When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I have a pretty terrible (for me) whining noise when i’m at ~60mph.
I plan to jack up the car and simulate it, BUT even if i do disable the air suspension it will
automatically reenable itself at smth like 20mph.
Basically the question is: how do i avoid this happening?
Hmm yeah it re-enables because it thinks you just drove away with it off.
Assuming you will be up on a two post or some similar very stable platform, and with a helper to drive while you poke around underneath?…
be sure to disable PSM too! Else you might get chassis warnings and possibly PSM trying odd things to “gain traction…”
have you changed your diff oil? Pretty easy DIY and metal flakes in the oil are nearly definitive for some kind of bearing failure inside.
FWIW other common whining/whirring noises are from PDCC if you have it (but more audible at lower RPM and speed, generally), or something in PCV (but that should be more like a whistle and based on RPM not vehicle speed).
for the air, I think the biggest reason to disable it is so it does not accidentally destabilize the car trying to level it as you jack it up.
there may also be other reasons, but if I had to guess, lots of people do not disable it, and nothing traumatic happens as a result.
if you were really concerned, you could pull the fuse and dump the air pressure after you lift it disabled with the button, but before you bring it up to speed (being sure to te-enable before setting it on its feet again).
Pressing the PSM button won't help. After a certain speed, it'll reengage and act like a cat thrown off a 10 story building by trying to get traction anywhere it can.
There are posts explaining what fuse(s) to pull to disable the system.
Front differential is the main culprit on these vehicles. Draining the diff oil will either pinpoint the problem or at least rule it out. If you're not sure, stick a magnet in the oil and then rub it against a dark cloth to clearly see all the metal shavings. And of course, make sure you can remove the fill plug before removing the drain plug!
I did an autopsy on mine last night just to see what went wrong. When rotating by hand, the passenger side outer bearing was very noisy compared to the left side. I pulled both bearings but still need to break them apart to look deeper. Rollers don't look bad, I expected much worse considering the amount of shavings and noise at 55 mph.
All the silver is metal. I'm not sure if I'm going to replace those two bearing and keep the diff as a backup or just toss it in the trash.
Going through this at the moment too, and have decided to work with dirtpig in Colorado Springs based on a referral from Harry Schoen. Ian knows his stuff and has done these diffs a bunch of times.
- salvage: < $1K (eBay or other. Mo’ problems?)
- rebuilt from dirtpig: $1700
- add front locker with rebuild + $2500 I think
- rear factory locker $2400.
I am going with adding a factory rear LSD/locker with a custom integration module to allow engagement at any time without the factory requirement for low and center locked first. Hoon mode!
And oh yeah, rebuild the front. Undecided on adding the front locker too…
Pressing the PSM button won't help. After a certain speed, it'll reengage and act like a cat thrown off a 10 story building by trying to get traction anywhere it can.
There are posts explaining what fuse(s) to pull to disable the system.
I didn’t know that PSM would re-engage above ~20 MPH on the lift. It stays off when turned off driving spiritedly on the ground… it will be interesting to know for when I need to do this again some day, fingers-crossed hopefully never.
Unfortunately I'm not in the US, and will have to diagnose this with a local indy. Hence the inquiry how I disable all this electronics so the car won't start playing tricks on me while jacked up.
I didn’t know that PSM would re-engage above ~20 MPH on the lift. It stays off when turned off driving spiritedly on the ground… it will be interesting to know for when I need to do this again some day, fingers-crossed hopefully never.
I know the air turns back on…
good luck with the diff!
I shouldn't have said speed. Best I've heard it explained is that turning PSM OFF just increases the tolerance level. If you get into a really bad situation, it takes over again. It's not actually speed dependent.
With all 4 wheels in the air, it's seeing a worst case scenario. Iirc, I didn't get more than 10 mph before the drivetrain started bucking and chattering whether it was on or off.
I shouldn't have said speed. Best I've heard it explained is that turning PSM OFF just increases the tolerance level. If you get into a really bad situation, it takes over again. It's not actually speed dependent.
With all 4 wheels in the air, it's seeing a worst case scenario. Iirc, I didn't get more than 10 mph before the drivetrain started bucking and chattering whether it was on or off.
Yes, I've had this happen several times. It loosens up how much fun you're allowed to have, but it's still the fun police. If you're smooth and deliberate you can make it do some stuff. Gotta stay composed and if you don't it says NEIN.
If you hit the brakes at a higher-than-it-likes slip angle it seems to come back on full force.
I can only imagine it will be in full on freak out mode pretty much immediately above idle in drive with no wheels on the ground. This all seems like the wrong way to go about diagnosing this issue. Checking for sparkly oil and bearing runout would be my initial tries. Who knows if - let's say it is a bearing - will even make any noise when it's not under the load of the weight of the vehicle.
Yes, I've had this happen several times. It loosens up how much fun you're allowed to have, but it's still the fun police. If you're smooth and deliberate you can make it do some stuff. Gotta stay composed and if you don't it says NEIN.
If you hit the brakes at a higher-than-it-likes slip angle it seems to come back on full force.
I can only imagine it will be in full on freak out mode pretty much immediately above idle in drive with no wheels on the ground. This all seems like the wrong way to go about diagnosing this issue. Checking for sparkly oil and bearing runout would be my initial tries. Who knows if - let's say it is a bearing - will even make any noise when it's not under the load of the weight of the vehicle.
how exactly to check for bearing runout? you mean wheel bearing?
if so, it should change its tone if i wiggle left/right. but it isn't.
how exactly to check for bearing runout? you mean wheel bearing?
if so, it should change its tone if i wiggle left/right. but it isn't.
I mean any of the bearings. I don't know what's wrong - I can't see it or hear it. But I'd be under the with a long bar pushing/pulling/prying everywhere something is supposed to move in one direction and seeing if it moves in a different plane than it should be. This isn't possible without disassembly for a lot of things that could be your issue, but for the basics like wheel bearings it should be pretty straightforward (grab a wheel at 12:00 and 6:00 and push/pull on the top/bottom and see if it moves/clunks, for example).
Again, I don't see how running it in the air is a good diagnostic method. It's unlikely to cause any damage, but it's also unlikely to provide any answers. So rather than agonizing about how to disable PSM/PASM put the thing in the air and use your hands, ears and eyes.
05-21-2023, 10:56 AM
2004 CTT- jack up to find the whining noise
