Noise, oh that noise

[denverbronco]

About a month ago we purchased a 86 Bronco along side the road. Fun adventure time. The truck itself runs excellent. Typical rusted out gas tank and exhaust, to be expected for the age. After those replacements, and felling kinda good about ourselves, we wanted to take on the "noise", oh the noise. While running the truck at a speed of 25 mph we noticed a Whrrrring sound coming from, what we believe the front end of the truck. At first we though it could be Front end wheel bearings, but we noticed that when we took our foot off the gas the noise went away. Strange, we have a automatic transmission, and as we gain speed the noise gets so loud you can't hear yourself think. We took it down to some AAMCO mechanics and after leave her with these people for a week for major repair work, you guessed it, the noise is still there. I don't feel bad about the repairs, the parts really needed to be replaced: front end differential rebuild and some gears. I am however as you guess rather disapointed with the experts. HA, ha. That same day we took the front drive shaft off the truck and drove it down the road. Yep you guessed it again the noise is back. After talking with several other experts we came to the conclusion the noise only could be coming from the Transfer Case. Called around fround a rebuilt transfer case and after swapping them out, I bet you can fiqure out the NOISE IS STILL THERE! The noise sounds alot like a throw out bearing in a manual just alot louder. Come on Bronco Experts this could not be a rare problem. Let me know.

 

[Bully Bob]

Veh. noises have a way of "throwing their voices"... I would set it on 4 (sturdy) jack-stands, put it in gear & give a listen. This is very dangerous...no one under truck. One person in the cab with foot just above brake pedal. Change throttle position slowly.

Obviously a "shop hoist" is much better, if you have access.

My guess is the rear pumpkin pinion bearing -or- a trannie out-put bearing. :-B

 

[Seabronc]

Do you still have the air pump installed? If it is not getting the right vacuum signal, it will be dumping air thru the bypass valve. When mine is dumping, durring engine warm up, it noiser than all ****.

If you still have it installed, remove the drive belt from it and see if that makes the noise go away.

Just a shot in the dark.

Good luck,

>-

 

[yusuebronko2_86]

i recently discovered my tranny took a turn for the worst (damn Toyo Kogyo Mazda trannys) and the input bearing is just like that. but mine is a standard, might wanna check it out....

 

[denverbronco]

I did forget to mention we did jack the truck up and carefully placed it in gear increased speed slowly to 35 mph, unfortunately no noises were found. My guess is that the "bearing" causing the noise only sounds off under a load. Do you think that the trannie out-put bearing would sound off all the time or just under load. I will check on the easier of the two and start with the rear pumpkin pinion bearing. I am taking off the rear drive shaft as we speak to discount the rear differential. Stand by and thanks for the direction.

 

[denverbronco]

Am I wrong in my thinking, I did not think an automatic transmission had a throwout bearing. Is it called something else?

 

[Justshootme84]

Like posted, those odd noises can come from many areas. Possible causes are a worn fan clutch, idler pulley or other pulley bearings on the motor, even the power steering pump. The heat shield for the cat can vibrate/rattle, and a worn u-joint can really make noise. You can often use a long piece of rubber hose like a stethoscope to listen to the motor whole running, to pick up on internal noises.

The auto tranny does not have a throw-out bearing like a manual tranny. If the noise seems to be coming from the tranny area or center of the Bronco, a few possibilities come to mind. I have had a bolt come loose from the flywheel, a torque converter go out, and motor/tranny mounts come loose or be so worn that they make noise, so take a close look there. Try 2WD, 4Hi and 4LO to check for any change in the noises that may come from the transfer case. Good Luck!!!

 

[denverbronco]

Ok, after removing the rear drive shaft and driving around I am happy to state that we have narrowed down the problem "No noise". We will have the pleasure of tearing down the rear differential and replacing the input bearing. You know the one that is a Bit.. to get to. The drive shaft itself looks like it has been replaced recently. The bushings and universal joints look new. Maybe the prior owner gave up on the noise issue and just gave the truck away. Bad for him good for us. Thanks again everyone who knows more than we did. Your directions were great. Anyone knows how to tear down a rear differential and what parts to look for to replace? Do we need any special tools to do this right the first time?

Thanks again

Denverbronco

 

[Bully Bob]

WOW...! I got it right on the first shot..! That's a rareity

I've not done a diff. as it takes gages & patience to get the gear lash correct.

(You might want to put a "Posi" or even a locker in there while it's appart.)

I let my local driveline shop handle it....that way, THEY have to re-do it if it howls ( You can take the 3rd. member to them & save some $$

Bob

 

[Justshootme84]

The 86 Bronco could have one of 2 different rear axles, either a Ford 9" or Ford 8.8". THe 8.8" has a cover plate with several bolts on the back side of the center section, the 9" cover plate is welded on. IF it's a 9", you can simply remove the center assembly from the front side. The 8.8" requires removing the plate and pulling the ring&pinion out the back.

If you have no experience with differentials, I strongly suggest taking the Bronco to a shop/garage, regardless of which type you have. IT takes some careful set-up with shims and dial gauges to get the ring&pinion gears to align properly. IF done wrong, you will eat them up. Even simply replacing the bearing for the driveshaft yoke requires a "preload" or proper torque setting for the 8.8".

There is some info on rebuilding/repairing these axles in my links in the "Tech Articles" forum on general Bronco repairs. Glad you found the noise-maker!!!

 

[Thadoggma]

i had a 69' f250 that did that, but that was because the rear diff was filled with muddy gear oil. drove it around for 6 years never had a prob, just loud as **** at about 20 mph it would start whining and get louder until about 40, then stop... good luck with that project.

 

[cowboydan]

the only time mine whines is when i'm i 4L. other than that, she has a vib that comes up on the highway... rear driveshaft angle is steep.