Vibration In Drivetrain

[chilkoot]

I've got a vibration in my drivetrain during specific RPMs. It's kind of a rumbling, and I suspect that the crankshaft pulley bolt is not torqued on tightly enough. It rumbles 1300-1500RPMS and smooths out until about 1750RPMS when it starts to rumble again. I haven't tried to take it higher than 2k rpms. I can see a little bit of vibration on the crankshaft pulley with the hood up, but it's barely noticable. I can't drive it anywhere because of plate and title transfer issues, this is in neutral in the parking lot of my apartment. I can feel it through the steering wheel. Idles just fine, comes to temp, no air bubbles in the cooling system, it's completely filled as per normal procedure.

I just did a water pump change myself, and the car seems to work beautifully otherwise. If I take it to a mechanic or a dealer can I have them put it on a lift and take an air wrench to the crank pulley bolt without removing the drive belts or fan clutch? Am I right in assuming I could get away with less than half an hour of labor, or is there a high risk of getting screwed by an ambitious mechanic eyeing a lexus that's mad they're only getting $30-$40 for a quick job?

If anything happens while it's in the shop it's his word against mine as to what condition it was in when I drove it there and who screwed it up, so am I better off just buying an air wrench myself and going underneath the car with jackstands?

could there be anything else from a TB/water pump service that could cause drivetrain vibration? It certainly wasn't there before. I estimate current torque on the crank pulley bolt to be around 150ish (was using a breaker bar and a chain wrench, my torque wrench was too short to get enough leverage)

[larryp]

While i don't have a specific recommendation on the rumble, i doubt its the crankshaft pulley bolt. As you know the pulley only goes on one way and it's a pretty tight fit anyway. Doubt that a few more pounds of torque will make any difference. Rev it up to 2500-3000 and see what happens.

some guesses on possible causes: worn main crankshaft bearings (i think you said car was not "lovingly maintained"). Could you be one tooth off on the cam timing? i would think this would cause it run run rougher than you describe but its a thought.

[mehullica]

did the vibrations start after the water pump job?

[chilkoot]

yes, when I first started the car and did the coolant refilling procedure after the water pump job (in the Advance parking) lot everything was fine, but I wasn't the one in the driver's seat. I was under the hood topping off coolant.

There's nothing visibly wrong under the hood even with the engine running, it's only noticable in the cabin through the steering wheel and maybe seat, but I certainly didn't notice it before I started. It revved to 3k fine, and I checked the timing multiple times as I was putting it back together. It roars when it revs up, but in a good way.

Motor mounts maybe? I was thinking it had to be the crank pulley because that's the only thing I touched during the water pump removal that could have affected the rotating assembly so severely. However, before I got my chain wrench I did try to use the starter trick to break the torque on the crank pulley bolt, and destroyed a 1/2" drive to 3/8" reducer at the weld...twice...that could've put some pretty serious jolts on the engine, is the starter strong enough to toast the mounts? When I did it I definitely felt the jolt in the driver's seat.

When I get new plates and can actually drive it around that might help some too.

it hasn't been lovingly maintained, but it was grandmad when it was driven. more neglect than abuse.

[HomerTHX1138]

yes, when I first started the car and did the coolant refilling procedure after the water pump job (in the Advance parking) lot everything was fine, but I wasn't the one in the driver's seat. I was under the hood topping off coolant.

There's nothing visibly wrong under the hood even with the engine running, it's only noticable in the cabin through the steering wheel and maybe seat, but I certainly didn't notice it before I started. It revved to 3k fine, and I checked the timing multiple times as I was putting it back together. It roars when it revs up, but in a good way.

Motor mounts maybe? I was thinking it had to be the crank pulley because that's the only thing I touched during the water pump removal that could have affected the rotating assembly so severely. However, before I got my chain wrench I did try to use the starter trick to break the torque on the crank pulley bolt, and destroyed a 1/2" drive to 3/8" reducer at the weld...twice...that could've put some pretty serious jolts on the engine, is the starter strong enough to toast the mounts? When I did it I definitely felt the jolt in the driver's seat.

When I get new plates and can actually drive it around that might help some too.

it hasn't been lovingly maintained, but it was grandmad when it was driven. more neglect than abuse.

Motor mounts fix:

I recently had my 93 LS400 in the Toyota dealership to address many old issues. My car too literally had been grandma'ed (my grandma owned it), but neglected some.

Among the issues was an RPM-specific rumble that could be heard slightly and felt. It was kind of a HUMM. Mine occured at 1100-1200 RPMs. Now that it is fixed, I know too it caused a bit of a "thwock!" on engine start. It was indeed the motor mounts. The dealership caught them wheras a now defunct-tranny place did not. It made the engine much smoother at idle too, to the point I've thought it was off and started it twice.

Even though mine occured at slightly less RPMs, the same age of the cars and very similar symptoms makes me think that your mounts are bad. I seem to recall two were replaced. I can get the invoice if you want additional info.

[chilkoot]

that sounds like it's my problem. the rumble feels the same in the steering wheel and seat as my '90 did at 75mph on the freeway when my tires weren't balanced, but it's in neutral in my parking lot. anything else that could cause such a low and steady rpm-specific rumble?

is it likely that bracing a breaker bar on the crank pulley bolt against the ground shot my motor mounts when I tried to crank it (twice)?

and yes, knowing which mounts you had replaced and how much it cost you would be great. IIRC, one can be done by hand under the car and the other two need to have the engine pulled, or at least lifted.

[HomerTHX1138]

that sounds like it's my problem. the rumble feels the same in the steering wheel and seat as my '90 did at 75mph on the freeway when my tires weren't balanced, but it's in neutral in my parking lot. anything else that could cause such a low and steady rpm-specific rumble?

is it likely that bracing a breaker bar on the crank pulley bolt against the ground shot my motor mounts when I tried to crank it (twice)?

and yes, knowing which mounts you had replaced and how much it cost you would be great. IIRC, one can be done by hand under the car and the other two need to have the engine pulled, or at least lifted.

I will say that my rumble was very much RPM specific. Now that the mounts are replaced it's much, much better. You still hear the motor at that RPM --it's like it's the engine's rough spot or something-- but clearly the vibration and noise are 95% better.

It should be noted that I did not experience the problem at any other RPM wheras you say yours smooths out and gets rough again.

Regarding the question on the breaker bar - no idea. I'm not a mechanic or even a DIY type other than very basic stuff.

I'll pull the invoice this weekend and let you know what I paid for what.

[HomerTHX1138]

OK, sorry so late to reply.

Motor mounts part of bill:

11TOZ R&R MOTOR MOUNTS

2 1236150100HL MOUNTS 128.51 -2- 257.02

LABOR 271.55

TOTAL: 528.57

[VBdenny]

Look under the hood at night with the engine running and look to see if there is a park arc on any of the plug wires. One misfiring cyliner will be apparent at low RPM's, but not at higher. Probably not the cause but worth checking as I have seen it happen.