Transaxle clunks when up-shifting...
 

... only when driving. Clutch fully depressed, shifting up, you hear a good clunk - but not usually when down shifting. And only while moving.

This is in my 83 NA. I installed this transaxle in 2009, and it should have only about 104,000 miles on it. I've changed the oil a couple times; it's currently running Redline MT-90.

Just sitting, it makes no noise at all when shifting.

Also, it makes a clunk when you let the clutch out quickly. I played with this yesterday (letting the clutch out almost all the way, then quickly depressing it), with my son listening, and was able to narrow it to the left side of the transaxle (he thought).

I put the car up on jackstands and made a visual inspection: nothing's out of the ordinary. I was hoping maybe one of the CV joints was hanging by a couple bolts or something, but no - everything was tight.

Turning the wheels back and forth by hand, it seemed like you could hear a noise from the area where the axles connect (the diff?). It's like there was some slop in those gears and perhaps that was the clunk I hear shifting.

Would sloppy gear teeth account for something like this? Or something else?

It does shift kinda hard, but it doesn't whine or make any other noises.

Right now, I'm thinking I'm gonna change the oil - Maybe Swepco 201 - and drive it and see what happens.

Anyone had this problem before?

There's nothing wrong with your lubricant. I recommend swapping the CV from one side to the other and see if the noise moves to the other side of the car. Then you'll know for sure that it's CV's. It's easier than it sounds to do this. If it doesn't move, then it's possible you have an internal issue with the transaxle.

Have you completely ruled out the clutch? Clunking and hard shifting sound like it's not fully disengaging.

When you have the CVs off you should open the diff inspection portal.

+1^

Check the transaxle coupler to make sure the 2 bolts are tight.

Or check a few more noises ;) (credit A.....AZ)



Porsche Noise Troubleshooting:
Troubleshooting Noises (Is Your Porsche Trying to Tell You Something?)


Troubleshooting those weird noises coming from your Porsche can help you determine needed repairs. It's important that you listen to what your car is trying to tell you.

Although many people still use the old broomstick-held-to-the-ear method of zeroing in on noises, the best method these days is a stethoscope. Indispensable in finding the source of a sound, it's also a lot easier to place it where you want it than the clunky end of a broomstick.

Here are a few general guidelines to what your Porsche's noises might mean:

BANG: A sharp, startling sound, like a rifle shot, means you're dealing with the dreaded backfire. You'll probably be able to trace this to something that's causing a rich air/fuel mixture.

In the past you might have zeroed in on a heavy carb float, but today think about faulty signals from coolant temp or O2 sensors. The catalytic converter may also be damaged.

Another possibility is a clogged monolithic converter blowing through. This will only occur once and will be accompanied by an amazing increase in power. If your car has air injection, perhaps the diverter valve is no longer diverting.

BOOM: A hollow, low-frequency sound/sensation, this makes you feel as if you're riding inside a metal drum and the atmospheric pressure is rapidly changing between positive and negative.

On rear wheel-drive cars, check out the driveshaft and its u-joints because if it's spinning out-of-true, it will cause waves that push up on the floor of your car.

BUZZ: An annoying "bzzzzzzzzz" sound, like a trapped insect, can usually be traced to unfortunate positioning of interior trim parts. Have somebody else drive while you press, pry and pound on every likely spot.

CHIRP: This sounds like birds are nesting under your hood. You can probably blame a maladjusted or misaligned belt, but don't ignore the idler pulley. Or, it could just be your tires when you hit second gear.

CLANG or CLANK: This sound couldn't possibly be emitted by any light, flimsy parts. It's coming from a heavy, essential component, such as a set of gears. A good example is the sound a bad rear axle pinion bearing makes when you drop the transmission into Drive, then Reverse.

CLICK or CLACK: This sounds like 007 working the slide of his Beretta automatic. When in an engine, it's typically repeated rhythmically.

With OHV, perhaps a stuck lifter is allowing clearance in the pushrod/rocker valve, or maybe a solid lifter is just out of adjustment. On carbureted cars, check out the fuel pump before you start opening up the motor.

When emanating from the nether regions of the front end during a turn, this sound may be traced to an outboard CV joint.

CLUNK: A heavy bumping sound, softer than a clang, usually indicates you should look at suspension bushings, including shock or strut mounts. Or how about a loose strut gland nut?

FLAPPING: If it's not due to a colony of bats under the hood, maybe a belt's coming apart. Fan interference is another possibility. Regardless, this is a visual inspection sort of thing.

GRINDING: A horrible, torturous sound, like a bad dentist would make while working with obsolete equipment, means something's going awry - and fast.

If it occurs when the brakes are applied, either the linings are gone or you've got one of those unpleasantly-aggressive friction material formulas that tend to eat rotors.

GROAN: Something's dry, probably a suspension component. If it's metal, it's going to break really soon. If it's rubber, try some silicone lube.

GRUNT: Again, a dry joint somewhere in the underpinnings is likely. If it's in the stoppers, suspect rear drum shoes contaminated with brake fluid or gear lube from a defunct axle seal.

HISS: If it's continuous and changes with rpms, it may be normal belt noise. Otherwise, a slow leak in the cooling system is likely. A black light will help you find this.

HUM: We don't mean what the radio does between stations, but the noise a differential or wheel bearing makes. If it responds to acceleration/deceleration, suspect the differential. Then look into the bearings. Unfortunately, it's often very difficult to tell which side (or even which end) the hum's coming from.

KNOCK: Like knuckles on a wooden door, this sound is deep and hollow. Often it's a warning that something important (and expensive) is about to let go.

It's unfortunate that a loose pin sounds pretty much the same as a defunct rod bearing, but with a little patience you should be able to determine what's at fault.

First, check idle oil pressure even if you have to screw in a mechanical gauge. If it's low, you can bias your decision toward bearings.

Next, listen with your stethoscope. A rod bearing makes more noise at the oil pan than elsewhere, and a wrist pin more racket up on the water jacket. Hold RPMs at 2500, jerk the throttle open and let it snap closed. This will accentuate rod knock, whereas pin noise won't change very much.

Now's the time to starting shorting out cylinders. A bad pin will quiet down, but a rod knock will double its cadence.

Finally, you can pull the pan for a visual inspection. If the bearings are good, you know you've got a pin problem.

PING: Sort of like little ball bearings being poured on a tin roof, this sound is detonation (aka spark knock) - a phenomenon in which the air/fuel charge explodes violently instead of burning smoothly.

There are many potential causes here from clogged EGR passages and overheating to excessive spark advance and, with spark knock suppression, a defunct detonation sensor. Hook up your timing light then tap on the engine near the sensor to see if the spark retards.

POP: This sounds like a shotgun being fired through a mattress. It usually means the engine's coughing back through the intake.

A sticking or leaking valve is a distinct possibility, as is jumped valve timing, particularly with a belt-driven OHC.

Then there's ignition, which may be firing way too early due to a twisted distributor, cap/rotor/wire problems, a faulty position sensor or a breakdown in the module.

Also, if your Porsche's running quite lean, opening the throttle to lots of cold air can induce this reaction.

RATTLE: They didn't coin the term "rattle trap" for nothing, you know. People have been fighting this annoying noise since the automobile was invented.

Thanks to plastics, better rubbers and more highly engineered fasteners, rattles are less prevalent than they once were. But you'll still get them, usually in the undercarriage somewhere. Likely culprits include exhaust system parts, calipers or loose brake pads.

ROAR: If it's not something obvious like a blown exhaust system, maybe the transmission is never shifting into high or overdrive.

With a manual transmission, the clutch might be slipping. Fan clutches usually fail by never engaging, not the opposite, but it's still a possibility.

If it's general road noise, you could switch to less aggressive tires or add undercoating to your Porsche.

RUMBLE: While a pleasant enough throaty sound when it's from a free-flowing exhaust system, it can easily cross over into the unacceptable sound range. But don't choke the power down with an overly restrictive cheap muffler. For tire and road noise, see "ROAR".

SCRAPING: Something like "jeet-jeet-jeet-jeet" that speeds up as the car gathers speed probably means an object of one sort or another is contacting the driveshaft, possibly an exhaust shield or hanger or the parking brake cable. Your brake system, especially drum hardware, is also a distinct possibility.

SCREECH: "SQUEAL" taken to the max. See "SQUEAL".

SIZZLING: Like the sound of bacon frying, this is usually only audible with the engine off. Oil may be leaking onto the exhaust manifold or a minor coolant seepage may be occurring.

SQUEAL: This sound is usually related to brakes and belts. On the former, maybe you're down to the pad wear indicators. Or the discs and semi-metallic linings aren't getting along due to poor rotor finishing or washing, an assembly error, a troublesome friction formula or the like. Squealing is certainly common in disc brakes, but clunking can also occur on initial application if the shoes are loosely mounted.

In the case of belts, check if they are loose, worn or contaminated.

TAP: Much the same as a click, sort of like beating on the intake manifold with a screwdriver blade, this is usually valvetrain-related. Think about stuck lifters or an adjustment that provides too much lash.

WHINE: Not what an impatient 3-year old does but just as annoying. This is a hard one to pin down, but it's apt to come from worn ball or roller bearings, mismatched gears, too light a lube in a manual gearbox (ATF, maybe?) or alternator bushings getting ready to go.

WHIR: The sound made by happy mechanicals. It's one of the few noises you probably shouldn't worry about.

WHISTLE: Usually occurring at higher speeds, it's probably wind noise. But do double check if the latches and tumblehome are properly adjusted. Are the body gaskets in good shape?

GL
John

I have poopy flange bearings that gave the symptoms of a bad wheel bearing but added the clunks of the differential carrier bouncing around.

remove the axles and check your axial and radial play at the cv flange. I had 40/1000" radial and 100/1000" axial so on the verge of destruction.

mines a six speed so I can swap them with the tranny installed. if the Prussian blue turns up anything strange, I will be taking it to kevin gross who is been very helpful.

Thanks everyone for the suggestions.

I checked the clamping sleeve and it's tight.

I don't believe it's the CV's. Grabbing the ends of each joint and twisting, there's no play. And in any event, every CV joint I've ever had fail clicked or squeaked, not clunked.

And it's definitely not the clutch. It's a rear of the car noise.

The only place there's any play at all is in the transaxle itself. Grabbing and turning the both flanges on either side (where the CV's bolt on) I can turn it maybe 1/4 inch. Possibly the differential carrier? But then I tested my good spare 951 transaxle and it had about the same amount of play.

I don't have time for further diagnostic work right now, so I guess I'll just drive it and see what happens.

Could it be a bad clutch rubber center disk?

Not sure of the clunking noise. A 944 transmission with "only" 104,000 miles on it is almost certainly in need of a rebuild. If the noise is coming from within the gearbox, it isn't because of the fluid and it does indicate a non-negotiable need to open it up and service it.

MT-90 is the wrong fluid to use in a 944-series transmission: use a quality 75W90, you need the viscosity range. (I know that my saying this will ignite a flame war from all the lubrication specialists reading this forum. But with 18 years servicing, rebuilding, and race prep'ing these gearboxes, I stand by this statement.)

No matter what your ears are telling you, I would start by inspecting the clutch. Easy to be deceived as to where a sound is coming from. Good luck!

+1 and again +1^

IMO, there is too much incorrect information on the boards about the "brass syncro rings" in the 944 transaxle.

J_AZ

Yeah, the MT-90 isn't hypoid-safe. Although they supposedly made a statement explicitly saying it was fine for the 944 gearbox... Mobil Delvac is worth a look IMO. No friction modifiers. Why not just install the 951 trans if you have it sitting around? The NA box is a time bomb waiting to go off, even on a well maintained and modestly driven car. Seen enough cases on here and Rennlist to be confident in that statement.

The clutch is a newer Sachs spring centered. I installed it in 2007. Maybe 50,000 miles on it.

I've read through many discussions on gear lube and everyone has their favorite. I can remember reading one thread, where an oil distributor contributed his very technical thoughts. Everyone has their opinions.

Redline MT-90 works well for bunches of people. It's worked well for me; all I've used in my 944's is MT-90 or MTL.

I got the transaxle from a guy who bought a "little old guy" car - that had about 20,000 miles on it. The little old guy had bought the car new and it'd mostly sat in his garage since 1983 until he sold it in about 2004. The new owner drove the car a couple years until he got T-boned by a tow truck. When I bought the transaxle from him in 2007, the car had 79,000 miles on it. So it was in really good shape when I got it.

Most of the 944's I'm aware of have great luck with transaxles - I don't think 200,000 miles or more is uncommon.

The noise I hear in mine is coming from the transaxle. And it probably does need to come out. I'm going to look into what it would cost for a rebuild. But I also know where there's an NA transaxle I can get for $250.

My spare 951 transaxle is a LSD I got out of I car I parted that had 116,000 Miles on it. I'm saving it to put it in my 951 at some later date.

I wouldn't put a 951 transaxle in an NA.

In the meantime, I've got AAA Plus.

The flange side bearing is easily replaceable with a hair dryer and a two armed puller. The bearing can be had for 25-30 bucks but they do normally sell in the 50-70 range. Google the bearing part number to see the spread.

Checking rotational play is your backlash. Yes, there should be some. Setting backlash is critical for quiet operation but the tolerance is pretty wide. I am going to three-d print the backlash tool.

The carrier shaft is preloaded at room temp. There should be zero axial play. In and out along the direction of the shaft is bad. Yes, the axles will move this way but not the flange.

When your preload is less than specification, you will have radial play, up and down at the flange, as the bearing is not sitting tight in its tapper. This is bad.

If you decide to replace the flange side bearing, you could feeler gauge the cover with your old shims to see how bad the bearing is on the other side of the carrier. If it checks, drive the crap out of it for 200,000 miles. It 'could' really be a low cost repair if you can push the flange around.

Just sayin'

Engine oil, antifreeze and transaxle threads are always funny. I like to count the number of threads before the popcorn smiley shows up. Personally, I started using redline products in the early 90's in my diesels and considered their products liquid magic.

The differential carrier bearings cannot be set up with feeler blades under the cover. As taper roller bearings in a transmission, they have to be set with the proper preload, which means going over the free play you might measure with feeler blades. The factory workshop manual says you need 2 - 4 Nm of turning torque (roughly 31 in-lbs) for new bearings, and a small fraction of this for used bearings. Bearing manufacturers give the same guidance, and you can download informational books from SKF, FAG, etc for no cost from their web sites.

I like your idea, Thomas, of 3D printing the factory backlash tool! Of all their transmission tools, it is an expensive PITA to work with. Years ago and before I owned it, I made my own tool, quite simple. It actually works better with open differentials and used bearings than the factory tool. Pictures here:

backlash 001

backlash 002

..so no string through the fill plug with a spring scale wrapped around the pinion?)) Lol

I love homemade tools. I bought a house last year from retired mechanic that was a Pearl Harbor survivor....lots of interesting stuff))

Hahaha. Dumb ass!

When I had the car up on jack stands, I noticed there was some play in the left rear wheel. I'd replaced the wheel bearing in that wheel sometime before, and apparently either the bearing had worn in or I hadn't torqued it enough.

So I hit it with my impact wrench; now there's no play.

I test drove the car today and voila: no clunking noise.

I wouldn't have thought a loose wheel bearing could have made the clunking noise I heard, but apparently it did.

What a dumb ass!

Well at least I didn't have the transaxle rebuilt.

Good to hear it was something simple and cheap!

Always surprising how little things like that can drive you nuts.

Thank you, Mike, for the follow up on what you found was the cause of your clunk sound.

Cheers,
Larry

Mike, congrats! Nice to solve a mystery, isn't it?

For real. Especially when it's a low-cost solution.

I just want to say I've been hearing this for a while and finally checked it out today after finding this thread. My axle nut on the rear drivers side was hand tight.
It was whirring, humming, and clunking on shifts. Really badly. Tightened it up to 260lbs, barely any play, no humming, no clunking. Like a new car.
Bravo.

Gotta love it! Congrats on a good, easy fix!