Bronco II "weird" Trans Noise

[BIICory]

Hey there guys, new to the ranger station here. Broncoii.org has gotten pretty dead :sad: so i figured id move over to a new site!

SO.. Ive got an 84 BII. 76000 original miles on a 2.8 and c5 trans. Durasparked. Truck runs great but has recently developed some ODD noise from underneath. Thinking its the trans. Ima be as detailed as i can.

First up, fluid level is fine, not too dark, and smells fresh. When i am in park, no noise comes from anywhere. But when in drive under load, between 2500-3200 rpm there is an almost "burp sounding grinding noise" that is of medium loudness. Thing is... The trans shifts GREAT with absolutely no hesitation or slipping. The noise is audibly different when it changes gear. then it just seemingly goes away. Its only under about half throttle too.

Bit stumped as there are no driveablity issues. Any ideas Guys? I apprecciate it

CB

 

[unoleisu]

I heard that "burp sounding grinding noise" that is of medium loudness, in mine the other day. Pretty sure it was the awesome cilli I had the night before. Didn't smell fresh, though.

 

[CHKNFKR]

Not sure about others on here, but burp sounding grinding noise isn't all that descriptive to me. Is there any shake or shimmy that accompanies this noise? The only sound i can think of that could be described as such is a driveline vibration caused by an imbalance in the driveline or a failed ujoint. Usually that'll shake the snot out of you though....

 

[BIICory]

No see thats the weird thing. No shimmy or shake or vibration. Shifting wonderfully. Strangest thing is it ONLY happens under about half throttle. not full or little

 

[adsm08]

I'm going to need a real description before I can help on this one. Something I can understand.

 

[BIICory]

I'm going to need a real description before I can help on this one. Something I can understand.

What would make myself more clear? Thanks for your interest in my thread

 

[adsm08]

Put the truck in front of me.

 

[BIICory]

Put the truck in front of me.

.... I can describe it again in hopes of more legit responses than this..


Low pitch grinding/fast deep vibration sound coming from seemingly the transmission area of the truck. ONLY under half throttle. No shimmy or vibration noted. Noise is still present with 4x4 on. Changes pitch when gear is shifted. No noise whatsoever in park or N. However i have no way to be sure its the trans at all.

Thats about good as i can do unless you have a real suggestion as to making my description better..

 

[4x4junkie]

Can you somehow record the sound with decent fidelity and upload it somewhere as a .WAV or .MP3 file maybe?

I'm tempted to say it's not the trans at all if there's absolutely no symptom other than a vibration noise (and all fluids look good)... How are your motor and trans mounts?

 

[PetesPonies]

Have you been under neath to check obvious things?? Anything loose? Mounts? vibrations from from catalytic converter shield?? Driveshaft?

 

[BIICory]

Ill see about recording the sound in the next few days. But there is no cat anymore, driveshaft seems completely solid. Mounts are good and solid. and yes all fluid is good. The only indication it is trans related is because of the noise change when it shifts gear from higher to lower pitch. Ill see about recording it

 

[gribly]

I vote something is loose in the exhaust. Also, no RBV is exempt from being required to run a cat unless it's never taken on a public road, and even then it's ignorant. Go put on some sort of exhaust that includes a cat (c'mon, they're like $50 and modern ones aren't restrictive) and I bet the rattle goes away.

 

[BIICory]

Well the exhaust is new as of last year. From header back. No cat because i didnt have the money at the time, and honestly it isnt a big deal on an almost 30 year old truck... Especially because itd have to be a good one so the salt in michigan didnt eat it alive. I mean, its possible that its something in the exhaust. i could always disconnect it and see... maybe i will when it stops snowing like a mad fool

 

[BIICory]

But.... if it was exhaust related... it wouldnt only be doing it in drive. it would be in neutral, and park also..

 

[gribly]

Not necessarily. The exhaust will resonate differently depending on rpm and load. Crawl under and grab ahold of different things and shake them, figure out which part is rattling. If it was the tranny or drivetrain making that much noise, I'd think you feel it through the seat going down the road.

 

[Nathan123]

Could it be the driveshaft clicking? Mine did it only under medium accelerations, not while cruising or idling around. I doubt that a u-joint style shaft would make a clicking without vibrations, so this is only an answer if you have a cv style shaft.

 

[PetesPonies]

Vibrations are difficult to find. The factor that might cause the vibration can be specific to many things, rpms, vehicle speed, gear reductions, harmonics etc. So don't rule out an exhaust noise because you can't reproduce it at idle.

As for needing a cat for the sake of mankind . . . jeesh

 

[unoleisu]

It might possibly be the Torque Converter. Inside the TC are empeller blades that are often rivited in place, the others are spot welded. They have been known to come loose, and gradually create sounds like you're describing. When they finally come loose, it trashes the TC, and sends metal shavings through your tranny.
Before you panic about that, do as sudgested, and crawl around under the truck trying to find loose stuff. It took me awhile to finaly descover my muffler was actually rusted out on the intake side. That, after welding the crap out of the heat shield on my Cat, that was also loose and rattly. (I only heard the rattle from the muffler occasionaly, on acceleration).

 

[unoleisu]

Save the children of the future from global warming, use a catelytic converter!!!
oh, sorry, global warming already started. never mind.

 

[BIICory]

SO i was underneath earlier and shaking/pounding like mad. Nothing seems loose, vibrating. I grabbed the driveshaft and it doesnt budge at all. it could possibly be the torque converter? i may change my tranny and torque conv fluid soon just to see if that changes anything. But its just nothing violent. Just noise. Not a vibration at all. SO maybe it is exhaust related. How does one troubleshoot though?