Mechanics

CHEVY BLAZER (SLUGGISH, CLANKING, AND HUMMING)

2000 Chevrolet Truck

I know ya'll are busy answering questions but it would be great if you could find a lil extra time to help me out cuz I'm completely stumped. I'll try to keep this short and if I miss details you would like to know. Pm me please and i'll be happy to include them

2000 Chevy Blazer LS 4wd 4.3L 2door 130k aprox miles automatic trans

first problem that is most recent is it makes a humming/vibration (almost like when u drive over worn out rumble strips on road) when driving between 45 and 60+mph. Funny thing is it only does it when u DEcelerate. Drives smooth until u let off gas, then after a second or two it starts vibrating but quits as soon as u give it even just a quick tap on the gas pedal but will start back up again after a second or two if u dont continue the small trickle of gas. Most noticable at 50-60+mph. Quits completely once u decelerate below 40mph. Very faint hum between 40-45mph. Felt through front of truck and maybe part of middle(between front seats). Doesnt make a difference if u brake or not. Just quits sooner cuz u get to 40mph sooner : P

Truck also seems sluggish at times. Doesnt always happen (no pattern) but at the times it does happen it acts like it doesnt want to shift from first to second gear no matter how much u press on gas, rpms dont even move. And then after a second it lunges like it just got the blast of gas. Makes a gurglish sound so I know the truck wants to go. It just cant. Gurglish sounds faster the harder u press on gas but rpms dont move. After second gear its fine and has no problems. Doesnt seem to matter if truck has been sitting for a while or been running all day nor seems to be consistent w/ weather or temperater. Just does it whenever but only when truck should be shifting from 1st to 2nd. And since I cant recreat problem. I cant test to see if I can manually shift from 1st to 2nd to see if it still has problem. Doesnt happen too often but seems to happen more often when I need to take off quick. Doesnt give any warning. I try to take off quick and I suddenly find I dont have any acceleration power (been a few close calls cuz of that)

another problem that cant really be recreated either is a clanking sound beneath car in middle leaning toward front. (About right between front seats). Clanking speeds up and slows down when the truck speeds up and slows down. Clanking is worse when first starting out and taking corners a little too fast or too tight. Dad says it sounds like u-joints. Sounds almost like a rock is stuck in the wheel well. Only of course its not even near the wheels. A similar sound can be heard (sometimes not always) is when switching from drive to reverse, but not back to drive. However that one sounds to be in a slightly diff location, more toward engine but still in general location.

the order of the problems occuring is first the sluggish not wanting to switch from 1st to 2nd starting about 4 month after I bought it May 2005, second the clanking sound starting 2 months ago, and third the humming/vibration on coast 1 month ago.

history:
bought from an auction and salvaged truck from a rear end hit. Did need frame straightened but no other major damage other than cosmetics. Changed oil regularly. Replaced tires right after purchase including both front wheel bearings. Not to sure on this on but something was causing gas tank to leak when fuel pump was engaged, bad seal or somthing. Had it taken in to shop and repaired. This was prolly 5 months after I bought the car. (It didnt change the problem w/ shifting from 1st to 2nd)
had serpentine replace last week, along w/ air filter and oil change and took thottle body cleaner to throttle body. No change to performance problems. S

so much for trying to keep it short. Sorry
Id greatly appreciate any advice as to what this/these problems may be and how I might be able to handle them on my own.

thanks in advance
Avatar
Scorpio1025
May 15, 2007.




Just let me say, you did a fine job of decribing your symptoms.

First thing I would do is check the tires.I know you replaced them but didnt say how many miles are on them. There may be a knot in one. Also, blazers can cup the front tires if you dont keep up on the pressure, so, if you rotated them to the back it could be more pronounced.

Next, replace the u-joints in the rear driveshaft.
(could make all the diffrence.)
((when you decelerate there is no torque on the shaft and componants its kinda like, if you twist a rag real tight its hard and stiff but if you let off on the pressure its flexable thus, bad vibration))

as for the slugishness, sounds like eather fuel pressure, or, it kinda sounds like sometimes you are sucking air into the line somehow, or, somekind of fuel restriction(fuel pump, filter.)

well, this should give you a few things to check let us know how it goes.

P.S. If you want to check the u-joints crawl under and see if you can move the driveshaft up and down or side to side. If you can there bad.
AD

Tiny
De3n8fan
May 16, 2007.
Well I checked my U-joint. It doesnt seem to have play but I had a few friends listen to it engaging (while stopped) from reverse to neutral to drive and back again and they are certain its the u-joint beginning to go bad. It looks rustier than any other part underneath the truck. The tire pressure is fine though I've got a squealing sound on the front passenger wheel (stops when I turn right) now so I look closer into it when I check/replace my brakes. The tires havent been rotated and i'm going to guess they have about 20k miles on them. Still got those lil nob thingys on the inside and a few on the outside.

Got a new question. I have a directional/thermometer device above my rear view mirror and its havnt some issues that I dont have a clue on how to go about diagnosing. The directional is fine. But the thermometer says its 110F outside when its only 30F. It goes back and forth but never under 100 even when I first start the truck or if I try to reset the device. Where is it getting the temperater and how do I fix it? Its not a major thing but somthing that is starting to bug me : P

thanks,
jenn

Tiny
Scorpio1025
May 24, 2007.
I hate to be the bringer of bad news buddy but it sounds like no attention has been paid to the Rear end. A decelrating humming acompanied by vibrations is the sign of a Ring and Pinion gear on the verge of going out. The gears faces have worn off leaving you with a large gap between the gears. Put the truck in park on a level surface and push it back and forth, if the truck move over a foot in either direction you need to rebuild the rear end. If you dont you could end up replacing the entire rear end. I have had teeth break off and that was lucky. I have also had the entire differential housing crack in half ending up tearing the entire rear end apart.

Tiny
Toypar
Jun 26, 2007.
You will need to replace the sending unit. The thermocouple that sends a temp signal to the readout.

Tiny
Toypar
Jun 26, 2007.
Wow. So then do I still need to replace my u-joints? I tried wiggling them and there is no play at all but my truck still makes that clanking sound when shifting from drive down to reverse as if the joints were going out. So is it then my differential making that noise? I cant get it to move when its in park. Jiggle it and wiggle it like most vehicles but not roll it one direction or the other

Tiny
Scorpio1025
Jun 26, 2007.
Did you m ove it forward and backward? All cars move naturally 3 to 6 inches due to clearances in the drivetrain

Tiny
Toypar
Jun 26, 2007.
Lol yes I moved it forward and backward. It didnt move at all but then im only 100 lbs so not like I can put a lot of force into it anyway. My lil berretta I could move and that was bout what u described as normal. My truck is much heavier.

Tiny
Scorpio1025
Jun 26, 2007.
And suddenly my thermometer is working fine again. Must not like reading winter temperature. Y would it bounce back and forth? Where do I find the sending unit? Far as I can tell it goes up into the roof of my truck since its positioned above my mirror. Im not that desperate to fix this to tear apart the lining and I dont see anything outside on the roof. Aside from the luggage carrier bars. Does it run down the frame and somewhere into the engine compartment? Sorry I ask so many questions. I want to learn

Tiny
Scorpio1025
Jun 26, 2007.
Dont worry about the questions, thats why they make sites like this. In the future someone with your problem will read this and get the same questions awnsered. I would suggest that you go to autozone or napa and purchase the Chiltons or Hayes repair manual. It will have all the awnsers. As for your Humming noise, the typical way to know your rear end is about to go is a humming during deceleration just like you are explaining. As fo the sending unit you would have to call a dealer and ask them where it is located.

Tiny
Toypar
Jun 28, 2007.
Ok thanks so much for all ur opinions. One more question. What are the symtpoms of a transmision going out? I listed above what my truck is doing as far as lack of power when in 1st gear. Ive been listening and watching more closely to understand it better and I noticed that it sometimes has a longer than normal delay when dropping from a high gear to a lower one to accelerate faster when already moving (ex accelerating from 45 to 70 to catch up w/ traffic when merging off ramps). This isnt as much of a problem as when its first started and no willing to get up and go. It seems to act better when I let it idle a bit when first started before engaging but still does it now and then. Someone said it sounds like air is getting into the fuel lines. But im wondering if my transmission may be going out so I would like to know what those symptoms often are.

Tiny
Scorpio1025
Jun 28, 2007.

AD