Piston Slap: Can a new part kill its old neighbors?
![](https://hagerty-media-prod.imgix.net/2022/02/porsche-944-piston-slap-bannered-lead.jpg?auto=format%2Ccompress&ixlib=php-3.3.0)
S.L. writes:
I recently spent an awful lot of money on a new clutch for my 1984 Porsche 944. Within 30 days, I came out one morning and my clutch pedal went almost all the way to the floor. I figured it was an adjustment that was made when I had the clutch put in that had loosened and caused the slack in the pedal. I took it in and was told that I had to replace the Clutch Master Cylinder and Slave Cylinder along with the required hoses.
I felt that with this old of a car, after all these years it seemed unusually coincidental that I would have to replace them just after getting a new clutch. Is it so unusual? Or is this a more normal occurrence than I think? The car has only 63K miles, to boot. Just seems awfully early for both to go out, and Porsche is pretty well known for building their cars well.
Sajeev answers:
Hate to say it, but this is a common occurrence when it comes to old cars with old rubber parts: replacing one thing puts undue stress on parts that could be nearing a catastrophic 40th birthday. It’s no coincidence the hydraulic system failed after installing a new clutch; they were already dying a slow death.
A good analogy is when hot rodders install a souped-up engine behind a transmission of unknown health. In this (highly generalized) case, putting the new engine though its paces radically shortens the life of the already threadbare clutches inside the borderline-healthy transmission. Or go do a burnout in a beat up minivan—the extreme effort in a big vehicle with a small, overworked transmission also proves the point.
While an old transmission might not die as quickly as Porsche/VW hydraulic clutch parts, the seals and o-rings in the master/slave cylinders eventually shrink and cause a leak. Add a new pressure plate (presumably installed with the new clutch), and those little rubber bits are truly put to the test. Vehicle mileage is irrelevant; your 944 could have 20,000 miles on the clock and this would still happen. Hydraulic clutches use rubber parts, and rubber goes bad over time.
![Porsche 944 slave cylinder rebuild kit](https://hagerty-media-prod.imgix.net/2022/02/928.116.901.00-2.jpg?auto=format%2Ccompress&fit=crop&h=422&ixlib=php-3.3.0&w=565)
I’m surprised your mechanic didn’t recommend/insist on replacing and rebuilding the whole system from the beginning. My years in automotive retail taught me this is the best way to set expectations with customers needing non-warranty work on older vehicles. It’s a sad fact that you cannot replace one weathered link in an ancient chain and not expect other problems down the line. And if your mechanic did make such a request, next time trust the fact that 30+ year old cars will fail anywhere and everywhere they possibly can. Doesn’t matter if it’s a Porsche or a Hyundai Excel; nothing ages well if you let enough time pass.
More to the point, one of my buddies in Detroit messaged me about a 1979 Mercedes he wishes to add to his garage. I suggested the vehicle will hoover out his savings at a furious rate, especially if it lacks a comprehensive service history. I’m gonna forward this Piston Slap article to him as proof of my concerns, because that’s what real friends do for their compadres!
Have a question you’d like answered on Piston Slap? Send your queries to pistonslap@hagerty.com, and give us as much detail as possible so we can help! If you need an expedited resolution, make a post on the Hagerty Community.