tapping/knocking sound

[rio21]

Hi all. My 95 chevy has a tapping/knocking/metal on metal sound. It only happens when foot on throttle, accelerating from about 2nd gear on. The sound gets louder and faster the higher the gear. 305 v8, 5spd.
i've changed the oil to a 10-30w and added a tank of 93 octane. motor has around 40k miles. Did compression test and compression looks good, around 150 across all cylinders if I remember correctly. Any ideas?

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[Erik the Awful]

Does it keep increasing in speed if you shift gears, or does drop down with the engine speed?

If it follows vehicle speed, it's probably a driveshaft problem.

If it follows engine speed, it sounds an awful lot like a rod knock. Now's the time to decide if you want to keep an original 305 in the truck or if you want to upgrade to a 350. If you want a 350, start asking friends and you can likely find a rebuildable engine for under $300, or a good used engine for under $500.

 

[rio21]

Does it keep increasing in speed if you shift gears, or does drop down with the engine speed?

If it follows vehicle speed, it's probably a driveshaft problem.

If it follows engine speed, it sounds an awful lot like a rod knock. Now's the time to decide if you want to keep an original 305 in the truck or if you want to upgrade to a 350. If you want a 350, start asking friends and you can likely find a rebuildable engine for under $300, or a good used engine for under $500.

I definitely notice it as I row through the gears. High rpms cause a loud banging. I had a shop look at it and they think it's the rear differential missing teeth and want to rebuild it. Ive added pics

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[Erik the Awful]

Yeah, you absolutely need to fix that. If you have a Pull-A-Part nearby, get a junkyard rearend and swap it in yourself.

 

[DerekTheGreat]

Yeah, I wouldn't pay to have that rebuilt. Just go to a treasure yard and find one with the ratio you want and preferably a G80. This a 2WD or 4WD? If it's a 4WD, you could look for a 14 bolt SF from another 4WD (with the same ratio as your truck) and swap that in. Better brakes and more beef. Direct swap short of the U-joint. Be sure to pull the diff cover and inspect it before pulling. If you end up going with a different ratio, be sure to pull the DRAC module from the donor truck. (if donor is a '92 & up)

 

[rio21]

Yeah, I wouldn't pay to have that rebuilt. Just go to a treasure yard and find one with the ratio you want and preferably a G80. This a 2WD or 4WD? If it's a 4WD, you could look for a 14 bolt SF from another 4WD (with the same ratio as your truck) and swap that in. Better brakes and more beef. Direct swap short of the U-joint. Be sure to pull the diff cover and inspect it before pulling. If you end up going with a different ratio, be sure to pull the DRAC module from the donor truck. (if donor is a '92 & up)

It's 2wd. By inspecting you mean turn the wheels and see if broken metal or missing parts?

 

[Schurkey]

WHAT VEHICLE??? PICKUP? SUV?

Piece-of-crap 8.5" rear axle failure. Exaggerating to make a point, that thing isn't worth putting fresh grease into, never mind a rebuild.

Time to upgrade to a 9.5" axle from a 6-lug C2500 of the same gear ratio , and likely get better rear brakes in the process. The difficulty will be with the 6-lug wheels.

 

[rio21]

WHAT VEHICLE??? PICKUP? SUV?

Piece-of-crap 8.5" rear axle failure. Exaggerating to make a point, that thing isn't worth putting fresh grease into, never mind a rebuild.

Time to upgrade to a 9.5" axle from a 6-lug C2500 of the same gear ratio , and likely get better rear brakes in the process. The difficulty will be with the 6-lug wheels.

Pickup. That sounds like a good option.

 

[GoToGuy]

If you start with , make , model , year, eng, you will get the best answers, advice. What works for suburban won't be best for K3500 HD always.

 

[rio21]

If you start with , make , model , year, eng, you will get the best answers, advice. What works for suburban won't be best for K3500 HD always.

Sorry about that. 1995 Chevy C1500 305 V8 5 speed extended cab