Hey guys.

85 pickup with a SFA and a recently installed front e-locker, w/ new gears, new seals etc.

I just experienced a bad grinding noise when I brake hard(ish) going downhill with the hubs locked and the transfer case in 2hi. With the hubs unlocked in 2hi there was no grinding when I braked. Steering seemed fine. Pads looked fine a week ago. I didnt notice any noise when i was just driving around town to break in my gears with any combination of [locked hubs & 2hi] or [unlocked hubs & 4wd]. I wasnt able to climb anything in 4wd as my local trail is closed, but I didnt hear anything when I climbed up a couple of small dirt piles on the side of the road.

Anybody know whats going on here? Bad hubs? partially engaged locker? Something in the t-case?

Thanks

 

Does it do it, in the same situation, with the T-case shifted to 4H or 4L? I'm leaning toward a hub but would like to know if it does in in 4WD. Trying to rule out the t-case so we can move forward and shorten our list of suspects.

 

I just took it for a couple of laps around the block to test more. It does appear make the same grinding noise in 4hi (w hubs engaged). The grinding will go away if I unlock one hub and leave the other locked but it doesn't appear to matter which side is locked or unlocked.

Also, I locked and unlocked my e-locker at super low speeds. Seems like that is engaging and disengaging. Steering gets super awful when locked and is fine when unlocked.

 

Do you have Aisin hubs or something else? Mine are Warn which are nothing like the factory hubs. Far simpler but a third as tough in my opinion. I plan on going back to Aisin when I get a chance. I can't remember exactly what the deal was with mine but one time I was putting them back together after going through them and before I lowered the jack, I locked the hub and spun the wheel to check by work. Had some kind of similar issue. I had to take the hub about half way down and adjust something but can't remember what it was. May have been the orientation of the outer housing but can't remember. I do know that I could feel the problem with one wheel off the ground and rotating it with hub locked and then unlocked. I could feel the issue and knew it wasn't right but never tried to drive it that way so I don't know if it would have given the symptom you are getting.

Steering on pavement is going to be close to impossible with that locker engaged. Avoid it if at all possible as you can damage it if your wheels can't easily slip.

 

Yes, the locking hubs are Aisin. I tested their operation on the jackstands when I reassembled the axle recently and they seemed to operate correctly when i did that. I had some trouble reassembling one but I think it went back in correctly. Perhaps ill jack em up and try again. Is there anything visual I would see if I pulled them off and had a look? shredded up teeth or something?

 

The problem occurring only when you hit the brakes hard has me a little thrown off. Especially when you only have the problem with hubs locked. You can just about rule out the brakes in that case. It does it in 2WD and 4WD so that would almost rule out the T-case. So now let's think about it, When you hit the brakes with the hubs unlocked the stress is limited to the wheel bearings and the brakes and you get no grinding. When you hit the brakes with hubs locked, the stress is transferred to the axle shaft all the way to the diff. I know that's not what you want to hear but we're just about there. Is there any way you can simulate the conditions in which it grinds with the vehicle off the ground where someone could safely listen for the source of the noise? All of my experience with lockers is with log trucks which are air actuated. I can tell you that if an air actuated diff lock is receiving some but not the required air pressure, for whatever reason, you will get a grinding similar to what it sounds like when you let a 10 year old girl drive your stick shift.

Try to rule out the hubs by unlocking one and locking the other. The odds that both are causing it is slim to nil. Then move on back to the diff.

 

So i put it in 4wd jacked up each front wheel and rotated the wheels back and forth. The jacked up wheel doesn't spin with the hubs locked. spins fine with them unlocked. same results for both sides.

One thing i did notice was that there was some free play if you shook the wheel back and forth (hands on the top and bottom of the tire). Perhaps my wheel hubs are a bit loose? I could see how this could cause vibration that might be confused with a grinding noise, but i can't see how it would make any difference if the hubs were locked or not.

 

Charchee,
Your logic pointing to the differential makes sense, but I can't figure out how the brakes would effect the diff? with the hubs engaged I can still do 60 and drive around on windy roads with no whine or grind etc. If the locker was partially engaged/ partially disengaged i would expect it to make a racket when I'm going around hairpin turns and the wheels are spinning at vastly different speeds right? The noise I'm hearing is happening in straight line braking situations. Would a trying to brake hard with the clutch in vs clutch out make any difference? It would take the load off, but there shouldn't be a load when its in 2hi, hubs locked...

 

Man I just wrote you three paragraphs and then confused myself. It's been a long time since I owned a solid axle vehicle and never one with hubs that could unlock. I really feel like I'm feeling my way around in the dark without being able to hear the grinding sound along with the duration and without being able to feel it in my hands and feet. Does it pull at all to either direction when you hit the brakes? Your best bet is to try and get it to make the sound with the wheels off the ground or at least put the same torque on it somehow in the other direction by dumping the clutch in 4WD climbing a hill and see if it does it.

What I was trying to communicate before I deleted it was only going to be the case if the front and back drivetrain was all connected like with the t-case engaged. In that case when you hit the front brakes which will apply before the rears, you would be applying negative torque on the front drivetrain components because you are stopping the front axles while the back half of the truck is still moving forward. If say, you had no back brakes and you hit the front brakes in 4WD, the back tires would stop as well because when you slowed down the front wheels, which are locked to the axle with the hubs locked, you would be slowing the entire dirvetrain with only the front brakes and every joint in the drivetrain would be loaded up with torque. That's the only way I know of that you can load up the drivetrain by hitting the brakes. Where the weak link is, is what we would have to figure out.

I am absolutely not trying to tell you where your problem is. I'm only bouncing ideas off you. I feel like, if it's in the front diff, you will be able to replicate the sound in forward gear if you can find a way to load up the front end with torque in that direction. One more test that I would try would be to get the truck off the ground and make sure the T-case is not trying to pull the front end in 2WD for some reason. Hubs locked in 2WD will be spinning the shaft all the way back to the case. If the case gears are not making some kind of minor contact with the output shaft, which you would see with the vehicle off the ground and maybe your hand on the forward drive shaft, then move on forward to the diff and start trying to rule it out.

If I were forced to bet on it, I would put my money on the new locker making minor contact when not engaged. You said it's an e-locker. Is there any way you can engage it while in 2WD with the hubs locked? I know you can on that old truck. If you had it engaged all the way and then couldn't make it grind when braking 2WD hubs locked, that would give you a real target to inspect.

 

Hmm, those are all lots of good things to think about. Im also completely confused by this situation…..

Im wondering if maybe i should try pulling off the rear driveshaft and trying it out in 4hi. I could isolate the front drivetrain and load up the front end if I hit the gas hard in (effectively) FWD. Hitting it hard in reverse would replicate the same negative load that braking hard would cause right? Likewise if I put it in 2hi with no rear driveshaft and the vehicle creeps forward it would suggest that the front end is getting contact/ power from the t-case when its not supposed to.

The locker-engaged brake test is a good idea but Im not sure how to do the test with the locker engaged. The grind happens when I brake hard so i need to be traveling at least 25. If I did it on a dirt road Id probably just lock up all 4 wheels and slide (no abs) and if I did it on the road Id probably snap a birfield or worse. When I engaged on the pavement before i was doing like 1or2 mph.

Seriously grateful for the idea bouncing btw. Please keep the suggestions coming

 

I agree with all of that. Like I said before, I don't have much experience with the lockers and didn't think about the potentially high speeds that you would need to test it with the locker engaged. Good call. I hate for you to have to pull the drive shaft. Like I said before, you can verify that your T-case isn't partially engaging by setting the truck on blocks and putting it in gear but taking the shaft out would absolutely rule out the half of the drivetrain. It probably doesn't have anything to do with the rear brakes but they would still be in the equation however unlikely. The only thing that could put them into consideration would be the fact that it only happens when you brake hard which would be when they really kick in.

I'd really like to hear this grind. Does it sound like gravel in the brakes or does it sound more like trying to put a truck in gear without having the clutch pressed in all the way? Is it high pitch and erratic like a tire sounds when it drags across gravel, or is it like click click click click / pop pop pop pop etc. very fast and with equal intervals between the clicks or pops?

 

I'd say the noise sounds somewhere between gravel getting crushed and grinding gears. Not a click click pop pop or a screach. Maybe I can record it if I kill the engine when I hit the brakes.

I've read about some similar symptoms in the 86+ ifs generations that were attributed to dry/bad spindle bushings. Anybody got thoughts about those? I'm assuming this axle has something similar right?

 

To specify what I mean by halfway between the two noises, the grind does not have a perfect tempo of teeth hitting each other at perfect spaces/ perfectly timed to a consistent rotation like trying to jam a tranny into gear without the clutch

 

I've been thinking about this all day today and I still don't have it figured out. I did think of a couple things to test.

#1 Jack up one of your front wheels while in 2WD and shake the fire out of that tire while feeling for slack anywhere up there. Rotate the tire slowly and then spin it while listening and watching for any evidence of binding. Put it in 4WD with hubs locked and try to turn the tire with the axle locked in position. See if you can force that hub to slip. I know you are checking a lot of things here but you can do all of this in a matter of a few minutes. Repeat on the other side. You are looking for a bad wheel bearing which can only make noise when braking. They normally do it all the time and not just when braking but I have had one that only did it while braking until it really started to come apart. You will also be looking for a hub to slip which isn't likely if you put them all back together correctly the last time they were apart.

#2 Remove the front drive shaft and see if it still makes the noise. This is going to rule out your transfer case or indicate that it's the problem. The way I see it, there are only two joints in the drive line that are selectively coupled and could slip. They are the locking hubs and the transfer case. I've never been inside the transfer case on one of these so I can't help you too much if you trace your problem to it. My only theory on it would be that if you had some minor contact like partially engagement you wouldn't hear the noise in 2WD going forward because the rear wheels are pushing the truck forward and contact with the ground at all four tires keeps everything synchronized. When you hit the brakes, the front drive line will slow down before the rear drive line does. For just a second, when you hit your brakes, if anything was touching inside the case, you would hear a grinding sound under you until the front and rear drive lines match speed again. Make sense? Whatever you find here, you will cut your list of suspects way down and if you still hear the noise, you breathe a little easier knowing you don't have to crack open the case. If you don't hear it anymore, I would drain the transfer case and inspect the fluid and plug for metal pieces.

Let us know what you find.

 

Ok. So i did two experiments last night...

#1 I removed the rear driveshaft so i could see what happens in FWD. Even with the front drivetrain isolated I could not replicate the grind when accelerating hard in forward or reverse. It did still make the grind when braking hard. This did make all the noises a lot more clear though. With the rear shaft removed I started to hear more of a rattle at certain speeds.

#2 I put the rear driveshaft back in and removed the front driveshaft. with the front driveshaft removed it does NOT make the grinding noise when braking, or the rattle noise at the speeds mentioned in my first experiment. 2hi/4hi doesn't seem to matter.

So this seems to indicate one of 2 things to me. Either it is the driveshaft itself (bad u-joints or out of balance) or Charchee is right and there could be something going on in the t-case. Reeally hoping its not the t-case….

Some of the clues are pointing me towards the u-joints. I had an old bimmer that had some similar symptoms when the rear u-joints went bad. In any case I can replace those first for a lot less money than the transfer case.

Anybody got any thoughts on the u-joints?

 

Now pull both drive shafts at the same time and try it. Just kidding.

You probably would have noticed a damaged u-joint when you took out the front shaft but if it's still out, go ahead and change them just for fun if you like. If you installed a locker, it's clear that you intend to put some stress on that shaft and some new, maybe upgrade, u-joints wouldn't be a bad idea. That will also go ahead and rule out the drive shaft all together. If you have the shaft back in, try greasing the heck out of them and see if that quiets your noise any.

Maybe somebody out there can fill you in on exactly what is and isn't supposed to be making contact when you are in 2WD with hubs locked.

 

Mystery solved! (I think)

Apparently the driveshaft and my exhaust were interfering. The exhaust and driveshaft are on the same side on my 2lt diesel. Upon closer inspection I found a fresh scrape/ grind in my exhaust just after the downpipe and a corresponding spiky bit of metal where the factory had done a sloppy weld on the driveshaft. It looks like when the suspension compressed under braking the driveshaft angle changed and the spiky teeth starting grinding into the pipe. I still cant explain why this wouldnt happen when Im in 4hi with the hubs unlocked, but it seems to be the culprit. Should be good to go with a little grinding or a BFH mod. Worst case it could be a good excuse for an inch or two more lift!

I did change the axle side u-joint and grease up the double cardan side and that seems to be in worlds better shape now. So at least my driveshaft got some love