Well today I was on the highway doing 75mph and i looked in my rear view and saw blue smoke pouring out the back of my truck. I let off the gas and it stoped smoking, so i got home and got under the truck and felt the rear end where it looks like a bulb and it was hot to the touch as in burning HOT and it does not look like it's leaking anywhere on it. it's a 1990 F-150 4x2 auto. I know the tranny is going and the rear end also but it never smoked like that when it was not this hot out, it's about 87f out.

so my question is, is she gonna blow, if not how long till she blows and oh ya the rear end makes a howling noise everytime i'm on the gas but stops when i let off.

thanks again everyone.

-jack

 

A rear end will run hot and destroy itself if it runs low on gear lubricant. It is simple enough to check this. Remove the pipe plug in the rear pumpkin and check to see if the gear oil level is up to the level of the plug.

If the oil level is low, add some quick. If you ran too long without sufficient gear lube, the rear end is damaged. Blue smoke is bad news. After you add some gear oil it might run for a while - depends on how lucky you are.

If you fix it correctly now (tear down the rear end), you might avoid having a major repair bill later.

Lou Braun

 

ok thanks for the reply, but it does not look like it's leaking any oil any place, at the wheels, cover and the input shift all look dry! a qt. was add back in feb.

 

A quart is a lot of gear oil to have to add! Does the rear end have a vent on the pumpkin or one of the axle tubes? Wondering if maybe the lube is going out from there.............

 

an axle shaft seal can also be the culprit, and you might not notice unless you had the drums off..

 

Quote: "I let off the gas and it stopped smoking"....

This sounds to me more like smoke comming from the engine tailpipe, due to blowby through the piston rings. If your rear end was that hot that it was pouring out blue smoke from somewhere, then it was burning oil, and rear ends take forever to cool off, not just a few seconds after letting off the gas, so it should have continued smoking even after you stopped the truck. Engines with bad rings will smoke on acceleration and high speed cruise, and will stop smoking shortly after letting off the gas, as you described. I would start monitoring what's comming out the tailpipe (especially when you first start it in the morning and when accelerating, pulling weight, or climbing a hill) and keeping track of engine oil consumption as a clue to how your engine is doing and if you suspect it has bad rings, do a compression test and see what kind of shape they're in. If the tranny and rear end are both in bad shape, then I suspect the truck and the engine have alot of miles on them and the engine is probably just as tired as the tranny and the axle. Of course you should make sure you have proper oil levels in the axle and the tranny as well as the engine .

 

> it was hot to the touch as in burning HOT

Might be dragging the rear brakes, is the parking brake properly releasing? Drums would be very hot too.

 

no the eng. does not burn oil just leaks from the rear main seal about 2 qt. every 3,000 miles. The only thing burning to the touch is the rear end where the gears are not at the ends where the drums are. Also my rear ABS light has been coming on, but no anymore since I have not been on the high way. Also my tranny is over filled by a 1qt. Would that hurt it? also would that make the tranny psi go up?

 

Well now my rear ABS light comes on every so offen and stays on till i shut the eng off and start it again.

 

That rear ABS light might be caused by a faulty or dirty sensor in the rear end. Check the top of the rear end and see if there is an electrical connection near the top. The sensor is held in place with one bolt (often rusty) and can be removed for cleaning. Take care not to break the bolt when removing it.

Also having the transmission overfilled a bit should not cause any of the problems you are describing. As others have already mentioned, look hard at dragging brakes, oil on the exhaust system burning, engine blowby and rear end bearings.

Rear ends can get too hot to touch - that's about 160 degrees F and not be a problem. Just be 100% sure that the oil level is at least up to the bottom of the fill plug. Use either 80W-90 or 75W-140 gear oil and you should be OK.

Lou Braun