I have a 1999 4.2 liter F-150 with automatic transmission/overdrive two-wheel drive, 8-foot box.

There is a very loud buzzing noise that originates in the rear mount for the transmission. The noise is there only at low engine rpm as when I am at a stop light or maneuvering to park or turning a corner.

I tried wedging a wooden shim between a cross member of the frame and the mount and that seemed to quiet the noise but didn't stop it entirely. Not feeling happy about the shim and any stress it might put on things, I took it out.

I was under the pickup a week ago and loosened the two nuts that I think attach the mount, and using a pry bar tried slightly shifting the mount back and forth, left and right, hoping that would allow the transmission to find its correct position and maybe stop the noise. After retightening the nuts, the noise was still there.

I could squeeze under again and get a photo and try posting it here in hopes someone has an idea of what's wrong and whether I can do a simple repair or even replace the mount.

Meanwhile, I'd be very grateful for any tips or suggestions on how to handle this.

 

If you're sure the noise is coming from that mount, put a jack under the trans tailhousing, & REMOVE the mount. Then let the engine idle & check for the buzz. If it's gone, install a new mount. If it's still there, put the original mount back & find the true source of the buzz.

I bet it's the catalytic converter. With the exhaust system cold (engine off), pound on the cat with the side of your fist.

 

I've decided to replace the transmission mount because I'm positive that is the source of the buzzing noise. I was under the pickup most of today trying to coax the mount out from between the transmission and the crossmember with no luck.

Before starting the job, I had referred to my Chilton manual and it says to lift the transmission slightly to allow the two studs to clear the crossmember. I jacked the automatic transmission as high as I could but still couldn't get the mount's studs to clear the holes in the crossmember.

Then I went back to the Chilton and it was then I realized I had been reading the Chilton under manual transmission. When I turned to automatic transmission (where I should have looked first) it says the transmission is to be supported with a jack while the crossmember is removed so that the mount can be removed.

This is turning out to be much more of a job than I had anticipated!

I'll probably go back to the effort on Monday and support the transmission while removing the crossmember. I certainly don't look forward to that effort.

I'd be very grateful for any advice on whether I am approaching the job right now.

 

I got the replacement of the transmission mount done yesterday, but although the buzzing seems a little less severe, its still there on idling.

I tried loosening the nuts on the two mount studs, driving forward a few feet and then reversing the same distance and re-tightening the nuts to neutralize any strain on the mount, but that didn't help.

The bolts that fasten the heat shield for the catalytic converters to both sides of the crossmember don't really tighten to "tight". Maybe it is supposed to be that way to allow the shields to move with expansion or to deaden sound.

I'll be back under the pickup tomorrow to see if I can do anything more.

I've bashed the catalytic converters with my fists but there is no rattling.

Any ideas, anyone?

 

I rolled under the pickup again this afternoon, blocks in front and back of the tires, parking brake on tight, and had my daughter start the engine and idle in forward and reverse while I listened for the buzz and levered here and there with a pry bar. The noise seems related to a kind of L-shaped steel hanger with elastomer inside that links the transmission mount to the exhaust line from the drivers side.

Can anyone tell me what this "hanger" is called? I'll probably take a trip down to my friendly local exhaust shop this week and see what they say.

 

A mechanic's stethoscope is cheap. I've seen them for less than $10.

 

Yes, I've thought of getting a stethoscope, but the noise is so loud it would probably burst an eardrum!

 

Those annoying buzzing sounds sound like something in a tin can?
i had an annoying buzzing sound, and it ended up being a couple of bb size pebbles in the cat converter heat shield. also could be some sediment/ pebbles beneath the tranny mount on the crossmember.
I had a ranger that thumped every time i took off. lots of lifting and prying while rocking the truck back and forth. ended up being dirt had found its way underneath the tranny mount between that and the crossmember. i took that apart, cleaned it, and voila! no damn more thumpin noise.
2 dealerships could'nt figure that noise out, but i sure did

 

I replaced the transmission mount, and in doing that had to remove the crossmember and didn't see any debris. The noise can get pretty violent if I lever near that other bracket that connects the transmission (via the transmission mount) to the exhaust pipe. Wish I could describe the bracket better.

 

A scanned photo of the brackets connecting the exhaust pipe beneath the transmission mount of the 1999 F-150 with manual transmission can be seen at https://www.f150online.com/galleries...cfm?gnum=10571

My transmission is automatic, and the bracket is only connected on the drivers side. It is as if the passenger side of the "tray-shaped" bracket in the photo has been removed, and there is only one clamp on the exhaust pipe.

This bracket is sandwiched between the transmission mount and the transmission. I don't see any cracks in the bracket and it is firmly attached at its other end to the exhaust pipe where it crosses over to join the pipe from the passenger side.

 

Could it possibly be that I am missing the passenger side of the bracket? Maybe there was exhaust work done on this pickup in the past and half of the bracket was left-off.

 

Get a stethoscope & use it. You'll be surprised. Just don't strike the probe against anything. Press it firmly against a part, then move it a SHORT distance, and listen again. Keep going until you find the spot where the buzz is loudest.

 

The noise was caused by a cracked exhaust and converter support that is sandwiched between the transmission and the transmission mount. Wish I had noticed that when I had the crossmember and the old transmission off! I put a photo of the support on the gallery section (only way I seem to be able to post photos here) at

https://www.f150online.com/galleries...cfm?gnum=10571

 

Once you upload a photo onto the web ANYWHERE (or find one already on the web), you can right-click it, click Properties, then triple-click the URL and hit CTRL+C to copy it. The paste it (CTRL+V) between [img] tags in your post and it'll appear. But you uploaded a thumbnail instead of the fullsize image:



For easy, free image hosting that provides the full text needed to post to BBSs like this one, I recommend SMO. That's where all my pics are.