I have had this noise for awhile now. I thought there a connection to my hub asssembly/wheel bearing being shot but after replacing that item the noise still persists. It is only under hard acceleration and after the vehicle is droven some distance and very warm there feels like there is a vibration when accelerated and a metallic clicking. Could it be a u-joint? Any help appreciated.

 

Check to see if your cruise or throttle cable is resting on the vacuum tube from the PCV valve. If it is, you could be hearing the PCV valve operation.

 

Thanks for responding, the noise is originating from the transfer case area. When I had the truck up on axle stands the and had my father accelerate the auto very slowly while I perched on the ground and looked and listened for the sound and it was coming from the transfer case, clicking and ckunking.

I searched through the forums and seen some threads that seemed similar to mine and noticed about filling the transfer case with fluid or the C.V boot or axle located near the front of the axle shaft being worn out. I recently had the vehicle in at a dealership for a diagnosis for a hub assembly and they said they found a torn boot and fluid and wanted to replace it.

I can't afford to have my truck fixed at over 95 dollars an hour by GM service so I had to decline. I looked at the boot and axle on the drivers side and noticed no tear or fluid but now I realize I may have been looking at the wrong one. Besides the drivers and passengers, how many C.V's are there? THe front drive shaft also has some play when I grip it and try to turn it ny hand. The clunking clanging noise is also evident to. I hope some of this info helps as I'm trying to learn how to fix this Blazer myself as something always seems to need replacing.

 

To isolate the noise you might try unbolting the front driveline from the trans axle...if the noise persists then you know that it will be internal components from the transfer case...one wild guess would be the chain drive system and either a sloppy chain or bad sprocket....

 

I have also seen the front driveshaft joint at the transfer case go bad. This is evident once removed from the truck from the slop in the joint itself.

But I would definitely inspect the front drive axles. They are the only location where there are CV joints, 2 on each drive axle.

 

I had the same sort of problem with my 98 blazer. some major vibration at speeds of 15-40mph and after that only when the motor had upshift and work hard for climbing hills. turns out it was the rear driveshaft ujoint. So from what it sounds like it might be a drive shaft ujoint. It all started after I replaced the differential fluids front and back and the transfer case fluid. which I should say was probably never changed before I owned the vehicle. so the ujoint problem was caused by doing prevenitive/needed service and ended up just taking it to a shop and they fixed it for $150 for parts and labor.

-Lenny

 

I haven't had a chance to check anything yet, worked all day, now kids soccer and hopefully an hour or two to fish and then to bed to rise and begin the routine again. I will not drive the truck the next few days as the problems appears to be getting worse evident at low speeds and now inaudible above 80 km/hr. Sounds like someone sticking a screwdriver into some spokes of a bicycle wheel. I appreciate the suggestions and hopefully will get around to looking at it this weekend but having to work7 days this week hurts. Any other suggestions with similar experiences are appreciated.

 

I would definately take a look at the u joints on both the front and rear drive shafts. Mine started real quiet and actually I felt the vibration first, then it started clicking, and once I changed the front and rear differential fluid and the transfercase fluid (first time known off, has 133k miles on it) it got even worse and I just took it to the shop, they had it fixed in 2 hours and it was perfect afterwords. Definately worth a look. Test to see if there is slop in the drive shafts at the ujoints, and this would be the most likely culprit.

-Lenny

 

Thanks for the suggestions Lenny. When I had the truck on axle stands my father checked the slop on the driveshafts and said they were bad. But I think the clicking is throwing him off in diagnosing the problem as the sound is coming from the case. I will relay waht you and others have suggested in hopes of eradicating this problem, as I have almost had it with this Blazer, seems every month there is a new problem. Problem is I love the truck.

 

Finally had time to check the truck out this weekend, it had sat awhile as I had no time to work on it. It turned out to be the rear U-Joint. My father actually changed the U joint as he suspected it and wanted to fix it before moving on to more expensive things or me taking truck to a mechanic. Now I need to replace my rear caliper bracket as the metal clips holding the brake pads in basically disentegrated and when I unbolted the caliper the whole assembly fell to the ground in pieces. Brand new pads, rotor but I never replaced the bracket and now again the vehicle will sit as work and the kids beckon, Thank god I stillhave my 90 Mustang to drive but for the winter I need this truck in top shape as it will see alot of duty.