Triumph Repair/1975 Spitfire diff or wheel bearing?
I have a 1975 Triumph Spitfire 1500 with overdrive. It makes a 'clattering' sound when under power. It progressively gets worse from high second 2nd through 4th gear. When I get up to around 50 in 4th gear its the worst. When I let my foot off the gas it goes away. The noise sounds like a loose screwdriver bit bouncing around on metal.
I thought I had an exhaust leak too as I would get a pretty good amount in the cabin from a short drive. Looking under the car shows spray from either the transmission or diff forward on the exhaust pipe. I changed the transmission and diff oil. The diff was very low. Is Castrol 75W-90 Synthetic gear lube oil okay?
I've put the rear up on jack stands and have the wheels off. The U-joints seem okay. Not really sure how to check. Everything is tight with no slack. The noise in this position sounds more like a hub bouncing around hitting metal.
The motor itself makes no noise when revved. I'd love to hope it is a wheel bearing but am thinking it is the diff? Any suggestions on how to confirm?
It is sometimes difficult to ID noises. However, there are a few things you can do to narrow down the area it is in.
To ID a wheel bearing noise you first need to jack the rear up again and put the car in any gear with the hand brake off. Now rotate either wheel and note the direction that the other wheel turns. If the other wheel rotates in the opposite direction then you have established that you do not have a limited slip differential. If this it the case take the car out of a gear and put it into neutral. Now rotate one wheel and see that the other wheel rotates in the opposite direction again.
Now have someone hold the other wheel and you rotate the wheel again. It will be harder to turn but it will rotate. Now have them hold your wheel and rotate the other wheel and each time listen for your noise on each test.
Now, Start the engine and put it into gear and before you let out the clutch have someone with gloves on hold one wheel and you very slowly let the clutch out. The opposite wheel should run and the one holding the other wheel should be able to hold the wheel from turning. You may also be able to do this in the higher gears but you must release the clutch very slowly so the guy holding the one wheel can hold it. Listen for the noise then have the guy holding the wheel do it to the other wheel. Each time listening for your noise.
This should make it so you can tell if it is a wheel bearing or not. If the noise is still in there no matter which wheel is held then it is not a wheel bearing and has to be in either the differential, drive shaft or out put shaft of the overdrive. Since you said the noise is not present when in neutral that means it is not in the clutch, input shaft to the gearbox nor any gear in the gearbox because when you are in neutral every gear in the transmission is spinning and the only parts that are not turning are the mainshaft (out put shaft and the Over drive)
When a "U" joint gets bad enough to cause a noise under load it will usually show signs of rust coming out at one of the spicer "U" joints. and with a straight blade screwdriver you can force movement of the X of the "U" joint.
Next since you have already said that the differential was low you need to force the front pinion flange in different directions with a pry bar. You should not be able to force it in any direction except rotational.
The Spitfire is a "Swing axle" suspension so you have one "U" joint on each axle at the differential. Since you held each one stationary you have also eliminated them as a cause (if the noise was still there when you held each wheel.
If all this does not net you the noise then you need to put the car on a lift with someone in the car to run it up while you use a mechanics stethoscope to try to pinpoint the noise. A long screwdriver with the handle pressed into one ear works almost as good as a stethoscope. Put the point of the screwdriver against the differential case and the Overdrive unit to listen for internal noises.