clashmin

I had a new engine installed in my 1989 C4 and the transmission needle bearings failed soon after (less than 1000 miles). I figured it was because the trans had 110,000 miles on it. I replaced the trans with a unit from a dismantler (60,000 miles) and it also had needle bearing failure soon after installation (less than 1000 miles). Is this just bad luck or is there something else possibly wrong in the car? One theory someone told me was that the torque tube was misaligned. I need help!

Bill Wagner

It's probably bad luck. I've been on this site for over four years and it's rare to hear about a transmission failure (but it does happen). After looking at the diagram of the transaxle, I would think that misaligning it would be kind of difficult to do, particularly twice in a row.

Sten

I've seen three C4 gearboxes over the past year where the planet gears have broken free from the carrier, smashing the gears and splitting the clutch sleeve. The planet wheels run on pins in the carrier, which have three centre punch marks around their circumference to stop the pins from falling out. I suspect that this is not enough to stop the pins rotating in the carrier in some circumstances - the pins start to wear their mounting holes oval, until there is just enough play for one of the planet gears to jump out of mesh and cause mechanical mayhem. It's an expensive fix - the planet wheel carrier is c.£1200, I think the clutch sleeve is around £200 - and that's the least you get away with. I've spoken to the owners of two of the cars, both said that they weren't doing anything crazy when the gearbox went, and neither car had seen a track day. I'm currently looking into having the planet wheel carriers re-manufactured unless anybody else has any ideas?

Bill Wagner

Well that's not good news!!!

Do you have any idea how many miles were on the transmissions when they failed?

clashmin

The first had 110,000 miles and the second had 60,000. Both went bad after an engine rebuild. The engine is fine though... There was one other problem with the car that has since been fixed- one of the accelerometers was dirty and stuck, so the AWD would alarm after 10 minutes or so of driving. I did fix that by cleaning out the accelerometer but not until the trans was already mostly gone.

garrett376

True... unless the car's frame is tweaked or something is wrong with the engine.

Which needle bearing failed - same in both cases? Work done by the same mechanic? Under the same circumstances (engine R&R)?? Hmmm....

Adrian

Bill,
It is very difficult (impossible almost) to misalign the mounting of the transaxle to the engine. You can mess up the clutch fork but this will not cause a transmission bearing faulire.
The transmission was not disassembled so nothing happened internally.
However, it is possible to misalign the front drive shaft. If the drive shaft is not mounted dead straight and properly torqued you will get an uneven load between the power transfer unit and the front differential. This will create a side load within the tranmission.
Seeing as the problem occured after an engine change (twice) the issue may well be an installation problem at the power transfer end.
I would even look at the forward transmisison mount.
If any of this is off centre, I can imagine this happening over time.

The other issue mentioned about the planetary gears.
This is a failure of the differential lock.
The differential planetary and sun gears are forced into gear with each other by the clutch plate assembly which is operated by the slave cylinder. Their job is to lock the front and rear drive shafts together.
The failure occurs when the gears come together in a manner, which results in teeth hitting teeth instead of teeth meshing with teeth.
I have seen it a couple of times myself. Usually caused by severe treatment. Excessive torque on the gearing. Regular attempts at spinning of the rear wheels when exiting corners is one way. Doing burn outs in shopping centre car parks another.
People cannot imagine the torque these relatively small gears absorb when the lock is engaged. The engine is now driving through this tiny little plantetary and sun gear assembly.
Mind you such failures are still quite rare.
Ciao,
Adrian.

garrett376

Makes you wonder how well a C4 drivetrain will endure loads experienced in racing environments... I better change that oil more often! Out of every corner the rear differential is locking to some extent...

I would assume this same planetary gear structure weak-point exists in the C2 open differential (or any open differential for that matter), correct?

Adrian

Garrett,
Point 1: Ever wondered why the C4 was never turned into a racing car with the G64 transmission?

Point 1A: The rear differential lock assembly used (see point 2) in the G64 transmission was designed for the 928 originally. It is quite strong. However the centre differential lock was built for the 964 only and was recognised internally as being a weak point. Chalk it up to pooh happens.

Point 2: Nope wrong. The planetary and sun gears that I was talking about are found only in the 964 C4 G64 transmission differential locks. All explained in the book.

Ciao,
Adrian.

garrett376

Fortunately, I guess, the weaker longitudinal differential locks to a lesser extent than the lateral diff under racing conditions. I am happy to hear that the differential is the same as the very torquey 928.

I figured the C4 never made it into a race car since nobody ever had a series/class that would accept it back in the 90's... they should because it makes an outstanding racer... when it sheds some pounds!

Devils_son

On the circuits, when braking late into a tight corner I am used to having massive oversteer while exiting. Always figured that this was due to the fact that the PDAS wasn't working during braking. Does this mean that I am killing the car with that?

And another thing: when reducing understeer (and getting more oversteer situations) by changing the suspention... does this mean you will cut short the live of the fourwheel drive system?

C4Russ

I've been wanting to beef up the C4 with bigger, badder, faster everything. For some reason, it gets in the blood after driving them for a bit. One gets a little jaded with the acceleration, wanting more. Once wishes to corner a tad faster, wanting more.

In truth for street driving, a 5.4 0-60 is enough (for me) and the 160ish top speed is enough (for me). That I can hit the freeway exchanges at 65+ on D90's w/ 16" wheels is enough (for me).

I enjoy the car as is and having been following this board for awhile, it becomes obvious that enough is never enough so perhaps the best way for me to head this off is to just not do any modding of the car? I'll enjoy an already pretty dang fast car and put those dollars into something else, say a bank.

I do love to read about everyone's adventures though, I"m living vicariously through all of you. Please, don't any of you stop spending, this board would become quite boring.

garrett376

I think Adrian is spotlighting a potential weak point. There are several Rennlisters (including me) that regularly race C4's with no issues.

Additionally, there are a couple C4 owners I know about that run turbocharged engines, and the additional torque is handled without a problem. Plus, considering some C4's are running around with well over 100,000 miles with no issues, I think and hope that the cases Adrian mentions are isolated cases where people truly abuse the cars - trying to drop the clutch to accelerate fast... things like that.... I can only hope... I have a race coming up this weekend when I'll surely drive the heck out of the car!!!

Adrian

PDAS does not work under braking. It only works under acceleration and the massive understeer is caused by the centre diff lock being activated.
Are you killing the system, yes you are, very slowly.

A car is made up of thousands of moving parts all travelling along in formation. Everything from tyres to gears to bearings eventually wears out and fails. Nothing lasts forever. How long it lasts depends upon how it is used and MAINTAINED. Most C4 club racers will do much more maintenance than non racers.
Hard usage with maintenance and abuse without maintenance are two very different things.

One thing to remember is that PDAS system has NEVER been used on the race track in the professional world of motor racing.
The club sports racers have proven the system is quite strong and reliable, but under racing conditions wear and tear is accelerated. Many club racers disable the PDAS/ABS when on the race track.

The failures are quite rare I only know of a handful since 1998, when I got involved with the 964, but I do expect more to fail as the years roll by. This is perfectly normal and natural.

PDAS and the AWD are two different things. Unfortunately if you destroy a diff lock you will take out part of the transmission as well.

Ciao,
Adrian.

Adrian

I know 996s with 700HP as well and they were good for the 20,000km before things starting breaking.
You cannot compare cars in statements like this unless they have a similar history and the exact list of modifications are provided.
Turbocharging the 964C4 places more wear and tear on the transmission. How much more, and how much longer it lasts depends on so many factors.
Our cars are getting older, few owners here have had them from new. If you get 100-150,000 miles including racing before you break something that is an achievement for any brand of car.
Ciao,
Adrian.

PS: The Turbocharged C4 I know of very well, regularily had its G64 transmission replaced a number of times before it was replaced with another stronger transmission design. However, this was a pure competition car with the traction control (PDAS) disabled.
A proper RUF conversion includes the transmission being pulled apart and rebuilt. There are no standards from which to draw conclusions.