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Clunk!!! Update: Found Metal Bits in rear diff!!!

S

smier

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I've got a '91 blazer 350 tbi automatic trans, completely stock. Since I bought it a few years ago, it would clunk when going in gear you can feel it and hear it. So it has slowly gotten more noticable over time, so I decide it's time to replace the ujoints... Pull the driveshaft out at work and put the new ones in, no change... Still clunks and you can feel it engage. Time to rebuild the rear??? Also it will clunk when you left off the accelerator and when you get back on it. What and how do I check the rear axle? And no I'm not swapping rear ends yet, still my daily driver. Oh it has about 144,000 miles...
 
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Set the e-brake, put the trans in neutral and grab the pinion yoke. If it has in in/out or side/side play the pinion bearings (and probably the ring and pinion) are toast. A little rotational play is ok.
 
71chevy4x4 said:
Did you check for wear in the drive shaft slip joint?
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This is probably the problem.

All the 90's chevy's did this too. There is a dense grease stuff GM used pack the splines to try and quiet it, but it was a bandaid at best.

I wouldn't' worry about it if your pinion doesn't have any play, and your ujoints are good.
 
I had a cracked flexplate do the exact same thing in a 89 k2500 with a 350 and 700R4. The flexplate cracked around all the bolt holes and made the bad clunk when going into gear.

I was told that this was fairly common when GM went to the 1 peice rear main seal, because the bolt pattern is smaller than the old 2 peice style.
 
No apparent play at the splines of the slipjoint ( I fought to get it off and back on so I really examined it to see if something was wrong), but no visible signs of any grease used to pack it anymore... If it doesn't snow I'll check pinion yoke for play this afternoon when I get out of work. Somethings definately going to need to be done, it's getting real annoying driving to and from work!
 
could be your transfer case chain gettin worn out.my jeep did this before the transfer case broke.
 
Ok, I crawled under it again in neutral with brake on, only slight roatational play when I really force it to try and turn, I laid on my back and tried to force the yoke on the rear up and down and side to side, I really couldn't get it to budge either way. Driving it home i can't tell if the noise is in the rear or my transfer case or transmission... Transfer case has some fluid seapage I didn't like the looks of...
 
Chevy trucks klunk. Get used to it. Its when they go bang its time to worry. Yur griving a 20 year old truck it is going to make some noise.
 
X3 on tranny mount. Try to pry up on the T-case/tranny while watching the mount area. You'll likely find you can pry it up, meaning a bad tranny mount.

Rene
 
Is this lifted??


From the sounds of it, it's more in the case to me. Either the chain stretched, or there not being enough slip yoke in the case to mate properly.

NVM just re-read that it's completely stock.
 
Loose U-bolts at the rear springs can cause a clunk every time you put it in gear too,as the axle housing rotates under torque..bad spring bushings can do it too..or a worn side gear bore in the differential carrier,or a sloppy spider gears & the pin they ride on sometimes wears..(I see a lot of sheared off retaining bolts on the spider gear pin too)..a cracked sun gear in a 700R4 is a fairly common failure and they can clunk for awhile before going BANG!..
 
Thanks everybody, lots of great info... A lot of stuff to check, I'll post up what I find. I'm excited to have it back, was in my friends body shop for almost a year getting new rockers, tailpan, etc... Get a few little bugs worked out, then I'm going to bedline the interior and get it painted. Lifting it is pretty far down the list, but I have zero rust to contend with anymore!!!
 
It's been a while, but I just resolved some of the issues I have been having... I couldn't believe what was the cause of my clunking in my driveline. My intake manifold gasket was shot, replaced it and rebuilt the TBI and now my blazer runs and shifts like a brand new truck!!! Tons of power, no more stalling and stumbling, and no more clunk. It was idling too high and then actually starting to stall in overdrive when you would let off the throttle. It would also stumble and sometimes stall in traffic. Also resolved my slow loss of coolant, I was burning it(about 1/2 gallon of coolant every 3 months). Thanks for all the help and advice!!! I can't believe how great it runs now, it ran really good before we discovered this. I'm curious if my fuel economy will go up, I'm giving it so much less throttle now and she just purrs now...
 
smier said:
It's been a while, but I just resolved some of the issues I have been having... I couldn't believe what was the cause of my clunking in my driveline. My intake manifold gasket was shot, replaced it and rebuilt the TBI and now my blazer runs and shifts like a brand new truck!!! Tons of power, no more stalling and stumbling, and no more clunk. It was idling too high and then actually starting to stall in overdrive when you would let off the throttle. It would also stumble and sometimes stall in traffic. Also resolved my slow loss of coolant, I was burning it(about 1/2 gallon of coolant every 3 months). Thanks for all the help and advice!!! I can't believe how great it runs now, it ran really good before we discovered this. I'm curious if my fuel economy will go up, I'm giving it so much less throttle now and she just purrs now...
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Bet you whatever was clunking is still bad but your not noticing it because you dont have a super high idle from a vacuum leak.

My vote is still a trans or engine mount.
 
Yeah, I agree with you, truck is pretty much original with 145,000 miles... But I'm getting there, just glad I'm finally making some forward progress instead of going backwards!!!
 
Did a fuel economy test, I used to average 11 to 12 mpg to and from work.... 41 miles round trip of stop and go on 2.5 gallons or a new average of 16.4 mpg!!! Now I'm curious to take her for a run on the highway, my blazer may have just gotten a new lease on life. I was starting have doubts about the amount of $$$ I've put into thi project and how much more is needed. I'm really pleased with the progress lately, plus I can drive it daily again, I love driving this truck!!!
 
x4 on the motor/trans mount.

Have someone sit in the truck and put it in gear while you watch the trans and motor mounts. It will be pretty obvious.
 
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