727 Making Weird Noise

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Divenut

Divenut

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Hey Folks,

So the Duster started making an odd noise before I put it up to do the disc brake swap last year. The noise comes and goes sporadically and I final was able get it on video.

History:
1972 Duster 340
727 w/RMVB, No Low Band Apply, Hughes 35 series converter, cooler in front of radiator
Ran well, stout shifts but leaked.
Pulled the trans a year ago to replace the seals and torque converter. Ran well, stout shifts but leaked. Button it up and put it back in the car. The car ran great, better than ever, converter is tight enough to drive around town at low speeds, stout shifts, great acceleration.

After about 200+/- miles (Much of it "Spirited" driving LOL) I notice an occassional slight hydraulic humming sort of noise. Usually after higher RPM shifts. At first it would do it for a few seconds when I came to a stop, then in would stop. Then it got more frequent, often when idling at stops, then when cruising at lower RPMs after brisk acceleration. The transmission continues to shift firm and quickly, no slippage etc.

Pulled the pan to find a lot of what looked like clutch material covering the filter. Thinking the clogged filter was starving the pump, I thought that was the problem. Added fresh fluid and new filter. And again, it drives great, but makes the noise again. Sounds hydraulic, and does sporadically after transmission is hot and when idling down after higher RPM shifts.

Flushed the cooler and lines. No change.

Noise occurs in neutral and 1-2-3. Then stops when I accelerate again. Can't get it to do it when sitting still, so I haven't been able to get a listen from outside of the car.

Obviously the transmission is coming back out. Guessing the pump may be acting up (though it appeared to be in good shape when I replaced the seals, bushing and gaskets) Or maybe some of that debris found it's way into an the valvebody causing some blockage? Or the trans is just eating itself? But I'm wondering if anyone has encountered something similar?

Just really weird because it's so sporatic.

Here's the video, not the best quality, but you should be able to hear it pretty easily.



Be well,
Pat
 
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Converter starting to fail? It could also explain the debris in the pan. If you are pulling the trans it would be worth having a good converter shop cut it open and freshen it.
 
Thanks D55. The converter is new. So hopefully that's not the issue. I wonder if it would it more likely be the pump if the noise continues in neutral? That said, I'm not a transmission guy and I guess anything is possible.

Thanks again!
Pat
 
plymouth67 said:
Does it do it in reverse also?
Click to expand...

I recall hearing it for a few seconds when backing out of the garage last year. Hasn't happened since though. I will have to try getting it into reverse at a stop if I can. But it typically stops so fast upon stopping it may be difficult. Though I'm guess it would make the noise. No change in pitch when moving through N123.

Thanks much!
 
Put the shifter in Drive or third. Pull the cable out of the hole at the trans shift lever. The arm should not move at all. Then shift the arm by hand into park then count the clicks or detents and put it in drive or third.See if the shifter cable will slip right into the arm without moving the arm.
 
SGBARRACUDA said:
Put the shifter in Drive or third. Pull the cable out of the hole at the trans shift lever. The arm should not move at all. Then shift the arm by hand into park then count the clicks or detents and put it in drive or third.See if the shifter cable will slip right into the arm without moving the arm.
Click to expand...

Got it. I'll give it a try next time I work on the car. Thanks again man.

Pat
 
When you put the trans in did it have a lot of gap between the flex plate and the pads for the converter bolts? I have seen people try to put spacers in between converter and flex plate instead of just pulling the converter forward a bit to close the gap. If you put spacers the converter is putting pressure on the pump gears. Kinda hard to explain hopefully you understand what I'm trying to say.
 
Not a detent ball vibration in the valve body , didn’t they loose a steel ball for a fiber one ? Might be on newer electronic ones ?
 
plymouth67 said:
When you put the trans in did it have a lot of gap between the flex plate and the pads for the converter bolts? I have seen people try to put spacers in between converter and flex plate instead of just pulling the converter forward a bit to close the gap. If you put spacers the converter is putting pressure on the pump gears. Kinda hard to explain hopefully you understand what I'm trying to say.
Click to expand...

Nope, everything aligned right up. No spacers. Stuck the 727 back in, bolted everything up. Pretty typical install. Other then me being a lot older than I was last time I did one. Swear them transmissions gain weight! Lol!
 
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Divenut said:
Nope, everything aligned right up. No spacers. Stuck the 727 back in, bolted everything up. Pretty typical install. Other the me being a lot older than I was last time I did one. Swear them transmissions gain weight! Lol!
Click to expand...
Hell yes they do!!!
 
A lot of times, humming or buzzing is a fluid transfer problem. Low fluid or clogged filter, but you seem to have ruled that out. Are you running a paper filter ot the brass screen? Mopar always recommended the brass screen for HP transmissions. Could be that the paper filter is too much of a restriction. Just a thought. Would be cheap enough to try if you're running the paper filter.
 
Does the noise change when it shifts gears? Or with road speed. Have u checked ur power steering fluid level. Try turning the wheel lock to lock and see if the noise changes. The pump could be getting weak. Of ourselves this doesn’t apply if u have manual steering. Kim
 
oldkimmer said:
Does the noise change when it shifts gears? Or with road speed. Have u checked ur power steering fluid level. Try turning the wheel lock to lock and see if the noise changes. The pump could be getting weak. Of ourselves this doesn’t apply if u have manual steering. Kim
Click to expand...

Thanks for the input Kimmer. No gear N123 related change in pitch or tone. It does soften and/or stop when I bring up the RPMs. (Though the exhaust may be masking it) Then resumes when I slow and/or get off it. Just kinda starts humming softly and gets louder going up the pitch in the video. Other than the noise the transmission is operating normally. It's the darnedest thing.

No PS, manual everything.

Be well,
Pat
 
oldkimmer said:
Could be the planetary gear train. Kim
Click to expand...

Thanks again Kimmer. I'm not very knowledgeable with transmissions other the basic stuff. Would the gear train make the noise but still function normally? Guessing they wear out over time, anything visible I should look for? I'm thinking about pulling the 727 apart when I take it out. If for no other reason than to get a better understanding of their inner workings. Guess it'll need to come apart anyway if I bring it someplace for a bench build. So what the heck!

Take care,
Pat
 
Realized I never closed the loop on this one. Turns out the noise is coming from a bad passenger side wheel bearing that would make the noise when it got hot. Will be replacing the bearings in the next month or so. Glad I didn't pop for a new transmission!!!

Thanks again for the assistance while I was trouble shooting!
 
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