Trans occasionally thunks

Nixon1 · 05-09-2004, 11:07 PM

I know what the instant reply is going to be...check trans mounts. Yes, I beat the hell out of the car. But if I nail the gas from a stop, there is no thump or jerk. This thunk is different. I can't physically feel anything, but I hear a dull metallic whack when I'm idling and step on the gas to go sometimes. Feels like something INSIDE the transmission is thunking. The trans has over 150,000 miles on it and slips badly. It's loaded with 2 bottles of Lucas Slipfix, the line pressure is bumped very high, and the fluid has a tendency to aerate, which I suspect is from being overfilled.

Could the sound I'm hearing actually be coming from INSIDE the transmission because it's so totally shot? I know I can hear it thunk when it grabs overdrive solidly (on the throttle or completely off the throttle). Cruising, it bounces into OD. That is, it engages, slips, and then reengages every time.

Capri306 · 05-09-2004, 11:16 PM

It could very well be happening inside the transmission; I do not doubt it for a second. One possibility is you're hearing a hydraulic thumping, just the fluid smacking into components. Kinda like a thump tank off of a moonshine still.

The other is that it's just some play in the driveline somewhere, but I'd tag the trans as the most likely source. Either way, with the amount of work you've put into it to keep it functioning, I'd venture to say you're going to need a new/rebuilt AOD within a short amount of time.

stang_racer20 · 05-10-2004, 12:45 AM

Check your u-joints as well. But I agree it sounds like the trans is going.

Nixon1 · 05-10-2004, 09:00 AM

Alright, thanks guys. Oddly enough, that's good news. I'd much rather the problem be the trasmission itself, which I KNOW is totally shot, rather than a problem somewhere else. I WILL check my u-joints though...theyre fairly new, but I have bad bad vibrations on the interstate. At the moment I'm attributing that to a set of bent rims and a lack of rebalancing lately though.

crazypete · 05-10-2004, 11:18 AM

Ok, obvious answer!

Check the tv cable and make sure the pressure isnt too high. Thunk sounds like something is being overpressured.

Now the innards of an AOD are still fresh in my mind and I cannot think of anything that would thunk immediatley off-idle. Immediatley off idle is when the converter starts the rotating assembly going. Perhaps the support for the TC is broken, I've had that happen...it's the outermost "input shaft" (it cannot rotate, it just suports the tc) on the front of the trans. That might make a thunk as the broken end rotates past the broken collar. Just a thought.

There is another thought in my mind. There is a little c-shaped spring wedged about halfway down....maybe the second cluster.... between the cluster castle teeth on the very outside and the body of the aod. It's an anti-rattle clip. Now, when you first start moving and the clip isnt there (fell out and is at the bottom of the case), the whole rotating assembly would rotate about 15 degrees and probably make a good clunking sound as it hit the tab thats there...Nothing you can do about that right now and probably nothing to worry about either. Just an aesthetic difference.

Hope this helps!

Pete

05-09-2004, 11:07 PM	#1
Nixon1 Registered Member Join Date: Jan 2003 Location: Palm Bay, FL Posts: 432	Trans occasionally thunks I know what the instant reply is going to be...check trans mounts. Yes, I beat the hell out of the car. But if I nail the gas from a stop, there is no thump or jerk. This thunk is different. I can't physically feel anything, but I hear a dull metallic whack when I'm idling and step on the gas to go sometimes. Feels like something INSIDE the transmission is thunking. The trans has over 150,000 miles on it and slips badly. It's loaded with 2 bottles of Lucas Slipfix, the line pressure is bumped very high, and the fluid has a tendency to aerate, which I suspect is from being overfilled. Could the sound I'm hearing actually be coming from INSIDE the transmission because it's so totally shot? I know I can hear it thunk when it grabs overdrive solidly (on the throttle or completely off the throttle). Cruising, it bounces into OD. That is, it engages, slips, and then reengages every time. __________________ '91 Mustang GT 5.0 AOD Daily Driver Current stats: NEW 302 short block, E-303 cam (@.050, 220/220, .498/.498, 110 degrees), 1.6 roller rockers, Performer RPM heads (aluminum, 1.9/1.6, 60cc chambers), Cobra intake, Granatelli 75mm MAF, Billet AFPR, Equal-Length Shorty Headers, Off-Road X Pipe, Flowmasters, 4.10 POSI 13.73 at 103.8, ~2.2 60'

05-09-2004, 11:16 PM	#2
Capri306 Moderator Join Date: Sep 1998 Location: Grand Rapids, Michigan, USA Posts: 1,001	It could very well be happening inside the transmission; I do not doubt it for a second. One possibility is you're hearing a hydraulic thumping, just the fluid smacking into components. Kinda like a thump tank off of a moonshine still. The other is that it's just some play in the driveline somewhere, but I'd tag the trans as the most likely source. Either way, with the amount of work you've put into it to keep it functioning, I'd venture to say you're going to need a new/rebuilt AOD within a short amount of time. __________________ Capri306, Moderator The Mustang Works Online 1979 Mercury Capri 1987 5.0L Mustang LX Notchback 1993 5.8L Eddie Bauer Bronco

05-10-2004, 12:45 AM	#3
stang_racer20 Registered Member Join Date: Jun 2003 Location: Wisconsin Posts: 348	Check your u-joints as well. But I agree it sounds like the trans is going. __________________ 92 Mustang GT, 347 Stroker(Forged Steel Crank/Rods-Balanced, Forged Aluminum Dished Pistons), Trick Flow Track Heat Intake, Trick Flow Twisted Wedge Heads w/ Stage 3 port/polish, 80mm C&L MAF, FMS 30# Inj., BBK AFPR, Trick Flow Stage 2 Cam, Trick Flow 1.6R Rockers, BBK E.L. Headers, Flowmaster Cat-Back, MAC CAI, FMS Pulleys, Griffin Alum. Radiator, MSD Pro-Billet Distributor; AOD, Dynamic 3300 Lockup Converter, B & M Super Cooler, B&M Ratchet Shifter; 3:73 gears.

05-10-2004, 09:00 AM	#4
Nixon1 Registered Member Join Date: Jan 2003 Location: Palm Bay, FL Posts: 432	Alright, thanks guys. Oddly enough, that's good news. I'd much rather the problem be the trasmission itself, which I KNOW is totally shot, rather than a problem somewhere else. I WILL check my u-joints though...theyre fairly new, but I have bad bad vibrations on the interstate. At the moment I'm attributing that to a set of bent rims and a lack of rebalancing lately though. __________________ '91 Mustang GT 5.0 AOD Daily Driver Current stats: NEW 302 short block, E-303 cam (@.050, 220/220, .498/.498, 110 degrees), 1.6 roller rockers, Performer RPM heads (aluminum, 1.9/1.6, 60cc chambers), Cobra intake, Granatelli 75mm MAF, Billet AFPR, Equal-Length Shorty Headers, Off-Road X Pipe, Flowmasters, 4.10 POSI 13.73 at 103.8, ~2.2 60'

05-10-2004, 11:18 AM	#5
crazypete Registered Member Join Date: Sep 2002 Location: Boston Posts: 592	Ok, obvious answer! Check the tv cable and make sure the pressure isnt too high. Thunk sounds like something is being overpressured. Now the innards of an AOD are still fresh in my mind and I cannot think of anything that would thunk immediatley off-idle. Immediatley off idle is when the converter starts the rotating assembly going. Perhaps the support for the TC is broken, I've had that happen...it's the outermost "input shaft" (it cannot rotate, it just suports the tc) on the front of the trans. That might make a thunk as the broken end rotates past the broken collar. Just a thought. There is another thought in my mind. There is a little c-shaped spring wedged about halfway down....maybe the second cluster.... between the cluster castle teeth on the very outside and the body of the aod. It's an anti-rattle clip. Now, when you first start moving and the clip isnt there (fell out and is at the bottom of the case), the whole rotating assembly would rotate about 15 degrees and probably make a good clunking sound as it hit the tab thats there...Nothing you can do about that right now and probably nothing to worry about either. Just an aesthetic difference. Hope this helps! Pete __________________ 91 GT Carb conversion, holley 600 double pumper, edelbrock performer intake, FMS "C" drop springs, march 1000 underdrive pullies, crane 1.7 roller rockers, GT-40P headers, bassani x pipe, american thunder catback, FMS 4.56's, msd aL6, trunkmount battery, A/C eliminator kit, 3000 stall tci streetfighter, AOD with transgo kit, A+ servo, 300M hardened lockup shaft, kevlar bands and 28,000 gvw trans cooler, 3 core radiator, 300 lbs stripped with a full interior

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