My 66 has a loud rattle that seems to be coming from behind the dash when I hit speeds between 55 and 60 MPH; normally happens when I’m heavy on the throttle, and most always at the same speed. What seems so strange is that if you ease up off of the throttle the rattle will slowly fade away, at which point I can speed up and everything seems normal; it won’t come back until I slow down considerably or come to a stop and then accelerate again. This isn’t an intermittent problem; it happens almost every time I get up to speed under normal to heavy acceleration. If I baby it and accelerate slowly I can keep it from happening, but that's not how I drive. The person that I bought the car from was told that it was the torque converter, but the two transmission specialists that I've taken for a ride tell me that there is no way that the noise is coming from the TC or the trans (700R4). I have a hard time believing that it is something like a cracked flexplate because it is too specifically tied to the speed of the car and not the load on the engine (327). It sure sounds like it’s coming from behind the dash, but I can’t think of anything back there that that could cause such a racket (except for the speedometer cable). The dash does not vibrate or feel like anything is hitting it when the rattle is present, but I’m not sure that it isn’t something hitting the firewall.

I think I’ll disconnect the speedo at the trans and see if it has any effect at all.

Let me know if anyone has any other suggestions.

Thanks,
Bryan

Radio bracket or dash support bracket :D

You might check your bellhousing bolts.

Rob

This may sound stupid, but based on your description, it almost sounds like it's in detonation (pinging). What compression is the motor/how much timing/what kind of fuel are you running?

HEI distributor hitting firewall?

HEI distributor hitting firewall?
Bad engine mounts?

speedo cable??

This isn’t an intermittent problem; it happens almost every time I get up to speed under normal to heavy acceleration. If I baby it and accelerate slowly I can keep it from happening, but that's not how I drive.

And then.

I have a hard time believing that it is something like a cracked flexplate because it is too specifically tied to the speed of the car and not the load on the engine (327).

You describe this occuring under load, that it doesnt happen when babying it, but then state it doesnt happen under load?

Which is it?

Radio bracket or dash support bracket :D

I thought about that, but it seems too specific to the speed of the car.

You might check your bellhousing bolts.

Rob

Hadn't really thought about that one. Doesn't seem like that would cause the noise that I'm hearing, but I've seen stranger things in the past.

This may sound stupid, but based on your description, it almost sounds like it's in detonation (pinging). What compression is the motor/how much timing/what kind of fuel are you running?

I've had engine detonation on other vehicles, and this is nothing like that at all. Detonation should stop immediately after easing off of the throttle (in my experience), but this lingers for a bit and slowly fades away. Other than a mild cam and camel humps the engine hasn't really been worked over. I would have to say that the compression is low, don't know where the timing is at currently, and always run 91-93 octane from the pump.

HEI distributor hitting firewall?
Bad engine mounts?

Doesn't have an HEI dist, so clearance isn't a problem. There don't seem to be any other indicators that it might be a motor mount, but I'll add it to the checklist and look into as I go.

speedo cable??

I am thinking that it does have something to do with the speedo cable. I was going to disconnect it at the trans last night and give it a test drive, but the rain never let up. If the noise stops after the cable has been removed from the trans, at least I'll know that it is the cable itself or something inside the speedometer.

I do appreciate the input folks, it gives me a number of different avenues of approach. I can't imagine that it'll take me too long to track this down once I set my sights on it (didn't really give it a lot of thought since it was supposed to be the TC).

Bryan

Maybe it has something to do with the loose nut behind the steering wheel ;) :waving:

Sorry, I just couldn't resist :beers:

And then.



You describe this occuring under load, that it doesnt happen when babying it, but then state it doesnt happen under load?

Which is it?

When I say it's tied to the speed and not the load I was trying to emphasize that it starts at the same speed (55-60 MPH). If I am heavy on the accelerator, it will start rattling every time I reach that speed range, but if I baby it up to that point it might start rattling or it might not. If the problem was directly tied to the load on the engine, I would tend to think the noise would occur at any speed whenever I stomped on the throttle, which it does not do (unless I'm around 55-60 MPH).

Maybe it has something to do with the loose nut behind the steering wheel ;) :waving:


No, if that were the case I'd be tracking the same gremlins on my bike and in my other car. That's not to say that I'm not a loose nut, just that I'm not the loose nut causing this particular noise. Thankfully my mental deficiencies stop just short of hearing things that aren't there. For now.

:clonk:

Well, it's not the speedometer or the speedo cable... disconnected cable at the trans and it made no difference. It's not the radio bracket either. Guess I'll pull the dash and look for anything back there that might be causing it. Hell, if nothing else it'll give me a good excuse to replace all of the dash bulbs and clean up the wiring back there.

check the motor mounts. tom