SLP Underdrive Pully question.....
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Instructor
Joined: Apr 2009
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From: Gurnee IL
SLP Underdrive Pully question.....
My Underdrive Pully needs to be replaced.
I purchased a new SLP one to replace my factory one, but it doesn't come with a new seal. Does this mean I can just use the old one?
I had previously brought it into a shop to see what it would cost, and they quoted me on a new factory Underdrive Pully and seal, plus labor.
A friend who has the same engine, and also does the work on my car, told me to get the SLP one instead of replacing the factory one, so I am doing so. It comes with instructions, and a new bolt, but again... no seal.
So my question is... do I need to replace the seal? And if so, where might I find one? Thanx.
PS - Speed Inc, were I ordered the part, told me I didnt need to replace the seal, just that I would need a different sized belt.
I purchased a new SLP one to replace my factory one, but it doesn't come with a new seal. Does this mean I can just use the old one?
I had previously brought it into a shop to see what it would cost, and they quoted me on a new factory Underdrive Pully and seal, plus labor.
A friend who has the same engine, and also does the work on my car, told me to get the SLP one instead of replacing the factory one, so I am doing so. It comes with instructions, and a new bolt, but again... no seal.
So my question is... do I need to replace the seal? And if so, where might I find one? Thanx.
PS - Speed Inc, were I ordered the part, told me I didnt need to replace the seal, just that I would need a different sized belt.
Burning Brakes
Joined: Apr 2008
Posts: 855
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From: Liverpool NY
The seal does not come with a new pulley it has to be purchased separately. If your pulley is wobbling then most would suggest that you replace the seal while you have it off because the seal is probably damaged from the wobble.
Race Director
Joined: Oct 2002
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From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
When the belt sheave begins to wobble, it is indicative of the isolator deforming, deteriorating, or simply becoming unattached from the hub.
When this happens, the pulley may wobble, but the hub part of it that's pressed on the crank does NOT wobble. It seems to be a common myth though, that a wobbling pulley will damage the seal or the crankshaft...it's simply not true.
I would recommend replacing the seal though. It's not an expensive part, maybe $10-15, and it's not that difficult to change...even if not removing the timing cover.
Tech Contributor
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
CHANGE the seal. You can most likely get it from Advance or Autozone, and surly at NAPA. If the seal wears out later,,,,you will have to remove everything just to replace it again. The old OEM seals are very hard and they normally wear a deep grove in the damper sealing surface like this:
Bill
Bill
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Joined: Apr 2009
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From: Gurnee IL
Guys - I got the new seal and the SLP underdrive Pully. But is the term underdrive pully and Harmonic Balancer used interchangeably? Im replacing a pully, with a bolt. That seems like it could be part of a harmonic balancer, but I dont see how the pully itself can be called a HB too... it just doesnt make sense. Maybe the pully, and the bolt, and what ever the bolt screws into makes up the 'harmonic balancer'? New to all of this, am am not really a gear head. Im having a friend fix this for me, he does all the mods in my car, but im just trying to understand for myself.
Race Director
Joined: Feb 1999
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From: Lenoir City Tennessee
Ci 6, 8 & 10 Veteran
St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15
The HB does have a pulley groove on its outside circumference on the C5. So, pulley or HB its all the same.
Some of the other LS motors have a pulley mounted on the front of the HB. For example on the Camaro's the HB runs all the accessories except the AC. The AC is driven off of a pulley mounted to the HB.
Some of the other LS motors have a pulley mounted on the front of the HB. For example on the Camaro's the HB runs all the accessories except the AC. The AC is driven off of a pulley mounted to the HB.
Tech Contributor
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
The HUB (center part of the device) connects to the crank shaft. Theres a rubber belt that bonds to outside of the center hub.
Theres an outside ring that the serpentine belt connects to. That ring is also bonded to that rubber belt on the center hub. The rubber belt between the hub and outer ring is what absorbs or dampens the oscillations that the crank shaft endures during the combustion process and driving the pistons/connecting rods from top to bottom of the cylinder. The device described above is commonly refereed to as a harmonic dampener.
The term under drive pulley comes from the fact that some dampeners have a smaller diameter drive pulley and that lessens the force that the engine needs to rotate the engine driven accessories. alternator, power steering pump AC etc..... All that stuff turns slower when they are driven by an under-drive dampener. It also requires that you get a different length serpentine belt!
So,,,yes there the same sort of.
Theres an outside ring that the serpentine belt connects to. That ring is also bonded to that rubber belt on the center hub. The rubber belt between the hub and outer ring is what absorbs or dampens the oscillations that the crank shaft endures during the combustion process and driving the pistons/connecting rods from top to bottom of the cylinder. The device described above is commonly refereed to as a harmonic dampener.
The term under drive pulley comes from the fact that some dampeners have a smaller diameter drive pulley and that lessens the force that the engine needs to rotate the engine driven accessories. alternator, power steering pump AC etc..... All that stuff turns slower when they are driven by an under-drive dampener. It also requires that you get a different length serpentine belt!
So,,,yes there the same sort of.
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Tech Contributor
Joined: Dec 1999
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
If you look carefully in this picture of the backside of the power bond 25% under drive dampener/pulley 
you can see a thin rubber band that separates the hub from the outer ring.
The bolt that you have is most likely a stock GM damper bolt. It is a ONE TIME USE BOLT! That bolt secures the damper to the crank. It is EXTREMELY important that the person who installs the bolt, installs it exactly as per the GM damper bolt installation procedure directs. Failure to do so will cause damper failure or engine damage.
Theres also a special damper installation tool that needs to be used. Failure to use the tool or a home made tool can cause crank damage. People have stripped out the threads inside the center of the crank where the bolt threads into;
Heres a pic of my home made damper install tool:
I use this strap wrench to hold the pulley while loosening or tightening the bolt:
you can see a thin rubber band that separates the hub from the outer ring.The bolt that you have is most likely a stock GM damper bolt. It is a ONE TIME USE BOLT! That bolt secures the damper to the crank. It is EXTREMELY important that the person who installs the bolt, installs it exactly as per the GM damper bolt installation procedure directs. Failure to do so will cause damper failure or engine damage.
Theres also a special damper installation tool that needs to be used. Failure to use the tool or a home made tool can cause crank damage. People have stripped out the threads inside the center of the crank where the bolt threads into;
Heres a pic of my home made damper install tool:
I use this strap wrench to hold the pulley while loosening or tightening the bolt:
Thread Starter
Instructor
Joined: Apr 2009
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From: Gurnee IL
having a big problem getting the bolt loose. Any ideas? I cant figure out how to get my trans to stop moving with the bolt. When the bolt is turn, the engine turns. The SLP instructions say to "install a suitable flyweel holding tool", but I dont know what that is.
Tech Contributor
Joined: Dec 1999
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
,,,,Unless you have the correct fly wheel tool,,,,,thats the SOLUTION!
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Instructor
Joined: Apr 2009
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From: Gurnee IL
Got the bolt off, but the universal chevy Harmonic balancer puller I bought doesnt work.... as the HB on my C5 has no holes!! So pepboys has 3 different options for sale, all with 2 or three teeth, I just dont know what size to get. What did you guys use to pull out the old HB?
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Instructor
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From: Gurnee IL
Now we cant get the old Underdrive pully out...... thoughts?
Burning Brakes
Joined: Apr 2009
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To get that bolt off easily, get a big (1/2 or 3/4 drive) impact driver with suffcient torque (mine does ~800ft/lbs) and a 1/2" compressor hose. You don't even have to look at the pulley when removing it 
I use a big, 3 leg gear puller to remove my pulleys. You can rent one from a parts store.
To install the pulley -- READ BILL'S POST ABOVE. Do NOT hammer it on.
If you need one, I recently made 7 or so install tools (price was the same to me -- I had to buy bulk for the nuts and the smallest shaft I could get was 4' long lol). Just shoot me a PM.
I use a big, 3 leg gear puller to remove my pulleys. You can rent one from a parts store.
To install the pulley -- READ BILL'S POST ABOVE. Do NOT hammer it on.
If you need one, I recently made 7 or so install tools (price was the same to me -- I had to buy bulk for the nuts and the smallest shaft I could get was 4' long lol). Just shoot me a PM.
Thread Starter
Instructor
Joined: Apr 2009
Posts: 115
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From: Gurnee IL
Got the new one in finally. Took 9 hours! Putting everything back together now, but I have one more question: The new SLP undrive pully said I would need a new Delco serpentine belt, which I got, but now my stock AC belt is to large.... What size ac belt do I need to buy to fit now? The SLP papers said nothing about this.... So im clueless. hELP!
Race Director
Joined: Oct 2002
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From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
Unless they recently changed it, the 25% SLP pulley does not underdrive the a/c, and should use the stock a/c belt (4 rib 420 length).
The main (accessory) belt should be a 6 rib 775.
The main (accessory) belt should be a 6 rib 775.
Thread Starter
Instructor
Joined: Apr 2009
Posts: 115
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From: Gurnee IL
Oddly enough, I had to drop down an inch to a 41 inch AC belt after installing the SLP pully. I had to do some searches to find out this was needed. Thanx for all your help guys! Project done.