3 spd Gear Noise

[1strodeo]

Hello, Ive been loving my Bronco and driving it almost every day for months now, runs great, but all along there's been a gear noise in 3rd gear. If I'm on the gas there's no noise, but as I let off the gas to even out my speed, the gear noise starts. Anyone else experienced this?

thanks,
Jeff

 

[Broncobowsher]

Sounds more like a rear end gear noise.

Since you are talking highway speeds in 3rd gear I presume you are still running the stock 3-speed transmission. Not any gears under any load in the transmission in 3rd gear, just a direct connection through. But rear end gears are known for being noisy, typically under coast. Do you know if the rear end has ever been regeared?

Note: you will always hear gear noise in low range. That is the straight cut gears used for low range in the transfer case. But does not apply in high range.

 

[1strodeo]

Yes still has the 3.03 trans, and the only thing I know about the rear end is it has a dark spot around the fill plug.
That makes sense that the noise would be coming from there though, probably just carries the noise/vibe up to the cab area through the driveshaft.

 

[DirtDonk]

Those kinds of noises can definitely travel.

But since you've owned the Bronco have you changed the gear lube in either unit? You really need to since most PO's probably never did anything other than (maybe) making sure they were full.

Doing the trans should be easy on yours as it probably has the unit with the simple drain plug right in the bottom. Some new 75w/90 or 80weight would do the trick I'm sure. Whatever you use, it can be used in either box so find one that's suitable and go from there.

If you have not already, doing the full drain on the rear end is always a good idea for an CO (current owner) so you can not only change the lube, but inspect all the goodies inside. And especially the rear wheel bearings that only have a limited life expectancy.
Seems like we already talked about this though, so if it's redundant sorry about that.

Paul

 

[bdavis70]

I have the same problem with mine. When I let off the gas in second or third I get a noise that reminds me of gears meshing together. I dropped the rear drive line and took it for a drive and no noise. I pulled the rear end and checked the gears and bearings. My Bronco sat for 6 or 7 years and in that time all the oil drained on my ring gear. Half my ring gear is pitted. After I put the rear end back together I filled it with synthetic oil. I think that has help but I have another issue that I am trying to resolve before I can really test drive it. Once you figure out your issue please share it so I can fix mine too. Good luck. Brian

 

[DirtDonk]

While this type of noise is more typical of the rear end, as was said, it's still possible after all these years for the other boxes to get loose and tired and to allow more noise to either be made at different bearings, or transmitted farther up from the offending rear end.
A worn out u-joint or especially CV yoke/centering ball can make some funny noises. A worn out bearing in the intermediate housing could do it too.

Lots of things to play with, but certainly the rear gears would be a first place to have a look-see.

Good luck.

Paul

 

[1strodeo]

I noticed my radiator hoses were old, and we've had really low temps lately, and I've also noticed my heater is probably not performing to its full potential, so I wanted to do a cooling system flush and replace the hoses. Couldn't do it at home due to the weather so I took it to the AF base where i work where they rent stalls (and have a hose).

After the coolant flush I suctioned out the rear end and what came out looked more like fudge with caramel swirl than gear oil...refilled it with fresh gear oil. Drained the trans and the drain plug had 3/4 inch of goop on top of it, like the texture of mud. Once I saw this I reached my pinky finger into the bottom of the trans and felt 1/4 inch of sludge all along the bottom, like oil pan sludge. Also the oil out of the trans was black.

I cleaned the magnetic plug as best i could and refilled the trans...according to the book it should hold 3.75 pints but I only got about 2 pints into it, so I'm guessing it must be more sludged up than I thought.

The good news is the heater works great, and I'd say about 80% of the gear noise is gone, but still present somewhat.

The pic is of the magnetic trans plug after I dug out a bunch of crap (which is on the rag) and the filler plug.

Should I remove the trans and open it up to clean it out, or just keep driving it because once I do that i may as well do a rebuild?

 

[1strodeo]

Sounds more like a rear end gear noise.

Since you are talking highway speeds in 3rd gear I presume you are still running the stock 3-speed transmission.

Broncobowsher my Bronco doesn't have highway speeds, more like State Route speeds at best

 

[DirtDonk]

I'd be tempted to fill all four boxes (frt & rear diffs, trans and transfer case) with some sort of flush fluid, drive them around just a bit and then drain them again.
Not sure if something like diesel fuel, or kerosene, or ATF would do the trick, or if there are any additives that attack other components, but once you find a benign solvent that would break down the sludge I'd do it.

You don't always want to do such high-mileage/low-maintenance flushes on the engine, but the tolerances inside the gear boxes are much looser and can tolerate gunk floating around in suspension waiting to be drained.

Then I'd refill with a high quality lubricant appropriate for each unit.
In our many discussions about what's best, I like the one-fluid-to-rule-them-all approach. Normally there are at least two, if not three different types you use on a Bronco, but I like simplicity.
The transfer case is supposed to get 50w motor oil (as oppose to gear lube), but I've used a thin, easy flowing 75w/90 fully synthetic gear lube in all boxes with good results.

Back to yours, with such high mileage and unknown internal condition, it might be best to just use the factory spec stuff and don't go all exotic with synthetics yet. You still don't know if they're going to require more work to bring them up to snuff.
Which means an 80 or 90 weight single-vis, or 75w/90 multi-vis lube in the diffs and trans, and the aforementioned 50w motor oil in the transfer case.

Sorry for the rambling. For sure glad you reduced the noise, but they've obviously done without good fluids for a good long time.

Good luck

Paul

 

[73azbronco]

rodeo you may want to heat the rear diff and see if you can get more gunk out.

 

[1strodeo]

Man such a huge difference just from 'sort of' cleaning out the rear end and tranny, its like they're saying "THANK YOU" when I'm driving down the road now. Only gear noise now is if I ride 3rd gear too long while coasting to a stop, or if I'm
hard on the gas and suddenly let off, in other words trying to replicate the sound. I ALMOST feel bad for driving it these last couple months now that i know it was calling for help, but at the same time I know that Im the best thing thats happened to it in 15 years +
Thanks guys for all the input.

Jeff

 

[Broncobowsher]

when it warms up do another fluid flush and see how clean it comes out.
I am a little leary of putting solvents into the boxes and shocking loose the grunge. If it readily dissolves in fresh oil, a few oil changes will clear it up. If it is that clung to the inside, it is just going to sit there peacefully.

The fuzz on the magnet, that looks fairly normal. Chunks, or at least bit you can see the fractured and machined edges to, that is bad stuff.

 

[1strodeo]

when it warms up do another fluid flush and see how clean it comes out.

You mean when the weather warms up, or after a good long drive?
I did drive it about 20 miles before the coolant flush, but it was at least an hour before I drained the rear end and even longer for trans.

 

[Broncobowsher]

Wait til spring.

 

[DirtDonk]

That's great news on the new quieter gears!
You might still find that, if the damage done was not too severe, your noise might even get better and better until it goes away completely down the road a bit.
As you drive the gears are getting to know one another once again, and should play nicer together.
And any bearings that were effected might just experience the same thing.

Not doubt they were "aged" just a bit more than normal, but if you caught it soon enough you should be good.
And besides, that noise just gives rigs like ours some of that old truck character!

Paul