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Topic: rat tat tat noise, right rear

in Forum: C3 Fuel, Emission Control, and Exhaust Systems

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Re: rat tat tat noise, right rear (17/27)
5/12/14 3:31pm

JonsVette
Former Member
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Eldridge, IA - USA

Vette(s):
Have owned a 1966 Convertible, 1974 Convertible, 1978 Coupe, 1988 35th Anniversary, 1997 Coupe. All have gone on to new owners.

Joined: 4/26/2014
Posts: 28

Thank for the response. I dont have caliper covers. I had pinpointed the noise at the rear area of fuel lines. After meeting up with a couple of mechanic buddies this past Saturday, we all came to the conclusion that air maybe getting into the fuel line somehow. The noise and the pulsation action felt on the line is equal to getting air trapped in a water line. Anyway, since this past Sunday was a "no work in the garage day" I will tackle the issue this week. Any other ideas are appreciated. If I am off my rocker on this, let me know ! It is one of those issues that doesnt happen often enough to generate any history from someone. Thanks again. Jon

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Re: rat tat tat noise, right rear (18/27)
5/12/14 4:14pm

dskopp
Limited Member
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Oak Creek, WI - USA

Vette(s):
1981 Great White Shark. Red Interior, 350/190hp. PS, PB (SS), A/C CC, T-Tops, Going to remain as Stock as possible. Served three years in Active Duty Army, then Retired Air Force after 34 years! Badger State Vetts Car Club. 175,000 Original miles!!

Joined: 5/21/2008
Posts: 1958

JonsVette said: Thank for the response. I dont have caliper covers. I had pinpointed the noise at the rear area of fuel lines. After meeting up with a couple of mechanic buddies this past Saturday, we all came to the conclusion that air maybe getting into the fuel line somehow. The noise and the pulsation action felt on the line is equal to getting air trapped in a water line. Anyway, since this past Sunday was a "no work in the garage day" I will tackle the issue this week. Any other ideas are appreciated. If I am off my rocker on this, let me know ! It is one of those issues that doesnt happen often enough to generate any history from someone. Thanks again. Jon

Ya, Jon I got one of those "mystery" problems also. Mine is that the drivers window does not want to go up and down sometimes. I have checked the window switch and I have followed all the wires through the door and to the motor but I cannot find a problem. I have power at the switch and also checked for continuity. JOEL!!! HELP!!

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Re: rat tat tat noise, right rear (19/27)
5/12/14 7:05pm

rraider1
Former Member
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Woodland, WA - USA

Vette(s):
1977 T-Top,350,Auto Black Ruby Pearl,Steeroids R&P conversion

Joined: 10/14/2003
Posts: 1165

possibly the grounding of the motor itself?

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Re: rat tat tat noise, right rear (20/27)
5/12/14 7:34pm

Hi, electrical issues are a pain in the arss. Anyway, I would agree with the other poster about the ground issue with the window motor. Maybe get a replacement motor and trial run it and see if the issue develops again. There maybe something internally with the motor that acts up under certain conditions. Good luck. Jon

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Re: rat tat tat noise, right rear (21/27)
5/12/14 8:00pm

rraider1 said:

possibly the grounding of the motor itself?

Seems to me that if it was a moto grounding problem, it would either work or not work!! I can be sitting still and try the window switch and it will not work. Then I can wait for a couple of minutes and it will work!!! W@TF?????

Dan da Man

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Re: rat tat tat noise, right rear (22/27)
5/13/14 6:22am

Assuming you have tested the switch for weak contacts and checked the wiring for any breaks, then it would default to the motor assembly. I have seen motors with "weak spots" or in other words, internally something is going out or has a weakness. I have even seen a new replacement motor work fine on bench testing then upon installation into the door cavity and after hooking up the regulator and window it went weak and failed. I figured it was the weight and the force of resistance after hooking up the motor. I installed another replacement and it worked fine and sent the faulty motor in for warranty. Anyway,I would still just opt to put a new motor in and see what happens. Process of elimination. Of course it could be the dreaded electrical gremlins. Jon

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Re: rat tat tat noise, right rear (23/27)
5/13/14 12:19pm

Ya, replacement of the motor is the next thing for me to do....after the gathering. Did you fix yopur rata-tat-tat?? I see you are on the site now!!

Dan

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Re: rat tat tat noise, right rear (24/27)
5/13/14 7:01pm

Hi, I started last night by working on the rubber lines off the fuel pump. Next will be to fire it up and see if the noise is gone. If not, then onto the tank area where I will replace the rubber lines there. (I see there is some kind of bracket on the feed line right off the sending unit of the tank. Not sure how to remove that to access the rubber line if I need to. Any suggestions?) So will see what happens. ....All the females of the house are leaving Friday night till Sunday afternoon so it will be Steely Dan on the garage stereo and lots of Vette tinker time ! Yes, I joined the registry as a standard member and will probably go life member sometime soon, since the C3 is my favorite Vette generation. (But that 66 convertible I had was nice too.) Jon

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Re: rat tat tat noise, right rear (25/27)
5/18/14 11:07am

Ok, here is the rat tat tat update. After having Steely Dans' album finish up and somewhere in the middle of Bob Seger, my buddy and I came to the conclusion that air is definitely getting trapped in the fuel line back by the tank. Instead of spending a lot of time (which we had wasted already on beverages and song) I mentioned that maybe plugging the return line off the fuel pump could address the issue. So, on Sat. that is what I did. After driving the 78 almost 50 miles in various speed zones, the rat tat tat noise has gone away. Even though I havent repaired the cause, at least the cause has been determined. So the next step is to replace all the rubber connections on the fuel lines and tank and hook it back up to see what happens. But for now, I am keeping the line plugged because it is too nice out to work on the car, I need to go for a couple of drives. Anyway, there you have it, if this happens to your vehicle, I hope this thread helps in your diagnosing the issue. Jon

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Re: rat tat tat noise, right rear (26/27)
5/18/14 9:21pm

dwright
Standard Member
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Victor, NY - USA

Vette(s):
2004 Commemorative Edition Coupe, Auto w/HUD. 13K miles in 2015. Sold 1982 Red Coupe

Joined: 7/12/2004
Posts: 6836

Jon,

When you replaced the sending unit and sock did it look OK inside the tank?

Was the bladder OK?

Did it sound any different with the new parts?

Does the sound go away when the rpms go up and you are not moving?

Did you try it with a full tank yet?

Does it idle smooth and still make the sound?

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Re: rat tat tat noise, right rear (27/27)
5/19/14 8:10pm

Hi, to answer your questions......

When you replaced the sending unit and sock did it look OK inside the tank? I didnt get to that part yet as I only plugged the return line. I did purchase a sending unit though as I was heading that direction.

Was the bladder OK? From what I can see through the fill hole it appears clean but again I didnt remove the sending unit yet.

Did it sound any different with the new parts? Not to that point yet.

Does the sound go away when the rpms go up and you are not moving? The sound did disappear on high rpm, 1500-2500 but reappeared at curb idle.

Did you try it with a full tank yet? I did fill the tank prior to disconnecting the return line and the problem remained.

Does it idle smooth and still make the sound? There was never any idle or performance issues with the rpms. The car would idle fine even with the noise going on.

Anyway, so far that is all I got done. I drove the Vette a bunch of miles on both Sat & Sunday with no noise reappearing.

I seen where you had some brake issues returning home. I would bet the master cylinder failed. Anyway, fine piece of driving !

Thanks Jon

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