees. I offset the marks so that the IMP/pressure plate was now 180 degrees and reinstalled.

The vibration is now gone and with the replaced IMP it shifts beautifully.


Of course the "white dots" on the two friction discs have to be offset but I did not know about offsetting the IMP/ pressure plate 180 degrees. Now I do.

My last clutch job several years ago I used the same IMP from the factory and I must have gotten lucky with the offset/ placement.

Having three IMP's to look at I noticed that weight was taken out close to the two pins for reading timing ( which is useless unless you have the diagnostic tool to read it) and the WSM states that the IMP has to be positioned on the flywheel in one position for this reason.
I am guessing with MY '85 '86 using the IMP with the two pins that this calls for the offset of 180 degrees to the pressure plate not only for the diagnostic tool but for balance as well.

This IMP has the " white" dot at 4 o'clock. The other marks at 8 o'clock were from marking the clutch pack before removal and servicing.

Rob Edwards

Yep, gotta make sure everything is balanced. The PP and intermediate plate that Mark A. had modified for me got re-balanced as part of the process. Not sure how a machine shop manages to balance the rotating assembly, somehow they got it mounted up and spun.

Note the black paint stripe:

Mako 928

Unfortunately I could only find one machine shop that could balance the pieces and they had a back log of two weeks ( which really means a month) so I could not get the entire assembly balanced as a unit. I had to move the car.
I would have liked to.

WOW, that is one big paint stripe.
I see your tube of optimoly HT. Good stuff.

tailpipe

Have you checked to make sure the torque tube bearing hasn't walked down the tube?

jheis

Greg:

Does this mean it's fixed - or are you saying you still have the problem? Not quite sure after reading your post.

James

Mako 928

Yes all is well. No vibration and shifts beautifully.

Podguy

Greg failed to mention Porsche's insanity in the evolution of the clutch design.

In 1984 Porsche decided to add two timing sensor pins to the Intermediate plate. They also added a sensor to the bell housing. I never researched out what these pins do since no one uses them. Having added the sensor pins Porsche had to compensate for the additional weigh. Solution - easy just add some weight to the pressure plate to offset the heavy side of the Intermediate plate. Thus when the clutch is installed the pressure plate has to be aligned so the heavy side away opposite the pins.

78 to 83 does not suffer from this level of insanity. The strange thing is that no one here suggested this as a source of vibration. Surely someone must have run into this before. The marks are only paint marks and not stamped into the respective parts.

Bill Ball

HALLELUJAH!!

I don't recall this being an issue with S4 or GTS clutches. They can only be assembled in one way, so no marking before disassembly is required, and I haven't done any balancing of the assembly after installing new parts. However, the WSM is very clear that the early 80s clutches need balancing or at least care regarding the orientation of parts, as Greg found out.

jheis

Cool - On the road again!

James

Podguy

Bill,

In all fairness, I read the manual. One would have to twist things written there to mean that the clutch is balanced separately. The manual pointed out three things that needed to be lined up. The wording was not the best - but then again the WSM is not very verbose.

The alignment of the componets only apply to the 84 to 86. Early years the components are balanced in the normal fashion. An intentional heavy one sided balance is quite different and something I have never seen before. It makes sense but a 84-86 pressure plate will not work in a pre 84 unless it is balanced with and 84-86 intermediate plate. Even though they look identical and can be swapped in.

Of course the S4 clutch is not going to have this issue - there is only one component. What would you counter balance it with?

I will write this up on my tips page. There are peobably more than one 84-86 owner running around with an out of balance clutch. The funny thing is if you put in an 83 clutch then there is no balance issue.

Bill Ball

That's right - it says the flywheel, pressure plate and intermediate plate were balanced as a unit, and they need to be marked and reassembled in the same orientation, as you and Greg did. That solved the problem. You could interpret that to mean that since they were originally balanced as a unit, you should redo that when the parts are changed, but all it really says is to pay attention to factory paint marks on the intermediate and pressure plates and on the clutch discs. In Greg's case, aligning the marks on the pressure plate and intermediate disc 180 degrees apart, something Greg hadn't attended to before, were the key to solving the problem. That's buried in the WSM and you have to read several sections to get it.

BRB-83-911SC

I may be experiencing this same issue upon re-installation of my clutch (84 Euro LH with sensor pins on IP Ring Gear, and stepped pin for alignment to Flywheel).

Can the OP or anyone else who has had an out of balance DD clutch where re-indexing of the PP/IP cured it comment on the vibrations? RPM's; at speed; at idle; clutch in; clutch out; load; no load; etc.? What did the vibes feel/sound like? Thanks.

tilac999

So the key to proper balance is indexing the white dots/marks 180 degrees apart?