Looking for source of the rattle in my 76

[Eissmann]

I'm chasing a rattle that comes from somewhere forward of the dashboard. I searched this forum and ruled out many of the rattles' causes that turned up in my search.

I've tried disconnecting the speedo cable at the tranny. That didn't stop the noise. 

I found a loose flap on the lower portion of the firewall that needed to re-fastened. That didn't stop the noise, either.

I checked the exhaust-to-down pipe, the exhaust heat shield. Bell housing bolts. Nothing.  The rattle is still there.

So I decided to record the noise and put it out here on the faq. Maybe some one here will listen to my woeful noise and offer the solution to this puzzle.

Please visit this YouTube video to take a listen....

 

https://www.youtube.com/watch?v=SSZfahwlDvU

 

[Son of Marty]

For starters check the heat shields on the steering arm and center bearing for looseness, then next on my list to eliminate would be the center resonator. 

[Eissmann]

I was looking at the resonator too and forgot to mention it. I reckoned the sound wouldn't be in front of the driver. It does rattle a bit if I knock on it. I didn't even know my car was supposed to have a heat shield for the steering arm. Mine is gone so nothing there to rattle. I suppose it critical with the reactor?  

Edited January 11, 2022 by Eissmann
added details

[zinz]

I had a buzzing rattle on my 2000CS that I swore was under the dash.  Ray was in the car at one point and I asked him what he thought it was.  He thought the noise was inside the passenger door.  We parked and it was still buzzing, Ray gets out and it was the nose beltline trim on the passenger side.  I couldn't believe it, but sure enough it was the culprit. It drove me crazy before that.

 

Have someone else ride in the car and poke their head under the dash to try to pinpoint the source?

If it's under the dash, maybe it's in the heater box? Try moving the selector switch to open the vent doors?

 

Get under the car and hit things with a rubber mallet and see if anything rattles?

 

I couldn't tell anything from the video...  Hope you find it.

 

Ed

[John76]

Nothing's more annoying than a mystery rattle!

This almost sounds like a fan blade nicking something as it speeds up.

Blower motor fan?

Other stuff I would check:

- Bottom of the washer pump/bottle holder (put something (rubber) between it and the brake housing).

-The EGR/Reactor service box speedometer cable connections (if a CA '76).

- The wire spring on the clutch lever.

-The throttle rod & lever clips and return spring.

- Air cleaner mounts.

- Loose relays on the firewall (speed, choke and EGR )

- Missing/loose fasteners on the brake assembly (including the brake light switch).

- Antenna mast and mounting. Try retracting or extending in different positions.

-Drip rail trim.

- Hood release cable & handle.

 

John

 

 

[Mike Self]

A '76 will have a sheet metal heat shield/warm air provider that's bolted to the exhaust manifold.  Over the years the metal around the bolts that fasten the heat shield to the manifold rusts, and even if the bolt looks tight, it's not really holding the shield in place.  

 

If that turns out to be the problem, be very careful removing the 6mm bolts that hold the heat shield in place.  Chances are that they're firmly rusted in place, and will break off if you're not careful.   If you do get 'em out intact (or if you have to drill and re-tap) replace 'em with stainless steel bolts, slathered with anti-seize compound.

 

mike

 

PS--masking tape is your friend if you're trying to find a rattle or whistle on exterior trim.  The tape will disrupt the air flow and usually stop the sound.  Just do one piece at a time so you'll know when you find it.

[Eissmann]

Thanks for the many great ideas so far. The noise I'm looking for seems independent of the engine.  It must have something to do with wheels or something that turns while the car is moving. 

[tzei]

Jack up the car and rotate each wheel by hand. How are bearings? See/feel if brake shields aren’t flapping, a rock or something jammed in there etc. 

[popovm]

Any witness marks on or around the guibo? Maybe something is loose around that area like the shift platform and it's just barely clipping the guibo or driveshaft. Or, any chance you installed a new guibo and forgot to remove the metal band? I think it would be louder than that, but since we're throwing spaghetti against the wall...

[Eissmann]

3 hours ago, popovm said:

Any witness marks on or around the guibo? Maybe something is loose around that area like the shift platform and it's just barely clipping the guibo or driveshaft. Or, any chance you installed a new guibo and forgot to remove the metal band? I think it would be louder than that, but since we're throwing spaghetti against the wall...

I'm doubting the guibo/shifter/driveshaft angle. The racket was going on before I had a trusted mechanic  replace shifter bushings, drive shaft support bearing, and guibo. He didn't know what the noise was but suggested taking out the passenger seat so someone (me) could listen while someone else drives. 

[Eissmann]

4 hours ago, tzei said:

Jack up the car and rotate each wheel by hand. How are bearings? See/feel if brake shields aren’t flapping, a rock or something jammed in there etc. 

I did rotate the right front wheel  when car was in the air and it seemed fine. but I didn't get it going hundreds of rpms.

Who knows if I still missed something there. 

 

I've been thinking about throwing the dice and putting some new wheel bearings on. I have no service history for the car and it is probably over due anyway.

[2002iii]

That sound is very familiar, I would check the rubber bushings on the exhaust bracket that bolts to the transmission. Mine looked fine until I unbolted them and they crumbled into a lot of little pieces.

 

If it's not the bushings, I would Jack the whole car up and secure it on Jack stands with the tires off the ground. Have a friend put the transmission in gear while you listen with a stethoscope or screwdriver to your ear on the transmission and engine until you find the source of the rattle. 

[Eissmann]

I was working on something else when I discovered this. After I pushed the EGR connector into the manifold it was a bit quieter. 

[John76]

Looks like your check valve may have been hitting the fan. Cause of rattle??

It should have a bracket on the front valve cover bolt.

 

 

 

[Eissmann]

on RealOEM that looks like #6. I am also missing #1, a slip ring  

Edited January 21, 2022 by Eissmann
another typo, dammit