Need Help Diagnosing Rattling Noise

[Conaway2]

Even though it’s a Model A, the rattling noise that has developed in the past couple of months isn’t a typical rattle I’ve ever heard in 55 years of owning Model A’s.

The noise is a metallic rattle that occurs when I let off the throttle at 25-30 mph and make a broad right turn, like going around a curve. The noise disappears if I give the engine a little more throttle. There is no noise when decelerating while going straight or making a left turn.

At first, I thought the noise was tools under the front seat (‘31 Deluxe Roadster) rattling against the sheet metal, but I’ve ruled that out. The noise also sounds like it’s coming from the transmission or U-joint area.

The usual suspects - loose brake rods, engine pans, brake cross shafts - are all tight and definitely not the source of the noise. The wishbone and radius rods on the rear axle are all tight - or at least I cannot move them with my hands.

I followed Tom Endy’s article to do a full bearing and race replacement on the rear axle almost 2 years (~2,000 miles ago) and have had no problem or funny noises coming from the differential. The U-joint was not replaced, as it had very little wear.

I’m thinking I probably have to pull the rear axle to find the source of the noise.

Before I do that, I would appreciate any suggestions as to what else I might check.

Many thanks - Jim

[Rob Doe]

I had a rattle that sounded like it was under the floorboard near the shifter. Turned out to be the hood prop device attached to the radiator support rods. One side was not retracted and was rattling intermittently.

[springerpete]

Universal joint ?

[Conaway2]

Rob doe, Springerpete - thanks very much for your suggestions.

My car doesn’t have a hood prop device and the radiator support rods are both tight - I think - need to check those.

The universal joint is a strong possibility.

Jim

[nkaminar]

Things to check:

Since it is related to turning and decelerating, the first thing to check is the rear end. Check the in and out play in the rear axles. Look for metallic residue in the differential oil (use a magnet and coffee filter). Jack up one rear wheel and check for play in the ring/pinion gear.

See if there is evidence of the drums rubbing against the backing plates or brake components.

It does not sound like the universal joint but you could check that too while the one rear wheel is up in the air by putting the car in low or reverse and moving the wheel back and forth. Having a helper will help.

[JayJay]

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These things can be a bear to track down. I'll toss in my unusual rattle, also happened when accelerating and decelerating. Turns out that at a certain RPM there was a harmonic that caused the right front turn signal (the LED type that nestles between the two bumper pieces and mounts to the bumper via the mounting bolt, similar to the Logo-Lights) to rattle enough to hit the bumper. A bit of work with sheet metal shears allowed me to trim down the width of the stainless steel backing plate to the LED light so that it doesn't hit the bumper any more. Suggestion - at a minimum, check that all your bumper mounting bolts are tight.

I also had a rattle from a loose inspection plate on the top of the bell housing. Hard to find unless you remove the floorboard.

JayJay

[Reelnative]

Originally Posted by Rob Doe

I had a rattle that sounded like it was under the floorboard near the shifter. Turned out to be the hood prop device attached to the radiator support rods. One side was not retracted and was rattling intermittently.

I had the same problem,

[TJMack]

Also check the hub caps. I put the rubber "O" rings on and it help get rid of a lot of noise