Question about 2003 Chevrolet Trailblazer Ext

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Sounds like I am dragging a Tree branch under the front of the Trailblazer. It starts at about 5 mile/hr and continues at all speeds. When applying the brakes, no difference in noice and when I turn right or left the same sound is made. We replaced the Rotors, and put mid grade brakes on last weekend. Someone said it could be the Front Differential? Just wanting to make sure before I throw more money towards it.

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  • klahue99 Apr 24, 2009

    I had someone else tell me it was the Front Dif. as well. They also told me it was easier to buy a used Front Dif and replace the whole thing.... Best price I have found for a replacement is 475.00. I'm not a mechanic by any means, but I think I could buy a lot of broken parts to fix the one I have for 475.00. Any thoughts on fixing old one vs replacing with new Used Front Dif. Thanks

  • Richard Scordino May 11, 2010

    Take the cover off and look at the gears



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Differentials are not a "bolt the parts in and go" item....Gear positioning, pre-load, lash etc all need to be set with micrometers, dial indicators , torque wrenches etc.You also need to have the ability to "read" gear patterning for proper operation. Even most good techs leave this to specialists. Putting a bunch of parts from other broken rears is actually more difficult because patterns are set from wear during use, and will not match any other gear except the one that it had been mated with. If you check the price on new components you will find that new components alone without setup cost is likely higher than a drum to drum diff from a scrapyard.
When you are buying a complete diff, you MUST match the gear ratio of the one not being replaced exactly or you will cause catastrophic failure of the transfer case. If there is no ID tag on the diff, count the number of teeth on the ring gear and divide that by the number of teeth on the pinion gear (should come out to something like 3.23 which is expressed as 3.23:1) this means that the driveshaft turns 3.23 times for each time the wheel turns once. (the # i just used is a common ratio, but you need to find out what yours is. It is also good to count same on rear diff to make sure that no one put the wrong gears in the front on yours.
When buying a used unit, make sure that the gears turn freely and are not excessively worn. also look at the remaining lube in it to see if there is metal or if it's burned...if it is you don't want it.
Hope this helps you!!!!

Posted on Apr 24, 2009

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Pull your front driveshaft, if it stops making the noise, it's the frond dif.

Posted on Apr 23, 2009


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