Strong Vibration at 3000 RPM

tranmkp · Post by **tranmkp** » 26 Mar 2013, 15:04

94, 940 wagon - 150,000 miles. Runs great. However there has been this annoying vibration at 3000 rpm - esp annoying at freeway cruise which is 3000 rpm. You can feel it everywhere in the car, very much so on the gas pedal.

I have new motor mounts, new trans mount. Harmonic bal is fine. I have a hunch, no, I am almost sure it is the belts. At 3000 I noticed a lot of deflection on the alternator belt. I installed new belts and the rubber mounts for the alt bracket. I really got them tight. Now, the car is as smooth as melted butter at idle all the way up to 2800 rpm and at 3000 the vibration comes back. It feels the same. When observing the belts there is very little deflection at all.

I am beginning to wonder if it coming from the ac. The car was converted to r134 with the volvo kit from the dealer years ago, I think the kit may be amplifying the problem - The return hose seems to be a bit shorter than I remember, it is rubbing against the firewall and the throttle cable. I put some pool noodle around it and it did have an effect.

So, the question is to all 700/900 owners who have switched over to r134. Have you noticed any excessive vibrations? Could you post some pictures? (I will shortly)

Cheers

Post by **98T5** » 27 Mar 2013, 07:30

I have a 93'940 that rumbles at idle. I found out it was my motor mounts. I will be changing those soon. if yours rumbles at high speed, I would suggest checking/cleaning your IAC valve, TPS sensor and intake with some carb cleaner. best case scenario. worse case scenario would be the injectors clogged and not adjusting to the need for fuel starving the carb. and hit your CAT with a rubber hammer, if it rattles, it's toast and that could be why you lose power also. also Check your O2 sensor, those are known to rob the car of power and will create a similar "rumble" to the engine at high rev.

Also, check your wheel hubs on both side, are they tight or loose? if loose, that could be your problem. jack up LF wheel and grab it at 10/2 and see if wobbles, if so, your wheel hub assembly is bad on that side. do the same with the other side. they may be trying to go out. I have a slight wobble in my RF wheel so I will chagning that one when I do my motor mounts.

Also check to see if your muffler hangers are tight. I found a few of mine loose when I bought it and tighten them up making the rattle less rattally to help me track down my rumble problem

G'luck.

tranmkp · Post by **tranmkp** » 27 Mar 2013, 07:59

Thanks for all the info. Its a vibration (Buzz) more that a rumble. Motor mounts are new, injectors were pulled and blueprint4d a year ago. I do not know about the IAC valve or TPS, I will check. Wheels are tight, I just out on new calipers, I checked. Front stabilizer bar mounts are dry.

I adjusted the compressor hose a little. Gave it more of a loop. Wrapped more pool noodle around it. I did make a difference, therefore it has to be the way the r134 kit was designed. (badly) I think I will go to a hose shop and have a longer setup made. Hell, I should go back to R12...

Post by **precopster** » 27 Mar 2013, 11:43

If the A/C is not running and the compressor is off the vibration is likely not anything to do with the a/c system or type of refrigerant.

If the vibration only occurs during a/c operation when the compressor cuts in (you'll hear this as the solenoid clicks at intervals of between 10 and 40 secs) then the compressor itself may be failing.

tranmkp · Post by **tranmkp** » 27 Mar 2013, 13:15

The vibration is there AC system on or off. Its only related to the AC system as I think the conversion used an ass clown sort of a hose design/location. The source of the vibration is in the belts - no matter how tight they are there is deflection at 3000 rpm. That frequeny is then transmitted through the compressor and to the discharge hose and amplified like a guitar string. Padding the string reduces the frequency.

I know of know serpentine belt conversion for the B230. I could fab a idler pully to the alternator belt. Of course, these are big 4 cylinders, they are never going to be that smooth. The dealer kit has that hose attached with a P clamp to the firewall where it touches the brake booster and throttle cable. Just a nasty job.

BTW, when the belts are disconnected - there is no vibration at all. Nada. I might investigate getting shorter belts.

Post by **98T5** » 27 Mar 2013, 15:30

tranmkp wrote:The vibration is there AC system on or off. Its only related to the AC system as I think the conversion used an ass clown sort of a hose design/location. The source of the vibration is in the belts - no matter how tight they are there is deflection at 3000 rpm. That frequeny is then transmitted through the compressor and to the discharge hose and amplified like a guitar string. Padding the string reduces the frequency.

I know of know serpentine belt conversion for the B230. I could fab a idler pully to the alternator belt. Of course, these are big 4 cylinders, they are never going to be that smooth. The dealer kit has that hose attached with a P clamp to the firewall where it touches the brake booster and throttle cable. Just a nasty job.

BTW, when the belts are disconnected - there is no vibration at all. Nada. I might investigate getting shorter belts.

hahaha

don't give up hope man!!...these cars are old but much better than owning an American car of the same year...if it worked perfectly you'd try to sell it off out of boredom, so be happy you got some tinkering to do...

...I like wrenching on these Volvos and you do to or you wouldn't be here.

tranmkp · Post by **tranmkp** » 27 Mar 2013, 16:02

F)kikin A!!!

Although, an LS-1 in the wagon would be very smooooooth...

warcraftjunkie · Post by **warcraftjunkie** » 27 Mar 2013, 17:40

tranmkp wrote:94, 940 wagon - 150,000 miles. Runs great. However there has been this annoying vibration at 3000 rpm - esp annoying at freeway cruise which is 3000 rpm. You can feel it everywhere in the car, very much so on the gas pedal.

Cheers

One thing I haven't noticed in your thread is if it's at 3000 RPM in neutral or only when driving, or both? If it's only when driving may I suggest you look at the drive shaft that delivers the power to your rear wheels. I had a truck that used to make a horrible noise that could be felt/heard at higher speeds. Turns out I had a failing Ujoint on my drive shaft causing a vibration at a specific RPM range.

tranmkp · Post by **tranmkp** » 27 Jan 2014, 14:22

only at 3000 rpm - smooth otherwise - I can actually watch the belt - as it approaches 3000 I can then begin to see the belt oscillate.

lummert · Post by **lummert** » 27 Jan 2014, 17:09

Are you sure the crankshaft pulley isn't slipping?