noise when decelerating

[Keenan]

I bought a 1998 z71.5.7, 265k miles, a few months ago, and am in the process of restoring it to a respectable level. When I bought it, the cats were deleted and had the loudest muffler known to man. Long story short, I added the cats and changed the exhaust. With a drastic noise reduction I noticed this issue: When on the highway at say 65mph and I let off the gas, I hear a rumble noise, almost like a tran brake. It is there until the truck down shifts and then goes away. It only occures at highway speeds when decelerating, not accelerating and not around town at lower speeds. Any tips or direction to solve the issue is grealy appreciated.

 

[stutaeng]

Have you inspected your driveline? U joints and center carrier (if you are extended cab) are items that are certain wear items on anything 200k+.

A rumble? Um, not sure what can cause that... I do know some gears inside the transmission such as the sun gear do have a "drive" side and "coast" side, as well as the differential gears. I believe if there is excessive wear you'd hear a whine? I'm not sure. Also, perhaps a sprag has developed "chatter" on the mating ridding race? Do you know if either are original?

Truck on a lift and spinning wheels is probably going to be the best way to try to pinpoint this. Otherwise disconnect the driveshaft to try to isolate noise from rear end vs transmission.

 

[Schurkey]

Does this engine have an AIR pump? Does the diverter valve work like it should?

 

[Zerio29]

Have you inspected your driveline? U joints and center carrier (if you are extended cab) are items that are certain wear items on anything 200k+.

A rumble? Um, not sure what can cause that... I do know some gears inside the transmission such as the sun gear do have a "drive" side and "coast" side, as well as the differential gears. I believe if there is excessive wear you'd hear a whine? I'm not sure. Also, perhaps a sprag has developed "chatter" on the mating ridding race? Do you know if either are original?

Truck on a lift and spinning wheels is probably going to be the best way to try to pinpoint this. Otherwise disconnect the driveshaft to try to isolate noise from rear end vs transmission.

x2 on the u-joints or steady/carrier bearing, definitely worth checking. I feel like changing out the exhaust was not the cause of the noise, but just quieted it down enough where you could actually hear it. Steady bearings are very easily diagnosed by just crawling under and wiggling the driveshaft. u-joints are sometimes difficult to diagnose without pulling the driveshaft and pushing them to the maximum angles.

 

[Keenan]

To my novice eyes, everything looks good. I am taking it in to a transmission shop next week. I will update the string with findings and results.

 

[chevyrider838]

To my novice eyes, everything looks good. I am taking it in to a transmission shop next week. I will update the string with findings and results.

Any updates?

 

[Donald Mitchell]

Does this engine have an AIR pump? Does the diverter valve work like it should?

The first thing that popped into my head. 2nd was the distributor.

 

[stutaeng]

Any updates?

OP hasn't been seen since October of last year. I hope he figured it out.

Perhaps you can start a new thread to get more feedback from other members?

 

[Tjlracerx]

I bought a 1998 z71.5.7, 265k miles, a few months ago, and am in the process of restoring it to a respectable level. When I bought it, the cats were deleted and had the loudest muffler known to man. Long story short, I added the cats and changed the exhaust. With a drastic noise reduction I noticed this issue: When on the highway at say 65mph and I let off the gas, I hear a rumble noise, almost like a tran brake. It is there until the truck down shifts and then goes away. It only occures at highway speeds when decelerating, not accelerating and not around town at lower speeds. Any tips or direction to solve the issue is grealy appreciated.

I had kinda the same issue. I thought it was transmission but ended up being the yoke bearing in the rear-end. it also ended up causing the u joint in my driveshaft to fail