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I hate this grinding noise

Kocher93

Kocher93

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Campbell, CA
About a month ago I was driving and I heard the worst noise I could hear (in my opinion) a grind. I figured I'll start small and change all the wheel bearings. Still that dam grind. So now I'm looking at my truck thinking what it could be. The grind happens more often when turning, but does happen when going straight. And its only when I'm on the gas pretty good.(350 to th400 to np241 to 10bolt with posi) When the grind does occur there is a loss of power, it'll stutter and make me shiver with fear of something breaking. So I have in my mind two culprits. Either the shift fork pads in my 241, or my rear diff. Any ideas?
 
This one may be tricky. When you say loss of power, does the engine bog like its under a load, or race like something is slipping?


Obviously you can't tell what direction its coming from, or you wouldn't be asking, but if its not really doing either one, could it be a misfire?

Usually a noise like that in a turn is the clutches in the posi unit. I run synthetic in mine, and it has the additive in it.
But after a couple of years the additive wears out, and then if I drive a good distance in a more or less straight line, stop and then make a turn, there is a shuddering sensation and some noise from the rear end.
The clutches have stuck together and are unsticking. I just change the fluid, and its fine for another couple of years.

Been doing that since about 1991, no problems yet.

But, I don't notice any loss of power.

If you can get it to do it at low speed, try getting someone to stand next to the truck while you turn and see if they can at least isolate it between the midsection or the rear.
 
also the transfercase may be making noises. it could be resonating down the driveshaft (or up the driveshaft)

double check your rear end and transfercase,
 
It just races like its slipping, it happened while I was stopped. The motor idled very low and then when I have it gas it wound a little and kinda clunked in and moved. Also I just replaced the U joints. I have plans to get a 14 bsf soon so if it's the rear end I'll gladly just replace it, but if its the tcase I'll have to hold off.
 
Kocher93 said:
It just races like its slipping, it happened while I was stopped. The motor idled very low and then when I have it gas it wound a little and kinda clunked in and moved. Also I just replaced the U joints. I have plans to get a 14 bsf soon so if it's the rear end I'll gladly just replace it, but if its the tcase I'll have to hold off.
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Damn, wish you had not said that.

I'm still recovering from an all day session at the office trying to get some paperwork straight, so my head is not completely in the game, but I'm afraid that you are looking at transmission problems.

There is not a lot in the rest of the drivetrain that can slip like that. Its all gears.
If a spline was slipping, or something like that, it might grab a couple of times, but its going to just slip all the time after that.

In theory, if you had a broken axle, or one side of the rear chunk not working, then the posi unit might still drive the truck and slip like that.

You might jack up one side or the other and try to turn the rear wheel to see if there is any noise or massive slop.

But it sure sounds like the transmission is not engaging when it downshifts.
You might luck out though. First, check the fluid level in the transmission. If its low, you might have damaged the clutches or not, but filling it up and fixing the leak should get you by for a while.

I'm sure someone else will chime in, but I am also thinking the governor on the side might be slipping.
Also, pull the hose off the vacuum modulator on the side of the transmission and check for fluid inside.
If you find any at all, the modulator is bad plus the engine is sucking fluid out and burning it. So, its going to be low.

What bothers me, is the grinding noise. Most of the time an automatic transmission does not make that kind of noise for this problem.
 
Plus its hydraulic isn't it?, so it wouldn't grind would it? Someone told me there's pads on the shift fork inside the 241 that if they wear off it can slip out of gear while driving, can anyone confirm? Also I just recently replaced the drums, but when I jack up the rear end it has the same feeling as an out of round brake drum.
 
Well, the transmission is hydraulicly controlled, and the input is a fluid drive. But there are plenty of gears and bearings inside that can grind.
Plus the front pump and torque converter.

The problem with it being the shifter pads, is that when it slips out of gear, it stays out of gear until you shift if back in.
So, its unlikely to be that.
I would check the fluid level in the transmission with the dipstick under the hood before you do anything else.
The grinding noise might be separate.

Give me a little better description about the out of round drums. Do you mean the drums are wobbling as they turn?

Or there is a vibration?
The only time I notice an out of round drum is when I am braking. Then it pulses.

If something is wobbling on the back, it may be the problem.
 
I have 33s with 4.88 in the diffs, if it's jacked up the rear will go a little and then it will get really hard to push, then it will get easy and repeat. Yes it shutters in 2hi, I just got back from a drive and the motor doesn't change it just doesn't feel like something is engaging somewhere if I let off the gas it feels like it slips in.
 
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I'm not ruling out the t-case yet but as said earlier it will typically pop out of gear and stay there till you mess with the shifter again. I can see how if it is just slightly off it may be enough to force it out and slip back in when the RPMs drop back down. I had a t-case shift fork failure that would just pop out of gear and start grinding away for no real reason. But wouldn't go again till I fussed with the shifter.

The other culprit is the rear axle. Stripped out pinion or ring gear or both. 4.88s on a 10b? I hear that can be a common issue.
 
Stripped out pinion or ring gear or both
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I thought of that too, but it should be jumping all the time. What if one axle or pinion gear was stripped and it was running on the posi?
 
New update: drove it in 4 hi on the street, still made the grinding noise, but kept going. I'm thinking the rear end needs to be replaced.....with a 14 bolt.
 
Well, without opening stuff up for visual inspection, you can think anything you want. It's probably worth jacking up the rear and spinning things by hand, see if anything is loose, etc. Time to get hands on with this thing.
 
Well, he is using a valid diagnostic technique. One I have had to use from time to time. Just drive it until something either seizes, breaks or falls off.............

BTW, he is wrong about that being the worst noise you can hear......

The worst noise, is when you are half way out a window, naked. A guy has your nads in one hand.
Then you hear the worst noise.
The sound of him trying to open a pocket knife with his teeth...............
 
Fordum said:
Well, he is using a valid diagnostic technique. One I have had to use from time to time. Just drive it until something either seizes, breaks or falls off.............

BTW, he is wrong about that being the worst noise you can hear......

The worst noise, is when you are half way out a window, naked. A guy has your nads in one hand.
Then you hear the worst noise.
The sound of him trying to open a pocket knife with his teeth...............
Click to expand...

I agree on both points.

And am wondering if there's a story to go along with the second. :haha:
 
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