Funny noise at 1350-1500 RPM

[Vintage]

Hi all.
I am getting a funny noise from the engine area while under load at 1350 to 1500 RPM.
It sounds like a whirring noise or like a zzzzzzzzzzzzzzzzzzzzzzzzzz noise. Kinda like an old GM power steering pump going out. (No offense)
It only happens under load. In any gear. only at the 1350 to 1500 RPM range. Will not do it while in draw mode, only under load and full throttle.
We are leaving soon on a tour of what will be 2500 miles and I want to get this diagnosed before we hit the road.
Anyone have any ideas please chime in.

It is a '97 3126 with allison 3060.

[rver98]

You may want to crawl under your rig and check your drivetrain and see if anything is loose. When was the last time you had your u joints lubed? Since it is only at a certain rpm I would think something may either be unbalanced or loose. Hope this helps a little.

[Vintage]

U-joints were lubed at my regular oil change about 5K miles ago.
Doesn't have the vibration that an out of balance thing would cause.

I was thinking turbo but why only at that one RPM range and only under WOT.

[Billieg]

If you find out let me know. I have a horn type sound when I hit 55 mph. It will stay there as long as I do 55. 54 - 56 it isn't there.... At first I thought someone was blowing their horn at me.

[Sammie]

Quote:

Originally Posted by Billieg If you find out let me know. I have a horn type sound when I hit 55 mph. It will stay there as long as I do 55. 54 - 56 it isn't there.... At first I thought someone was blowing their horn at me.

I had a similar problem with my 1990 Pace Arrow. Turns out the guy that bought it from me found out that it was the front grill vibrating at a certain speed. He put some duct tape down across all the grill pieces and then would drive for a while and then pull off a piece of tape until he found out which grill was vibrating. I can't remember how he finally fixed it. I think maybe he just braced that particular grill to get it to stop vibrating.

Good Luck, Sammie

[Mr_D]

Quote:

Originally Posted by Vintage U-joints were lubed at my regular oil change about 5K miles ago. Doesn't have the vibration that an out of balance thing would cause. I was thinking turbo but why only at that one RPM range and only under WOT.

The slip joint needs to be lubed every 5,000 miles. This is a relatively new thing that Spartan has added. Guess they found out once a year or 15,000 miles wasn't often enough.

[Billieg]

Quote:

Originally Posted by Sammie I had a similar problem with my 1990 Pace Arrow. Turns out the guy that bought it from me found out that it was the front grill vibrating at a certain speed. He put some duct tape down across all the grill pieces and then would drive for a while and then pull off a piece of tape until he found out which grill was vibrating. I can't remember how he finally fixed it. I think maybe he just braced that particular grill to get it to stop vibrating. Good Luck, Sammie

Thanks, I'll check that out.

[MaverickBBD]

Can you determine if it is "engine" or chassis noise? Does your fan pulley have a zerk fitting? Know several C-7's that don't (sealed and supposedly perm. lubed) that have seized.

[Skip426]

Vintage, I didn't see a post re a fix for your noise, so I thought I'd share this .I just got through, tracking a raspy whistle, noise on a 5.9 Cummins,for a friend. Noise was load & RPM sensitive also. What we found was the multi layer,metal exhaust flange gasket at the cylinder head, had blown out one of the layers, and the other layers were buzzing as the back pressure from the turbo built up and was reduced as the waste gate opened and reduced the back pressure. Tell-tale trace of carbon from the #6 cyl. flange was the only indicator.

[Vintage]

OK sorry I did not reply before. The sound I was hearing turned out to be the metal cover on the breaker box under the bed side pedistal/drawer. Wierd that it ony happened at one rpm range and under load.

[Skip426]

Not at all weird, harmonics from the engine, torqued up against the mounts, setting something else off; happens all the time and drives mechanics crazy. Good that you tracked it down.
Safe travels.

[SCVJeff]

My demon is the bathroon sink drain stopper. Drives me nuts