Engine/Drivetrain Vibration Issues

[apardal]

Hi! My on-going project listed in the projects sections is giving me some head aches...

I have a problem left to solve that is an excessive backlash (with a clunk sound, but not the same as the tomei lsd) from my rear end that I think comes from the half axles, but I'm not sure. The ring and pinion (4.77 were installed by the book and had no excessive backlash, new bearings, etc.

This clunk sound that suggests excessive half axle backlash is heard when I'm changing from lightly tapping the accelerator or not accelerating at all. It will bounce back and forth until I decide whether to brake or push the throttle a little harder.

Along with this, is a massive vibration that appears when I decelerate and the car rolls in gear at 3000 rpm or so. Don't really know whats wrong and if it is related to the backlash.

I have prothane bushing kit and greddy coilovers that don't help at all with these vibrations, but I think this is out of the ordinary.

I also have tried another propeller shaft to check the vibration issue, but it was exactly the same (although I'm not sure if this prop shaft I used was in good condition).

The clutch release fork (installed new 2 years ago) was also uninstalled a installed again with a lot of MP grease to see if the problem came from there.

Let me know your thoughts.

[apardal]

Meanwhile, I'm leaning to another possibility for the decelerating vibration ----> unbalanced crankshaft / flywheel...

The set was balanced altogether. I don't know if they balanced each piece and then everything assembled, but I don't think so. I think they only balanced the whole thing (pulley, crank, flywheel and pressure plate).

The vibration appears when decelerating on gear, between 3000 and 2500 rpm.

Let me know your thoughts

Best regards

[jondee86]

To help with understanding this problem, please advise :

Q1. Does the vibration stop if you press in the clutch (or flick the gear
lever into neutral) while decelerating between 3000 and 2500 rpm ??

Q2. Does the vibration stop if you lift your foot completely off the
throttle (while still in gear and decelerating) and allow fuel cut to occur ??

Q3. Does the "clunking" noise and the vibration exist at the same time ??

Cheers... jondee86

[apardal]

A1. The vibration will stop with a slight touch on the clutch and it doesn't vibrate in neutral! A slight touch on the throttle will also stop the vibration.

A2. The vibration only occurs with the foot OFF the throttle and between 3000-2500.

A3. No.

Thank you for your reply

[apardal]

Clutch is a Paradise Racing 6 puk sprung clutch and OEM pressure plate. Flywheel is a TODA 3,6Kg.

Crank pulley was cutted to lose the A/C or P/S part.

Best regards

[dikolotour]

I thought it would be from unbalanced central axis but you say that it doesn't vibrate when neutral so i'm wrong.

Just have it in mind that an unbalanced central axis gives vinration.

Regards

Dennis

[jondee86]

If the vibration does not happen with the gearbox in neutral, then
it is safe to say that the problem lies further forward. That it only
occurs when decelerating probably rules out an engine imbalance.

The fact that the vibration stops when you touch the clutch pedal
or throttle, and that it only occurs at certain rpm's, indicates that
you may have a resonance problem.

When the car is decelerating, the momentum of the car is placing a
load on the engine and gears. Each time the engine fires, it unloads
the drive train. This causes a cyclic torque reversal on the gears and
the clutch, taking up the clearances first in one direction, and then
in the reverse direction. At certain frequencies this can cause
rattling of the gears and/or the clutch plate sprung centre.

This type of problem is more likely if the engine is fueling while on
the overrun (decelerating). That is why I asked if your ECU supports
fuel cut on closed throttle. Some people have found that solid centre
clutches cause gear rattle, and changing to a sprung centre solved
the problem.

Did the vibration start/get worse when you installed the 6 puk clutch
or the lightweight flywheel ??

Cheers... jondee86

[apardal]

The vibration started after the last assembly.

Items assembled:
- 4.778 new ring and pinion with solid spacer (backlashes correctly set)
- wiseco pistons 81.5
- ARP main studs, conrod and flywheel bolts
- cut crankshaft pulley
- bored block
- balanced crank with pulley, flywheel and pressure plate.
- new crankshaft bearings

Before this last assembly, I ran the engine 100 miles before it broke 2 pistons. None of these symptoms were felt, except maybe the clunking from the rear axle. I'm sure the rattle wasn't there, and the flywheel and clutch were there already.

To help ruling out possibilities, when assemblying the ring and pinion, new bearings were used, although the first spacer/washer that goes in the pinion (before the first bearing) wasn't changed. The rolling torque was set without backlash as the manual states but I didn't use dye to check if I had to use a different spacer/washer, only because I had no SST to remove the bearing (other than a hammer, that would damage the bearing after a few attempts, for sure). But everything else was assembled by the book.

The other misassembly that I'm about to correct refers to crankshaft bearings. I thought I had to order the crank bearings the same way as the rod bearings. I looked at the numbers printed on the block and ordered (11211). Now I know that I should have looked for the numbers printed on the crank (11111). So I have crank bearings ~0.003mm thinner than I should, but I don't think that it would cause this rattle (and I didn't lose oil pressure yet). I already have plastigauge at home to measure the oil clearance.

Best regards

[Jezza_hr]

If it helps any, I seem to be suffering a similar problem since installing my Helix Padde Clutch 212mm with 20V lightened flywheel.

The decceleration problem occurs along with the vibration, however the rear axle noise has always been an issue anyway.

[apardal]

Jezza, thank you for your reply, but I don't think it would be for assemblying the clutch and flywheel, because I had it assembled before and I had no issues.

Best regards