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4/27/14 1:07pm - Original Message: 'rat tat tat noise, right rear'
JonsVette
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Eldridge, IA - USA

Vette(s):
Have owned a 1966 Convertible, 1974 Convertible, 1988 35th Anniversary, 1997 Coupe. All have gone on to new owners. Presently own a 1978 white coupe with less then 10k original miles. It is a special ordered. L82 4 spd. with 11 options.

Joined: 4/26/2014
Posts: 27
Hello to all, here is my first post for help. I posted in the fuel section because I am leaning toward the fuel pump being the source. Anyway,  I have bought a low mile 78 Coupe. After filling the tank up and driving it about 150 miles home, there was no issue except typical anti freeze drips from the hose edges etc....The next morning, after some clamp tightening and what not, I took it out for a spin and after drive 10 miles, returned home. As I was pulling into the garage, low RPM, I heard a rat tat tat noise from the right rear. I did not hear this as I was driving the speed limits. At idle, in the garage, the noise continued. So, I blocked the car and got out to inspect. I narrowed it down to the right rear wheel area. As the noise continued, I banged on the catalytic converter (thinking something had broken loose inside the converter) but it didnt change the sound. Baffled, I put my fingers on the fuel lines that sit on top of the frame in the right wheel well. The pulsation of the rat tat tat sound could be felt. So I proceeded to take the car out for another spin to trouble shoot this. Again at high RPM, I didnt hear the noise. Upon finding a flat stretch of road, I pushed the clutch in and let the engine idle down and I could hear the rat tat tat noise again. I shut the engine off and coasted down the road. No rat tat tat noise. So,  and Thanks for bearing with me, I am leaning toward the fuel pump being the culprit. If I am off base, please input your thoughts. I really appreciate it. Jon  

|UPDATED|4/27/2014 11:07:45 AM (AZT)|/UPDATED|


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4/27/14 11:52am - Reply: 'Re: rat tat tat noise, right rear'
Dejablu Lifetime Member
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Wichita, KS - USA

Vette(s):
2005 Daytona Sunset Orange Coupe ----------- Sold 1974 T-top, 4 spd to BillKS

Joined: 11/10/2003
Posts: 6834
Jon, you might check your exhaust pipe and muffler for a loose clamp or baffle in the muffler.  I had that happen to mine and had a rattle like you describe.  Good luck.
 
Larry


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4/27/14 1:16pm - Reply: 'Re: rat tat tat noise, right rear'
JonsVette
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Eldridge, IA - USA

Vette(s):
Have owned a 1966 Convertible, 1974 Convertible, 1988 35th Anniversary, 1997 Coupe. All have gone on to new owners. Presently own a 1978 white coupe with less then 10k original miles. It is a special ordered. L82 4 spd. with 11 options.

Joined: 4/26/2014
Posts: 27

Larry, I appreciate the response. I had checked all exhaust connections and nothing found. If you can imagine taking a hammer and hitting a 1 inch steel pipe, that is what the sound is similar to. A constant rapping, or rat tat tat, that doesnt stop unless I shut off the engine. When the engine is off and the clutch is in, there is no noise. So I ruled out rear end issues and parking brake hang ups etc.... I first thought I had lost a valve but the drive train/valve train is solid and quiet. When the noise happens, I can feel the pulse of the "tat tats" on the fuel lines laying on top of the rear frame where it arches over the rear axle area. My assumption is that the fuel pump may be failing inside. Just not 100 percent on that theory. It drives me nuts at a stop as you can hear it loud and clear. As soon as the rpms go up, the sound disappears or at least goes faint and absorbs itself within the roar of the exhaust and road noise. Jon 



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4/27/14 1:46pm - Reply: 'Re: rat tat tat noise, right rear'
johnu
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Eagan, MN - USA

Vette(s):
1981 Corvette Two-Tone Claret color, 4 spd, C7 Vert

Joined: 5/23/2007
Posts: 507
What does it sound like up on the lower right side of the engine block where the fuel pump is?  The rat-tat-tat could be the short rod that drives the pump.  I replaced my pump last summer.  Mine was spraying gas out the vent hole....removal-replacement was not the most fun I've had.


|UPDATED|4/27/2014 11:46:45 AM (AZT)|/UPDATED|


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4/27/14 2:03pm - Reply: 'Re: rat tat tat noise, right rear'
JonsVette
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Eldridge, IA - USA

Vette(s):
Have owned a 1966 Convertible, 1974 Convertible, 1988 35th Anniversary, 1997 Coupe. All have gone on to new owners. Presently own a 1978 white coupe with less then 10k original miles. It is a special ordered. L82 4 spd. with 11 options.

Joined: 4/26/2014
Posts: 27
Thanks for the response. When checking it out, it was louder on the back end of the car. My first thought after I felt the fuel lines was the same - the fuel pump was giving it up - and since the pump is not in a great spot, I didnt get a chance to put a hand on the housing. But I am certain I felt the percussion of the tat tat on those fuel lines, or something was knocking against the lines somewhere on the frame bottom. I did look from the top side to see if he pump mounting bolts were loose or coming loose but all was tight against the block. Ugh. I will try to troubleshoot it more. Thanks. Jon

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4/27/14 6:02pm - Reply: 'Re: rat tat tat noise, right rear'
dyoes
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Zachary, LA - USA

Vette(s):
1974 L-48 Auto. Just your basic Vette. GM crate motor w/vortec heads and intake. Crane cam. Scorpion rockers, Edelbrock carb. Lots of parts still in boxes... :(

Joined: 1/27/2013
Posts: 201
Take a long piece of metal (crowbar or similar) and rest it on the fuel pump, then to your ear.  I doubt the fuel pump internals are making that much of a noise, but it may be the pump pushrod that's driven by the engine cam.  If you need a new fuel pump, PM me...  I have a brand new stock Corvette pump (with the built in vapor return) that I'll make you a hell of a deal on. 

I bought an Edelbrock pump and was convinced it wasn't working so I bought another stock one.  Turns out you have to have enough fuel in the tank for ANY fuel pump to work, and once I put enough gas in the tank the Edelbrock pump worked fine.  Embarrassed




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4/27/14 6:36pm - Reply: 'Re: rat tat tat noise, right rear'
JonsVette
Former Member
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Eldridge, IA - USA

Vette(s):
Have owned a 1966 Convertible, 1974 Convertible, 1988 35th Anniversary, 1997 Coupe. All have gone on to new owners. Presently own a 1978 white coupe with less then 10k original miles. It is a special ordered. L82 4 spd. with 11 options.

Joined: 4/26/2014
Posts: 27
Thanks for the reply. I actually was trying to find my Texas screwdriver (about 3ft long) to do just what you said, put it against the pump, but I will be damn if I can find it. (its hard to lose) I appreciate the offer and will contact you about the fuel pump when I get a chance to find that screwdriver and then fire up the Vette and do further diagnosis. I guess when I am thinking the internals are failing- it also means the fuel pump rod maybe part of that equation as well. I dunno. Been working on cars a long time, never came across this scenerio before. Jon  

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4/28/14 12:03pm - Reply: 'Re: rat tat tat noise, right rear'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19454
I'd find it hard to believe a fuel pump noise would travel all the way back to the rear of the car.....the pump is connected to the fuel lines with rubber hoses. The only way a noise could travel like that would be if the hoses are rock hard....in which case ya need to change them anyway! A fuel pump can certainly make a rat-a-tat noise like that, either from an internal failure, OR the pump rod wearing....I've seen/heard both....but never from the rear of the car. If the pump or pump rod is creating the noise, you would be able to hear it at the front, and you could put your hand/fingers on the pump and feel it.
Check those hoses!
Another thought is that possibly the sock filter on the pick-up tube on the fuel sender is collapsed, or otherwise damaged. If so, it could allow the fuel pump to create pulses back there that would possibly transfer to the line by the tire, but it would not indicate a problem with the pump itself.
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dam spel-chek....Angry


|UPDATED|4/28/2014 10:03:33 AM (AZT)|/UPDATED|


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Joel Adams
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4/28/14 1:25pm - Reply: 'Re: rat tat tat noise, right rear'
JonsVette
Former Member
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Eldridge, IA - USA

Vette(s):
Have owned a 1966 Convertible, 1974 Convertible, 1988 35th Anniversary, 1997 Coupe. All have gone on to new owners. Presently own a 1978 white coupe with less then 10k original miles. It is a special ordered. L82 4 spd. with 11 options.

Joined: 4/26/2014
Posts: 27
Joel, excellent response. That is an angle I didnt think about. Yes, the rubber hoses are there of course so maybe checking the fuel tank area is a more viable option. I was double thinkin g my routine from that day and it seems that this noise started after the tank got to quarter level. Up to that point it was quiet. Not sure if theres a connection there or not. Anyway, great response and some more fuel for the thought process, I really appreciate the help. Jon  

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4/28/14 1:28pm - Reply: 'Re: rat tat tat noise, right rear'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19454
I believe the '78 up cars also had some sort of roll-over valve in the tank, since the fuel sender comes out the top. Could be something with that thing, too. Try loosening the fuel cap while the noise is happening, and see if that makes any difference....might lead us to a different solution.

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4/28/14 7:15pm - Reply: 'Re: rat tat tat noise, right rear'
JonsVette
Former Member
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Eldridge, IA - USA

Vette(s):
Have owned a 1966 Convertible, 1974 Convertible, 1988 35th Anniversary, 1997 Coupe. All have gone on to new owners. Presently own a 1978 white coupe with less then 10k original miles. It is a special ordered. L82 4 spd. with 11 options.

Joined: 4/26/2014
Posts: 27
Joel, Thanks again for responding. I will pull the sending unit out. I believe I can pull the unit out from the fill cap area on this year of Vette, so at least I wont have to drop the tank. I will verify that procedure before I begin- as the memory isnt as it once was. Jon

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4/28/14 8:43pm - Reply: 'Re: rat tat tat noise, right rear'
dyoes
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Zachary, LA - USA

Vette(s):
1974 L-48 Auto. Just your basic Vette. GM crate motor w/vortec heads and intake. Crane cam. Scorpion rockers, Edelbrock carb. Lots of parts still in boxes... :(

Joined: 1/27/2013
Posts: 201
Adams' Apple said: I'd find it hard to believe a fuel pump noise would travel all the way back to the rear of the car.....the pump is connected to the fuel lines with rubber hoses.


Dang, you're right.  Didn't think about the rubber hoses. 


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5/3/14 11:17am - Reply: 'Re: rat tat tat noise, right rear'
JonsVette
Former Member
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Eldridge, IA - USA

Vette(s):
Have owned a 1966 Convertible, 1974 Convertible, 1988 35th Anniversary, 1997 Coupe. All have gone on to new owners. Presently own a 1978 white coupe with less then 10k original miles. It is a special ordered. L82 4 spd. with 11 options.

Joined: 4/26/2014
Posts: 27
I will let everyone know what I find out on this issue. I am setting aside some time on Sunday to check into it. If there are any other ideas or suggestions, please pass them on. Thanks Jon 

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5/4/14 5:02pm - Reply: 'Re: rat tat tat noise, right rear'
JonsVette
Former Member
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Eldridge, IA - USA

Vette(s):
Have owned a 1966 Convertible, 1974 Convertible, 1988 35th Anniversary, 1997 Coupe. All have gone on to new owners. Presently own a 1978 white coupe with less then 10k original miles. It is a special ordered. L82 4 spd. with 11 options.

Joined: 4/26/2014
Posts: 27
Sunday May 4th.......OK, here is the story. Ran the vette for half an hour. Gas level at 1/4 tank. After reaching operating temp, ran high idle (55mph equal) for 1-2 minutes. After idle went to curb, rat a tat a tat started up again in the right rear. Put the long screwdriver to the surface of the fuel pump and no abnormal noise at all. Sounded good. Removed the fuel cap and issue did not change. I pressed the screwdriver on the fuel lines riding on top of rear frame arch and positively pinpointed the sound. Plain as day, rat a tat tat , loud and clear. Lines running toward bottom where the rear dog leg meets the straight run of the frame were quiet. So, something is affecting the fuel lines from appx a 2-3 ft run from the fuel tank until they make the slope down the right rear dog leg. Supply line was cold to the touch and a fuel return line was allowing a steady stream of fuel back to the tank. The only two things I can think of are- as previously mentioned, something collapsed with the fuel sock (I looked in the tank through the fuel fill hole but all looked normal) or some kind of line shock is happening or combo of both. The only time this has done it was when the fuel level got this low. When I bought the car and drove it home, there was 3/4 of a tank of fuel and never had the noise. Drove it a couple of more times before this noise started appearing which was just about the 3/8th area of the fuel gauge. So, at my wits end. Any ideas? ?  Thanks Jon 
 ADDENDUM- Decided to just remove the fuel sending unit and replace it. For the cost its worth eliminating that as a possibility. Was hoping to keep the car with as many of the original parts but sometimes it just wont happen that way. Thanks for the suggestions, will let you know if the problem is solved......


|UPDATED|5/4/2014 3:02:33 PM (AZT)|/UPDATED|


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5/12/14 12:08pm - Reply: 'Re: rat tat tat noise, right rear--update'
JonsVette
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Eldridge, IA - USA

Vette(s):
Have owned a 1966 Convertible, 1974 Convertible, 1988 35th Anniversary, 1997 Coupe. All have gone on to new owners. Presently own a 1978 white coupe with less then 10k original miles. It is a special ordered. L82 4 spd. with 11 options.

Joined: 4/26/2014
Posts: 27
Ok everyone, need some opinion input. I think I have narrowed down what is causing this noise. It has to be air getting into the line somehow. Since the car is bone stock original, I am assuming that maybe the rubber hoses are dried up and the clamps are weakening. I dont believe it is the sending unit, fuel pump or fuel pump drive rod. I believe it is time to replace all the original rubber connection hoses and the original clamps. I hate to do this as I want the car as original as it was from day one, but I like driving my cars so- its a love hate thing. Any suggestions are much appreciated. Thanks Jon

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5/12/14 1:20pm - Reply: 'Re: rat tat tat noise, right rear'
cingraham
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Brookline, NH - USA

Vette(s):
1976 corvette L82 red interior with white seats and door panels with ceramic headers and flow master exhaust and a Crane Cam

Joined: 5/2/2014
Posts: 46
see if you have brake dust covers and see if they are hitting the brake caliper mine does this and it hits in certain areas only !! I pushed on the  the cover a little bit were you can see scratch marks on the cover where it hits the caliper very little clearance and it made a rat tat noise that was driving me crazy !!! from the right rear. Sometimes it's just something stupid it fixed the noise but cam back a month later had to push on the covers again and noise is gone !! 

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5/12/14 2:31pm - Reply: 'Re: rat tat tat noise, right rear'
JonsVette
Former Member
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Eldridge, IA - USA

Vette(s):
Have owned a 1966 Convertible, 1974 Convertible, 1988 35th Anniversary, 1997 Coupe. All have gone on to new owners. Presently own a 1978 white coupe with less then 10k original miles. It is a special ordered. L82 4 spd. with 11 options.

Joined: 4/26/2014
Posts: 27
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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5/12/14 3:14pm - Reply: 'Re: rat tat tat noise, right rear'
dskopp
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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: 1956
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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5/12/14 6:05pm - Reply: 'Re: rat tat tat noise, right rear'
rraider1
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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: 1152

possibly the grounding of the motor itself?



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5/12/14 6:34pm - Reply: 'Re: rat tat tat noise, right rear'
JonsVette
Former Member
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Eldridge, IA - USA

Vette(s):
Have owned a 1966 Convertible, 1974 Convertible, 1988 35th Anniversary, 1997 Coupe. All have gone on to new owners. Presently own a 1978 white coupe with less then 10k original miles. It is a special ordered. L82 4 spd. with 11 options.

Joined: 4/26/2014
Posts: 27

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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