I'm stumpted.. about a week ago, my 95Z28 makes a loud metallic chattering sound when I ease off the gas while still in gear. Once I give it some gas, the sound disappears. Normally, it will happen while coasting in 4th or 3rd before I engage the clutch to shift to another gear. It almost sounds like valve tapping, but since the engine sounds fine at idle or under power, I'm assuming it's related to the driveshaft or exhaust. Any insight would be appreciated.... Thanks

 

Pull the rear diff cover and look for any shiny metal particulates, if you see any that's chrome from the bearings, you need new bearings. if you see dull grey metal particulates, that's metal from the gears, you need new gears. Since it's only noisey on coast, you probly just need bearings. All this is provided your trans is OK.

 

You may also want to check the universal joints on the driveshaft.

 

Thanks for the info.. I hope it's only the differential because it still sounds like it's the engine. It happens right around 2000 RPMs when coasting in 3rd or 4th. When it's just beyond that RPM barrier (either higher or lower), it goes away. Could it be an emissions (EGR) or backpressure problem?? I'll take your advice and inspect the trans and differential when I next change the fluids.

 

I have a 94 LT1 and my problem is similar to the other. Except mine makes a whining noise when letting off the accelerator. It goes away when you get back on it. I am not sure what all the common problems are with this year, but I've been having a couple, such as unexplainable temp problems, dash light annoyances, and unusually low oil pressure for a full oil pan, and anyone's advice would be greatly appreciated. Thank you

Chris

 

In my line of work we call this condition "coast howl" and it is typicaly due to excessive wear or imporper gear set up. I recently installed a set of 4.10's in a 2006 Mustang GT with only 289 miles on it. that rear end had .010 backlash when it came in, should be no more than .008. After I fought with it awhile it finally set up and laid out a good pattern, at .010 backlash, it would not set up below that. During my road test it would howl like a Basset hound every time I let off the gas. other than that it drove great. I ended up installing a set of ford performance gears and and still had the coast howl only not as loud. The car had 3.32's in it and Ford now uses a two peice double CV driveshaft. This coupled with the way too low for street use 4.10's is what we think is cuasing the howl.

 

Well.. after changing the transmission and differential fluids and inspecting the driveshaft, the noise was still there. The final solution entailed removing the EGR valve and thoroughily cleaning the valve seat -- very painful if you don't have long arms.

 

hah, so is that what it was? sounds weird, metallic clank noise and it ended up being the egr?!

 

That's interesting. I would not have thought an EGR valve could be that noisy.