Topic: rat tat tat noise, right rear
in Forum: C3 Fuel, Emission Control, and Exhaust Systems
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Oak Creek, WI - USA
Joined: 5/21/2008
Posts: 1965
Vette(s): 1981 Great White Shark. Red Interior, 350/190 hp. PS, PB (SS), A/C CC, T-Tops. Served three years in Active Duty Army, then Retired Air Force after 34 years! Badger State Vettes Car Club. 175,000 Original miles!! Now own a 1998 C-5!
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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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
Former Member
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Oak Creek, WI - USA
Joined: 5/21/2008
Posts: 1965
Vette(s): 1981 Great White Shark. Red Interior, 350/190 hp. PS, PB (SS), A/C CC, T-Tops. Served three years in Active Duty Army, then Retired Air Force after 34 years! Badger State Vettes Car Club. 175,000 Original miles!! Now own a 1998 C-5!
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
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
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
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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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
in Forum: C3 Fuel, Emission Control, and Exhaust Systems
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