Searching for noise source - need to rebuild rear diff?

[Sheehanigans]

Hey all,

Finally got my recently acquired bronco fixed enough to go drive it and find more things to fix. I'm hunting down a grinding/whirring noise that occurs on deceleration while in gear. Acceleration sounds good, and coasting with a little gas is good, but as soon as I let off the gas and it starts engine braking, it makes an uncomfortable racket that sounds like its coming from the transmission tunnel or the floorboards. Clutch in and the noise goes away.

While putting in new brake lines and hoses, I realized my rear diff breather bolt was blocked and the hole was rusted shut. It let out a hiss of pressure as I unscrewed it, even though the truck was cold and hadn't moved in weeks. Hmm...

Cleaned out the breather and put it back on, but now I'm thinking the rear gears are in need of some help due to the pressure and who knows what else has gotten in there.

Could this be the source of my noise? Research so far says that a deceleration noise from the rear end indicates a problem with the pinion bearing. But they describe it as a howling, where mine seems more mechanical grinding. Or could this noise be coming from a similarly neglected transmission? If it is the rear, how difficult is a drain/clean/relube?

 

[WILDHORSES]

Pull the axles and then the diff and take a look. It would be a good idea anyway if it's sat idle for some time. You can check axle bearings, brakes and then get a look at the gears. If it's all good put it back together and add some new gear oil.

As far as pressure build up from a plugged breather that would typically cause an oil leak by blowing through one of the axle seals. I can't see where it could cause the gear problem if that's what's wrong.

Jim

 

[DirtDonk]

And that points out two things critical for any new-ish Bronco owner to take care of.
One is to change every fluid/lubricant in every component of your new-to-you rig. Over the years most EB owners, like owners of most vehicles, might change the engine oil religiously, maybe the coolant semi-religiously, but still think a transmission, master cylinder, steering gear box and differential are somehow magically "lubed for life" and have never touched them. So it's just cheap insurance to change them all anyway.

The second is the rear wheel bearings. As just mentioned, pulling a few things apart back there is a great way to inspect the bearings. Even if everything in the diff turns out to be perfect, you won't regret a little extra time and effort if you discover your wheels were in danger of falling off! ;D

If you've never done anything like this, when the intimidation factor wears off after the first time you'll be glad to know just how easy all that stuff comes apart.
Well, after the axles finally let go their grip on the housing from being rusted and stuck in place for 40+ years that is!

And who knows... Maybe that noise you're hearing is in fact the bearings, or the u-joints in the driveshaft, instead of the ring & pinion gears.
Hey, we can get lucky sometimes too, right? Right!

Oh, welcome to CB too by the way! What year is your Bronco?

Paul

 

[Firedog67]

Mine had a corroded ring and pinion from sitting that caused a similar noise.
Just a thought

Bought and Replaced R/P, installation kit, axle brgs/seals and purchased a Detroit locker.

 

[DirtDonk]

Did it ever get "un-corroded" by any chance? Or did you end up doing something about it before that?

And Sheenanigans, I already mentioned the driveshaft, but forgot to ask what transmission you have. And what suspension mods?
When you first mentioned deceleration noise I thought of the newer tranny swaps such as the NV3550 and the relatively looseness of their inner workings. When they make a noise due to other driveline issues, it's usually more of a rattle than a whine, so might not be your issue. But we have to at least explore the possibility until we know more about your rig.

Maybe some more history and known modification info would help?

Paul

 

[Sheehanigans]

1968 U15, repainted, new interior, and 302 rebuilt around 2001. Original transmission with 3 on the floor. No lift, cut fenders with 31" tires. Driven regularly, then parked and sat for the last 4 years. I picked it up in June and have re-done fuel lines, ignition, all new brake lines, coolant, and some electrical work.

The noise is very odd, as it sounds great on throttle, and with throttle cracked while cruising steady speed, but if at any time the wheels are trying to turn the motor faster the noise comes through the floorboards and sounds like its from the clutch area, but I know noise travels well down there. Its certainly concerning and doesn't sound very cool rolling to a light.

Now that I think of it, it sounds more severe when decelerating in a first gear than in second gear at the same speed. That points away from rear and and more toward the transmission, right?

I noticed both mufflers (true duals, no cats, stock manifolds) have a leak on the seams so I'm going to try and putty those because there is some after-fire and popping that which makes the gear noise harder to trace.

I'll get a video up after I fix the exhaust to get some more ears on it.

 

[DirtDonk]

Could be the trans, but like you've surmised, it could still be just about anything from the transmission all the way back to the differential at this point.
But one more thing to check first would be to make sure that the transfer case is not shifted into 4-high instead of 2-high. Not much difference in the stroke, so it's not uncommon.

Count the detents from front to back and make sure it's in the second from the back. In other words. If you don't still have the factory indicator, all the way forward (longest stretch between clicks too) is 4-low, then one long one back is usually Neutral, then 2-high and 4-high.
The reason I say "usually" Neutral is that in some cases you can click into a 2-low position that is not officially recognized after '66.
It's easy enough to tell the difference once you've fiddled with it a bit. If you have an abnormally long throw between 4-low and Neutral, you're good. If there's a click in-between, just count five positions instead of four. As long as you have one click backward from Neutral, you're in 2-wheel drive.

It's just a long-shot hope anyway. The noise you describe still sounds more like issues other than it being in 4-wheel drive. It's just that any angle is worth looking at.

Paul

 

[Sheehanigans]

Make sure it's all the way back towards the driver, and count the detents from front to back. If you don't still have the factory indicator, all the way forward (longest stretch between clicks too) is 4-low, then one back is usually Neutral, then 4-high and 2-high.

Is that the order that it should be? I have the indicator bezel but its not bolted down so it just floats around but the order on the bezel says:

4L
N
2H
4H

So I'm in the second click from the bottom. Although the T handle has a lot of play, the clicks are pretty vague, and even Thor has to use both arms to move the thing...

Anyways, I'm under it today looking for anything that can vibrate or rattle, and I see these bolt holes. It looks like I'm missing 3 bolts on the lower side of the bell housing? Or starter plate? Not sure what to call this part.

Anyways, whats the threading of these holes?

I really appreciate your insight, Paul.

 

[R.P. Coltrane]

I would pull the rear driveshaft, inspect for flat rollers or loose joints. Feel the pinion with the shaft out, excessive play will cause noise. Good luck!

 

[66Bronco]

Check to make sure that the T-case output shaft yoke nut is tight. Sometimes they will loosen.

I try to check the easy stuff first. Might be drive shaft U-joints too.


-Terry

 

[Sheehanigans]

If you guessed 5/16-18, you're right! Got the bolts, I'll tighten that plate back up tomorrow. Is there any potential problem of that being open and loose for so long?

Both drive shafts are tight with no play in any direction that I can feel by yanking on them. I'll add to my list of things to do this weekend to pull the rear and spin the pinion by hand and see how that feels.

Terry, you say the "output shaft yoke nut" - is that one of the four nuts and a U-Bolt that hold the universal joint in place?

 

[DirtDonk]

Is that the order that it should be?

Oopy doopy, big mistake! Sorry about that. I'll go correct my previous posts. Your indicator is obviously correct and I was getting carried away. I knew what I meant (not really) but didn't write it correctly.

So I'm in the second click from the bottom. Although the T handle has a lot of play, the clicks are pretty vague, and even Thor has to use both arms to move the thing...

If the looseness is in the handle itself, the pivot bolt has probably come loose and the little thin plastic bushings have probably long-since worn out.
New bushings are available (http://www.wildhorses4x4.com/product/Tshifter_Bushings_Pair) and are easy enough to replace.
If the locking nut on the bolt/pivot is no longer locking, a simple Nyloc nut can take it's place.
With bushings and grease, and the nut tightened down just lightly, your pivot looseness should go away. If any of the looseness is in the shifting transfer rod or cross-bar, those can be addressed as well.

Unfortunately very common for some T-shift t-cases to be difficult to shift in and out of the different positions, but they don't have to be. Mine is like buttah and always has been. Doesn't look like lack of lube is an issue under there(!;D ) but it doesn't hurt to inspect the shift rods and cross-bar for dirt buildup and/or dryness. Then, as always, make sure that new fluid of the appropriate weight is installed in the case. Factory spec was 50wt motor oil (racing oils are still easy to find in single-viscosity weights like that) but many of us use a lightweight synthetic gear lube in the 75w/90 range with good results.

Lastly, make sure that your shifter's "quadrant" plate (has another name but I forget what it is) is tight, and the little tab on the shift lever is fully out of the slots when you push the button on the T-shift handle.

Anyways, I'm under it today looking for anything that can vibrate or rattle, and I see these bolt holes. It looks like I'm missing 3 bolts on the lower side of the bell housing? Or starter plate? Not sure what to call this part.

Commonly called the "engine plate" and while not critical in the short term to have those bolts, it's just a little extra support to have them installed. I think it's mostly to keep it sealed, so maybe the PO removed them to let the oil drain out of the bell housing? Looks like a lot of oil around there. Probably a combination of leaky valve covers and oil pan, maybe an intake manifold and perhaps even a rear main seal. Too many possibilities!

If you guessed 5/16-18, you're right! Got the bolts, I'll tighten that plate back up tomorrow. Is there any potential problem of that being open and loose for so long?

As mentioned, I don't think so. You're probably fine. Most of the support between the engine and transmission is in the big bolts, with the engine plate simply sandwiched in-between.

Both drive shafts are tight with no play in any direction that I can feel by yanking on them. I'll add to my list of things to do this weekend to pull the rear and spin the pinion by hand and see how that feels.

When you do, and then put them back on, remember that the u-bolts that clamp the rear joint to the differentials are only torqued very lightly to something like 5-7 lbs or so. Maybe someone can quote the exact rating before you get to that point.
The bolts that hold the double-cardan end to the transfer case end do get torqued to a more normal torque, so that's usually not an issue.

Terry, you say the "output shaft yoke nut" - is that one of the four nuts and a U-Bolt that hold the universal joint in place?

Nope, he's talking about the part that the joints are secured to. The big chunk with the ears that the u-joints fit into is the yoke. There are four on an EB, one each on front and rear differentials and two (front and rear) on the transfer case.
You can probably see a big nut behind the u-joints. That's the nut that actually holds the yoke to the pinion shaft of the diff (rear diff in your case) and the output shaft of the transfer case.

Paul