Thump when I hit the brakes or back up

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Old 08-15-06, 07:39 PM
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Question Thump when I hit the brakes or back up

I have a '92 gmc jimmy 4x4 and when Im on the brakes right before it stops I hear a thump. It also does it when I take off in reverse and then again when I step on the brake in reverse. It happens every time when I stop. Before I would hear it only when I got on the brakes hard but now I hear it alot. I can feel it through the floor to under the driver side. Does anyone know what this is? Im afraid it will be something thats a pain in the butt to fix.
 
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Old 08-15-06, 09:11 PM
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Sounds like universal joints to me, but lets see what others say.
 
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Old 08-15-06, 09:13 PM
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Originally Posted by goldstar
Sounds like universal joints to me, but lets see what others say.
I hope thats it I was afraid of a control arm bushing
 
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Old 08-16-06, 09:59 AM
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Another reason is that the driveshaft spline shaft needs lubrication. Which i think you would have to drop the tranny end of the driveshaft spline and re-lubricate it. It works for awhile then you may have to do it again.
 
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Old 08-16-06, 11:02 AM
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Another possibility could be the brake caliper bushings worn out allowing the caliper to "knock" when braking. Can you determine where the noise is coming from for sure? Normally though, if the problem is the caliper bushings, you'll feel it in the steering wheel also.
 
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Old 08-16-06, 02:28 PM
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It's been awhile since I was working on cars for a living but I remember something about little jimmies and their chevy counterpart.

It seems like something to do with the transmission mount crossmember mount was a problem. It seems like the crossmember mount is a rubber mount and it had a habit of going bad.

Can't swear as to the years involved.

Maybe davzack ( a poster and forum mod) will catch this. I suspect he would know for sure.
 
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Old 08-16-06, 04:32 PM
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Originally Posted by nap
It's been awhile since I was working on cars for a living but I remember something about little jimmies and their chevy counterpart.

It seems like something to do with the transmission mount crossmember mount was a problem. It seems like the crossmember mount is a rubber mount and it had a habit of going bad.

Can't swear as to the years involved.

Maybe davzack ( a poster and forum mod) will catch this. I suspect he would know for sure.
From the description, I think you hit it - '92 was definitely involved.
At least 1 of the 2 frame mounts is likely broken.
 
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Old 08-16-06, 07:02 PM
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I dont feel nothing in the steering wheel and I looked today and the U joints are fine. Tomarrow Ill try to see something with the transmission mounts.
 
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Old 08-17-06, 06:18 AM
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I'd definitely check the mounts...and your rear brakes as well. I've seen rear brake systems (drums and shoes) come apart or a wheel cylinder start leaking that can cause the noise you are hearing.
 
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Old 08-17-06, 11:47 AM
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I looked today for a transmission mount problem and the only mount I seen was a crossmember that looks like a peice of pipe that goes from each side of the frame and the rear end of the tranny sits on this and is bolted down. I didnt see anythink broke or wore out. I looked up front and couldnt find nothing either. Is there a transmission mount somewhere other then this cross member? And could it be a engine mount?
 
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Old 08-17-06, 01:40 PM
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You are at the correct crossmount. It is the one the trans sets on.

Like I said, it has been awhile so the memory is fuzzy so the details may be lacking absolute correctness.


At the frame ends the crossmember is either encapsulated in a rubber mount or it is attached to a rubber mount.

I remember having to pry the crossmember at the frame end to check for the damaged area. It should be secured via its' mount to the frame but with it broken, the crossmember would lift from the frame.


sideline to davzack. Was this the series of GMs that used that clip to retain the wheel cylinder. The one that allowed the backing plate to wear out and as a not complete fix, the used those clamp on retainers???

If so, the wheel cyliner is allowed to rock (sometimes a very considerable amount) and could cause a sound when hitting the brakes as well. Especially if you were to go from forward to reverse or the inverse.
 
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Old 08-17-06, 01:46 PM
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Ok this sounds like it can be many things, did you check your wheel to see if there is any play? (wheel bearing) Check your brake housing and make sure nothing is loose or out of place. Sounds to me like it almost has to be something going wrong with your brake system if your pressing on the brakes and you feel a thump. But be safe and drive that vehicle at slow speeds.....And another thing I really dont think it would be any type of mounts, if so your motor would vibrate the whole dang vehicle while at a a stand still. GL
 
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Old 08-17-06, 02:29 PM
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Originally Posted by Deestylez
.....And another thing I really dont think it would be any type of mounts, if so your motor would vibrate the whole dang vehicle while at a a stand still. GL
Wrong, at least for these mounts. Thumping on braking, accelerating and cornering. This was an ongoing issue with these vehicles for as long as they used that design.

Nap, your memory is good.
 
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Old 08-17-06, 07:39 PM
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When it goes thump it only does it once, its not like a thump thump thump when you have a warped rotor. Its like something is getting shoved around because of some play in something like a wore out bushing. Tomarrow Ill look at the cross member again. its bolted solid to the frame so the rubber must be between the tranny and the bar.
 
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