Author Topic: 390 shakes at 1000 rpm – 1500 rpm – 2000 rpm, runs smoothly at 3000-3500 rpm.  (Read 12306 times)

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Clark Coe

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A couple of things.

1 - Compression check is smart, doesn't hurt to know what you are seeing even if it is good
2 - Do you have any valve train noise when the shake starts?
3 - Have you looked at the advance curve as it comes in?  Might be hard to do with one person, but it should be consistent with RPM, if it jumps, maybe the advance weights are sticking and its retarded then releases.  You could add 10 degrees initial after it starts (can't really drive it that way, but if it changes it tells you something.  No load it'll be fine)
4 - Could you record a movie of the exhaust when it's in the shake?
5 - When it is hot, and the choke is open, if you cup your hands over the carb, does it rev up slightly before it chokes? (Don't use the choke plate, use your hands, watch your jacket and hoodie for the fan etc)

After that,  likely smart to bolt on either a 600 I have or a 3310 and see what it does.  I am working out my schedule, sorry I vanished, we can likely get together soon if you don't figure it out


Ross, here are some answers:

1.) I have completed a dynamic, running compression test and here are the results. Static compression looks good for 9.5 CR pistons. All of the 3000 snap readings are too high, suggesting some restriction in the exhaust system. What next? My Mustang has a complete, stock exhaust system, complete with twin exhaust resonators and crossover muffler behind the rear axle. Remove the muffler?

 (This running test consumed three Schrader valves. The valves have a limit of how much pounding they will tolerate. Tried removing the Schrader valve, but the gauge was too difficult to read.)


2.) Valve train makes no odd noises. Have Pumpbuilder rocker spacers and end stands. Have adjustable, factory rocker arms.

3.) Mechanical advance starts to move at 1750 rpm, then moves smoothly for 21 degrees to be fully advanced at 3000 rpm. I adjusted the initial to 24 degrees and that did not make a difference in the vibration.

4.) I do not know how to post videos of my exhaust? Will Postimages.com host videos?

5.) Clamping my hand on the carb inlet chokes out the engine without any rise in speed....no vacuum leaks.


Was the Torino that you pulled the engine from crashed? If not, did you drive it b4 pulling it, noticing any vibration? You had this vibration from day one of the rebuild? I had a 289 that I went through with this. Pulled it from a crashed Mustang that was hit hard and low in the front. I just put up with it until one day a rod nut vibrated loose and it puked it's cookies. I too had changed transmission, clutch & flywheel to no avail.
Shady: In 1980, I bought the 1968 GT Torino for $50, drove it home and removed the motor. The Torino was not wrecked and I do not recall any clues of substantial body or frame damage. It was a very odd Jade Green Torino, GT option with 2V-premium gas 390, three on the tree, AC, bench seat and a open rear differential.

sixty9cobra

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Not sure if this has been mentioned hopefully you have checked the firing order. Have you tried pulling one wire off at a time to see if they make any difference in the idle.

Blueoval77

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Clark , if you stand over the thing running with a light pointed down into the choke horn . If you slowly raise the RPM does the roughness start with the "Dribble" from the carb ?

Clark Coe

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Not sure if this has been mentioned hopefully you have checked the firing order. Have you tried pulling one wire off at a time to see if they make any difference in the idle.
sixty9cobra:   Checked that, all okay. And rechecked it again when I installed new NAPA spark plug wires two weeks ago.

Clark , if you stand over the thing running with a light pointed down into the choke horn . If you slowly raise the RPM does the roughness start with the "Dribble" from the carb ?

Blueoval77:  The vibration sort of begins before the "dribble", maybe 1950 rpm. When the dribble at the booster appears, the engine speed surges 200-250 rpm to 2200 - 2250 rpm. The carburetor's transition from idle to the booster circuit seems abrupt, not smooth.

I have battled with this '68 390GT C8OF-D carburetor before.
http://fepower.net/simplemachinesforum/index.php?topic=3042.0;all
The primary #211 butterflies have small factory holes and the carb has two, separate idle adjustments for each primary plate. See old thread. I finally got the engine to idle very well, but there still is some idle/primary transfer tuning required that is not yet in my skill set. The idle screws in the metering block are 1.5 turns out.

This vibration is more pronounced in the interior of the car, like the vibration becomes an audible sound. This vibration/sound may have always been there and now I am more fussy about it and really noticed it.

As I am thinking about this, my new reduced height TKO 600 conversion is still very tightly positioned up near the transmission tunnel. It is possible that the transmission is just touching the body somewhere. I have already looked at this but could not see or feel any transmission/body interference. I would have to remove the transmission to look for any witness marks. Have to fix the vibration first.

« Last Edit: March 05, 2021, 03:10:17 PM by Clark Coe »

Blueoval77

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Well along those lines . I had a 2017 Subaru that I got for my niece and put back together from the Salvage auction . This thing had pretty light damage in the front end mostly involving strut , control arm , etc....Once it was all back together and running it had the same thing you describe . You could feel and maybe more hear something was off. Everyone else that got in the car said Oh its fine !!! And it nagged at me....At a certain RPM it would do this thing . Not a shake so much as a sound and feeling that something was off... After going over and over and over this thing on the lift about a million times I finally found that in the impact the trans mount had a sort of limiter inside of the rubber isolator that got bent and it was touching metal. This was no more than maybe a .250 rod inside of there and it annoyed me to no end...I pried it back straight and that was that... So it doesnt take much to get what you are describing....

WConley

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I did a lot of NVH work at Ford.  ANY metal-metal contact with a powertrain component will cause booming in the cabin and drive you nuts.  That TKO conversion has me wondering if you've got a clearance issue in the tunnel.  Maybe the trans mount is twisted or hard against a stop?
A careful study of failure will yield the ingredients for success.

My427stang

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Clark,
Sorry I haven't been around to help out, more excuses, but have a bit more things going on than I generally do, or intend to in the future. 

However, at this point.  Potential contact points for the TKO

1 - Directly under the radio - it gets tight at and around the vent valve
2 - Right at the seat cross member on the bottom of the floor
3 - At the shift lever depending how you trimmed

If you dropped the tail of the tranny to avoid cutting or hammering too much, I would look at the angle of your Z-bar and see if it is binding slightly at a different agnle or pushed too tightly together causing metal to metal.

Then the normal exhaust chasing for hangers or pipes being tight, etc
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Ross
Bullock's Power Service, LLC
- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, Erson SFT cam, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 461 cid FE, headers, Victor Pro-flo EFI, Comp Custom HFT cam, 3.50 9 inch

Clark Coe

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I did a lot of NVH work at Ford.  ANY metal-metal contact with a powertrain component will cause booming in the cabin and drive you nuts.  That TKO conversion has me wondering if you've got a clearance issue in the tunnel.  Maybe the trans mount is twisted or hard against a stop?

Bill, I think I am on to something concerning the annoying drumming sound in my Mustang cabin. Thanks for encouraging me to take a second look. When I completed the TKO conversion, I was careful with the clearance and fit in the tunnel area. Even with the optional cut-down case, a few well-placed hammer blows were required. Did not look that close at the trans mount area.

Today I pulled out a untried, Holley 4150 1850-2 from under the bench. It already had a fresh renew kit in it, but I have never run it on any engine. Took a couple hours to work out some bugs and install it on my 390. Anyway, the vibration and cabin sound remained at 1950 rpm - 2200 rpm range. However, this carburetor did not dribble as much at 2000 rpm.

Turned the idle up to 2000 rpm, slid under the car and held my hands on the underside of the tunnel. It was really vibrating.

While I was lying on concrete, on my back and trying not to burn myself on the exhaust, inspected the TKO transmission mount. Thought this looked suspicious


Took a break to allow the exhaust to cool, moved the Mustang to the middle of the garage and put it up on four jack stands. Removed the transmission mount and found a contact mark where the transmission case and the mount were touching. Those are not cracks in the transmission case, just casting parting lines and a scratch in the aluminum.





By now, it was time to grill some pork tenderloins, enjoy a Shiner beer and have some supper with my wife.

Tomorrow, I will get out my trusty grinder and create some clearance between the trans case and the mount.

Once again, I really appreciate everyone's input.

Clark

« Last Edit: March 12, 2021, 09:34:01 AM by Clark Coe »

WConley

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... After going over and over and over this thing on the lift about a million times I finally found that in the impact the trans mount had a sort of limiter inside of the rubber isolator that got bent and it was touching metal.

Clark-

It was Blueoval77's Subaru story that really got me thinking about your issue.  I can't take much credit, but I was reminded of a couple of Mustangs I've worked on over the years with degraded transmission mounts.  It's amazing what a tiny contact patch can do!

Make sure you give yourself a good quarter inch if possible.  Stuff moves around a lot in that area.  Hope you enjoyed the nice steaks and the Shiner!
A careful study of failure will yield the ingredients for success.

My427stang

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Good detective work Clark, that will certainly make a noise....give it as much room as you are comfortable.  Although it shouldn't move much fore/aft, certainly can see it does some
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Ross
Bullock's Power Service, LLC
- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, Erson SFT cam, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 461 cid FE, headers, Victor Pro-flo EFI, Comp Custom HFT cam, 3.50 9 inch

machoneman

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I'd take it all off the steel crossmember. Good catch and I'll venture that was the cause. Know you will fill us all in after your grinding session and a test drive.

Great example of how Jay's Forum has allowed a ton of replies, all in the spirit of helping out another member, eh?
Bob Maag

Clark Coe

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Found my vibration and the source of the 2000 rpm cabin noise!   :)

This is from an assessment by running the Mustang in the garage. There is too much embedded salt dust in Nebraska's roadways and a few snow piles still melting into the street, so I did not take it out for a drive.
After removing the interference between the transmission case and cross-member, the maddening vibration/sound is gone. :D Plus, the Mustang now has an updated ignition system. Another plus is the faint gear whirling noise at idle with the clutch out, that could be heard in the cabin is gone.




You could feel and maybe more hear something was off. And it nagged at me....At a certain RPM it would do this thing . Not a shake so much as a sound and feeling that something was off... After going over and over and over this thing on the lift about a million times I finally found that in the impact the trans mount had a sort of limiter inside of the rubber isolator that got bent and it was touching metal. So it doesnt take much to get what you are describing....

Blueoval77, Thank you for sharing your Subura story. That was great motivation for me to keep looking.


This clearance crack required alot of time with a 7" disc grinder. Had to weld the opposite side of the bracket because this clearance removed all of the origin welds. Will need to repaint it.


Great example of how Jay's Forum has allowed a ton of replies, all in the spirit of helping out another member, eh?

machoneman: Isn't that the truth! I am so appreciative of everyone here on Jay's forum that commented and contributed to finding a remedy to this vibration.
Thank you all.

Clark

WConley

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Nice!

I love it when a plan comes together  :D
A careful study of failure will yield the ingredients for success.

Skeeter65

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Great news and good that it was not something costly.

Blueoval77

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Whats the odds of that one being the trans mount too in the end.... Thats crazy and awesome at the same time..... Man Im glad that worked out. I indeed understand how annoying of a thing that is and mine was with a 4 banger ......
It will all feel three times as good after being able to make a run down the road..