My ’84 K20 Suburban with a diesel (was 6.2 now 6.5 non-turbo) is making some racket above and beyond the normal diesel noise. In the last few days I am hearing a phit, phit, phit (kind of like a loud vacuum leak that cycles twice a second) from the bell housing area. It only occurs when the tranny is in gear (O/D, D, 2, 1 and R). If the t-case (NP208) is in neutral and the tranny is in gear, there is no noise. The noise can’t be heard in the engine compartment (too much clatter). I can only hear it at an idle from under the rig, although I suspect it is present at higher rpms, but can’t be heard over the clatter. I pulled off the inspection plate on the bottom of the bell housing and inspected the flex plate, I can’t see any problems (no cracks visible). I risked my life and got under it while it was idling in gear with the inspection cover off (e-brake on, wheels blocked and the brake pedal wedged with a block to the seat). It sure sounds like the torque converter is the source of the sound, but hard to say for 100% sure. The tranny is shifting fine, no symptoms other than this new noise. The tranny was rebuilt (new clutch pack) one year and 10k miles ago and the fluid level is good as well as clean and not burned. Anyone have any idea what the source of the noise is?

Thanks all. (Yes I did use the search function first).

Cracked flex plate, I bet.

Is it constant or does it come and go? I had a TC in a 700R4 do something similar and sometimes it shifted fine while it was clacking but in short order it got to the point where whatever it was doing was keeping the truck from even shifting out of first until everything cooled back off.

Originally posted by Kevin108
Is it constant or does it come and go? I had a TC in a 700R4 do something similar and sometimes it shifted fine while it was clacking but in short order it got to the point where whatever it was doing was keeping the truck from even shifting out of first until everything cooled back off.

Yes it is constant. I confirmed the noise is there upto what I'd guess to be 2000 rpm. Too much clatter after that to hear anything over the engine. No shift problems whatsoever. The torque converter is new (one year and 10k miles) as well. Thanks for the suggestions. Any other help is welcomed.

The noise my cracked flex plate made went away around 1800 rpm in my truck.

Ditch the piece of !@#$ and get a 4L80E. You would be the man

Originally posted by LAME
The noise my cracked flex plate made went away around 1800 rpm in my truck.

yeah i know what ya mean i had the prob with a van and the thing was cracked all away around the bolts to the crank. I'll bet with a good tug that thing would of poped off with out undoing the cap screws. what the hell causes them to crack :confused:

Simple thing would be a missing or loose torque convertor bolt. Mine in my 85 Jimmy was making a terrible racket from that same area, when I removed the tranny last week, one of my TC bolts was gone and one of the others was loose. :eek:

Thanks to all for the help. This board and the local mechanics I've spoken with tend to agree it is likely a cracked flex plate. I will check the T/C bolts prior to yanking the tranny just in case (boy would that be nice). Will post back with the results once the wrenching is done (maybe a while).

Originally posted by ToyFord
Thanks to all for the help. This board and the local mechanics I've spoken with tend to agree it is likely a cracked flex plate. I will check the T/C bolts prior to yanking the tranny just in case (boy would that be nice). Will post back with the results once the wrenching is done (maybe a while).

When I changed flexplates (it cracked 1 week after I installed a new tranny) I unbolted the x-member, the shafts, lines t-case linkage, TC and bell housing, I supported the tranny with a jacked, and moved the whole assembly back enough to get my hand up to the bolts. Un bolt, slide flex plate out, install new one, reassemble. Took me 2 hours w/o air tools, and on a cold garge floor:)

Thanks for the advise. Are you saying the bell housing can be removed from the tyranny and slid off the input shaft w/ the T/C after the tranny/t-case is slid back on the jack? Also how much AFT comes out of the lines after disconnecting from the case (like every drop that is in the tranny cooler coil)?

You pull off the dust sheild and you can get to the TC bolts (15mm or 9/16th..one of the two). The bellhousing doesn't come off the tranny. If your X-member is below the frame on your rig, put a jack under the t-case and lower the unit down, this will tip the engine and tranny down. You do this because you can get to the top two bellhousing bolts with a long extension and a u-joint adaptor, instead of crawling on top of the engine and doing it with a flat wrench. One you have the bolts out of the bellhousing, jack the ass end of the tranny t-case up a bit, until you can pull the whole until back. Sometimes 700R4's like to fuse themselves to the alignment pins, so you might have to do a little prying to get it to break loose. It would be best to have a couple jacks under it when you slide it back the couple inches. Once you do that you will see the 6 bolts holding the flexplate on the crank. Pull those out, and the plate should pop out. Reverse the to assemble. Make sure you use red locktite (ask parts store to be sure) on the flex plate bolts and TC bolts. You might or might not have to remove the lines, depending on how they are routed. I did on mine because the newer (4L60E's) have quick dissconnect connections. I don't recall if I even lost any fluid. Also make sure you have ALL wires out of the way so they don't get pinched between the tranny and motor. Guaranteed short if you do pinch wires. Let me know if you have any more questions:)

Thanks for the help. Will be a few weeks 'til I get to it yet.