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Haven't driven my S2 in a while, since I gave it to my father as a daily driver. Today I "opened it up" a bit and notice it "groans" when I brake hard to make a sudden stop.
The car has 144K miles, shocks and ball joints are new. New Porsche (Pagid) brake pads and noise dampeners just 7K miles ago.
ABS works fine, but there is this "groan" when I brake hard to make a stop. Could this be it? ->
Groaning Noise From Front Brakes.
December 3, 1992
Model
1989 944T 944 S2, 968
Part Identifier
4636
Group
4
Number
9205
Subject:
Groaning Noise from Front Brakes
ATTENTION:
Service Manager/Service Technician
This bulletin supersedes Technical Bulletin Group 4, Number 9205, dated 8-25-92.
Models Affected:
944 Turbo MY 1989, 944 S2 and 968
Concern:
Fog horn type noise on brake application can occur during braking. If this noise occurs, it is usually during warm outside temperature and a warm brake system.
General Information:
Noise is transmitted through the front axle by harmonic resonance caused by braking. Damping plates are installed on the top side of the spring strut mount to eliminate this noise.
Parts Information:
Damping Plate (Qty. 2) Part Number 944 343 903 01
Two component glue (Terokal 221) Part Number 000 043 176 00
Work Procedure:
1. The damping plates are to be glued to the upper strut plates. For this reason, it is very important that the damping plates and contact area of the upper strut mount be cleaned thoroughly with acetone.
2. Apply a 3-to-4 cm bead of both glue components side by side on a piece of cardboard. A mixing ratio of 1:1 must be observed. Mix the glue components thoroughly. This will be enough glue for both damping plates. The working time of the mixed glue is two hours at room temperature.
3. Apply adhesive to the underside of each damping plate and install damping plates on upper strut mount as shown in Figure A. Remove excess adhesive. NOTE: Flat side of damping plate faces up.
Adhesive Information:
The cure time of the adhesive is 24 hours at room temperature. The vehicle should not be moved during this period.
Hmmm. Might it be something other than brakes? Maybe something related to the springs / shocks compressing as the nose of the car "dips" under hard braking?
I had this problem on the 951Cup and after doing 10 or so hard stops from 200+ down to almost standstill the noise dissapeared and the feel in the pedal was a lot better.. Spoke to the PO about and it he said that it could be since the car more or less had been standing still for a year..
Can anyone find the Figures that go along this service bulletin? I'm getting unbearable groan and vibration on my 968 with new factory original pads, new piston vibration dampeners, and Zimmerman rotors, although in my case it does it only at very slow speeds (0-10mph) on light to moderate braking force. Brakes work and feel great in all other driving conditions.
I'd like to see exactly where these damping plates mount.
Also, anyone knows whether these plates came installed on 968? I can see the plate part number in the factory parts catalog, but the exact location isn't shown on the actual diagram. I'm asking because my car had all shocks replaced by the dealership a few years ago, the car hardly got driven since, I'm wondering if the techn may have forgotten to install the damping plates (provided they are meant to be installed on all cars rather than to fix an infrequent groaning problem).
I don't have a picture, but the dampers plug into the recesses on the pistons. The only examples I have on hand are not mounted and most of the part is missing, so it wouldn't be much help. Here's a link to the unmounted piece: https://www.paragon-products.com/Bra...351.096.01.htm
That little flower looking thing goes into the piston and then the wider part rides against the pad. I'm pretty sure that they are standard equipment on the 968 but they also go missing a lot during brake changes.
I don't have a picture, but the dampers plug into the recesses on the pistons. The only examples I have on hand are not mounted and most of the part is missing, so it wouldn't be much help. Here's a link to the unmounted piece: https://www.paragon-products.com/Bra...351.096.01.htm
That little flower looking thing goes into the piston and then the wider part rides against the pad. I'm pretty sure that they are standard equipment on the 968 but they also go missing a lot during brake changes.
Good luck
Thanks, but these are not the same parts referenced in the service bulletin. The link you supplied shows vibration dampers that mount inside the caliper pistons. Mine were missing, I ordered and installed them, it transformed a screeching squeal at low speeds into a vibration groan, very much like the fog horn description in the porsche bulletin.
The OP referenced parts that are glued to the shock somewhere, to prevent resonance through suspension components. That is what I'm after.
I know of a 88 TS that was bought back by the dealer under the lemon law for noisy brakes, the dealer could not fix to the customers satisfaction. Several of us who tracked MO30 cars with stock pads would experience a "singing" of the brakes when hot, and on softer street use they can make foghorn type noises. While this does not help you out, I just want to say a lot of us with the MO30 know those big brakes can and do sing.
I know of a 88 TS that was bought back by the dealer under the lemon law for noisy brakes, the dealer could not fix to the customers satisfaction. Several of us who tracked MO30 cars with stock pads would experience a "singing" of the brakes when hot, and on softer street use they can make foghorn type noises. While this does not help you out, I just want to say a lot of us with the MO30 know those big brakes can and do sing.
The 968 stock brakes have been widely produced since the 951, I would be interested to know if anyone else experienced this problem.
I will try a different brand of pads, maybe factory pads don't like Zimmerman rotors (how unlikely is this theory?), but there is a possibility these damper plates have been omitted when shocks were replaced (with new factory units), provided these plates are part of the design rather than a fix to be used only when necessary.
The OP referenced parts that are glued to the shock somewhere, to prevent resonance through suspension components. That is what I'm after.
I've seen pictures of these damping plates on cars on Rennlist, but don't seem to have any in my saved images. They are little crescent shaped metal pieces that look to be 3/8" thick or so that attach to the top of the strut mount. I don't get any noises like this in my S2, but it has totally different brakes and suspension and resulting resonance.
If these parts were installed, replacing shocks would not affect them unless the top strut mounts were also replaced, which is doubtful.
Last edited by Tom Pultz; 08-08-2021 at 03:54 PM.
Reason: Add information
I understand now. Obviously, I didn't read the original, transcribed Tech Service Bulletin. Here's what you're looking for:
944 S2, adjustable Koni shocks but otherwise stock AFAICT. Please excuse the mess in the background
Abused 968, everything stock and uncared for.
That little crescent looks to be some sort of steel, given that it's rust that you see on there. It must be some kind of glue that they used, those things seem super solid on the strut mounts.
Have you just tried to re-bleed the system? During the pad replacement 7000 miles ago there could have been gas (air) inadvertently introduced into the system. Now you have a compressible fluid in the calipers and during the very hard braking, the heat generated could be causing erratic gas expansion/contraction (flutter) in the calipers. It is a pretty simple and inexpensive thing to check. FWIW!
Good Luck!
10-16-2004, 09:56 AM
S2 Brakes Groaning Under Hard Braking to a Stop?
