65 365 w/p pulley wobble ?

[Jim R.]

I have noticed at low idle a slight wobble in the water pump pulley 750-850rpm and then it appears to goes away at about 1000rpm could this be from the belt being to tight or to loose, car does also have the idler pulley and belt, I have had the same original rebuilt water pump on for the last 5,000 miles or so, I just wanted to see if anyone else has noticed this on there cars. thanks Jim

[Paul J.]

Re: 65 365 w/p pulley wobble ?

Most of the time, excentric rotation of the shaft causes the wobble, as in the bearings are worn and in the process of failing. Is there a swishing noise when it is idling, if so, this is the bearings (unless it's a Ford). Belt tightness has nothing to do with it, other than causing the bearings to fail prematurely if the tension is too tight.

It is possible that the hub on the pulley is warped, but this is less likely. You can check this by removing the belt, and measuring from a point on the pulley to any point on the block. Then rotate the pulley 180 degrees and take another measurement. If there is a significant difference, remove the pully and investigate closer.

Finally there could be an issue with the idler pulley, although it should'nt cause a wobble in the water pump pulley.

Paul

[Tom R.]

Re: 65 365 w/p pulley wobble ?

Another thing I just ran into is you have to be sure the pilot shaft of the water pump is the same diameter as your fan clutch. Water pumps were made with either 5/8" or 3/4" shafts and likewise fan clutches. It's possible to install a 3/4" fan clutch and fan on a 5/8" shaft water pump/pulley and not know any better until either the bearing fails or the pump casting gives out from fatigue. Happened to me and hard to detect until it fails. Luckily mine exploded in the garage.

[Joe L.]

Re: 65 365 w/p pulley wobble ?

Another thing I just ran into is you have to be sure the pilot shaft of the water pump is the same diameter as your fan clutch. Water pumps were made with either 5/8" or 3/4" shafts and likewise fan clutches. It's possible to install a 3/4" fan clutch and fan on a 5/8" shaft water pump/pulley and not know any better until either the bearing fails or the pump casting gives out from fatigue. Happened to me and hard to detect until it fails. Luckily mine exploded in the garage.

Tom-----

Absolutely correct. All 1955-70 Corvettes, small block or big block, used waterpumps with a 5/8" pilot shaft while all 1971-82 Corvettes used a waterpump with a 3/4" pilot shaft. However, many replacement fan clutches, particularly aftermarket, have a 3/4" pilot orifice. When these clutches are used on a pump having a 5/8" pilot shaft, a special bushing MUST BE USED to convert the orifice to 5/8". Otherwise, one WILL end up with the same problem you experienced. Usually, the bushing is supplied with the fan clutch (unless someone previously returned the fan clutch and "left the bushing out"). If one needs a bushing, a 3/4" OD, 5/8" ID precision bushing can be obtained in most hardware stores although it will usually have to be shortened.

[Loren L.]

Re: 65 365 w/p pulley wobble ?

If it's been on for 5K miles and is NOW exhibiting a wobble, the bearing is starting to fail and the water pump needs a rebuild before it introduces your fan blade to the back of the radiator. Trust me, the water pump rebuild is cheap.

[Jim R.]

Re: 65 365 w/p pulley wobble ?

Anyone have a suggestion for a waterpump rebuilder, for some reason it looks like the pressed on mounting plate for the pulley is the problem not being pressed on accuratley and is causing the pulley wobble, its been on the car for 20 years so I think I will send it in and have it rebuilt and a new mounting plate pressed on, it is a original rebuilt pump I bought at bloomington years ago but it doesn't have the correct four hole mounting plate it has a eight hole universal piece on it now so I would like to have that changed as well as being rebuilt, if anyone has a reliable rebuilder that they use please let me know. JR

[Joe L.]

Re: 65 365 w/p pulley wobble ?

Anyone have a suggestion for a waterpump rebuilder, for some reason it looks like the pressed on mounting plate for the pulley is the problem not being pressed on accuratley and is causing the pulley wobble, its been on the car for 20 years so I think I will send it in and have it rebuilt and a new mounting plate pressed on, it is a original rebuilt pump I bought at bloomington years ago but it doesn't have the correct four hole mounting plate it has a eight hole universal piece on it now so I would like to have that changed as well as being rebuilt, if anyone has a reliable rebuilder that they use please let me know. JR

Jim-----


Bill Mock has been doing this about as long as anyone. Plus, he does it on a "custom rebuild" basis. A lot of the other rebuilt pumps on the market are done by large scale commercial rebuilders on an "assembly line" type operation. Quality on these can be "spotty" since these pumps are generally sold into the "low buck" automotive aftermarket which motivates cutting every possible corner to keep the price low. In other words, in this market, price trumps quality at every turn.