Author Topic: Clunk sound when in reverse  (Read 1034 times)

Offline Captain J

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Clunk sound when in reverse
« on: October 18, 2021, 11:28:29 AM »
Hello
My 1986 GMC Sierra K2500, make a clunk sound when I put it in revere?
Anyone know why, and the solution?
Thanks

Online bd

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Re: Clunk sound when in reverse
« Reply #1 on: October 18, 2021, 12:34:32 PM »
Clunking with the engine fully warmed up at idle RPM or cold with the choke still partially closed? 

Check the driveline u-joints to make sure they are tight with no visible evidence of rust tracks.  Give them a shot of grease if they are greaseable.  Then, with the park brake set, engine not running, and the transmission in neutral, check how many degrees of free rotation there are in the driveline, stop-to-stop.  Check the condition of the transmission mount.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Shifty

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Re: Clunk sound when in reverse
« Reply #2 on: October 18, 2021, 01:01:46 PM »
BD has the most likely answer, but....does it do the clunking while putting it into reverse?  A lot of shift kits make the hit into reverse hit harder as a side effect.   
87 V20 Standard Cab Longbed (current)

87 R30 3+3 Longbed (days of yore)

98 C2500 ext cab longbed

Offline Captain J

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Re: Clunk sound when in reverse
« Reply #3 on: October 18, 2021, 02:07:25 PM »
Clunking with the engine fully warmed up at idle RPM or cold with the choke still partially closed? 

With engine fully warmed up at idle.

Check the driveline u-joints to make sure they are tight with no visible evidence of rust tracks.  Give them a shot of grease if they are greaseable.  Then, with the park brake set, engine not running, and the transmission in neutral, check how many degrees of free rotation there are in the driveline, stop-to-stop.  Check the condition of the transmission mount.

Iíll check that, thanks 👍🏻

Offline Captain J

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Re: Clunk sound when in reverse
« Reply #4 on: October 18, 2021, 02:08:29 PM »
BD has the most likely answer, but....does it do the clunking while putting it into reverse?  A lot of shift kits make the hit into reverse hit harder as a side effect.
Yep only in reverse,
No shift kit installed
👋🏻

Offline JohnnyPopper

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Re: Clunk sound when in reverse
« Reply #5 on: October 18, 2021, 03:27:12 PM »
2 or 4 wheel drive?
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline Captain J

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Re: Clunk sound when in reverse
« Reply #6 on: October 19, 2021, 07:14:12 AM »
2 or 4 wheel drive?
4 wheel drive K2500

Offline JohnnyPopper

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Re: Clunk sound when in reverse
« Reply #7 on: October 19, 2021, 10:55:48 AM »
Have someone shift from inside while you listen to isolate the location.

E-Brakes are your friend... ;)
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline Captain J

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Re: Clunk sound when in reverse
« Reply #8 on: October 20, 2021, 06:56:55 AM »
Have someone shift from inside while you listen to isolate the location. 👍🏻👋🏻

E-Brakes are your friend... ;)

Online bd

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Re: Clunk sound when in reverse
« Reply #9 on: November 17, 2021, 11:19:44 AM »
I did what you suggested (to put gear in N, parking brake on, check the shaft to check movement), the shaft moves from stop to stop less than 4-6mm, very minimal movement.
The transmission mount is factory original, have some cracks.
I may need to change it, but itís not causing the loud clunk noise.

You never answered the earlier questions:  Does the clunk occur only when the engine is cold and idling fast or every time the transmission is shifted into reverse, both at operating temperature and cold?  Are the u-joints tight and serviceable?  Any evidence of rust tracks?

Disconnect the rear driveline from the transfer case.  With the transfer case in 2H and the transmission in park, using a pair of channel-lock pliers or similar to firmly grasp the transfer case output shaft, how many degrees of rotation stop-to-stop?
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline JohnnyPopper

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Re: Clunk sound when in reverse
« Reply #10 on: November 17, 2021, 07:49:09 PM »
'You vill ansure ze question!'
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline Shifty

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Re: Clunk sound when in reverse
« Reply #11 on: November 18, 2021, 08:27:02 AM »
Vee haff vays....
87 V20 Standard Cab Longbed (current)

87 R30 3+3 Longbed (days of yore)

98 C2500 ext cab longbed

Offline Captain J

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Re: Clunk sound when in reverse
« Reply #12 on: December 13, 2021, 06:38:40 AM »

Sorry for late reply, I had some medical issues with my back, preventing me from moving or conducting what you recommended, Dr orders.
So I asked someone to check, he said all u joints are ok, he said the clunck occurred at cold and hot temp. all I see is the transmission mount need to be replaced.
So I hope itís all that,
Next week it will be in the garage for full service and Iíll ask the mechanic to conduct a full check including {{Disconnect the rear driveline from the transfer case.  With the transfer case in 2H and the transmission in park, using a pair of channel-lock pliers or similar to firmly grasp the transfer case output shaft, how many degrees of rotation stop-to-stop?}}👍🏻👍🏻👍🏻


I did what you suggested (to put gear in N, parking brake on, check the shaft to check movement), the shaft moves from stop to stop less than 4-6mm, very minimal movement.
The transmission mount is factory original, have some cracks.
I may need to change it, but itís not causing the loud clunk noise.

You never answered the earlier questions:  Does the clunk occur only when the engine is cold and idling fast or every time the transmission is shifted into reverse, both at operating temperature and cold?  Are the u-joints tight and serviceable?  Any evidence of rust tracks?

Disconnect the rear driveline from the transfer case.  With the transfer case in 2H and the transmission in park, using a pair of channel-lock pliers or similar to firmly grasp the transfer case output shaft, how many degrees of rotation stop-to-stop?

Online bd

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Re: Clunk sound when in reverse
« Reply #13 on: December 13, 2021, 10:58:28 AM »
I understand being incapacitated.  I've enjoyed little use of my hands and arms and struggled to walk for months on end.  Follow your doctor's orders and recover!

From my earlier PM:

I should explain that the recommended checks are intended to determine whether there is excessive wear concentrated in a particular part of the drivetrain.  Splined shafts wear, thus accumulate clearance.  It is a normal process.  Wear, however, is additive.  Small amounts of localized wear in the various splined connections, when added together, become significant and audible.  For instance, when changing the direction of rotation in the drivetrain, such as when shifting from a forward gear or park to reverse, the small amounts of play at each splined connection can add to produce a significant amount of rotation across the full length of the rotating assembly.  The result?  CLUNK!  So follow the recommendations and you may be able to determine if there is one or multiple sources causing the symptoms.

If you are going to take the truck to a shop you trust, just ask them to diagnose the clunk.  A full-service shop should have no problem evaluating the noise and whether it should be addressed.

Best wishes for your recovery!
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)