Water Pump
Thread Starter
7th Gear
Joined: Nov 2011
Posts: 7
Likes: 2
Water Pump
I have a 1968 Corvette 327/350. I have changed the water pump three times in the last 6 months. I don't believe I am tightening the belt too much. In addition, I get an engine/transmission vibration at 3000 RPMs in all four gears. It seems when the pump fails (Pump leaks), the vibration goes away and the engine runs without vibration after 3000 RPMs. Any suggestions.
Safety Car
Joined: Sep 2007
Posts: 4,454
Likes: 328
From: Indy Indiana
disconnect all your belts, and run your engine. according to your diagnosis, the engine should run without vibration. add 1 belt at a time until your vibration is back.. that is where your problem is.
Burning Brakes
Joined: Jan 2007
Posts: 1,057
Likes: 4
From: Concord Calif
Also check the size of the water pump shaft. There are two different size shafts maybe more. If you have the wrong size shaft as compared to your fan clutch there will be nothing to index the clutch other than the bolt holes which is not enough. I ran across this on my 68 and vibrations went away with the right combo. I believe the correct size shaft for a 68 is 3/4" and other GM cars were 5/8" Yea some pumps came with a small brass adapter the put the large clutch on the small pump but that was not always a good fix!
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Burning Brakes
Joined: May 2009
Posts: 1,232
Likes: 6
From: Tucson AZ
St. Jude Donor '12
If this is the case, then the imbalance of not centering the clutch (indexing it on the pilot shaft) will quickly wear your water pump.
Thread Starter
7th Gear
Joined: Nov 2011
Posts: 7
Likes: 2
I checked the old water pump shaft and the hole in the fan clutch. They are both 5/8 inch. So, that appears to be ok. After doing some research, I figured out that the fan clutch is not stock. The stock fan clutch has four holes that mate to the water pump. Instead, on mine, where the fan clutch holes should be, each hole is in the shape of a U, I guess to make it more universal to other water pumps. However, since both the center hole on the clutch is 5/8 and the shaft on the water pump is 5/8 then in theory it should not wobble. Once I install the new pump, I will run the engine without any belts.
Burning Brakes
Joined: Dec 2005
Posts: 992
Likes: 56
From: Baldwinsville, NY
What hole size is in the Pulley for the water pump? If it is 3/4" then the 5/8" shaft will not center the pulley. If you have a water pump with 5/8" shaft. Then do you have a water pump that is too long or short for a corvette application? Most Corvette's have a water pump based on year and not all short pumps are the same.
Just my 2 cents
Just my 2 cents
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Joined: Jan 2000
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From: Corsicana, Tx
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It's possible the fan clutch itself is bad internally....or a bent fan blade. You're on the right path.
JIM
JIM
Thread Starter
7th Gear
Joined: Nov 2011
Posts: 7
Likes: 2
Gents,
Today, I removed all of the belts checked the Harmonic Balancer; it looked fine. I installed a new water pump. I started the engine without the power steering or water pump belts. There was no vibration. I ran the engine with the water pump and belt but no fan clutch; still no vibration. When I installed the fan clutch the vibration was evident. I removed the fan clutch, and the vibration was once again gone. I have a new stock fan clutch on order.
I will keep you guys posted. Thanks for all of your advice.
Today, I removed all of the belts checked the Harmonic Balancer; it looked fine. I installed a new water pump. I started the engine without the power steering or water pump belts. There was no vibration. I ran the engine with the water pump and belt but no fan clutch; still no vibration. When I installed the fan clutch the vibration was evident. I removed the fan clutch, and the vibration was once again gone. I have a new stock fan clutch on order.
I will keep you guys posted. Thanks for all of your advice.
Last edited by TomAur; Nov 20, 2011 at 06:45 PM.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
ensure the replacement fan clutch has same size pilot hole ID as OD of forward end wp shaft.
Gents,
Today, I removed all of the belts checked the Harmonic Balancer; it looked fine. I installed a new water pump. I started the engine without the power steering or water pump belts. There was no vibration. I ran the engine with the water pump and belt but no fan clutch; still no vibration. When I installed the fan clutch the vibration was evident. I removed the fan clutch, and the vibration was once again gone. I have a new stock fan clutch on order.
I will keep you guys posted. Thanks for all of your advice.
Today, I removed all of the belts checked the Harmonic Balancer; it looked fine. I installed a new water pump. I started the engine without the power steering or water pump belts. There was no vibration. I ran the engine with the water pump and belt but no fan clutch; still no vibration. When I installed the fan clutch the vibration was evident. I removed the fan clutch, and the vibration was once again gone. I have a new stock fan clutch on order.
I will keep you guys posted. Thanks for all of your advice.
Thread Starter
7th Gear
Joined: Nov 2011
Posts: 7
Likes: 2
Gents,
Just installed an OEM fan clutch. It solved the problem. I can get the RPMs up to 4000 (3000RPMs used to vibrate the drive train) with no vibration. The new fan clutch is smaller in diameter and has a shorter shaft. I threw the old clutch in the scrap metal container.
Thanks for everyone's advice!!
Just installed an OEM fan clutch. It solved the problem. I can get the RPMs up to 4000 (3000RPMs used to vibrate the drive train) with no vibration. The new fan clutch is smaller in diameter and has a shorter shaft. I threw the old clutch in the scrap metal container.
Thanks for everyone's advice!!
