964 C4 issues

[beamonk]

I drove a C4 at the track yesterday and came away quite impressed. For a street car, what kind of issues do these cars have, aside from the early car cylinder sealing issues? How do the differentials hold up?
Thanks,

[Don Plumley]

They are a fairly robust car and a good value. By this age, any of the teething problems affecting the 89-91 cars should have been resolved if the PO took care of the car. Mostly it's a miles and care issue, as with any car of the vintage. I don't have any specific knowledge of problems with the differential longevity, though C4's use a special high pressure hydraulic system. You might check on the Rennlist 964 board for more specific issues.

C4's are not very common as track cars though. Most tend to be converted to RWD with faster lap times as a result. But others have reported good results with the inherent understeer if the car is set up properly.

Here's a Rennlist thread that talks about it, and they reference an article on Adrian's site.

[DustinTarditi]

C4s are a little bit heavier, and slower as a result.
I love my C4 and enjoy driving it daily - I haven't taken it to the track, but imagine a well-driven C2 will out pace it from weight difference alone.

The brakes are pressurized, so sort of a tough DIY (C2 are DIY friendly). The common 964 issues are as follows:
1) Dual Mass Flywheel (DMF) - by now, most have been replaced, many with light flywheels (which introduces a tendancy to stall on occasion when RPM drop is too sudden and car isn't warmed up)
2) Dual Distributor - design had issues with the timing belt oxidizing and breaking - simple vent kit remedies this
3) Leaky - most 911s leak a bit of oil... of them, most 964s leak more. They're just hard cars to keep dry for a number of reasons - none major, just stay on top of it.
4) Complicated electronics - requires the Bosch diagnostic tool "The Hammer" to chech error codes and reset faults.

That said, I drive mine regardless of weather - they have more tendancy to understeer vs any other 911. It's more of a "point-and-shoot" type of car. Quite fun to drive, still... Vic Elford liked them, too ;-)

If kept up they are great cars - exceptional for their time. Is a 993 better? Not necessarily - depends on what you're after. You can find a much better example of Porsche in a 964 for $25K than you will a 993 (generally speaking), for instance.

In classic Porsche parlance: "Buy the best 911 you can afford. Period."

[doubleurx]

^^ those seem to be the major issues.

I still have the original fly wheel on mine - 67,000 miles. I do have the vent kit, I do have some oil leaks that will hopefully be fixed next week. I have never (knock on wood) had any electronics issues.

Going with the larger diameter sways both front and rear made a drastic difference in reducing the understeer tendancy that most AWD cars exhibit.

[DustinTarditi]

The PO (one of them anyway!) installed a weltmeister bar up front - good product.

I also have a light flywheel, not the DMF.

The only things I've done were add a cone intake, new radio (old one was fubar), newer DME Relay (993), and a set of Lloyd's mats ;-)

[beamonk]

Do they have the same rear tire wear that the early 993's exhibited?

[DustinTarditi]

John,

I'm not familiar with the 993 issue.

Most 911s (from talking with the owners) seem to get 1 front set of tire life to 2 sets of rear tire life if driven in spirited fashion.
My C4 seems to fit into that model even though it's AWD, I think this is typical. It's probably not quite a 1:2 ratio, but by the time the 2nd set is ready for the rear the fronts could use fresh rubber anyway.

My assumption is that this has a bit to do with the tire compounds we run anyway - typical passenger cars use a much different compound than summer performance tires, of course... most people here in NC don't swap out summer tires for all-season/winters. I drive BFG G-Force year-round, for instance.

[trader220]

C4's I dont believe had the fly wheek issues. The leaking heads were 90 and some 91 cars , Porsche changed the setup in the 91 MY production i believe. Just about all of these cars that were made without the distributor belt vent kit have had them installed by now.

[kang]

Originally posted by beamonk
Do they have the same rear tire wear that the early 993's exhibited?

I don’t know why this issue is still alive. Perhaps because Bruce Anderson mentions it every time Excellence reviews the 993’s. But all you need to do is align the early 993’s to the later 993 specs and the issue is gone. Certainly most early 993’s have had an alignment by now…

[tjn]

beamonk, i have a '91 c4, was normally aspirated, now tt. the leakdown test when i purchased the car indicated a failure. the reason is that the cylinders became slightly eggshaped. this was documented in an "excellence" issue in the last several years. i just wish that i would have bookmarked the issue! this issue has caused me absolutely no problem. i have debated this with my wrench, i now think that he is a "believer"! best of luck, tjn/vk