View Full Version : Sachs Clutch Disc Failure

07-29-2012, 10:43 PM
Saturday I was leaving a friend and fellow club member's house when all of a sudden I heard a "POP" and then my engine began to rev. I thought to myself that this cant be good as the car was slowing to a stop. I had lost all motion, no gears forward or reverse. It felt as if all of the internals of the transmission had just vanished because there were no noises coming from the gearbox. I was able to put the car into any gear and push it! Now I know you can't do that but I did. Fortunately for me I only got a block away from the garage which is well stocked to perform any needed repairs. I came back with some help today to remove the transmission and to figure out what had gone wrong with it. I was preying it was nothing inside the gearbox. When we removed the transmission and the pressure plate this is what we found.
Clutch Photo (https://docs.google.com/document/d/1LUBtPNRCq9tIkUjc1s2i2v-yVXwue_sd4yp-kV9IMhQ/edit)
(Sorry having trouble posting the photo)
This was a 7 year old Sachs clutch disc with less than 25k miles on it. The clutch was not abused but the car is occasionally driven spiritedly. If you look carefully you will notice that the outer friction ring is held to the hub at only 3 points! On the LUK or Borg & Beck units they are held in place at 7 and 10 points and each point is fastened with 2 rivets not just 1 as Sachs does it. Fortunately one of my friends had a brand new LUK disc and we were able to get the car back on the road. This was such a strange mode of failure that I had to share it. Also I would reconsider ever installing one of these clutch discs ever again it just does not seem like a very robust design.

Andrew Mace
07-29-2012, 10:58 PM
I'm guessing we'd all need to "friend" you on Facebook to see the photo. :frown:

Meanwhile, I'm a bit surprised, as I'd thought Sachs was one of those well-respected names for clutches. Maybe they're not what they used to be, either?

07-29-2012, 11:00 PM
Sorry about that. I will upload to a different sight and edit the post.

07-30-2012, 07:17 AM
OUCH!! I've put Sachs "kits" in more than a few cars. Haven't seen THAT before.

Here's yer photo, Roman:

07-30-2012, 02:51 PM
Roman, it looks to me like it is held on in six (6) places on the ring and they all failed. From they way it looks to me (far away and not up close) that metal in the picture looks like it was fatigued from heat.

07-30-2012, 03:12 PM
BTW, I've always wondered how those little bits of metal actually hold up to transfer the full torque of the engine to the driveline (say compared to the driveshaft, u-joints, etc that you more often hear about failing).

07-30-2012, 03:48 PM
Several local club members have had the same failure, although I don't know offhand if they were running Sachs or something else. It is a very standard/common way of building a clutch plate. You can see that the LUK plate in the photo below is built the same way. (Photo courtesy Buckeye Triumphs)

Personally, I suspect the failure comes down to poor quality steel, not a design flaw. That plate is obviously made of spring steel, which says to me that it is supposed to flex in operation, likely to help provide some cushioning for the driveline (in addition to the springs).

One point, Darrell, is that the driveshaft etc has to handle engine torque multiplied by the first gear ratio. Also, that plate has a larger radius (meaning the actual force is less for the same torque), and the whole plate carries the torque, not just a small portion at any one time. Many if not most of the failure start as a bearing failure inside the U-joint caps, which if you think about it, is sending full torque through two or three contact lines.

07-30-2012, 06:26 PM
Hi Paul,
That Sachs disc was only held to the hub using the 3 rivets you can see on the hub. The remnants of the other 3 steel fingers were damaged as the hit the springs and other bits as the assembly let go. The distortion in the color that you see was caused by my dirty and greasy fingers and some friction material dust. I just wiped down the part and it looks fine. That section of the disc is made from spring steel so it is blue in color
I replaced it with a LUK clutch disc and I can definitely say that they are built differently. The LUK unit uses heavier gauge steel for the ring section and it has 8 finger connecting it to the hub and each one is held in place with 2 rivets for 16 total. You can see the difference in the construction right away and if you look carefully on the LUK hub you will see next to the springs 3 rivets. These 3 rivets are there to hold the hub assembly together. On the Sachs clutch the also held the disc to the hub. I will try to post a couple more pictures to try and clarify.
I can assure you that this clutch was not abused. I never tried doing burnouts or hole shots with my 6. I did use the car for several VTR convention autocross events and some spirited driving but the was it.

07-30-2012, 07:02 PM
I hope all of these pictures are accessible!. I need a lesson in posting photos on the board.
This first picture shows the Sachs clutch disc next to a Borg & Beck unit.
Clutch Comparison (https://picasaweb.google.com/100708703935167366551/Clutch?authkey=Gv1sRgCJbvhujn5s3_mwE#5771112038133 905666)
You can see how many more attachment points the Borg & beck unit has compared to the Sachs.
The second shot is a close up of the Sachs disc. Here you can see that it was only held together by the 3 rivets located on the hub.
Closeup (https://picasaweb.google.com/100708703935167366551/Clutch?authkey=Gv1sRgCJbvhujn5s3_mwE#5771112652452 178194)
And finally a closeup shot of the clutch as it came out of the transmission.
Exploded view (https://picasaweb.google.com/100708703935167366551/Clutch?authkey=Gv1sRgCJbvhujn5s3_mwE#5771112659342 663362)
If Sachs would have riveted the outer ring to the hub at the perimeter of the hub where there are already many holes punched just for this purpose. I don't think it would have ever come apart. But since rivets cost time and money to install they took a cheaper approach and assembled it the way they did. In my opinion this is an inferior method of assembly and I will not ever use a clutch that is made in the fashion again.

07-30-2012, 07:18 PM
Wow I've never seen that before. Do you by chance have one of those LS1 engines in you car that's on another thread?

07-30-2012, 10:55 PM
I wish!
I have the Triumph 6 cylinder with an S-2 cam. So in other words not a lot of horse power!
Besides the clutch went out with a whimper as I was only moving at 20-25MPH when it let go.

07-31-2012, 06:43 PM
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I can assure you that this clutch was not abused. I never tried doing burnouts or hole shots with my 6. I did use the car for several VTR convention autocross events and some spirited driving but the was it.[/QUOTE]

Roman, I can appreciate that and I was not suggesting that you did anything to abuse it. Metal fatigue can occur at anytime if the parent metal is not quality material. As I said "from afar" it "looks" like heat stress, but that was a guess from the color of the metal.

I do now see that there are only three rivets holding it in, which I missed on the previous picture.

FWIW, I just looked back at my website and I have the LUK style (Sachs) pressure plate with a clutch disc that has the same three rivets as yours. Hmmmmm

Here is the picture of the infamous Gunst with only 600 miles on it, squealing like a pig and the rust on the bearing and PP show why. That was the second complete replacement unit in less than 1,000 miles.

The "TRF Magic Kit" with Koyo bearing that is in my car today is shown on the left of the junk unit.

07-31-2012, 08:48 PM
Roman, I can appreciate that and I was not suggesting that you did anything to abuse it.

Paul, I did not think that you were implying anything but you made me think and I had to go out to the garage and take a better look at it. That is when I discovered that the blued spring steel had dirty finger print smudges on it making it appear to have over heated. Regardless of how the metal fatigued, because it obviously did, the system of assembly employed is simply substandard and cheap. It appears to be designed to be prone to failure.