strange rattling noise from rear, on idol

[Beirut944]

Hey everyone
If anyone can give me a clue what this might be, i d be grateful. Its definately coming from the rear and, as far as i can see, only when idling. Kinda like someone dropped some keys in the rear diff. A kind of grinding noise.

Could it just be that the gearbox could d with an oil change?

The car itself is a 1986 non turbo 944, 2.5 litre, manual transmission and i dont normallly drive it very fast. Hope that helps.

MJ in Beirut

[IdahoDoug]

Always good to report what vehicle we're talking about here. Engine? Transmission? Year? Miles? Also, some history. For instance if you just bought it yesterday and hear the noise. Or you've owned it for 20 years and never heard this and it suddenly started yesterday with no cause. Or you raced yesterday for 6 hours on a track and now it's doing the noise.

The less information you provide, the less accurate your response will be.

[Beirut944]

Originally Posted by IdahoDoug

Always good to report what vehicle we're talking about here. Engine? Transmission? Year? Miles? Also, some history. For instance if you just bought it yesterday and hear the noise. Or you've owned it for 20 years and never heard this and it suddenly started yesterday with no cause. Or you raced yesterday for 6 hours on a track and now it's doing the noise.

The less information you provide, the less accurate your response will be.

Good point. I amended it.
cheers

[mweinst]

Originally Posted by Beirut944

Hey everyone
If anyone can give me a clue what this might be, i d be grateful. Its definately coming from the rear and, as far as i can see, only when idling. Kinda like someone dropped some keys in the rear diff. A kind of grinding noise.

Could it just be that the gearbox could d with an oil change?

The car itself is a 1986 non turbo 944, 2.5 litre, manual transmission and i dont normallly drive it very fast. Hope that helps.

MJ in Beirut

It could be one of several things, MJ.

1) It could be one of the bearings in the torque tube. Generally, the one closest to the transaxle is the first to go. If it sounds like ball bearings being shaken in a coffee can, and it goes away while depressing the clutch pedal. that is sometimes the case. You can also tell if you hear a whining from the transaxle area during deceleration. The fix is to rebuild the torque tube.

2) It may be that the bearings in your transaxle are worn. This can be fixed by a specialist fairly easily, if I remember correctly. But, I wouldn’t trust it to a general transmission shop. You should go to a Porsche or Audi independent who knows these transaxles.

3) Finally, you can remove the passenger side CV axle and take off the differential cover. Be sure to drain the fluid first. Look for any metal bits on the surface of the old fluid. Behind the diff cover, look for damaged teeth on the ring and pinion. Sometimes the ring is broken, which is obvious. Look for metal bits at the bottom of the case. If the shavings are gold in color, that just indicates wear on the synchros, which is ok. Any other color is worrisome.

That’s all that I can suggest for you. If you find damage, you’re probably looking at a full rebuild. It’s usually much faster and cheaper to buy a good, used replacement.

Good luck

[RedCarGuy]

When you say "when idling" do you mean the car is stopped? Doesn't make sense that the gearbox would make noise if the car is not moving.

[Beirut944]

Originally Posted by RedCarGuy

When you say "when idling" do you mean the car is stopped? Doesn't make sense that the gearbox would make noise if the car is not moving.

yes, when the engine is ticking over but when the car is not moving.

[kdjones2000]

It's likely just the 5th gear rattling. A known condition on these transaxles. There was something mentioned about this in a PCA article a while back. No harm with it.

[mweinst]

When the car is idling and the clutch pedal is not pressed, the driveshaft still rotates with the engine. Since the driveshaft is bolted to the gearbox input shaft, by the driveshaft coupler, the input shaft bearings are still rotating even when the car is in neutral.

[mweinst]

Hi Keith,

It was my understanding that 5th gear rattle was only heard when the rear wheels were off of the ground. Is this not correct? Please let me know if I’m wrong. I don’t want to spread misinformation.

Mike.