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1972 BRONCO SPORT HUMMING/WHINING NOISE ISSUES

summerlife

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Feb 21, 2015
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Hello, first time posting hear. I've been a member for a long time but sold my first un-finished bronco when i went to college a while back. I just bout this rig about a week ago. I've driven it over 6hrs already around 55mph. Right before I got the 39.5" super swampers off I started getting this humming noise. It also sprung an oil leak somewhere but I'm not sure if that's related as it seems to be the valve covers.

So here is my issues. In 3rd or 4th gear i get this humming noise and maybe a little vibration. As soon as I let off the gas the noise stops and if I push the clutch in the noise stops. Brakes don't seem to make a difference In noise. Makes the same noise in 4hi, 4 lo, and 2hi. It's not as bad in 4low due to lower speeds I'm thinking. It specifically sounds the worse right when your about to let off the gas or if your lugging it a bit in a higher gear and trying to get up to speed. So far I changed the oil in my engine, transmission, and transfer case and they didn't show any signs of excessive metal and had appropriate levels.

Then I took the rear drive shaft out and drove it in 4hi and the noise was gone. This leads me to think its the rear end somewhere. The driveshaft seemed fine when it was off but I'm no expert. So I greased it up( has greaserts) and put it back on. The noise is still there with no change so the greasing didn't do anything so probably not the drive shaft. The rear diff is a 1977 9" out of a f100 and it has a full spool in it.

lastly I jacked up the rear end and spun the wheels and the pass side drum seems to be rubbing or something and there is more play on that side. I'm waiting on a spline drive set( has special lugs) and then i will take the tire off and see if the drum is all blown up or something and if not then I will take apart the rear diff and change fluids/ inspect.

I also noticed that when I jack the front end up with the lockers off and in neutral the tires are hard to turn even with two hands so not sure if that's normal or if the brakes are dragging? It has a Detroit true trac lockers in the front in a dana 44. Also not sure if the dragging brakes could be the issue because the symptoms don't really line up.

The noise started before the tires were changed so I'm confident it's not the tires. Also the brake system sucks and it could be that and if that's the case then I will know once i install the hydro boost from toms. I have video's of the sound if anyone thinks that will help diagnose. I'm swinging by a driveline shop tonight to see what they think after I run a couple more tests. The bronco was used as a plow with those giants 39.5" tires so not sure if that cause excessive strain and the mileage on the road is what did it in. It sat barely being used or moved for aprox 12 years

My question is what does the issue seam to be? I feel I have crossed off many things that could be the issue but to me it seems its one of four things
1: rear axle bearing
2: pinion bearing/gear
3: rear drum brakes
4: transfer case( although shouldn't this make noise still with the rear driveshaft off)

Also here is the general driveline setup if that helps
1990 ford f150 302
1977 ford f100 np435 with 4 speed manual hooked up to a np205
custom driveshaft with double cardan u joint in the front by t-case then normal in rear hookup to diff( same in the front)
9" rear diff with 4.56 gears and full spool and drum brakes in the back
dana 44 in front with Detroit true tracs in front and disc brakes
 
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summerlife

summerlife

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Ok so I brought it to a driveline shop to have the guy go for a ride in it and first off... he couldn't believe i drove this thing three hours home.. and that's with tighter steering and better tires lol. But hey gotta do what yah gotta do.

The owner of the shop said that he agrees that its the rear differential with the amount of noise it's making( getting worse quickly). I also got out and felt the rear diff when I parked at the gas station after only a 10 min drive and wow was that sucker blazing hot.

So when i got home I pulled the drain on the 9" differential and nothing came out but it wasn't far from the fill hole. Let me tell you what though that stuff absolutely reeaked. Almost stole my breathe away how nasty it smelled. I instantly knew i was on the right track with the smell and pulled the rear axles and bam metal glitter everywhere. might as well have been metal paste. I then pulled the third member and found even more shavings.

There is no damage to the axles that I could see so that was good and i also couldn't see the damage ( im no expert) to the third member but when i spin it in the forward direction it for sure makes odd noise. Thinking its the pinion gear or bearing.

I'll probably bring it to that guy and have them rebuild it as i don't have bearing equipment.

Still have two questions though.
1: How do I clean the axles tubes to get rid of the metallic oil before re-install
2: Am I ok with just getting the issue parts fixed or should all the bearings at the very least be replaced due to the presence of so much oil.
 

DirtDonk

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Just to let you know, that horrid smell may just have been the normal gear oil smell when it includes the friction modifier ("old stinky") used in limited-slip differentials.
With yours having already been modified, maybe the replacement gear lube had the additive in already, or someone still added it not knowing that yours did not need it.

Not sure the best way to clean the tubes, but there have been many tricks tried over the years. A rag on a stick soaked in degreaser is workable, but you might have to scrape the pasty stuff out first to give the solvent a fighting change at removing the rest of the residue.
Someone used to have a cute and clever signature line about using a cat on a string, or squirrel on a rope, or something like that, to clean your axle tubes. Don't remember the details, but it was pretty funny. If not exactly politically correct in certain company!

Yes, replace all the bearings! Unless you know they've been done in the last 30k miles or so, just do it. We call it cheap insurance!
Nothing to due with the "presence of so much oil" though. Not sure what you meant by that, but oil is supposed to be there. It gets everywhere, which is why there are seals at the outer ends of the axles.
While you've got it apart though, check to see what type of axle bearings you have. And how many splines your axle shafts have.
Stock was always 28-spline for EB's, but an upgrade is 31. As was mentioned already? But with all the mods done to yours, they may have been upgraded already and tapered roller bearings used.
If the axles have the tapered rollers rather than the stock sealed bearings, then there is no seal used in the end of the tube and the gear oil is expected to keep the wheel/axle bearings lubed.

If you have a spool in the rear and a Truetrac in the front, you don't need oil with the friction additive for limited-slips. Yours are all gears.

Paul
 
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summerlife

summerlife

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Thanks for the response. I brought it to the driveline shop everyone recommends and he showed me where the wear was on the gears and the excessive amount of backlash. He thinks it wasn't installed right and just took time to show itself. I checked the axle bearings and they seems fine. I will probably just use a rag on a stick like you said and clean the tubes out best I can. I'll be ordering a rebuild kit for the differential today.

Hoping this resolves the noise issue. If not I'll being the driveshaft in to make sure it's in good shape. Also it is a 31 spline set up in the back but not sure if the bearings are tapered. they look standard.

On the plus side my delivery from toms off-road got here but I won't have time to work on it until next week. Going to install the new Bilstein shocks and hydro boost. Reliability and safety are my first main goals with this build.
 
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summerlife

summerlife

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Ordered a new set of ring and pinion and bearing kit from toms. They recommend the motive all performance brand ring and pinion. Hoping they are decently quite and hold up. anything will be better then they are now.

I was surprised how much parts are when you can get complete third members for a couple hundred bucks more but at the end of the day its still cheaper and I know for sure that this one will be rebuilt.. never know what a used one is going to be like. Tried finding one new that was close but they run around 800$ and it wouldn't really be an upgrade. Hopefully I don't just hate the full spool... seems ok so far before this issue
 

Justin Palmer

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Ordered a new set of ring and pinion and bearing kit from toms. They recommend the motive all performance brand ring and pinion. Hoping they are decently quite and hold up. anything will be better then they are now.

I was surprised how much parts are when you can get complete third members for a couple hundred bucks more but at the end of the day its still cheaper and I know for sure that this one will be rebuilt.. never know what a used one is going to be like. Tried finding one new that was close but they run around 800$ and it wouldn't really be an upgrade. Hopefully I don't just hate the full spool... seems ok so far before this issue
Listen to DirtDonk and replace the wheel bearings while you’re already in there and everything is taken apart. It’s a pretty simple job.
 

DirtDonk

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Thanks Justin. Summerlife that’s because the bearings on these things often fail. And sometimes catastrophically so. And they are very rarely checked or replaced by previous owners.
However, since you say you’re not sure what the bearings are, but they are 31 spline axles, can you send some pictures? Either post them up here somehow, or send them to me and I can post them up.
If they are standard sealed, and they feel OK, they’re probably fairly new and quite expensive to replace.
If they are tapered, they can have trouble resealing and keeping the gear lube inside, but other than that they are probably not worn out.
If they are tapered, you might use a little extra sealer on the perimeter when you reinstall them.

So, either way, there are things to look out for.
 
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summerlife

summerlife

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Ok I'll take some pics when I get home. They don't seem like they will be hard to replace if I need to. I'll give them another look to make sure though.
 

DirtDonk

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Great. You can put them in your "garage" or "gallery" locations in your User CP above. Or you can e-mail them to me at paulb@wildhorses4x4.com and I can post them up into this thread.

Looking forward to seeing what you've got.
The good news is that, either way, since the axles have obviously been replaced at some point (spool and 31-splines guarantees that) then at least the bearings are not original with half a million miles on them!
But they definitely still deserve a look-see to make sure they're in good shape. Glad you had a pro check them out, but I'm still curious about them.

Thanks

Paul
 

raleigh_bronco

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Interesting post and I would vote to save it in the 9” archives here in the Tech section.

I was thinking the original issue was play in the bearings on the TC output shaft, but glad to hear that you’ve solved the issue.
 

DirtDonk

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And for any experts out there, does the presence of a spool in place of an actual differential have any indication for the reasons that the current gears are worn out or otherwise damaged?
I know spools are usually the bane of anyone's existence when used on the street, but thought they were relatively benign to the internals and anything upstream of the tires.

And I wonder too summerlife, could the fact that your rear end gears are wiped out have anything to do with why you're not bothered by driving around on the street with a spool. I hope not, but if you are going to see a bid difference (on the negative side of things) when the gears are fixed, are you still going to like driving around with a spool?

I drove in a Bronco with a spool on 37's for less than a few miles and realized within seconds of getting in that I would never tolerate that kind of action on a street Bronco. The owner felt the same way and after just a few months, swapped out his spool for a more street-friendly limited slip.
Maybe someone can tell us if the damaged gears and the spool and the lack of trouble on the street all have anything to do with each other.

Paul
 
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summerlife

summerlife

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Yes I was just debating that same issue with the drivability. I was debating Detroit true trac since I have one in the front already but that's the same cost as the rebuild just to get it so i figure I would just try it out first. I'm sure the spool has something to do with the wear issues but the pro said it seemed to have been set up wrong. Something about the backlash and he showed me and there did seem to be some sever amount of play. But he said the bearing actually felt fine( still replacing) and it was probably just the set up was wrong. I think me not minding the spool may have been due to how much of a beast this thing was to drive home.. white knuckling for 3.5hrs straight at night lol. There were so many handling issues that I may not have attributed or noticed the issue from the spool.

Combine that with what the previous owner told me- He said he barely drove it around over the last 12 years and has owned it for 22 years. It was used as a plow with 39.5" super swamper irocs for a good portion of that. So I'm thinking it has to do with the giant tires and the extra torque on top of that from plowing. Combine that with a full spool and id say it held up well for a good long time and just needs to be properly set up and rebuilt.

Also my pinion is pointed up quite a bit due to the 5.5" suspension lift and the pro said to try and overfill it a bit to help keep everything oiled due to the angle. I'm going to measure my angle and see if its way off and if I can do anything about it but if not ill just leave it.

The truck seems much happier with the smaller better balanced AT 35" firestone tires so I'm hoping this issue will be resolve but I won't know if it was truly the issue or just a symptom until I can drive again. If the truck still doesn't handle like i want with the updated brakes, tires and shocks then I will have to look into replacing the spool. nice thing with these third members is that is pretty easy to take out and get done. I like to do most of my own work to save money but also because i enjoy knowing i did it but things like differentials and transmissions I stay clear of... ill even do lifters in my 2010 Silverado but that's as far as I go.

raleigh_bronco- that was at the top of my list for one of the potential causes as well. It does leak it seems but hard to tell until i get the new valve covers on as they leaks like and sob and drip don and all over. I thought that or the driveshaft besides the rear diff. I also seemed to have a rear drum that was sticking or something( updating to disc since i don't feel like dealing with drums and the cost to fix/replace them isn't much less then a rear disc kit from summit. The front disc are run off the stock master cylinder and stick like and sob too due to not having the right valve pressure set up for discs. It already drives so much better so I can only imagine once i get all that fixed

Also out of curiosity I have a question. I want to keep updating and adding to this or a thread of the build and any issues/ updates I do to get to the " final" product. Is this thread ok to do that on or should I start one somewhere else for a full thread on a build type of thing?
 
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DirtDonk

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Well, to my way of thinking, if it has anything to do with the rear end, then whether it’s during the build, or just refurbishing the differential, I would add it here.
However, for the larger, overall build, I would start another thread with that in the title. Then add a link to this discussion if anything comes up about driving with a spool or the damage to the rear end that you want to fix.
That way they are at least linked, but you have a general overall build discussion going on. Rather than just the title about the rear end.
 
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summerlife

summerlife

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I'll have to send you the pics of the bearing. I'm thinking big bearing? Getting a rear disc conversion kit. I check them again and they seem fine..not sloppy and no bad noise and are smooth when turned.

I decided to go ahead and just swap the full spool out with a grizzly Yukon locker. Figured it was being rebuild already anyways and spool isn't preferable for me.
 
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summerlife

summerlife

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Attached some pictures from a page i made for my bronco on Facebook to be able to share pics here. Do the bearings look like they are the larger bearings or the smaller ones? I' assuming larger ones due to the upgrade 31 spline but i will measure tonight.

I took off one of the shocks and replaced it with a Bilstein 5100. The old shock was trashed... could easily bottom it out by hand. It was also smashed in at the bottom to clear the axle. So I'm thinking once i get the new shocks in, disc breaks, new limited slip (vs full spool) and upgraded hydro boost that this truck is going to ride like a new truck compared to before.

I'm thinking the lack of shocks mixed with full spool and 39.5" tires is probably why the gearing started to go south.
 

DirtDonk

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I can't imagine that the bad shocks had anything to do with the gear failure, but you never know. However the spool could easily have contributed.
Again though, it would be nice to hear from spool experts (which we must have around here!) their experiences and knowledge on the subject.
In some ways, a spool is actually quite mild on the components because there is no harsh locking and unlocking going on. Inputs are generally milder than a locker.
But then the inputs are also constant! Every time you even slightly transition direction, or if one tire is not precisely the same diameter as the other, there is stress being put on something.

Paul
 

DirtDonk

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And sorry i did not get the pics. Something is going on with my WH e-mail and, pictures or not, I don't seem to be getting them to my computer.
Working on it though...
In the meantime thanks for posting up the links.

Paul
 

DirtDonk

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Do the bearings look like they are the larger bearings or the smaller ones?
Just measuring them, or the hole in the axle tube, will tell the tale.
If it's just over 3" then it's a big bearing.

However, I believe that because your pic is showing a tapered roller bearing, it must be a Set-20 model and therefore a large bearing equivalent.
I assuming larger ones due to the upgrade 31 spline but i will measure tonight.
No guarantee with a sealed bearing, but with a tapered roller, I think it's pretty much guaranteed to be a big bearing. I could be wrong though.
There is a bearing that will fit with the small bearing housing end and 31 or even 35 spline axles. But if I remember it's only available in a sealed ball type, and not a tapered roller.

But we'll know 100% as soon as you put a tape measure to it.
If you have 11" drums too, it's a big bearing. If you have 10" drums in some years, it's a small bearing. But in some other years ('74 and '75 only I think?) you could get the big bearing with small drums. A setup we have called "medium duty" for quite a few years now, to differentiate the combinations.
But even with adding the "medium" and "tapered roller" to the mix, there are still only two bearing sizes. Small and large.

Paul
 

DirtDonk

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Oh yea, sorry I forgot you said originally it's a 9" out of a full size '77 truck. Different beast potentially.
I'll have to check the books (or wait for someone with a better memory to chime in) but by '77 I think the trucks were ONLY getting the tapered roller Set-20's right from the factory.
At one point there were other choices depending on the GAWR of the particular truck, but at some point in the mid to late seventies Ford used the big tapered bearing exclusively on the light duty pickups.
And big Broncos...

So your chances of it being a big bearing just went WAYYY up by about 100% (ok, maybe 99.9% or so).

Paul
 
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