Hey guys and gals. I have a 2001 with allison. Lately I started noticing that when I am in a tow/haul mode i get these weird noises between 2-3 shift. It sounds like a horn from a large cruise ship as if you heard it from far far away and it gives some vibration into the gas pedal. Kinda like a low tone drone type of noise. Has anyone had this or know what this could be? NSBU switch?
Thanks.

I just came back from a long ride. I had my windows rolled up and ac fan on 1 so I can hear any noises. When I was in tow/haul and ally shifting 2-3 I heard some sort of low tone drone as I mentioned above preceeded by some kind of scraping/ noise. It almost felt like it was trying to shift into third, then the noise comes on and ally hesitates to shift and then it shifts. Also at one point I was cruising at about 50 mph without tow/haul and I felt slight vibration and a lighter variation of the same noise coming from the tranny area and I felt it in a gas pedal. :help:

What you're hearing is the torque converter locking up. When the F solenoid activates it will sometimes rattle the valve and make a droning noise. Some trucks are louder then others and is nothing to worry about. However, the scraping noise may be of concern. You might want to check and make sure the torque converter bolts are all tight. They had a problem that model year with them backing out.

Thanks Mach. I noticed that this scaping/noise does not happen all the time. It happens randomly.

Does it only happen when the torque converter engages?

You know Mach, I spent like 2 hours today just listening to the noise again. When I am in tow/haul it happens between 2-3 shift, drone is brief like 2-3 seconds, defenitely felt in the gas pedal, slight vibration for the duration of the drone. When I am not in tow/haul I think I felt it a few times at about 50 mph cruising, maybe it was my imagination. It does not happen all the time during 2-3 shift. Sometimes it does not happen at all during 2-3 shift. I never noticed it during other shifts. But when it does happen its defenitely noticable in tow/haul during that specific shift and I believe verter locks up in a 3rd? Other then that, I dont get any shakes thank god, everything else is functioning properly, no ticking or anything like that. Also, I dont tow anything, I just got it to haul my ass in it cuz for me there is notin like a dually:ro) in case if that matters. So conditions I would say are normal, no stress. I have 53K miles on it. I recently did flush, installed deep pan, changed filters and put transynd in it and syntetic fluids everywhere else. I wonder if I had loose verter bolts would I not be getting shakes all the time while driving?Thanks for your help Mach.

Hey Guys/Gals-


Hope this is the right place to post- I also heard a strange noise today, but under different circumstances. While turning right from a stop sign and accelerating moderately, I went over some asphalt "washboard" (bad city road) and my rear end hopped a bit to the left, as you would expect. But just as that happened, I heard a failrly LOUD "chatter" from the front end. It reminded me of the chatter you hear and/or feel with anti-lock breaks engaging, but much louder. I lifted my foot off the pedal, and it stopped- put it back on the gas, and no more noise, just normal acceleration. Truck has the allison auto.

Steve

I picked the truck up yesterday- don't know if this is something to worry about or not.:confused:

Gustav: The torque converter locks up differently depending on what mode you are using. In Normal mode the TC will lock up around 50MPH at light to medium throttle and a little sooner at wide-open. In Tow/Haul mode it will always lock up around 25mph, right in between the 2-3 shift. The intensity of the noise will vary depending on throttle, temperature, and background noise. You are right though, if the TC bolts were loosening up it would rattle. But given the model year of your truck and the noise described it was the first thing I thought of.

Steelheader: I'm not as familiar with the whole truck as I am the transmission and in this case I don't think it's the trans. But you might want to check the bushings on the front suspension. I've heard those can give you a similar noise if they've gone bad. Hopefully someone else here can give you some better direction.

Thanks Mach for your help. I think that scraping noise may have been something on outside, maybe I drove over some crap coincidentially while tc made that lock up noise because I haven't heard scraping it since then and prior to. That was the only time I heard it.
Just out of curiousity, what kind of rattling or vibration can one expect to get when tc bolts are loosend, the whole truck would most likely shake right?

Depending on how loose they are you'll get some shake and a whole lot of noise especially if one or more of the bolts has backed out completely. Over time the transmission will also develop a front end leak.

Unfortunately, it's not an easy check as you have to pull off the starter to get to the bolts. If you are not hearing or feeling anything unusual I wouldn’t worry about it.

I am feeling something similar. In normal driving, when the truck shifts into 5th, I get a vibrations that lasts less than two seconds. I am also experiencing shifting problems. What could this be?

Sounds like it could be the same thing. Does it happen around 50MPH?

What kind of shifting problems are you noticing? The more information you can give the better we'll be able to help you.

When the torque is open as in not locked, oil is pumped to clutch side of the lock-up disk, this counter acts converter cooling charge. This allows the small spring to keep the clutch from locking-up. To get lock-up of the torque the pressure to disk side of torque is stopped & turned into a vent. Then the converter cooling charge doubles as lock-up apply pressure. The noise (pressure regulator buzz) is caused by the rise in line pressure as the supply is cut off from torque lock-up disk. But the nose quickly suppressed as the line pressure is lowered to the new requirement. About 100PSI less.

If you listen you can here the buzz just before the torque converter locks ether after 2 in T/H or after 4 or 5 in early 2001 to 2003 & only in 5th in 2004.5 units on normal mode (I'm not sure when they went to lock-up only in 5th but all the 2004.5 are).

I hope this sheds so light on it for you.
Tranytom

Yes, Machinator it is vibrating around 50mph. The vibration and shift problems were much more apparent and audible when I had the hypertech tune installed. I detuned it and the problems are still there. My shift problems consist of some of the shifts being very hard, and sometimes with the same shifts the truck will "defuel" during the shift. It also seems that the tranny doesn't disengage when I am trying to park the truck. Even standing still with the brake applied, the tranny is still pushing me, much more than normal. When the truck is cold, or after it sits for a couple of hours, it will shift up and down through the gears perfectly. I am stuck in Tulsa for the next week taking care of some things for work and there is a Chevy dealership with a commercial truck shop next to my hotel. I called the service manager and he said he was very familiar with all of my issues. I am taking it there on Wednesday.

By the way if the noise & fib is getting longer this would say that you torque is on it's way out. You'll also find that the lock-up sift starts to drag out or dubble apply with a bump at the end of the shift. If you have these symtoms & don't have a built trans you'd best start saving for one.
Tom

Thanks for the info, Tranytom. I do have those exact symptoms from time to time. What exactly is a "built" transmission? Are you referring to an upgraded transmission? I am really not interested in that. I do not tow, haul, or race. My truck is a comfortable, safe, and efficient vehicle that can drive through almost any weather condition, and gets me between work locations in five states. I put on the lift kit and bigger tires because I like the look. I only use the Hypertech to get a couple more miles to the gallon. I like to stay stock as much as possilbe because I generally use one convenient dealership for service and do not want to drive to different locations to receive service on different components. Your analysis of the torque converter pretty much matches what the service manager said the problem could be. If so, I will replace it and move on. Along with new brakes and a cure for that damn lopey idle. I now have 140k miles and will not quit until the big pieces fall off. Thanks for your help and take care........Tel.

Yes a "built" transmission. It's O.K. to stay stock for you, if that is your plan. I just have one question. Have you changed your spin-on filter? It filters all oil leaveing the torque going to the cooler. If it is starting to plug up you will see higher trans temps & slugish shifts. It's cheap ($20+-) only use a shock one GM or Allison. You can do it your self like an engine oil filter. You'll only lose about a cup or oil.

Drive Safe
Tom

Yes, Sir. I change the spin on every 15k when I do the fuel filter. I will let y'all know what happens at the dealership when I take it in on Wednesday. Thanks.

Took it to the dealer today. The tech could not find anything wrong with the tranny. He said that my carrier bearing and my rear ujoint needed to be replaced and this could very well be why my shifts seem hard and the converter takes a second to lock in. He said something about the tranny receiving mixed signals because of the ujoint and carrier bearings. My computer showed no codes of any kind. He said that if I had a serious issue, there would definitely be a code. He also is flushing the tranny. He was going to fix it and drive it again to seek if it took care of my tranny issues. He ran out of day so he kept my truck until tommorrow. Does this sound plausible?

I got it back from the dealership. The carrier bearing, ujoints, and tranny fluid change made a huge difference. Truck shifted perfectly and I did not hear the torque converter lock vibration. I put the Hypertech back on, and allowed it enough time to learn. I heard the torque converter noise again and my shifting was less than stellar. I took the Hypertech back off. The extra mpg is not worth ruining my transmission. Since I took it off, the tranny shifted perfectly again. I know many people use the hypertech and don't have any problems. Maybe it's because of my high mileage, who knows. Live and learn.