this is a tricky one...need help a.s.a.p.

lilgib12 · 03-15-2009, 05:45 PM

I have a 1989 light duty 3/4 ton GMC Sierra 4x4 long bed with a 350 engine and a 700R-4 transmission. the body has 305,000 miles on it and the engine has 105,000 miles. I was driving the truck home, going maybe 25-30 mph and it started making this sounds like gears were grinding together. When I stopped and got out I got down on the ground and had my mom pull it forward a little bit and it sounded like it was coming out the differential. The next day my dad and I were messing with it and a mechanic from up the street said the sound was coming from the transfercase. So we got one from a good junkyard and put it in but its still making the sound. Another mechanic that works with my dad stopped by and messed with it and said the sound was coming from the transmission. So we went to a junkyard and got another transmission. It was still in the truck when we went to get it so i took it for two test drives and checked the fluids before we took it. The guy at the junkyard even threw in the transfercase for free. (so if anyone needs a transfercase let me know, now i have an extra one) The truck makes the sound when its put in reverse even without moving. When its in drive it makes the sound under even the smalled load. After we put the new transmission in we started it up and put it in reverse before we even put the transfercase on and it still made the sound. It's a horrible sound, just like metal on metal, gears grinding or something but we can't figure out what it is. A friend of ours said it could be a broken engine mount but that isn't completely making sense to me. The truck doesn't make the sound if the transfercase is in neutral.

gmctrucks · 03-15-2009, 06:42 PM

Welcome to the forum and Howdy from TEXAS. Now don't go buying any more parts till you let us know whats going on to me it seems that the people around you are not knowing what there saying and it's costing you money get away from them. I would lift the rearend place jack stands on it and shock the front tires with blocks so it won't move and go from there to me it's sounds like the rearend is shelling out or place the whole truck on jack stands place it in gear so that you can find where the sound is coming from. Maybe the rearend has too much play in it that happened to my 87 Burb the posi unit shelled out and it messed up all the gears the sound was super bad.
Good luck! GMC

mudseeker · 03-15-2009, 07:22 PM

sounds like you learned your lesson the hard way about throwing parts at a problem. i would look at the rear end, your driveshaft can play tricks on you and transfer the sounds from the rear end.

lilgib12 · 03-15-2009, 07:29 PM

we did have the rearend up on jack stand and too the driveshaft off and ran it. the sound deffinetly isn't coming from the rear. it sounds like it's coming from the transmission or more from the torque converter but we just put another one it that is fine. have you ever heard anything like that being from a broken engine mount? my dad said he even saw something about it in the haynes manual saying that the engine mount being broken could be effecting the timing chain and gears

dothedew · 03-15-2009, 07:53 PM

I hate to say it but I'm thinking something is amiss with your engine. You said you've gone through two transmissions aside from the original one with no difference, that alone tells me its not that. Odds of two transfer cases making identical noises as well? Not to likely, but plausable. You said that it makes no noise when in neutral, and that it made a noise when you had just a transmission on and no transfer case. I'm assuming of course you didn't hook up a drinkshaft. Just throwing this out there, but if you spun a bearing it may not rear its ugly head until the engine is put under load, such as putting it into gear or reverse. This could be doubtful if the engine has a little of 100k, but there are a lot of shops that to economical grade work.

If you indeed think that it is the rear, just take out the 10 bolts holding the cover and catch the lube. If its going downhill, there will be many metallic filings, or even small chunks. If this is the case you might as well look for a replacement, since rebuilds cost as much or more than a scrapyard one. Any additional info you can give us would be helpful, let us know how you make out.

leolkfrm · 03-15-2009, 08:18 PM

Have you tried using a piece of PVC pipe to listen thru to try and isolate the problem?

scavanger · 03-15-2009, 08:27 PM

Did you check the flexplate for breaks or cracks ?

Scav.

gmctrucks · 03-16-2009, 07:54 AM

Quote:

Originally Posted by scavanger

Did you check the flexplate for breaks or cracks ?

Scav.

Good idea my flexplate cracked all around the bolts to where it fell down and right before it fell my truck felt like it was missing big times. Check trans mount they go out as well and motor mounts just to make sure there fine. Now when using a piece of PVC pipe place it where you think the noise is coming from then place the other end of pipe to your ear the sound will travel thought the pipe believe me it really works.

I can't figure why you can't find the noise if you have the whole truck on jack stands with you under it sounds dangerous but if it's jacked up correct with jack stands it can be done just don't gun it to where the truck is going to move.

Maybe take it to a muffler shop and have them lift the whole truck so you can listen for the sound under the truck. Maybe you didn't push in the converter all the way or the first one was bad and your using the same converter from first trans. Is it the same converter?

You can also check the flexplate by removing the inspection cover that way you won't have to remove the whole trans check with flash light or good drop light my flexplate made different sounds before it broke. I'm thinking you have play on the rearend make sure you check it good with PVC pipe.
Good luck! GMC

Scottsdale 2500 · 03-16-2009, 08:33 AM

Yea. Definatly look in the rear end for stuff. I know you had it up on stands but did you check the carrier bearing if it has one? Mine just went out last week and it sounded horrible.

Case 7230 · 03-16-2009, 09:44 AM

Quote:

Originally Posted by scavanger

Did you check the flexplate for breaks or cracks ?

Scav.
:)

Gets my vote

03-15-2009, 05:45 PM	#1
lilgib12 Full Member Join Date: Feb 2009 Posts: 14	this is a tricky one...need help a.s.a.p. I have a 1989 light duty 3/4 ton GMC Sierra 4x4 long bed with a 350 engine and a 700R-4 transmission. the body has 305,000 miles on it and the engine has 105,000 miles. I was driving the truck home, going maybe 25-30 mph and it started making this sounds like gears were grinding together. When I stopped and got out I got down on the ground and had my mom pull it forward a little bit and it sounded like it was coming out the differential. The next day my dad and I were messing with it and a mechanic from up the street said the sound was coming from the transfercase. So we got one from a good junkyard and put it in but its still making the sound. Another mechanic that works with my dad stopped by and messed with it and said the sound was coming from the transmission. So we went to a junkyard and got another transmission. It was still in the truck when we went to get it so i took it for two test drives and checked the fluids before we took it. The guy at the junkyard even threw in the transfercase for free. (so if anyone needs a transfercase let me know, now i have an extra one) The truck makes the sound when its put in reverse even without moving. When its in drive it makes the sound under even the smalled load. After we put the new transmission in we started it up and put it in reverse before we even put the transfercase on and it still made the sound. It's a horrible sound, just like metal on metal, gears grinding or something but we can't figure out what it is. A friend of ours said it could be a broken engine mount but that isn't completely making sense to me. The truck doesn't make the sound if the transfercase is in neutral.

03-15-2009, 07:22 PM	#3
mudseeker Senior Moderator Join Date: Feb 2006 Location: michigan Posts: 6,375	sounds like you learned your lesson the hard way about throwing parts at a problem. i would look at the rear end, your driveshaft can play tricks on you and transfer the sounds from the rear end. __________________ i'd rather be hunting

03-15-2009, 08:18 PM	#6
leolkfrm Senior Member Join Date: Mar 2008 Location: N.Y. Posts: 4,300	Have you tried using a piece of PVC pipe to listen thru to try and isolate the problem? __________________ 4 wheels move the body 2 wheels move the soul B.W.A.I

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03-15-2009, 06:42 PM	#2
gmctrucks Senior Member Join Date: Nov 2006 Location: Houston,Texas Posts: 4,035	Welcome to the forum and Howdy from TEXAS. Now don't go buying any more parts till you let us know whats going on to me it seems that the people around you are not knowing what there saying and it's costing you money get away from them. I would lift the rearend place jack stands on it and shock the front tires with blocks so it won't move and go from there to me it's sounds like the rearend is shelling out or place the whole truck on jack stands place it in gear so that you can find where the sound is coming from. Maybe the rearend has too much play in it that happened to my 87 Burb the posi unit shelled out and it messed up all the gears the sound was super bad. Good luck! GMC

03-15-2009, 07:29 PM	#4
lilgib12 Full Member Join Date: Feb 2009 Posts: 14	we did have the rearend up on jack stand and too the driveshaft off and ran it. the sound deffinetly isn't coming from the rear. it sounds like it's coming from the transmission or more from the torque converter but we just put another one it that is fine. have you ever heard anything like that being from a broken engine mount? my dad said he even saw something about it in the haynes manual saying that the engine mount being broken could be effecting the timing chain and gears

03-15-2009, 07:53 PM	#5
dothedew Junior Member Join Date: Mar 2009 Posts: 5	I hate to say it but I'm thinking something is amiss with your engine. You said you've gone through two transmissions aside from the original one with no difference, that alone tells me its not that. Odds of two transfer cases making identical noises as well? Not to likely, but plausable. You said that it makes no noise when in neutral, and that it made a noise when you had just a transmission on and no transfer case. I'm assuming of course you didn't hook up a drinkshaft. Just throwing this out there, but if you spun a bearing it may not rear its ugly head until the engine is put under load, such as putting it into gear or reverse. This could be doubtful if the engine has a little of 100k, but there are a lot of shops that to economical grade work. If you indeed think that it is the rear, just take out the 10 bolts holding the cover and catch the lube. If its going downhill, there will be many metallic filings, or even small chunks. If this is the case you might as well look for a replacement, since rebuilds cost as much or more than a scrapyard one. Any additional info you can give us would be helpful, let us know how you make out.

03-15-2009, 08:27 PM	#7
scavanger Senior Member Join Date: May 2007 Posts: 262	Did you check the flexplate for breaks or cracks ? Scav.

03-16-2009, 08:33 AM	#9
Scottsdale 2500 Full Member Join Date: Jan 2009 Location: Cody Wyoming Posts: 18	Yea. Definatly look in the rear end for stuff. I know you had it up on stands but did you check the carrier bearing if it has one? Mine just went out last week and it sounded horrible.