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#4436847 - 06/20/17 03:23 PM Rear end slap
Duffyjr Offline

Registered: 01/13/16
Posts: 508
Loc: Nebraska
Every once in a while when I put my truck (see sig) in reverse it makes a clunking sound, no other time does it do this. So the last time I had my truck into the mechanic I mentioned that and would he check every thing under there. When I picked up the truck he said every thing was solid but what I may be experiencing is rear end slap. He said it's normal for these old trucks but I gotta tell you it scares the heck of me when it happens, it sounds like something under there is breaking.

I have done little searching and apparently this is for real. But my questions is, were they like that when new, is it just the way it's designed or is it wearing out? I also see that guys with newer trucks are having the same thing happen, 2014/15/16.

Truck has 76k but don't know the history.
89 GMC Sierra T5 10w30/Wix
08 Lucerne Mobil 5000 5w30
99 LeSabre QSGB 10w30/TG
18 Toro Super Recycler T5 10w30

#4436852 - 06/20/17 03:30 PM Re: Rear end slap [Re: Duffyjr]
Eddie Online   sleepy

Registered: 12/07/03
Posts: 9569
Loc: Florida, Cape Coral
No expert here but, I'd be checking the universal Joint's and lubricate the splines where the driveshaft enters the rear of the transmission. Ed
CX5 Touring 2.5L :-)

#4436885 - 06/20/17 04:11 PM Re: Rear end slap [Re: Duffyjr]
old1 Offline

Registered: 01/04/11
Posts: 1001
Loc: Columbus Nebraska
I have had many older vehicles that do that. It is just the combination of all the clearances which were tight in the forward direction when stopped, then reversing direction and all the various normal clearances being taken up in the opposite direction. If the u-joints ate good, and surely the mechanic checked them, not to worry. Just don't rev up the engine, then drop it in gear.
2017 Nissan Frontier 4.0 5w30
1965 Mustang 200 c/4 10w30 QS defy
1964 Ford Ranchero 302 c/4 15/40 Delo
1929 ford model A No filters, and 15/40 oil

#4436916 - 06/20/17 04:55 PM Re: Rear end slap [Re: Duffyjr]
Elevguy Offline

Registered: 02/19/15
Posts: 64
Loc: Hamburg Michigan
It's the side gears in differential. You may be able to shim them. When I worked at a Mopar dealer in the 70's they had kits for that purpose

#4437018 - 06/20/17 07:04 PM Re: Rear end slap [Re: Duffyjr]
BrocLuno Offline

Registered: 09/06/15
Posts: 5519
Loc: Kalifornia Kollective
Two piece drive line?
Formerly in marine engineering. In an earlier life I owned my own petroleum tank truck, and hauled for the majors and independent's.

#4437031 - 06/20/17 07:18 PM Re: Rear end slap [Re: Duffyjr]
SilverSnake Offline

Registered: 05/29/13
Posts: 592
Loc: Florida
Used to have the same issue with my old Chevrolet and GMC pick ups. Switched to Rams in 2001 and have not had the problem since.
2016 Charger, 6.4L-485 HP (PUP 0W-40)
2017 BMW 330i, 2L-248 HP (BMW 0W-20)
2018 Jeep GC, 5.7L-360 HP (PUP 5W-20)
2008 20KW Generac (Amsoil 10W-30/30)

#4437124 - 06/20/17 09:24 PM Re: Rear end slap [Re: Duffyjr]
Kurtatron Online   content

Registered: 04/06/10
Posts: 168
Loc: Detroit
This thread wins for best thread title.