1966 289 Mustang Vibration - Vintage Mustang Forums
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post #1 of 27 (permalink) Old 05-20-2019, 09:04 PM Thread Starter
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1966 289 Mustang Vibration

I purchased my second classic mustang a few months ago. It’s a 1966 2 barrel 289 with a C4 automatic. It drove great during the test drive but it had issues on the highway home it kept cutting on and off at highway speeds I had to get it towed home. Anyways since then I have been trying to get the car to start running the way it should. However it has a bad vibration in idle, the hood shakes badly and so do the rest of the car. I have changed spark plugs and the wire, new carburetor, new gas take and fuel pump, new thermostat, temp sensor, water pump, new throttle linkage, new vacuum line, new distributor cap and rotor, new harmonic balancer. I have tested compression and the lowest was 115 And the highest was 120. I have set the timing to 6 degrees and it still has the vibration issue. I have probably done more but that’s all I can think of at this point. Any ideas or a list of things I can check... I love these cars but I’m at a loss on this one.
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post #2 of 27 (permalink) Old 05-20-2019, 10:52 PM
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Sounds frustrating! Have you checked it with a vacuum gauge? That might give you some more information. I would recommend more base timing (seems like 12* BTDC is the magic number for most). I wonder if your distributor could be the culprit? if the mechanical or vac advance were not working right, the result could be poor timing, although it doesn’t necessarily explain the idle situation. I’m sure my cars (C codes) would idle rough at 6* BTDC. In fact, with my manual trans car on manifold vac. advance, I am at about 20* BTDC at idle, and it just purrs. My other initial thoughts are timing chain stretched past the limit changing your valve timing, and just a straight vacuum leak. I’d love to know what you find out. You’ve eliminated a lot of possibilities so far, so shouldn’t be much more left!
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post #3 of 27 (permalink) Old 05-20-2019, 10:59 PM
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Sounds like your just missing something in doing a thorough tune-up. Points or electronic ignition? More timing maybe, set things watching vacuum gauge readings, spray some carb cleaner around the base plate and intake checking for leaks...rechecking the new carb settings...Plug gaps...it could be several things that are not set right vs one thing...with good, even compression you should be able to get the thing running like a swiss watch. No weird ticking noises right? Enough voltage to the coil? There's a lot of things to dial in. Heck, watch a bunch of utube videos on how to tune up a small block ford....keep at it !!
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post #4 of 27 (permalink) Old 05-20-2019, 11:07 PM
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If you have verified you are using the correct firing order (1-5-4-2-6-3-7-8) and cylinder numbering (from front to back..passenger side 1-2-3-4 and driver's side 5-6-7-8), counter-clockwise distributor rotation, and that you have #7 and #8 plug wire separated as far as possible, not touching and only crossing each other at a 90* angle (to prevent inductive crossfire) then I'd be suspecting a timing chain that has jumped a tooth or two on the cam sprocket, especially if it's a bit hard to start.

You can check for timing chain slack by watching the distributor rotor while you rotate (by hand) the engine back and forth. Start by rotating it CCW (from standing in front) until the rotor moves a bit. Then rotate it back CW and note how far the balancer travels before the rotor starts to move. It shouldn't be all that far....
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post #5 of 27 (permalink) Old 05-21-2019, 12:41 AM Thread Starter
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I’ve actually already done the timing chain check and I don’t believe there is any play in the timing chain. The rotor turns perfectly as I turn the harmonic balancer I’ve done it both directions and the rotor always moves smoothly along with it.
As far as vacuum there is only three lines right? The manifold vacuum to the power breaks and the transmission and then the line from the vacuum advance to the carburetor. Now I have noticed than all of the pictures I’ve looked up show that the vacuum advance should only have one outlet. Mine has two, I have plugged one of them. Should I try a correct one. The only issue I have with working on these cars is all of the aftermarket and mismatched parts that have been switched out over the years....
Should I switch to a pertronix ignition system. I have one it’s just not installed yet. A mechanically inclined family friend wants me to hold off. I have sent the points and all of the lobes on the distributor shaft look good. I haven’t replaced the condenser but if I switch to pertronix I won’t need to so I’ve been putting it off.
I’m not sure what was meant by the 7 and 8 spark plugs being 90 degree apart? I would like to check that if you can show me how or what you mean.
The firing order when I got the car was wrong. Two plugs were backwards on the cap. I thought for sure that was the problem but it’s not. I know the order is correct now I’ve checked it about 100 times.
I’ll get a vacuum gauge and I’ll see what I get as a reading.
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post #6 of 27 (permalink) Old 05-21-2019, 12:43 AM
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Sounds like bad timing or a bad vacuum leak...

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post #7 of 27 (permalink) Old 05-21-2019, 02:07 AM
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Now I have noticed than all of the pictures I’ve looked up show that the vacuum advance should only have one outlet. Mine has two, I have plugged one of them. Should I try a correct one. The only issue I have with working on these cars is all of the aftermarket and mismatched parts that have been switched out over the years....
Should I switch to a pertronix ignition system. I have one it’s just not installed yet.
Sounds like you have a vacuum advance meant for a later model engine. I would get the correct vacuum advance. I would also bump timing up to 10-12. You can try running the vacuum advance on the ported vacuum or manifold vacuum. I am running mine on manifold vacuum. Pertronix is a great ignition. I have the pertronix iii and it was super easy to install. That being said it should only make a mild improvement on your idle. If you can't mAke it idle with points there is something deeper wrong. When talking about #7 and #8 plug wires you can get some cross firing between them because they are next to each other on the cap and at the cylinder head. Try separating the two wires so that they don't touch.
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post #8 of 27 (permalink) Old 05-21-2019, 02:28 AM
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Be sure there is no vacuum leak at the small hose that connects the steel line for the trans to the modulator valve on the trans. Ask me how I know...

Is it possible someone installed a camshaft for a later 302 or 351 Windsor with the 351 firing order of 1-3-7-2-6-5-4-8 ? The crank is esentially same but this changes when the intake vs the exhaust are open and it fires.

Set the static timing and start with all vacuum lines plugged on the engine, then attach them AND a vacuum gauge, dial in your idle speed and carb mixture screws (if they make no difference your throttle is open too far) to achieve max vacuum at idle from 500-ish to 700-ish rpm depending on cam profile, then re-curve the distributor to get no more than 36 degrees total timing advance around 2500 rpm.

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post #9 of 27 (permalink) Old 05-21-2019, 07:45 AM
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As far as vacuum there is only three lines right? The manifold vacuum to the power breaks and the transmission and then the line from the vacuum advance to the carburetor. Now I have noticed than all of the pictures I’ve looked up show that the vacuum advance should only have one outlet. Mine has two, I have plugged one of them. Should I try a correct one.
Don’t forget there is another vacuum hose from the carb spacer to the PCV on the right valve cover. Any of these hoses (or something faulty in what’s attached) could be possible vacuum leaks.

I’d definitely switch that vac advance unit, it may be totally wrong for your application. The arms on those things are shaped differently, and it may be pulling your breaker plate off angle. Confirm that you have the right distributor for your car, because as mentioned, those double inlet vac-advances were from later cars. If my memory serves, the 66 auto 2v is C5AF-12127-N, it should be on the housing. If it’s an old one, the diaphragm most likely leaks anyway, so it’s an essential tune-up item.
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post #10 of 27 (permalink) Old 05-22-2019, 10:08 PM Thread Starter
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Ok just as an update I bought a new distributor and I set the initial timing to 12 degrees. The car still vibrated too much in idle so I bought a vacuum gauge/tester. I noticed there was a fitting on the intake manifold that had two nipples and one port for the transmission vacuum line. one of the two nipples was poorly plugged so I connected my vacuum tester. The vacuum gauge read 15/16 in idle I had read on a few other threads that the vacuum in idle should be around 20. So I determined that it much be a vacuum issue or at least the vacuum was part of my issue. I bought new rubber vacuum lines, a new pcv, and a new transmission vacuum modulator. I installed everything and to my surprise the vacuum still read 16 at idle. With the vacuum gauge still connected I adjusted the fast idle screw until the vacuum gauge read 20. I'm not sure what RMP the engine is running at during idle and I have now way of checking as I don't have a tach. To me it sounds like it is idling high however the vibration has completely stopped and the PCV now makes clicking sounds so I believe its working properly. Is there any way to check the RPM without a tach? I'm positive I've heard that you can check it with a multimeter? is this true? Anyways I've noticed that I get shocked when touching the spark plug wires on the top of the distributor. I'm sure this not normal and I don't know what else to do about it. The 7 and 8 spark plug wires are routed in such a way that they never cross and that they always stay at least 2 inches apart. Thanks for all the help and all of the ideas!
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post #11 of 27 (permalink) Old 05-22-2019, 11:26 PM
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To me it sounds like it is idling high however the vibration has completely stopped and the PCV now makes clicking sounds so I believe its working properly. Is there any way to check the RPM without a tach? I'm positive I've heard that you can check it with a multimeter? is this true? Anyways I've noticed that I get shocked when touching the spark plug wires on the top of the distributor. I'm sure this not normal and I don't know what else to do about it. The 7 and 8 spark plug wires are routed in such a way that they never cross and that they always stay at least 2 inches apart. Thanks for all the help and all of the ideas!
The PCV clicking does not mean it's working. Actually just the opposite. Its probably the wrong valve for the engine. If your plug wires are shocking you they are probably bad and cracking. Did you replace the plugs and wires with the distributor? Bad wire can cause and idle issue.
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post #12 of 27 (permalink) Old 05-23-2019, 08:42 AM
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Can you post a video of the engine running. That’ll be a big help.

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post #13 of 27 (permalink) Old 05-23-2019, 09:38 AM
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Anyways I've noticed that I get shocked when touching the spark plug wires on the top of the distributor. I'm sure this not normal and I don't know what else to do about it. The 7 and 8 spark plug wires are routed in such a way that they never cross and that they always stay at least 2 inches apart. Thanks for all the help and all of the ideas!
Put a new set of plug wires on, buy yourself a tach, tach dwell meter or a timing light with a tach. Hard to set a proper tune on a car without the necessary tools.

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post #14 of 27 (permalink) Old 05-23-2019, 10:11 AM Thread Starter
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The PCV valve I defiantly correct for the car I believe the clicking sound is because the vacuum hose was slightly to long therefore not allowing the PCV to sit properly. Like I said in my first post the spark plugs and wires were changed about a month ago right after I bought the car however they could have been defective out of box? I'm not sure. I can put a new set on but I'm not sure that that would fix the problem. As far a video of the car running I can post on later and I will buy a cheap tach to test the rpm.

Something I forgot to mention yesterday...While timing the car I plug the vacuum line running to carb. Usually I never noticed a difference neither sound or a difference in the amount of vibration. However after increasing the idle RPM when I adjusted timing I noted a major difference in sound when the vacuum line was unplugged from the vac advance.
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post #15 of 27 (permalink) Old 05-23-2019, 11:36 AM
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The PCV valve I defiantly correct for the car I believe the clicking sound is because the vacuum hose was slightly to long therefore not allowing the PCV to sit properly. Like I said in my first post the spark plugs and wires were changed about a month ago right after I bought the car however they could have been defective out of box? I'm not sure. I can put a new set on but I'm not sure that that would fix the problem. As far a video of the car running I can post on later and I will buy a cheap tach to test the rpm.

Something I forgot to mention yesterday...While timing the car I plug the vacuum line running to carb. Usually I never noticed a difference neither sound or a difference in the amount of vibration. However after increasing the idle RPM when I adjusted timing I noted a major difference in sound when the vacuum line was unplugged from the vac advance.
This is happening because you are running the engine fast enough to be off the idle circuit. Vacuum advance is being applied to your timing because the throttle blades are slightly open. This also suggests that you are connected to ported vacuum. When you are idling properly with ported vacuum advance, there *should* be no impact from it on your base timing. The trouble is that if your vacuum advance unit is poorly adjusted or mismatched to your carb/engine, the spring tension may be light enough to actually advance your base timing artificially or with just a slight amount of vacuum leaking past the throttle blades, this can make you think you are setting your base timing properly, when you actually may not be. That's why it's a good idea to disconnect the vacuum hose from the advance unit when setting base timing just to be safe. Did you adjust your idle mixture screws with the vacuum gauge connected? This could feasibly get you to run well at the proper RPMs and generate more vacuum. With a stock engine, 15 is too low. At least 18 would reflect a normal-ish amount of idle vacuum. I would also confirm at this point that your TDC marking on your balancer is accurate. It's possible the balancer outer ring has shifted. A TDC indicator that fits in your spark plug hole is what you need to check that.
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