Car idles rough and makes rattling sound in neutral

Question

I recently replaced the clutch in my 2000 E39 M5 with a stage 4 rigid hub 6 puck MIBA disc, high load self adjusting pressure plate (re-used allen bolts, torqued to "feels just slightly tighter than originally did, but can't go tighter for fear of stripping" as my torque wrench would not have faired well using the 4.5mm screwdriver bit placed into a 1/4" 1/4"-drive socket attached to a 1/4" to 3/8" adapter with a 6" extension (used this way with 3/8" ratchet and circle end of box wrench for torque) and then coupled to a 3/8" to 1/2" adapter for the torque wrench all while trying to hold flywheel in place), lightweight flywheel (new bolts, torqued to 110N-m (spec is 105N-m) without additional loctite), and new pilot bearing. Previous release bearing did not have many miles on it, so it was re-greased and put back into place.

I had a slight problem with the slave cylinder, which was not aligned properly on the release arm and caused it to blow apart the first time. I managed to re-assemble it and clip the seal cover back into place and installed it and via watching the output shaft I verified the clutch operated correctly, however it begins to disengage about one inch from its resting position at the top of the pedal, I was wondering if possibly the slave pushrod had bent or scraped the bore preventing it from retracting fully, or if this was a possible result of a non-oem clutch.

I proceeded to re-install the rest of the components, when installing the driveshaft for lack of sufficient time and patience the guibo bolts were not torqued very tight, just enough until they no longer slid back and forth in their holes, the rest of the job was done right.

1.5-2 weeks afterwards I started hearing a rattling from the transmission-area under the car (really anywhere between the back of the engine and the rear wheels, haven't gotten a chance to get under it yet) when it is in neutral at a standstill, but pressing in the clutch pedal or lightly pushing the gear selector against one of the synchros causes this noise to stop. I was thinking that this could be caused by one of those guibo bolts loosening and rattling around, pressing in the clutch would reduce vibrations through the transmission, and engaging a synchronizer would put a slight amount of torque on the driveshaft that could bind the bolt in place to stop it. I plan to re-torque these very soon.

About 3 weeks later, I replaced the completely shot radiator, all went normal. Shortly afterwards I noticed that along with the vibrating, if I come to a stop and release the clutch in neutral, the engine begins to jump up and down rapidly in speed oscillating between 300 and 800rpm. Pressing in the clutch causes this to stabilize, and I can normally release it at that point and it stays stable. Today, however when I released it again it started doing it after about 6 seconds.

I'm really at a loss for the rough idle issue, and if it can relate to the rattle noise. Anybody have something similar happen or know of possible causes/solutions?

Answer 1

I'm thinking you probably lost one of the bolts connecting the pressure plate to the flywheel. Something people don't realize is that the torque on these bolts is very important. Too tight and the pressure plate won't release the friction disk correctly. Too loose and you lose one (or two or ...) of the bolts out of the pressure plate. If you were to lose one of these bolts, it would cause an imbalance in the clutch assembly which would cause your engine to vibrate.

(As a for instance: The torque for the clutch on my Z28 Camaro with T56 transmission was ~22lb-ft, IIRC ... that really isn't much torque considering. If you got them too tight, the clutch wouldn't disconnect correctly and you'd not be going anywhere.)

I don't know if your M5 has an inspection access where you can see the pressure plate bolts. If you do, you should rotate your engine and inspect them to see if: 1) they are still in place; 2) they are torqued correctly (even if you have to use a jury rigged socket extension to do it). You may want to pull them out one at a time and get some Locktite on them as well, though they should really be torqued in a criss-cross pattern.

Answer 2

Issues found:

1. Slave cylinder retainer was slightly bent, allowing the clutch pin to rattle on the fork, some noise was gear rattle, as well as a guibo bolt that was not tightened properly
2. Idle issue turned out to be a 3cm hole in the intake elbow.

Still looking into other possible issues, but thats what it looks like.