I've had my M3 on the road for a little over a month now, painstakingly racking up the requisite 500 miles. I recently passed that mark and began doing some low boost street pulls to get the tune dialed. I have maybe 6 pulls ranging from 3rd only to 2nd, 3rd, part of 4rth. No racing or even fast shifting (datalogs show .6 sec shifts). Yesterday on the way home from work I did a 3rd gear pull after getting on the highway and then settled into a nice 80mph cruise in 6th. About 10 miles down the highway the car slows and starts to make a loud grinding noise. I pull off and the car would just make a metallic grinding noise any time movement was attempted. The noise is the same 1st through 6th and reverse. There was nothing leaking or hanging under the car so I had it towed to my shop.

Here is a video of said noise. You can see that if the clutch is very slowly released the car moves slightly. Any load and it makes the noise.

I also drained the trans fluid this morning and no metal came out. Due to the sound and no metal coming out in the trans fluid. The only thing I can think of is the clutch. Its going to be a couple weeks before I can get it out as I have a customers car on the lift. Anyone experience this? The troubling thing is that whatever came apart, let get at 1800rpm in 6th.


General rundown of the car is
95 M3
5.3 LM7, TU2 cam
T56, RXT, stock M/C, set up with .055" slave to finger clearance. This is with the parts out of the box. No shims. Pedal engaged in the middle of the travel.
PTE 7675cea turbo

Clutch felt amazing prior to this. Datalogs under boost showed absolutely no slippage. No chatter or rattles.

 

Hard to tell exactly what the sounds is, but the trans is going to have to get dropped to figure it out, whatever it is.

I too have an RXT twin and love it, but only have about 700 miles on mine as well.

 

Almost sounds like a bolt rattling around in the bellhousing

 

So you're saying there is no drive at all, not even 4th gear ?

The box has to come out, but if the above statement is correct, sounds more like either a clutch issue or broken input shaft.

Unless you can feel it select gears, engage a drive and perhaps the output shaft is broken. But again, without feeling what is happening when you select and release the clutch, impossible to say.

 

Correct. No movement in any forward or reverse gear, just grind. With the clutch pedal depressed, itll easily go into any gear and no metal came out of the tranny when drained.

I obviously know it needs to come out. That's not rocket surgery. Im more asking if anyone had ever experienced a similar failure. I would have expected at least some metal particulate to come out in the event of an input shaft failure. Particularly since it was at highway speed. I hope to have the transmission out this week as my lift is freed up tomorrow.

 

If the input shaft sheared, that would effectively be internal to the bellhousing, so the trans would be clean.

If part of the clutch failed, likewise. So really there would be little expectation for there to be anything in the oil.

The only other aspect, but again you should be able to hear/feel...is if the output shaft or yoke or even part of the driveshaft etc, or rear end broke. Again a clean break would leave the trans clean, but with no drive at all.

 

Good point on a possible input shaft failure within the bellhousing. Most that I had seen researching the issue failed at the bearing or where it mated within the tranny. We'll see when it comes out. With a 30 spline output shaft and the limited abuse, I doubt it's that, but never say never.

 

Could be a clutch issue with the friction disc. I broke the center hub out of one and it acted the same.

To clarify, it wasn't an RXT, it was a single disc with a sprung hub that didn't like the torque that my procharger made.

 

Spending 10 minutes with the rear in the air and some sensible diagnostic work will tell you a lot.

 

KUpdate: Finally found some time to get this thing in the air. Turns out one of the diff output flanges came lose. The grind was the LSD plates slipping and transmitting up through the driveshaft so it sounded like the trans. I pulled the tranny anyway to look at the clutch and everything was good.

The bad news is I just finished street tuning the car at 18psi. Now it's doing the classic high hp whine of a fluid starved gear set. A dozen 3rd and 4rth gear pulls with a 7675 will do that I guess. Hopefully it'll let me beat it a few more times before the snow flies and then tear it down over the winter and add a fluid pump to spray the main gear set, along with a new set of gears haha.


The RXT is going strong.

 

Were you running the trans with no oil or something ?

That sort of boost/turbo shouldnt trouble a T56 at all.

Does it make noise in 4th ?

 

No noise in 4rth. Fluid is full. I fill through the shifter and wait till it pours out the fill plug, then seal it up.


This sounds real familiar
https://ls1tech.com/forums/manual-tr...cs-inside.html

 

It sounds to me like rear end gear whine, but it's hard to tell from a video. Isn't the rear diff mounted to the frame in an IRS setup, so the sound would transmit through the car making it difficult to pinpoint.... that's my thought.

 

Rear gear would make the noise in fourth.

 

I missed that it didn't make the noise in fourth. My bad.