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Tracking down a persistent noise.

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frankBN6

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My 1959 BN6 makes a very unpleasant noise when I decelerate. The noise occurs whether I'm using the brakes or just using the engine to decelerate without applying the brakes. The sound is a very raspy noise coming from the engine area. Sometimes it sounds like it comes from the area of the carburetors and other times from the area of the radiator and fan. It sounds something like the hissing noise you hear when you remove the air filter and hit the accelerator, but with some other raspy or vibrating component. As the car decelerates, it eventually disappears before the car stops. There is no trace of it on resumed acceleration, but it happens every time I decelerate. I can't produce it with the car stopped and I have been unable to find anything loose or damaged to account for it. I'd appreciate any suggestions. The car runs great otherwise and doesn't seem to suffer in any way from the noise, but I'm sure I'm missing something and it isn't good! Thanks
 
Check to eliminate the possibility of the fan touching the radiator due to bad engine or transmission mounts, causing the whole assembly to move forward when you decelerate. Does it do it if you are slowing down by down shifting as opposed to using brakes? The front wheel is sort of between the radiator and the carbs. Possible brake noise?
 
Yeah, check the radiator for the fan blades rubbing a circular pattern. There is a tie rod on the rear bottom of the transmission at the back which keeps the motor from sloshing forward when slowing down. The rubber bushing on the tie rod has probably deteriorated from time and oil.
 
Jon, no sign of the fan rubbing (but that was something I hadn't thought to check) and the noise happens when I brake, when I downshift and when I simply back off the accelerator and use the engine compression to decelerate. Since it happens even when I don't apply the brakes, it doesn't seem to be brake related.
 
Greg, I checked for signs of fan blade contact and didn't find any. I was wondering if it could be the result of bad generator or water pump bearings, though I don't know why they would only make noise on deceleration.
 
Does it do it when you shift to neutral and then brake?

If braking under compression, could be something really stupid like an air cleaner rubbing with engine flex, an exhaust pipe rubbing.

Does it do it when turning left?
Right?
Or just straight ahead?
 
It happens when shifting into neutral and braking and it seems to happen when both turning or going straight. I've tried to find a rubbing or vibration source, but haven't located it yet. I'll check the exhaust system and air filters next as you suggest, but I doubt it's exhaust related unless I have a gasket leak. It worth looking again. Thanks.
 
How about the lack of clearance between the upper radiator hose and the generator pulley? The engine position changes slightly during those times you mention and the spinning pulley is touching the hose.

Rich
 
Rick, I'll look for signs of contact, it would be nice to find something simple and inexpensive to solve this. Thanks,
Frank
 
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