GAV

Help.
I have a 75 Stingray 61K miles I bought from original owner. The car has a rattle that I can't find. I talked to the original owner and she said the car had the rattle from day one and the dealer could never find the problem. Others have told me that the 75's had a rattle problem. The rattle noise does not pick up with acceleration it stays the same . It's sounds like a metal dinging ringing bell sound. The car has the L48 350 with the 400THM trans. HELP PLEASE!!!!!!!!!

7T1vette

The possibilities that come to mind are:

1) Ignition "pinging" due to the ignition timing being advanced too far. This sounds like a mechanical rattle, but the sound is actually coming from the engine...usually under moderate acceleration. To correct this condition, engine timing must be adjusted properly.

2) A small rock/stone is trapped in one of your wheel trim rings. Under acceleration, it becomes locked in place; but once at steady-state speed, it rattles around with turns/bumps or just from wheel rotation. [Of course, if you don't have ralley wheels, this wouldn't be your problem.]

3) A rock/stone is trapped in a frame rail (similar issue to #2).

4) An exhaust pipe/clamp/muffler is contacting a frame/body member.

Roco71

Possibly one of the dust shields slightly bent and the rotor hitting it.

GAV

Thanks.
It's not 1,2, or 3. 4 is possible I'll check the exhaust. The rattle does not start with a cold start it starts about 5 to 10 minutes into operation it does it in drive or in idle or in park. What is strange is the rattle sound at it's worse is when your in the car, the sound is less when your out of the car. The car has had this rattle for 37 years so it's not like it's something that's failing or breaking. The exhaust has been replaced from the cat back, it's most likely the the water pump and the generator have been replaced, it's not the fan clutch, maybe the air pump? I'm starting to think it's harmonic but from where!

fanmanbd

Is it effected by bumps or rough surface roads?

GAV

No. It rattles in park, when in gear, idle etc. The rattle does not get worse with acceleration. It's not the engine it purrs, it's not coming out of the exhaust, it seems to be in the area of the transmission. Take a BB or a bearing ball and put it in a tin can and shake it real fast, that's the sound it's making and when you hear it the most is when your in the car.

fanmanbd

Did you check your storage compartments behind the seats?

Roco71

Possible the inspection cover for the flex-plate ?

Easy Mike

HVAC blower fan. My guess is something is in the squirrel cage.

fanmanbd

A mechanical noise that does not change with RPM.

GAV

Nothing in the storage compartments. Does not have air. It is a mechanical noise. I think this weekend I'll do belt deduction to rule out the water pump, generator, power steering pump, or air pump, check the exhaust and I'm thinking I might pull the bell housing inspection plate if it gets louder when I pull the plate I might be on the right path. This is a 37 year old problem and the 75's were known to have a rattle, there was a recall for THM350 trans rattle but mine has a THM400. Please please keep throwing me suggestions I really appreciate it

mysixtynine

Not up on the 75 but does it have the exhaust flapper on the passenger side exhaust manifold to close off the exhaust when cold and then open when the engine is warmed up.

Easy Mike

Doesn't need AC. For some model years, the blower is on a low setting each time the engine is started. Flip the fan to High and see if the rattle clicks up a notch in time with the fan speed.

scottyp99

If it's not apparent where the sound is coming from, take a piece of heater hose, or garden hose, maybe 3-4 feet long, put one end up against your ear and listen while moving the other end of the hose around the car. You will be surprised how easy it is to home in on where sounds are coming from using this technique.


Keep the shiny side up!
Scott

7T1vette

How about the heat riser valve on the right-side exhaust manifold? It opens up when the engine is warmed and has no relevance to speed/rpms.

hugie82

The lug wrench and jack secure? Spare tire tub has something in it? A rubber mallet works wonders with the car off and just start banging the exhaust, frame hangers suspension, ect...

GAV

7T1vette you are the man. There is a heat riser valve on the right side, hooked on to the valve damper is an arm which hooks to a pull off valve that is vacuum driven, the vacuum line hooks up to the heat sensor on the cooling system thermostat elbow. What was happening was when the car was warming up the damper was opening and chattering and the more it opened the louder it got. I unhooked the arm restarted the car the damper was still chattering, I closed the damper and it stopped. I figure I will open the damper and shim it so it doesnt chatter and disable the pull off valve. Thank you so very much.

7T1vette

Hooahhh!

1969RAY

Side pipes and a good sound system will usually fix most rattles!