Bad Vibrations, Chicago Fury saga

I can't figure this out. Flex plate tightened, all mounts tight, u joints feel good and are pretty new, pig is tight. Vibration is rpm dependent it seems, not speed. I've got 2 videos I'll link here. You can see the speedo and the tach. Around 55-60mph it's a very cyclical vibration comes and goes every 1-2 seconds. When I accel it'll jump to every 1/2 sec then smooths out when I'm going 65mph or so and 3300rpm. Then repeats the cadence on decel. On the video it sounds a bit like an exhaust leak, but that's actually the vibration noise. I feel it in the front, don't feel it in my butt or from the rear at all, which makes sense since its rpm related. I get a bit of the vibes as it gets to the top of the rev band before shifting as well.

Anytime it's doing it if I flip OD on it instantly goes away on the shift.

This engine had been together for decades hooked to a 727 in this car and hooked to the a500 for 10yrs. The First engine with the a500 did not do this that I remember. It developed blow by and I stuck this engine back in. This setup has done it for years, but I'm just getting the car back out from a slumber of 2yrs

Any thoughts?

https://www.youtube.com/watch?v=EXHfeZko0nA

https://www.youtube.com/watch?v=elas8Yz5hgk

Seems to me like a mismatch between the type of crankshaft and the torque converter.

Forged crank = torque converter usually with no balance weight

Cast crank + cid = torque converter with some sort of balance weight


HTH , Paul

I had started to wonder that. Every combo I've had in the car is supposed to be internally balanced. I've been concerned cuz this block has an 'E' stapmed on the pad and is a 71, not original to the car but was in the car when I got it with 43k in it. Engine has been rebuilt by a cheap house back in the day, had a reman tag on it.
It'd be sad that if it's always had a cast crack in it and in 21 years of ownership I didn't realize it.
This would be the first one I've mismatched, do they normally act up in only 1 rpm range?

Generally once you get above a certain RPM , the vibration just stays with you. That being said, there are so many possible combos that it could limit itself to one RPM range , but I don't think its likely.


Also check your harmonic damper. Does the engine vibrate at RPM when in p/n?

Paul

This may be WAY too simple but I'd think internal trans related (or at least I would try & figure out what is changed/different when it goes into OD)

tomorrow I'll do the same test in 2nd gear. Those rpm's in OD create more speed than I should do without spending some time getting out of town

Sounds like a plan

What changes when it shifts into O/D? The engine RPM changes that's what. If the vibration is there in park or neutral then you know it's an engine balance issue.

hi

you have too much timing advance .

disconnect any vac advance and test drive it.

if it still does it back off timing or slow the advance rate.

I would get in the same RPM range where it is vibrating & get it there both in & out of OD & see if it vibrates both times, if so that would for sure point to an eng balance issue.

Timing was an interesting idea, a few taps of the keyboard ruled that out. Moved it from 38* to 32 to 28* made no difference.
It does it parked, first, and second gear but way more pronounced in drive for some reason.

Check the rear bushing in the transmission.
Mike

Can I do that with it in the car?

If you have the vibration sitting still it is not in the driveline. It only seems worse in drive because of the load it's under.

I'll check the dampner to make sure nothing goofy has happened there, but after that, pull the pan to see what the crank is?

Had a friend who's clutch fan went bad and cause a vibration issue.

interesting. cheap flex fan on this one. I did pay attention to the accessories this weekend, didn't notice anything out of whack with them.

anyone ever use a sirometer or this math?

https://grassrootsmotorsports.com/forum/tech-tips/cheap-simple-nvh-tool-and-write-up/117396/page1/

according to this, and my observation that the vibration is the worst at 2700 rpm means
2700/60 = 45hz if an external engine vibe. I think mine is internal so * 2 so 90hz vibration. How do I find which engine component that is?

Simple. Everything that is a suspect for vibration has a calculated frequency and there is the tool to count it.

I'm a little confused on the timeline but which transmission has it vibrated with, the 727, the A500 or both? If it shook with both, then it's in the engine. If it didn't shake with whichever trans was in it first but it does with what's in there now, it could be in the front of the transmission, whatever spins internally in neutral either directly or thru sympathetic motion.

I don't know if it was covered already but do you know the build history on the engine or did you get it the way it is? If it had say a cast crank and sixpak rods or a mix and match of LY's in it and it wasn't balanced, it would definitely have a shake. A cast crank and neutral balancer and flexplate could do it or any combination of the above.

Kevin

If your engine is marked "E"it's a 69 not a 71. 71 would be marked "G". All 69s are internally balanced.

No, e for cast crank, like later 440's were stamped. It's a 71 date engine by casting date

Also found a site that said take rpm/60=Hertz, don't need a sirometer.
2700rpm is about the worst spot. 45hz. Same site said for internal engine stuff take second order so 90hz. What I can't find is something that says what materials or component matches that frequency.

Prefix "E" would be for the date (1969 I think)/ suffix "E" would denote a cast crank (originally & likely still) eng.

Once you figure out your Hz, how do you figure out if it's a 1st or 2nd order harmonic? And then what is a guide for where to look at in/on the engine? I'm trying to read up, but it's almost over my head

I'm in that exact spot, I couldn't find any more info. the one site I found said that external stuff was 1st order, internal is 2nd order. I'm 99% sure it's not an accessory or physical interface with the chassis or something, so I went with 2nd order.

You can eliminate all the external accessories by removing all the belts. A few minutes without the waterpump turning won't be the end of the world and it will eliminate the one big accessory, the cooling fan.

How's the crank endplay?

Kevin