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Can someone please tell me why the auto/ diff makes a huge thump

Trevor cooke

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Can someone please tell me why the auto/ diff makes a huge thump when engaging reverse / drive in my vp Ute? I've replaced uni's, centre bearing, upper rear control arms, lower trailing arms and bushes x 4, diff oil and trans fluid and filter and yet it thumps really hard upon selecting gears from the park position. Please help as I'm going mad trying to solve the problem. Thanx's people's!
 

Trevor loves holden.

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Put the car up on stands select N get under and rock the driveshaft back and forwards if no extreme play in the diff it be coming from within the transmission it self, is it lagging when putting into reverse? Are the revs to high?
 

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Is it a solid/dull sort of thump or a metallic sounding thump

Backlash in the diff is primarily the cause of the thumping symptoms you are experiencing
Backlash is the clearance between 2 mating parts, in this case it would be the Crown Wheel and Pinion Gear teeth
Easy way to check this is grab the tailshaft and try and turn it by hand....It should only turn a small amount, not a 1/4 of a turn for example
The noise you are hearing will travel up the driveline and can sound like it's coming directly from the transmission
When the backlash is excessive enough you will also hear it when you slow down and then suddenly accelerate again
 

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Put the car up on stands select N get under and rock the driveshaft back and forwards if no extreme play in the diff it be coming from within the transmission it self, is it lagging when putting into reverse? Are the revs to high?
The revs are normal,850/900rpm,and it seems to select reverse without any lag, but the tailshaft has a little bit of movement, it doesn't seem too excessive but feels notchy if that makes any sense. It's a 3.08.
 

Trevor cooke

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Is it a solid/dull sort of thump or a metallic sounding thump

Backlash in the diff is primarily the cause of the thumping symptoms you are experiencing
Backlash is the clearance between 2 mating parts, in this case it would be the Crown Wheel and Pinion Gear teeth
Easy way to check this is grab the tailshaft and try and turn it by hand....It should only turn a small amount, not a 1/4 of a turn for example
The noise you are hearing will travel up the driveline and can sound like it's coming directly from the transmission
When the backlash is excessive enough you will also hear it when you slow down and then suddenly accelerate again
I
 

Trevor cooke

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It's a solid thump, there doesn't seem to be too much play in the tailshaft but does seem to be notchy when turning it back and forth. It's a 3.08 Salisbury type if that's any help.
 

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Possibly wear in the diff as suggested. Lay on the ground next to the car with a torch and watch/listen to the driveshaft at the diff input flange as someone puts the car into reverse/drive alternately. If it's the diff you'll see the shaft turn a bit and than hear the thump as the play is taken up. Obviously make sure the car is in park and someone has their foot on the brake and hand brake is on and lay next to the car, not anywhere near/under the wheels....
 

Trevor cooke

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Possibly wear in the diff as suggested. Lay on the ground next to the car with a torch and watch/listen to the driveshaft at the diff input flange as someone puts the car into reverse/drive alternately. If it's the diff you'll see the shaft turn a bit and than hear the thump as the play is taken up. Obviously make sure the car is in park and someone has their foot on the brake and hand brake is on and lay next to the car, not anywhere near/under the wheels....
I've been under the car and there is minimal movement in the tailshaft rotation by hand as in backlash, so I'm now leaning towards the transmission as there's a lot of noise in the rear of the box with hand rotation and it's very noisy in 1st and 2nd gear at idle with the hand brake on and I have noticed a constant noise while driving but it's not a diff howl / whine as in like a usual diff higher pitch whine. Hopefully I can find a good 2nd hand trans somewhere. Cheers for your assistance mate.
 

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Yip the 4l60 was known for burnt out clutch packs due to bad design, worn out body valves and leaking forward piston seal due to going hard, also the sun shell is another problem gear ring break away..
 

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