Clunking in reverse. UPDATE - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 03-15-2005, 10:35 AM   #1
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Default Clunking in reverse. UPDATE

OK i noticed a new problem. I'm gonna try and explain it as good as possible. When i'm backing up, and i step on the brake to slow and go into drive, i get a clunk. It sounds exactly like an engine moving with a busted motor mount. But the weird thing is that if i'm in reverse, and punch the gas up and down, fast and slow, it won't make the noise. I HAVE to press the brake to get it to do it. Hard or soft, it doesn't matter. I've checked all four motor mounts, 2 front 2 rear, and they are all intact as far as i can see. I've never gotten this sound in drive, only in reverse, and only when pressing and the brake. I can do it multiple times if i pump the pedal also, but if i just punch the gas nothing happens. This has got me stumped.
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Old 03-15-2005, 12:11 PM   #2
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I'm thinking rear brake cylinder. Does it happen more in the rain? Does it feel like the rear of car jumps up a little? I think the cylinder is stuck and pressure builds up until it finnally releases and causes a violent action in one of the rear drums.
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Old 03-15-2005, 12:31 PM   #3
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Have you watched to see all of the mounts in action with the aid of a helper?

I have seen all of the mounts on the older H bodies fail at one time or another... Usually the passenger front or passenger rear mounts will go first... I have replaced a driver front mount( trans ) and passenger rear( firewall side ) mounts<--- This one was supposedly fluid filled... Now the passenger front mount ( engine mount ) need to be replaced... Its intact, but it moves way too far, and when you goose the throttle and let off the engine drops back down with a thud... When I get to it, I'll do the front motor mount and the drivers side rear tranny mount together...

just check and see if the 3800 is moving a little too far... Look on the hood insulator and see if you have an alternator and or coil pack mark on it... Good luck

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Old 03-15-2005, 02:04 PM   #4
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I like the rear brake cylinder theory too. I do think my passenger rear one sticks, because i've seen the wheel slide on ice then the brakes aren't even applied. I have revved the motor by myself under the hood, nothing moves more than a little bit, the motor doesn't have any excessive movement. I can't see the underhood insulator marks because there is no insulator under the hood of mine.
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Old 03-15-2005, 03:42 PM   #5
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Yep... In that case check the wheel cylinders for broken springs, wear and tear...

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Old 03-15-2005, 11:04 PM   #6
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Is there any secret to the passenger side front mount ? Looks like the a/c must come off to get at the block bolts.
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Old 03-16-2005, 10:45 AM   #7
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Quote:
Originally Posted by padgett
Is there any secret to the passenger side front mount ? Looks like the a/c must come off to get at the block bolts.
I was actually wondering the same as thats the next one on my list... We have done a couple in the past, But I forget what we did for them..

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Old 03-16-2005, 04:49 PM   #8
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Mine are shot.. holy crap they are killer horrible. My engine moves about 1" in park! I don't even want to think how bad it is in drive. I can move the engine a little by hand also.. so I know mine are all gone. And alec, you need to get a helper to observe the engine when in drive or reverse. Revving in park doesn't really do a whole lot of good, because the engine isn't under load.


-justin
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Old 03-16-2005, 04:54 PM   #9
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Quote:
Originally Posted by opensourceguy
Mine are shot.. holy crap they are killer horrible. My engine moves about 1" in park! I don't even want to think how bad it is in drive. I can move the engine a little by hand also.. so I know mine are all gone. And alec, you need to get a helper to observe the engine when in drive or reverse. Revving in park doesn't really do a whole lot of good, because the engine isn't under load.


-justin
Damn... I hadn't even noticed that... I guess 20+ hours will do that...

Yes you will want to observe the mounts under load... Have a friend or someone hold their left foot on the brake with the emergency brake applied... Very important to keep the brakes firmly planted...

Place the car in reverse and observe the engine movement, Give the throttle a slight tap to see if these is any movement..

Then place the car in drive and see how much movement you have... Reverse will tell you about the rear mounts, and drive will tell you about the front mounts...

Good Luck

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Old 03-16-2005, 05:07 PM   #10
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Observe from the fender side and not from in front of the car. Sos ya dont get run over. If something happens, then all you hafta do is step outta the way of the mirror.
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