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Discussion Starter #1
The car is a '70 Nova, 355 SBC, 700r4 tranny, stock driveshaft cut down and balanced over two year ago, 8.5" posi rear w/3.42 gears installed last year. I have noticed that for quite a while, I get a vibration at about 1,800 rpm thru about 2,100 rpms and it seems to be getting worse, or I might just be noticing more! The vibration seems to not be near as bad when the drivetrain is under load ie. when accelerating normally. Under light load or cruising seems to be the worse. Also, it is not a steady vibration, but more of a rhythmic vibration that pulses about 1/2 to 1 sec on then about 1/2 sec off. It also does it in any gear, although first gear is not to tell since it shifts pretty fast!

At first I was thinking tranny, but now I'm not sure how to tell...

If anyone has a guess, I'd love to hear suggestions!

Thanks,
Bill C.


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Bill C.
Colorado Springs, CO

68 Camaro... someday!
71 Chevelle SS
70 Nova
 

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Wheel bearing? Trans? Rear pinion bearing? Bent wheel? Out of balance tire?
 

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Sounds like a harmonic. I've chased the same and found: bad tranny mount, worn universal, out-of-round rear tire.

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Rick Dorion
69 RS Conv,355,M20,4.10's and I don't worry about stone chips ( yet ).
 

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Discussion Starter #6
Thanks for the suggestions so far guys... sounds like everything I had imagined needs checked! I was just curious if the fact that is was more rythymic could help narrow down the hunt. The motor and tranny mounts are all Polyurethane and look good. The tries could probably use a balance, but I usually find that they are more sensitive to certain speeds and then vibrate like hell continuosly. The driveshaft balance and u-joints are about 2 1/2 years old... don't they last longer than that?

I haven't checked the pinion angle... maybe that will be first!
Thanks again, keep the suggestions coming!

Bill C.
 

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BC: I am getting some strnage vibrations out of my car too, though sounds like it is a bit different than yours. I have a couple different resonance RPM's, not "speed" specific. I was going to post and ask if oyu had poly mounts, but it looks like you do. I have them in my car, it is the first time I have used them. I thought that maybe that was what was transmitting vibrations into the frame. I thought also that the exhaust may be hitting the car underneath, but this is not the case either.

Now I am starting to wonder about the pinion angle relationships. I installed a TKO recently, but did not check angles, etc. I just assumed everything would be okay. Time to learn how to check that stuff I guess.

I did have a Chevelle years ago that had some nasty harmonics going, it was from a rear end that I had 4:10 gears put into. You could really hear the beat frequencies, and it was there through a large range of travelling speeds (it would change frequency with speed too).

Keep us posted, I am chasing the same demon.....

Mark

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69 SS, ZZ430 Look-alike, Tremec TKO, Hotchkis Suspension
 

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Discussion Starter #8
Mark,
I'll try to measure the pinion angle and see what I find out. I also think maybe it started bcak when I put the 700r4 in, but it didn't spend much time at 2,000 rpms until recently when i changed the governor weights.
How do you like the TKO? I'd like to get rid of the 700r4 and put in a TKO one of these days. What did you use for clutch and bell-housing?

Thanks,
Bill C.
 

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So far the TKO is great, I really like it. It fit in fine using the Forte's crossmember. My car was an auto, so I had to cut the floor for the shifter, but I have heard that the shifter is in the right location for manual trans cars. I used a Lakewood Scattershield, which is one really beefy piece. Takes a bit to index it properly, but it wasn't too bad. I used a Centerforce Dual Friction clutch, and I highly recommend it. The pedal effort is not that bad at all, actuation is really smooth. On the highway, I spin about 2300 RPM depending upon the traffic (I'm actually not certain what rear ratio I have, I think it is 3.73, when I rebuild it I am going with the same ratio though).

Like anything, you get what you pay for. It is not cheap, and considering the cost of a good flywheel (which you'll need to have balanced), the clutch, bellhousing, etc, it's really close to $3k. For me though, there was no question, I love manual trans cars. My Chevelle was an auto, I think I liked it alot less because of that.

I am wondering if the source of my vibration is the motor. It's a crate motor, with an aftermarket billet flywheel. I assumed it would be pretty close, no reason to think it's not, but something is making the car vibrate. Never ends I guess!

Mark

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69 SS, ZZ430 Look-alike, Tremec TKO, Hotchkis Suspension
 

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Discussion Starter #10
Well Mark, Hopefully early next year I'll get a little fun money and get me a TKO... then maybe I'll even get it installed someday!

I too love the manuals, especially in a quick car that I can rev high! Hopefully behind the little stout 327 I'm hoping to build it will be very happy.

Bill C.
 

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BC, Are you saying that you feel this vibration come on in EACH GEAR between 1800 and 2100 rpm? If true, then it couldn't speed related (drive shaft, rear end) and has to be something in the transmission or in front of the transmission. Have you looked at your flex plate and checked the bolts to the torque converter? Does it go away if you put it in neutral and let it coast down?
 

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BC: I'll tell you, I have not had enough time to get my new 350 dialed in, but I do have the rev limiter set at 6500 and have taken it up there a couple of times. Yahoo!!!! One of the other things I really love about a manual trans is the sound the motor makes when you let off the gas between shifts, that wonderful sucking gurgling noise. The car really moves, it is the first real small block I have had. I am sure the power drops off above around 6200 due to the hyd valvetrain, but it is not so apparent on late night blasts, the motor rocks out. In the future comes a full on mech. roller, etc. I'd really like to have a 7200 to 7500 engine, even though it might not be "quite" as much fun on a daily basis. Who cares? My car is a toy anyway.

Any news on the pinion angle? How are you measuring it?

M

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69 SS, ZZ430 Look-alike, Tremec TKO, Hotchkis Suspension
 

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Mean,

Build yourself a little 292, 302 or 327 and cam and gear accordingly if you want easy rpm's. Imho

I'm not saying the 350 can't go up there, but the shorter stroke engines do it soo much easier! pdq67
 

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Discussion Starter #14
Mean69,
SOunds like I need to get that TKO soon and have some fun! I want to put it behind a 327 I have in the garage... but I'm still a little undecided on the cam. I wanted to be able to rev to 6,500 or so but still have good street manners... all the cams I've seen that will rev that far start making power around 3,000 or higher rpms. Seems that even the mechanical lifters don't rev much higher than the hydrolics. Guess I still have some time while I try to find some money.

When I measured the pinion angle, it loks to be at about 4 1/2 degrees or so, so I started the other post on how do I fix it. Looks like I need to find some shims.

Thanks,
Bill C.
 
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