Hi guys!!

I have this problem, which I have noticed since I swapped my old C4 for a T5 in my 68 and I cant quite figure out what it is. When the engine drive train get hot, I noticed a whinny whistling noise coming from underneath the car, mostly toward the rear wheel and I can easily hear that while driving around with the windows down as the high pitch sound bounces of parked cars. I notice its always there when I drive, but its not affected by RPM and as soon as I come to a stop, the noise usually goes away ( or seems to) after a few second, until I drive off again. When it gets real hot, I can actually hear it at the end of a drive, if I park the car and leave it trunning.

Fact that its not affected by RPM or motion but usually shows up after about 30 min of city driving leaves me puzzled. I dont have power brakes, and since I always hear it in a straight line and it comes from the rear, I can eliminate the power steering pump. I recently upgraded the radiator to an aluminum 3 row and replaced the fan for a 6 blade one to make sure the 289 was kept at a decent temperature but still, it gets pretty hot.

Has anyone noticed something like that?
THanks!
Frank

 

Have you verified the problem isn't as simple as a wheel bearing starting to go, or that one of your rear brakes isn't dragging slightly? Have you tried recording the sound on your smart phone? Might help in diagnosing.


U-joints could be another thing to consider, but they don't normally make a whistling sound. There's usually other noises that occur.

 

HI!!
The bearings have been replaced last winter along with the seals the oil and the vent hose. I know its not the brakes because the noise can be heard when Im idling at a traffic light. Im starting to think it might be the fuel pump...because it makes 2 clear note at different time (2 different pump speed) and its located very near where the sound comes from. My next step will be to raise the axle until the wheels no longer touch the ground...and run the car in 4th gear untill I hear it and then Ill locate the source. Thanks for taking the time to reply, I can see not a lot of people have old mustangs here and its hard to get a single reply in general.
Have great one!!
FRank

 

No worries about replying - while I don't own an old Mustang, I've worked on a bunch. Probably forgotten more than I can recall, though. :-) I'm at the other end of the spectrum and will have had my 2017 Mustang for three weeks tomorrow.

Be careful when raising both wheels off the ground to do that test - make sure the car is very stable, and pay attention to the angle at which the driveshaft mates with the differential. Sometimes if the angle is very extreme, you can place a lot of strain on the u-joints. You might want to start in 1st, and not 4th gear, too. When the wheels have no load, they will spin a lot faster at idle than they would in first gear. I'm just thinking about your safety first. Depending on your differential, don't be alarmed if you see both rear wheels turning in opposite directions when it's off the ground. This behaviour is normal if you don't have limited slip, or posi-traction, or any other name you care to give it.

Is your fuel pump still mechanical, or have you modified the car for an electric pump?

 

Thanks for the concern, given you dont know me and my plan sounds shacky at best its totally justified. Just to put you at ease, Im planning to raise the axle then put blocs under it so when I lift it, its going to be the same as if I lifted the tires themselves therefor keeping the axle/driveshaft angle. Also gonna leave at least 2 inches from the ground to the tires to make sure that they dont go grabbing the pavement were they to expand while spinning. Also gonna have someone else in the car behind the wheel just in case

To answer your question about the fuel pump, I recently swapped my carburetor for an electronic one from Holley. It had its own electric pump which was installed near the fuel tank. The old mechanical one is gone.

So a 2017 huh?? Thats really cool. I guess you served your time with the classics, now you wanna have a trouble free ride that doesnt end with you placing an order at Mustangs Unlimited when you get home

 

My younger self would probably never believe me saying this, but yes - safety first! Doesn't matter if I know you or not. You seem like a decent guy, and I'd be unsettled to say the least if I learned of someone getting harmed after discussing a potential diagnosis & repair procedure I took part in. I've had cars fall on me because of sketchy ideas.

Just take every precaution possible, and it's definitely a good idea to have an assistant. With today's technology, I'd be tempted to set-up a bluetooth microphone somewhere under the car to help locate the noise.

Electric fuel pumps sometimes are quite noisy, and could make the noise you mention. Again, another safe way to confirm or eliminate this would be to install a temporary switch to kill the fuel pump when you hear the noise. If the noise continues once the fuel pump has been shut off, then you know it's something else. Naturally, do this on a road that isn't heavily used, because you will essentially be shutting off your car, too.

Ya, picked up the 2017 Mustang Convertible 3 weeks ago. It's the first Mustang I've ever owned. Never had a classic Mustang, though if the right one came along, I'd be game. I've worked on a lot of Mustangs of all different vintages - many friends owned them over the years. Mustangs, at least the old ones, are very easy to work on. I grew up with carburetted cars, and have been working on them since I was old enough to hold a wrench. I currently own a "classic" (not a Mustang) with a carburetted engine, and two vintage motorcycles that also have carbs. The old stuff is always super-easy to work on.

I guess you could say I'm still serving my time with classics. While I am not placing an order at Mustangs Unlimited, it's not uncommon for me to be ordering parts from Holland for my vintage Honda motorcycles. The hobby can be costly, but it's a lot of fun.

Post an update if you figure out what the noise it.