Bad vibrations

Stevehose

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Will post pics. The issue was caused by trying to get the guibo perfectly flush with the driveshaft flange. This required shimming the tranny at the mount. So I've removed some shims (left 2) and will compensate at the csb. If the guibo and driveshaft flange are not flush with no wobble then it's bye bye guibo in short order. I am also going to try and keep the engine/tranny in the place where it wants to settle and not move it left or right as this will probably want to cause problems later. I'll adjust that at the csb also by slotting the other side of the bracket. If that causes issues I will resort to adjusting sideways at the tranny.


Here's Rob's post (there are several others on the FAQ as well):

http://www.bmw2002faq.com/blog/67/e...alignment-from-hell-or-it-just-doesnt-matter/





Hi Steve, it would be great if you could post some pictures before and after the operation; what do you think the issue was that caused the misalignment in the first place? Just curious,when I did my first conversion there was allot of pushing and pulling to get things to fit but have not had any issues with vibration. Do you think the drive shaft was lengthened correctly? Maybe I should read Rob's post too :)

Thanks and it does look like you found your "gremlin".
 

Peter Coomaraswamy

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I like the idea of letting the engine settle in where it "should" I am wondering if the steel trans mount is correct because that could cause the high/low positioning. When you post the pics I can see if I'm using a different mount and if so I can send you one as somehow I ended up with an extra??
 

Stevehose

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The tranny vibration is solved by removing shims and lowering the CSB accordingly.

However it has revealed a slight vibration between 2600-2900 rpm, felt only through the gas pedal.

I have run the car without the ac and ps belts - no change.

The alternator is rebuilt and aligned straight with new belt. No movement of the belt or unit at that rpm.

It's not the tranny because I can feel it if revved in neutral while stopped with clutch in or out.

Motor mounts are a few years old and look fine but....

Flywheel and front damper don't appear to wobble at that rpm.

It's not bad, but just enough that it bugs me.

Felt in the pedal, not through the shift lever.

Any other thoughts?
 

Luis A.

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If the damper is original and its rubber old and hardened, could vibrations like that be evident because they aren't properly dampened by the damper? That is a bit of a mystery part for me. Never hear anything about it... Anyone ever replaced it and the engine gets 'smoother'...?
 

Stevehose

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Me too, no clue about what effect it has, it appeared ok but wonder what the symptoms are of a failing damper? It doesnt appear to wobble at all when I look at it at the problem rpm

If the damper is original and its rubber old and hardened, could vibrations like that be evident because they aren't properly dampened by the damper? That is a bit of a mystery part for me. Never hear anything about it... Anyone ever replaced it and the engine gets 'smoother'...?
 

61porsche

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I suggest

a careful examination of the accelerator bar, position, and bushings/ spacers. There are reference measurements in the repair manual.
 

Stevehose

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Hah, yours seems to be coming along very nicely, can't wait to see your Scheel seated stealth coupe.

Hopefully I won't ever have to part with my car and my skeleton will be clutching my Petri wheel like the one in Young Frankenstein that won't let go of the box to Igor.

Sell your beautiful coupe to me, and buy a better one?

just kidding Steve
 

Stevehose

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It's a narrow rpm range and happens on accel and decel. Will check the specs. Thanks

a careful examination of the accelerator bar, position, and bushings/ spacers. There are reference measurements in the repair manual.
 

Stevehose

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Solved (I think)

I was surprised to find the slop I did in the block lever since I have previously rebuilt it so I removed, cleaned and greased the bushings and added 2 plastic shift linkage washers i had left over to remove all play. Nice and smooth. Vibration less but still there so I guess that was magnifying it a bit.

Turns out it was the ac compressor, I must have misaligned it last time I took the bracket off, I added a couple washers on the 4 compressor mounting points to bring it back in line with the balancer as my bracket is maxed out adjustment-wise.

2600-2900 rpm vibration gone, now I'll see what next will be exposed! Still need to drive to confirm but it passed the garage test.

Thanks for all suggestions.


a careful examination of the accelerator bar, position, and bushings/ spacers. There are reference measurements in the repair manual.
 

Ed G

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I have run the car without the ac and ps belts - no change.

Very interesting. So the implication would be that the mass of the compressor (not the rotation) is causing a resonance issue due to support bracket dynamics? Certainly can't be good for the compressor internals.

Cool science project...in addition to stiffening the bracket, see if you can change the resonant frequency by-

-adding weight to compressor
-turning ac on (creating a gyroscopic effect)

Have fun and good luck.
 

Ohmess

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Steve -- on the driveshaft/guibo/diff alignment, how did you measure this?
 

Stevehose

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I have a washer in between the DS flange and the giubo in order to get a little more room for the nose of the DS as suggested by SFDon.

So I loosened the 3 DS to giubo bolts the same amount, just enough for the washer to spin freely. I turned the DS and watched the movement of the flange as well as spun each washer at 90 degree intervals. The 2 issues were that the washer would spin at the 6 o'clock position but not at 12. It would also spin at 9 o'clock but not at 3. So I had both a vertical and horizontal misalignment. I lowered the tranny to eliminate the vibration caused by it touching the tunnel (and checked fan/radiator clearance was approx the same top and bottom) then compensated by lowering the center bearing by installing longer bolts and adding 2 thick washers. I then turned the DS to confirm the washer spins freely at both vertical positions.

For the horizontal adjustment I had to grind out the mounting hole on the CSB frame so that it could move like the other side which is slotted. Then I moved it sidways a little until the washers spun freely in the horizontal positions and tightened it up.

Tightened the DS/guibo up and observed no rubber movement or stress. I also like the idea of letting the engine/tranny rest where it wants to and not trying to torque it side to side to line up the giubo.

So far no DS noise or vibrations at speed or taking off from a stop. You could install washers temporarily to use as indicators then remove them before bolting up for good. It makes checking the 12 o'clock position easy, otherwise difficult to measure up there as it's hard to access.

It seems eliminating one vibration exposes another from somewhere else, hopefully I will hunt them all down. I'm close.


Steve -- on the driveshaft/guibo/diff alignment, how did you measure this?
 
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