Rattle/Grinding noise under load

[az5oh]

Current issue: I have a rattle/grinding noise during acceleration (and deceleration under engine load) up to a certain RPM, at which point the exhaust noise drowns out the grinding. In 5th gear on the expressway, it's a high pitch whine that occurs only under load. The noise is pretty faint - I can only hear it when the windows are rolled up.

The noise goes away when the clutch pedal is pushed in or the car is in neutral. The car can be in motion or at a standstill and these two cases remain true.

This started to occur following my shift cables breaking and my having to drive the car home while stuck in 4th gear. Following the start of the noise, I drained the trans (which needed to be done and was full of some red fluid that one of the previous owners put in). I replaced it with 3 qts of Ford Honey.

I've searched CEG several times and have found similar noise issues being described, but nothing that occurs under the same loading conditions as I have described above.

 

[FrancisPennysac]

Maybe check into something called "Gear rollover", Or if it is only making those noises under a loaded condition, it could be something inside the trans .. I say this because my diff is making all kinds of weird grinding/knocking sounds before it let go...

 

[gmorrell]

Could be that driving home in 4th gear damaged the clutch and/or release bearing, that's one possibility, but I think it's low probability.

You might want to first check that your new shift cables are properly adjusted and are completely engaging each gear in the shift gate. Synchronizers that aren't completely engaged will be noisy, and they'll have a very short, unhappy life.

"Neutral gear rattle rollover noise" has been a known phenomena in Ford FWD manual gearbags since the late 1980's. It came to prominence with the first gen 1989 Taurus SHO, and it was primarily attributable to using low viscosity fluids like ATF in manual gearboxes to eek out a little bit more fuel economy and to give good shift feel when the trans was very cold, as in a Minnesota winter overnight cold soak. As the full term states, it occurred in neutral, engine idling, clutch pedal out, and typically went away when the clutch pedal was depressed. When these transaxles are in neutral and the engine is running, the spinning input shaft is also turning all five output gears, and none are locked to an output shaft by a synchronizer, so there is mucho tooth-to-tooth gear noise generated by all these spinning, unloaded gears. The Ford "Honey" is pretty effective at suppressing neutral gear rattle rollover noise.

If you have rattle/grinding in gear under load, accel and decel, it's not neutral gear rattle rollover, and if it occurs in all forward gears, it's probably something common, like the differential, or one of the big roller bearings on the trans' output side. When these diffs go to pieces during driving, they typically spit out chunks of hardened crap that do a lot of collateral damage to the rest of the transaxle, and sometimes they put pieces through the trans case. You can continue driving and await this failure mode at your peril.

After you check the shift cables, if nothing's wrong there, I think you should consider pulling the trans and first inspecting the clutch and release bearing, and if all is well there, you might want to have someone disassemble and inspect the transaxle innards.

 

[az5oh]

Thanks for the help, guys. Gmorrell: is there a way to ensure that the cables are DEFINITELY adjusted properly? We went through quite a trial and error process to get them to this point, but I guess I don't have a way of actually verifying that they are completely correct.

I was afraid you were going to say that it was the differential, but to play devils advocate...if the diff were going bad, wouldn't it be making noise all the time it was moving (ie. not just under load)?

 

[FrancisPennysac]

Tif the diff were going bad, wouldn't it be making noise all the time it was moving (ie. not just under load)?

I dont want to stick my foot in my mouth here, but Im pretty sure the diff only is moving when the wheels are turning..Hence why you hear it..

Thanks Gmorrell, for clearing up the "rollover" issue I wasn't quite sure about it fully myself but knew I remember reading about it before and thought it may have sounded familiar to his case.."The more you know!"

I'll add that up to my diff finally deciding to die, it would randomly lock/unlock and made a horrible clicking-knocking-es sound for about 2 weeks as the car was driving down the road..I thought the car spun a bearing or something was bad in my engine.

Now mind you my car only acted funny a handful of times as the diff hasn't completely exploded yet but after the 3rd time of the car "locking up" while coasting to a stop in N I stopped my car and took it home where it sits until It can be fixed.. I want to save my trans not just destroy it, for the sake of driving the car..

 

[gmorrell]

You could perform an experiment; find some quiet smooth pavement where you can coast the car for a distance with the trans in neutral, and maybe even the engine off for less noise (Remember, steering will be difficult with the engine off...), this would isolate things down to tire noise, wheel bearing noise, CV joints, the differential and the output shafts in the transaxle. Pay attention to see if the noise is synced to road speed.

If you have time and road, even try the above with the trans in different gears, but clutch pedal on the floor, see if one forward gear makes more noise than the others.

If the noise isn't locked to road speed, and changes depending on which gear the trans is in, maybe the problem is further upstream in the transaxle, meaning between the diff and the trans input shaft.

You may also be able to find this noise with the car safely up on jack stands, support it under the control arms so the CV shafts are at normal ride stance, engine running, trans in gear, crawl around underneath and listen for noise. Borrow a mechanic's stethoscope, or in a pinch, you can use a long shafted screwdriver as a stethoscope; put the handle against your ear and use the tip to probe around on the trans case and steering knuckles. Beware of moving parts, obviously.

Years ago, early 1990's, the trans in my Taurus SHO had a bad bearing on the 1-4 output shaft, and it made a low grinding noise that was locked to wheel speed even when the trans was in neutral. (I did both experiments described above) I tore apart the trans to find a roller bearing where metal had spalled off the rollers.

I'll be frank, these sorts of problems aren't easy to find, you have to be inventive with diagnoses (That's why I are an engineer...), and many times you still end up tearing stuff apart to find the real problem.