rear end whine under load

[73Manta72gt]

Hi all, my 72 GT has developed a whine when the engine is pulling...when I coast all is quiet..What is the best way to troubleshoot the problem....could it be anything other than the ring/pinion?..perhaps the center bearing or wheel bearings.

Thanks

:-)

[Wolf Spyder]

Funny you should post this question. In addition to the above request please answer this one as well.

I drained the diff. and re-filled with 90wt gear oil. now when I turn the rear wheels I can hear the gears. (Couldn't before I drained it.) I checked the manual and there was no recomendation for diff. gear oil. Should I use another weight oil or do I have a problem?

Thanks

[Dmcbrass]

You must run a hypoid gear oil in differentials. Hypoid gear units (differentials) experience sliding of the teeth due their design and need the the extreme EP additives found in hypoid oils. Any automotive differential oil will work like a 80W90. I personally like Mobil 1 75W90.
A whine under load is not consistent with a wheel bearing problem. Since the load on wheel bearings is independent of drive load, they will sound the same coasting as under power. If the wheel bearings also locate the axle such as in the later model GT's (71 - 73) they will often sound different when cornering because they are handling thrust.

[Dmcbrass]

Sorry, I told you what it wasn't but didn't say what it was. You are correct to suspect pinion problems. If the problem just recently popped up and the fluid level in the differential is correct, I would suspect a bad or worn pinion bearing. Less likely but possible would be that the pinion nut loosened up. If the problem showed up after a recent differential rebuild, I would suspect that the gears are set wrong, (backlash & mounting distance) or the preload was set incorrectly on the pinion. If the problem was in the car before you bought it, don't assume that it is fatal. I've known many cars that have run with a whine in the differential for years and never displayed a problem when inspected. By the way if the differential has been whining for very long at all, you will never get it quiet again without replacing both the pinion and ring gear. A pattern fairly quickly gets worn into the gear surfaces that makes it impossible to get perfect gear contact and quiet gears again.

[PROPEL]

I'm in agreement with everything Dmcbrass says.

I had the pinion nut loosen up shortly after a rebuild. You would notice immediately if that happened (quiet one moment...sudden whining the next.) Not a gradual thing.

I only drove about 20 miles with that noise before getting it fixed, but the rear axle's never been as quiet again since.

[73Manta72gt]

Thanks all, I noticed the noise about 3 months ago...maybe 2500 miles. how hard is the pinion bearing to replace?..does the entire diff have to dis assembled or can it be acessed where the torque tube bolts to the diff?

thanks again

:-)

[Dmcbrass]

The pinion bearings can be replaced with the axle in the car, however it would be easier with the axle out. The axle can be removed in about a 1/2 hour if you don't run into control arm bolts rusted in the bushing sleeves. You will need a shop manual that explains the procedure, bluing for checking tooth contact, bearings, a new crush sleeve and seal. In addition you will need a torque wrench capable of measuring inch/pounds in the less than 10 range to set the pinion preload. These are hard to find and expensive. I have heard of people using a fish scale attached to a breaker bar in place of the torque wrench. you will also need an old outer spline to hold the pinion shaft from turning while you set the preload. Replacing pinion bearings is one of the more technical tasks in auto repair. If you decide to have someone do this for you, make sure they have a proven track record. If you decide to take this work on and need a copy of the procedure from the shop manual, let me know.

[rstrel]

I've got the same problem as '73 Manta, except I have an automatic tran '69 GT(with original axle) and the thought of a bad axle bearing scares me stiff. Is the pinion bearing the same for all 1.9 GT's? Since I'm deployed in Europe(my Opel is with me) I have access to other Opel differentials from different rear drive cars up to the 80's. Does anyone know if the pinion and gear assembly would fit from any other car? Appreciate any help.

[Dmcbrass]

All 1.9's have the same differential case though the Mantas have a different length axle tube. Gear ratios vary also. Pinion bearings are the same for all 1.9's however, axle bearings on pre 1971's are different.