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Old 06-28-2021, 01:34 PM   #1
Hoseman1958
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Default Transmission Squeal when Braking

When downshifting in lower gears and especially when braking in my 1993 d21 4x4, there is a pretty loud squealing sound coming from what sounds like the transmission area.


There is a clicking when I depress the clutch which I have been told is an indicator that that clutch throw out bearing is going bad. I had this checked by a mechanic about 4 months ago and he said that the clutch still had some life in it.


The squealing happens when I put on the brake in lower gears (w/o clutch being depressed.) It will also make the noise somewhat when gliding downhill in lower gears. It also does it when I am downshifting in lower gears. I have hauled two loads of firewood in the past couple of days and the squealing does not happen at all when the truck has a load in the back.


I have replaced all 3 belts and get a different squealing sound from the AC belt when I first turn the AC on. That sound is not the same as what I assume as coming from the transmission when I brake at low speeds. Any diagnostic insight would be appreciated!
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Old 06-28-2021, 05:22 PM   #2
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Sounds like something is shifting out of place when you brake. Check engine and transmission mounts by jacking up on the engine and trans gently. You are just checking to see if the rubber is separated from the steel, allowing your junk to shift out of place.



Check your Radius rods that run from the lower control arms to the frame. Check those bushings. See if you can move the roods up or down by hand or by tapping with a hammer. If those are shifting, your alignment may be toeing out when you brake.


It might possibly be that your locking hubs need a little grease in the bushings. You can rule that out by locking them in and seeing if the sound stops.
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Old 06-30-2021, 02:19 PM   #3
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Thanks Res. On the way out to get a load of firewood this AM, I discovered that my hubs were locked.....and have been for the last 400 miles or so. I turned them, and still got the noise when braking or gliding downhill. Picked up the firewood and the noise went immediately away. Locked the hubs and put the truck in 4 wheel high for final uphill trek and then turned the hubs to free, put in 2 wheel drive after unloading. No noise. I'll bet I do need to grease the hubs. If it keeps on, I will get myself psyched up to do the first two examinations that you mentioned.
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Old 06-30-2021, 03:12 PM   #4
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When braking, or decelerating the rear axle stops being driven and begins driving. That is to say that the rear axle applies torque to the driveline.

So, starting at the rear axle, let's consider all of the things that could be affected by that torque:
The pinion tries to point downward. If it does, that can effectively shorten your driveshaft, relative to the center support bearing and the transfer case output. So take a gander at your center support bearing. Also, there may be interference between the dust shields at the trans output due to wear or misalignment of the outer shield. That's more of a metal-to-metal sound, though. Usually fixed by hammering the outer shield back in place against the t-case housing.
The torque may also try to twist your engine and trans in the opposite direction that it twists during acceleration. If the mounts are bad, it can cause weird noises.
We already talked about locking hubs, but when they are locked in, all internal parts are rotating at the same speed, so there should be no squealing UNLESS the needle bearings at the back of the spindles are shot. Those can squeal when the hubs ARE locked in, and can vary as the suspension is loaded or brakes are applied.


The noise's relation to braking and decelerating may be related to the front axle when the hubs are locked. In that case, the pinion tries to angle up, but (should) be held by the crossmember. That only leaves the brakes that can cause problems related to worn front end parts, i.e. radius rod bushings.
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Old 06-30-2021, 06:35 PM   #5
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Wow. Something tells me that in that post you have identified the problem. As usual, I'm going to have to get myself psyched up to, first, learn where the center support bearing, the transfer case, the dust shields, the engine mounts, the needle bearings, and the radius rod bushings are. You have already given me pretty good descriptions though.....and I'm finding some other posts in this forum and online that can help me. It may be awhile before I can tackle this....but I will update this post when I do. Is there a worst case scenario if I don't attack the problem in time?

I live on a mountain with gravel driveway and may decide to use your generous advice to communicate to a skilled mechanic what may need to be done. Haven't made that decision yet though.
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Old 07-03-2021, 04:01 PM   #6
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A neighbor with much experience looked at my drive shaft this morning and showed me that there is a big chunk of rubber missing from the center support bearing. We are going to remove the drive shaft in a week or so and replace that bearing while we try to see if there are any other damaged parts. Thank you again Reserector for lending your expertise!
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Old 07-03-2021, 08:02 PM   #7
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Make sure to mark the alignment of the DS's two halves, before removing. Reassemble with the same alignment.


Might as well do the U-joints while its out ...
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Old 07-06-2021, 07:33 PM   #8
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What LugNut said. ^^^^
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