mechanical advance stuck?
Thread Starter
Drifting
Joined: Sep 2004
Posts: 1,532
Likes: 4
From: Fairview Heights Illinois, near Saint Louis MO, STL C3 Shark
mechanical advance stuck?
What exactly is supposed to "move" on the mechanical advance. I took my cap and rotor off this afternoon and found that the weights move freely, but nothing else moves. Is the part that weights are attached to supposed to swivel compared to the part the rotor attaches to? I think that is where mine is stuck. How do you get this free? What would this do to how the car runs? It has terrible low end torque, the springs are really tight, even though the weights are loose as can bee, so perhaps it is stuck way advanced?
Do I keep pryingon it with screwdrivers and beating it with a hammer to get it loose?
Jeremy
Do I keep pryingon it with screwdrivers and beating it with a hammer to get it loose?
Jeremy
Tech Contributor
Joined: Aug 1999
Posts: 14,375
Likes: 6,374
From: At my Bar drinking and wrenching in Lafayette Colorado
The weights, when they move, should apply force against the conter cam and move the center cam relative to the outer cam plate. If the weights are loose but are not moving the one component relative to the other, the unit is seized up. This is very common on the HEI distributors. The fix is to yank the distributor out, disassemble it, clean up the parts with some ScotchBrite, lube it and put it back together. Very easy process. While you're in there, replace the vacuum advance control unit with NAPA part number VC1838 and install a soft set of advance springs.
Drifting
Joined: Mar 2005
Posts: 1,806
Likes: 3
From: Burlington WI
Interesting article about Vacuum Advance
My curiosity was piqued so I went looking around and found this thread on a Camaro board. There is a listing of Echlin Vacuum Advance part numbers.
http://www.nastyz28.com/ubb/Forum8/HTML/009276.html
http://www.nastyz28.com/ubb/Forum8/HTML/009276.html
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Drifting
Joined: Mar 2005
Posts: 1,806
Likes: 3
From: Burlington WI
Info about the 1838
The following listing (HEI) is as follows: The first four part number listings are the 4 numbers that are most commonly used in a Chevrolet performance application. The “AR12” can is the most versatile and user-friendly unit for a good performance street engine. The AR 15 and AR23 are almost identical, with only slight variations in their “start-stop” specs. The “AR31” can is the HEI equivalent to the “B28” Hi-Perf can used on the early engines: The advance comes in very quick on this unit – too quick for many performance engines. Do not use this very quick unit unless you have a cam/engine combination that really needs an advance like this. It can be used as a tuning aid for problem engines that do not respond well to other timing combinations, and can be successfully used in applications where direct manifold vacuum is applied to the can (see paragraph and discussion on this above)
After this, the listing is by Echlin part number. All GM HEI vacuum advance units are interchangeable, so you can use a Cadillac or GMC Truck unit on your Vette, if that’s what you want to do.
HEI Distributors:
P/N ID# Application Starts @ “Hg Max Adv
(Distr. Degrees @ “Hg.)
VC1838 AR12 1975 350 Buick 7-9 7 @ 10-12
After this, the listing is by Echlin part number. All GM HEI vacuum advance units are interchangeable, so you can use a Cadillac or GMC Truck unit on your Vette, if that’s what you want to do.
HEI Distributors:
P/N ID# Application Starts @ “Hg Max Adv
(Distr. Degrees @ “Hg.)
VC1838 AR12 1975 350 Buick 7-9 7 @ 10-12
Thread Starter
Drifting
Joined: Sep 2004
Posts: 1,532
Likes: 4
From: Fairview Heights Illinois, near Saint Louis MO, STL C3 Shark
You're right, I called and they have it, just not on the website....
So - would this explain my crappy low end power? because it's too advanced because it's stuck open?
So - would this explain my crappy low end power? because it's too advanced because it's stuck open?
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by ruby76
You're right, I called and they have it, just not on the website....
So - would this explain my crappy low end power? because it's too advanced because it's stuck open?
So - would this explain my crappy low end power? because it's too advanced because it's stuck open?
perhaps you are looking at this wrong....what if it was stuck open and then the car just wasn't running right...hard to start etc.....some one looks at the timing and says "no wonder its running like crap the timing is way off" so they retard it to where it should be at idle....now its ok at idle but there is no mechanical advance....the advance curve is flat giving crappy low end power
Thread Starter
Drifting
Joined: Sep 2004
Posts: 1,532
Likes: 4
From: Fairview Heights Illinois, near Saint Louis MO, STL C3 Shark
Originally Posted by bobs77vet
perhaps you are looking at this wrong....what if it was stuck open and then the car just wasn't running right...hard to start etc.....some one looks at the timing and says "no wonder its running like crap the timing is way off" so they retard it to where it should be at idle....now its ok at idle but there is no mechanical advance....the advance curve is flat giving crappy low end power
Thread Starter
Drifting
Joined: Sep 2004
Posts: 1,532
Likes: 4
From: Fairview Heights Illinois, near Saint Louis MO, STL C3 Shark
Woooowwww!!!!!!
Runs like a scalded cat!!!! - heard that the other day and thought it was funny, yet descriptive. That explains the difference in my "lazy dog" that it was with the mech advance stuck. I've heard Lars say you need at least a 10 hp increase to "feel" a difference, I'd say this was a 20 hp increase over the messed up mech advance. I can't wait to get my curve kit in!!!!!!!!!
My advice to ANYONE complaining about not enough power - and I don't mean like "i want 500 HP" but not enough power even for a stock 350, to have a look at your mechanical advance and verify that it is in fact working!!!!!!!!!!!
My advice to ANYONE complaining about not enough power - and I don't mean like "i want 500 HP" but not enough power even for a stock 350, to have a look at your mechanical advance and verify that it is in fact working!!!!!!!!!!!
Racer
Joined: Feb 2005
Posts: 258
Likes: 2
From: Boise ID
Me too. I couldn't believe how much difference it made when I unstuck mine! 
When I took it out to test it, I'm pretty sure I looked like this smiley -->
Now I just need to figure out how to get the starter to crank again...
Have Fun!
Dan
When I took it out to test it, I'm pretty sure I looked like this smiley -->
Now I just need to figure out how to get the starter to crank again...
Have Fun!
Dan
Safety Car
Joined: Jun 2002
Posts: 4,135
Likes: 1
Originally Posted by ruby76
Runs like a scalded cat!!!! - heard that the other day and thought it was funny, yet descriptive. That explains the difference in my "lazy dog" that it was with the mech advance stuck. I've heard Lars say you need at least a 10 hp increase to "feel" a difference, I'd say this was a 20 hp increase over the messed up mech advance. I can't wait to get my curve kit in!!!!!!!!!
My advice to ANYONE complaining about not enough power - and I don't mean like "i want 500 HP" but not enough power even for a stock 350, to have a look at your mechanical advance and verify that it is in fact working!!!!!!!!!!!
My advice to ANYONE complaining about not enough power - and I don't mean like "i want 500 HP" but not enough power even for a stock 350, to have a look at your mechanical advance and verify that it is in fact working!!!!!!!!!!!