390 shakes at 1000 rpm – 1500 rpm – 2000 rpm, runs smoothly at 3000-3500 rpm.

[Blueoval77]

Well he kind of dropped off but its not really that difficult. Is it load related or not . He said it was always rough . rough when ? With his current setup he may be seeing substantial load in that range which then dissipates as RPM increases . This can point at a few things real quick and then fans out to a broader range of items .  Was it rough in this fashion before ? Did this roughness/vibration come with the trans swap ?
If he shoves the clutch in at that speed is the vibration still there ? Not hard to narrow down ..

[MRadke]

If he never had it balanced in the first place, isn't everything else sort of chasing your tail?

[C6AE]

I have seen some out of balance (new) clutches.
Easy enough to prove, just remove the clutch/pressure plate and start it up!
(Well not that easy, but it will prove it)

[Clark Coe]

I've not been into the guts of a TKO but you can eliminate them buy disengaging the clutch. If it is still there the pressure plate or flywheel could be out of balance. If the pressure plate is off center you'll probably feel it easing off the clutch.

It could be a valve is not closing fast enough while running. Usually does not show up during cranking compression test. Pull your Shrader valve and do a running compression test. Your needle will be bouncing fast but will be readable. High side should be about 35psi. If a valve event is the cause that cylinder will have weak reading about 20 psi or less.

The 2000 rpm shake is not related to load. The 2000 rpm shake occurs while sitting in the driveway (with the clutch engaged and not engaged) and when in motion on the highway. The 2000 rpm shake is the strongest and most annoying…that is the one I need to fix.

The 2000 rpm shake occurred with the stock Ford flywheel, Ford three finger pressure plate and Ford clutch that was balanced and installed in 1980. Last year, a new McLeod steel flywheel and a new Kevlar/Organic clutch disc and diaphragm plate were installed with the new TKO600 5-speed conversion. This tells me the vibration problem is not in the drive train and must be in the engine.

The Streetmaster intake has been on this engine for twelve years. But, I have not driven my Mustang more that a couple of hundred miles in that time. I am getting old and it is time to get my car out on the road and enjoy it. It is time to finally get this 2000 rpm vibration problem figured out....I thought a new flywheel and clutch assembly would do the trick. I was wrong.

[machoneman]

Pull out both air/idle screws and blow out the passages with high pressure air. Point is to unblock any crap from the emulsion tubes. Fast, easy to do and may work to your advantage.

Next, swap on a known good carb and run it. Harder to do but it could help isolate on issue: is it carb related?

Very hard to do and a total PITA. Pull the tranny, remove the throwout bearing and arm, block up the engine at the pan and fire her up. If it still shakes, then yank the bell, remove the clutch and disc, refire it and see if your shake disappeared.

Story time! My late, great Uncle Bill bought a brand new black1957 Ford and love it. But, it had from Day 1 an odd vibration at various engine speeds. The dealer took the car in a few times but the local mechanics could not source the issue. Bill, being a stickler and standing by his rights (new car and all) pursued Ford with letters, etc. to fix the engine or give him a new one. Ford's Dearborn office did send a factory repr. as the dealer gave up. Bill took the car in on the appointed day and the factory guy pulled the engine, totally disassembled it and went to work. IIRC, it was two days later the call came in to Bill to visit the dealership. The rep, showed Bill all 8 connecting rods, pointing out the machined balance pads on each one's big end. One rod showed zero machining on its big end! He had taken all 8 to a local machine shop and had each one weighed. That one rod was way out of balance compared to the other 7. A touch of machining to match the others, a reassembly and the engine engine finally engine ran smoothly. 

Hope yours hasn't the same issue!
 

[chris401]

I've not been into the guts of a TKO but you can eliminate them buy disengaging the clutch. If it is still there the pressure plate or flywheel could be out of balance. If the pressure plate is off center you'll probably feel it easing off the clutch.

It could be a valve is not closing fast enough while running. Usually does not show up during cranking compression test. Pull your Shrader valve and do a running compression test. Your needle will be bouncing fast but will be readable. High side should be about 35psi. If a valve event is the cause that cylinder will have weak reading about 20 psi or less.

The 2000 rpm shake is not related to load. The 2000 rpm shake occurs while sitting in the driveway (with the clutch engaged and not engaged) and when in motion on the highway. The 2000 rpm shake is the strongest and most annoying…that is the one I need to fix.

The 2000 rpm shake occurred with the stock Ford flywheel, Ford three finger pressure plate and Ford clutch that was balanced and installed in 1980. Last year, a new McLeod steel flywheel and a new Kevlar/Organic clutch disc and diaphragm plate were installed with the new TKO600 5-speed conversion. This tells me the vibration problem is not in the drive train and must be in the engine.

The Streetmaster intake has been on this engine for twelve years. But, I have not driven my Mustang more that a couple of hundred miles in that time. I am getting old and it is time to get my car out on the road and enjoy it. It is time to finally get this 2000 rpm vibration problem figured out....I thought a new flywheel and clutch assembly would do the trick. I was wrong.

Ok, move on to my next paragraph.

EDIT: Don't let it overwhelm you. We all get so frustrated we don't always see everything.

[machoneman]

Check your balancer to see if it's cocked a tad due to dried-out elastomer that bonds the inner hub to the outer ring. Old balancers can in fact cause shakes if they are not running true.

[mike7570]

Very hard to do and a total PITA. Pull the tranny, remove the throwout bearing and arm, block up the engine at the pan and fire her up. If it still shakes, then yank the bell, remove the clutch and disc, refire it and see if your shake disappeared.

I bought a 67 Shelby in 1978 and it had the shakes the day I brought it home. It was a 4spd car and had been modified with a 427 short block. I pulled the pressure plate and right away I could see it was the problem. It had loose and misadjusted parts and wasn't even parallel to the flywheel.

[Clark Coe]

Check your balancer to see if it's cocked a tad due to dried-out elastomer that bonds the inner hub to the outer ring. Old balancers can in fact cause shakes if they are not running true.

Today I removed the three groove crank pulley to get a better look at the original, 52 year old balancer.

Using a dial indicator, I found the outer ring has .023" run-out, measured on front surface. The rubber strip between the two inner and outer rings is old and dry. The .023" variance corresponds to the two pooched out, cracked areas that are 180 degrees apart, see pictures below. This quite likely is the source of the 1000/1500/2000 vibration.

What to you guys think?

How long should a balancer last?     I would have looked at this sooner, but using a piston stop I determined that the outer ring had not slipped and the timing pointer indexed on TDC....on that observation, I thought the balancer was okay. I have never heard of the outer ring tipping horizonally











What brand do I look for in a quality OEM replacement? This is a street motor, but I still want a good one with precision timing marks.

Thanks for all of the replies and suggestions.....Clark

[My427stang]

Clark that balancer is junk, it is in the very least moving but it almost looks like it’s wet all the way around. Even if it’s not the source of your shake, which probably is, just swap it out before it comes off and breaks something

New replacements are cheap, Pioneer, and others. There is a decent company in Kansas I’ll see if I can find their card and post it here tomorrow

[Blueoval77]

Beautiful car  and yeah , ditch that balancer either way... I think you have narrowed this down pretty far with that last long post. Its going to be that balancer or something internal. Thats my two cents...Things like bad carbs or ignition issues are always exacerbated by load and usually get worse with time . Since your issue seems to have hung on and been consistent it seems like a hard balance issue. The nicer the car the more obvious small issues are and it looks like you have a really nice car there.
An old beat up car with a bunch of other issues covers up the small issues....

[Clark Coe]

Clark that balancer is junk, it is in the very least moving but it almost looks like it’s wet all the way around. Even if it’s not the source of your shake, which probably is, just swap it out before it comes off and breaks something

New replacements are cheap, Pioneer, and others. There is a decent company in Kansas I’ll see if I can find their card and post it here tomorrow

Thanks Ross, I will be looking forward for the info from the Kansas source. I have also found a Pioneer OEM balancer PIO-872056 for $232.99 at Summit Racing.

Beautiful car  and yeah , ditch that balancer either way... I think you have narrowed this down pretty far with that last long post. Its going to be that balancer or something internal. Thats my two cents...Things like bad carbs or ignition issues are always exacerbated by load and usually get worse with time . Since your issue seems to have hung on and been consistent it seems like a hard balance issue. The nicer the car the more obvious small issues are and it looks like you have a really nice car there.
An old beat up car with a bunch of other issues covers up the small issues....

Blueoval77, thanks for the compliment on my fastback. Yes, that car is extra special to me. Have owned it for 51 years, since 1970. I am the second owner. Currently has 69K miles, I would guess that half of those miles are on Nebraska gravel roads. Original paint, but the closer you get, the more worn out it is. I did a lot of back roads cruising in my long ago youth. The eight track player has been removed but the tunes still remain in my memory.

[475fetoploader]

I just got a power bond from Brent, looks like a nice piece, didn’t break the bank.

[Blueoval77]

Ditto on the one pictured above . Blykins..........

[My427stang]

Clark, my mistake, sold in KS, made in Mexico.  I have used a few of these and they are nice.  I don't pick them for strokers, only because most of them live up near 6000, but wouldn't think twice on a street GT.

Regardless, there are a ton of quality big balancers out there for a stock-ish 390 that work real well, I wouldn't spend more than 100 unless you are planning a high rpm engine or stroker later

https://aacincdirect-com.3dcartstores.com/1968--1976-Ford-360-390-428-Damper_p_61.html

The ones I had all came out right for TDC, and have graduated timing marks and were balanced correctly when stuck on the crank during balance