1996 GMC Jimmy Undercarriage Rattle..

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  #1  
Old 12-31-09, 04:12 PM
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1996 GMC Jimmy Undercarriage Rattle..

Its getting louder. With the Jimmy on ramps, I had the engine gently accelerated which I noticed increases the rattle somewhat but (when driving on the road seems to quite down after hitting a cruising speed). While listening under the car the sound seems quite apparently to be coming from the transmission housing. There seems to be no noticeable change in the operation of the transmission as it has gotten louder. Since the vehicle was in park during my sound inspection, it obviously has nothing to do with the drive axle. Any thoughts out there? If transmission, what's best rebuild existing? Buy a rebuilt? What kind of budget do I need to consider? Much obliged for any who will give this some thought.
 
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Old 12-31-09, 04:39 PM
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I would first look at a corroded exhaust heat shield. These like to make some noises when they crack.
 
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Old 12-31-09, 04:57 PM
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spent about 30 minutes under the cooled truck inspecting everything I could. Nothing seemed to be out of sorts, all parts seemed tight, heat shields appeared in good shape.
 
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Old 12-31-09, 05:29 PM
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Could be as simple as a cracked flex plate don't condem the trans yet.
 
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Old 01-01-10, 03:42 AM
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OK, I'll check that out. What is a flex plate?
 
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Old 01-01-10, 06:04 AM
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Check the entire length of the exhaust system. A loose support or broken weld could easily cause a rattle.
 
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Old 01-02-10, 06:48 AM
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Originally Posted by Maniac Mechanic View Post
Could be as simple as a cracked flex plate don't condem the trans yet.
I'm convinced it's the flexplate. So, can the flexplate be replaced (or bolts tightened) without removing the tranny, i.e. I gotta believe you need to move it back (U joint to be disassembled, etc). I haven't been able to get a good picture in my mind (or anywhere else I've looked) on exactly how to access the flexplate. Thinking it through in my head, I'm concerned how to get a torque wrench up into the thing. Found this which shows how to do this but not convinced I'm seeing everything: Transmission - Replacing the Flex Plate - Part 1. Again, much obliged for your consideration.
 
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Old 01-02-10, 07:13 AM
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I assume it is an automatic?
First check the flex plate.
From the bottom of the trans remove the "inspection plate"
You will see the ring gear where the starter pinion engages to turn the engine. That is the flex plate.
Rotate the flex plate and engine with a proper prybar. That is a slow job but you will be able to inspect the flexplate and ring gear proper. Helps to have a selection of bars to find the ideal one. Dont break your knuckels by slipping bars. Be ready for it.
Flex plate usually break where the bolt and nut attach the flex plate to the torque converter. Look carfully for cracks and loose bolts.
Should be 3 nuts and bolts holding them together, could be 4.
Mark where you start so you know how far to go.
Remember to be carefull and slow turning with the prybar.
I find a good spot on the trans housing to pry against with the other end of the pry bar on the ring gear and just go one tooth at a time. Get comfortable under the well secured vehicle. Dont trust jacks to hold vehicle up. Use jackstands or blocks or whatever you can depend on if the jack fails.
Good luck
Cant remember if starter has to come down or not.
Maybe someone else will remember.
What year is it and is it a 4by4?
 
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Old 01-02-10, 08:08 AM
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Originally Posted by Maniac Mechanic View Post
Could be as simple as a cracked flex plate don't condem the trans yet.
Originally Posted by frankiee View Post
I assume it is an automatic?
First check the flex plate.
From the bottom of the trans remove the "inspection plate"
You will see the ring gear where the starter pinion engages to turn the engine. That is the flex plate.
Rotate the flex plate and engine with a proper prybar. That is a slow job but you will be able to inspect the flexplate and ring gear proper. Helps to have a selection of bars to find the ideal one. Dont break your knuckels by slipping bars. Be ready for it.
Flex plate usually break where the bolt and nut attach the flex plate to the torque converter. Look carfully for cracks and loose bolts.
Should be 3 nuts and bolts holding them together, could be 4.
Mark where you start so you know how far to go.
Remember to be carefull and slow turning with the prybar.
I find a good spot on the trans housing to pry against with the other end of the pry bar on the ring gear and just go one tooth at a time. Get comfortable under the well secured vehicle. Dont trust jacks to hold vehicle up. Use jackstands or blocks or whatever you can depend on if the jack fails.
Good luck
Cant remember if starter has to come down or not.
Maybe someone else will remember.
What year is it and is it a 4by4?
Thanks, I'll give this a go - It's a 2WD, '96. And yes, it is an autotrans
 
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