Vibration at 3,500 RPM

[elerner]

My '03 with a Coldside setup has recently been sending a vibration that I feel in the steering wheel and the gas pedal while accelerating at around 3,500 RPM. I don't feel it below 3,500 rpm, and above that it disappears.

My thoughts are to inspect the motor mounts closely. I installed Mazdaspeed mounts when I did the Coldside install about 6,000 miles ago, but maybe one failed. I've got a little over 17,000 miles on the car. I also thought about removing the Supercharger belt and then driving to see if the vibration is caused by the Supercharger.

Any thoughts appreciated. Thanks.

[Tom @ Fast Forward]

I agree. Pull the belt and confirm the blower is the source of the vibration. If it is, I suggest going over all of the nuta and bolts that mount it, like the intake manifold to heand nuts and the under-brace bolts. Check the crank pulley bolts too.

Funny it is only at one RPM though. I would think it would simply start vibrating and then get worse?

Any associated sounds?

[elerner]

No real sounds to speak of and it runs just the same. If the intake manifold nuts were loose wouldn't there be an affect on how it runs? Also, if I pull the belt, do I have to zip tie the bypass valve or will there always be enough vacuum to keep it in bypass mode?

[Tom @ Fast Forward]

I guess it would depend on 'how loose'?

You could probably get away with leaving the bypass alone but better to tie the bypass open. Might make a difference?

[Steve in VC]

SocalPat had something similar, and it turned out to be the lock nuts on the intake manifold brace were loose.

[99mx5]

I had my intake manifold bolts and studs come loose soon after the install of the kit. I found that my IM brace developed play at the ends and caused vibration. I replaced it with a rigid bar and haven't had a problem since.

[elerner]

I think I found the problem, the air filter was sitting a little too much (?) on the steering rack. I also tightened a couple of other bolts a little from above, power steering, belt tensioner, (and also sadly found two of the small IM plate to IM bolts with heads missing) but none of the bolts were very loose. Vibration has gone away. I checked everything under the IM in May when I changed my oil and everything was ok. Maybe I'll check under there again one weekend when I have some free time on my hands (hah!).

[John Miles]

I still see a lot of vibration in the shift handle around 4000 RPM, but have not yet had a chance to follow up on the suggestions received earlier to check the exhaust heat shields for contact with the bell housing. It hasn't been severe enough to make a special trip to the shop to hunt down. (I did, however, check all of the SC mounting hardware.)

[elerner]

Vibration came back. I dug in this past weekend and it turns out my brace under the intake manifold failed at one of the eyelets on the end. It may have been too tight. Tom expressed me one on Saturday (let's see any other vendor do that on a Saturday). Installed it today and all is right again.

Thanks again Tom!!

[Tom @ Fast Forward]

My pleasure. If I didn't live in little Coolidge and your town was a tad larger, you could have had it on Sunday. :) But, alas, we choose tolive in small towns.

[99mx5]

Evan, I recommend replacing that brace with a solid one. My brace developed play at both ends and I replaced mine with a piece of 1/2" square pipe. I've never had a problem since then.

Edit: Also check your IM studs and bolts. Mine were loose because of the vibration.

[elerner]

Ari, where can I get a solid brace made? Do you have the name of a vendor you can forward? I checked my studs and bolts (forgot how much of a pain those suckers are to get to!) Thanks for the reminder.

[99mx5]

Good to hear your IM bolts and studs are still tight. I had to remove the entire IM to tighten the studs.

I used regular 1/2" square tubing from the local hardware store. I mounted the adjustable brace and adjusted its length. Then I removed it and transferred the distance between the holes to the tube and drilled the holes. Make sure the IM brace brackets are lined up so that the bar mounts flush to the brackets.

I snapped a pic of my brace after I painted it. Its the 6th pic down on my cardomain page.

http://www.cardomain.com/ride/810280/5

[Tom @ Fast Forward]

Evan,

Don't know if you noticed but your old broken part was aluminum and the new parts are steel. The problem should not re-occur.

[99mx5]

BTW, I don't mean to imply that this will occur in all kits. My car seemed to have more vibration than usual. ;) That is why some of the little parts are stainless steel and the IAC is remotely mounted. :D Tom's under-brace upgrade another example of the evolution of the kit. :cheers2:

[bogey]

I suggest everyone with earlier versions of the brace check it to see if its still in one piece. I have had to replace both ends that have broken off in the past two years. (One in his garage in Phoenix!) The aluminum mounting tabs (black) are now much beefier (silver). The adjustable brace portion is fine.

As usual, Tom just sent the upgraded piece right out - no questions asked...

[99mx5]

My mounting tabs are stainless steel (A VERY early version of the kit). I also redrilled and tapped the bottom of the IM for larger bracket bolts and replaced the IM top plate bolts with stainless steel bolts after having snapped 4 of them.

[Tom @ Fast Forward]

Just remember, the black 6mm screws are grade/class 12.9 and minimum tensile strength is 174,000 PSI. The stainless 6mm screws are not grade/class rated and have only 101,000 PSI tensile strength. If you went to stainless because they are prettier, OK. If you changed because you thought they were stronger, they are not.They upward pressure exerted by the top plate on the screws under boost relies on the tensile strength of the bolt.

[99mx5]

I changed them because I think they are too brittle. Ive removed cracked and snapped bolts. I consider this an experiment until another bolt snaps.

[Tom @ Fast Forward]

As long as you did it for good engineering reasons. ;)

[bogey]

Is the manifold bracket supposed to be under tension or compression?

Does the manifold really even need it?

[Tom @ Fast Forward]

I adjust the link to extend it until it is under compression. Just hand tight but a 'heavy' hand.

[99mx5]

The factory brace does not place any tension on the IM, as long as its supported with no play.

[Tom @ Fast Forward]

I think he was asking which way to adjust the brace? You can snug it up by adjusting it longer (compression) or adjusting it shorter (Tension). It would be tight in either case but I prefer compression.

[jwalton]

Compression would be best. You're sharing the load of supporting the weight of the supercharger and manifold vs. pulling on the mounting bolts/studs that go into the head. The small increase in load from the belt as it spins up would also be shared with the brace vs. just the bolts/studs.