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Shifter Viberation at 2500rpm
Hey Guys,
Just completed rebuild on 1972 351W. Assembled with balanced KB-151 Pistons & Forged Eagle SIR Rods. When Reving motor slowly from idle on up, when I get to about 2200 rpms, the shifter handle (Lokar shifter on a C4 tranny) starts viberating. (Pretty radically) Then, at about 2800rpm it mellows out back to normal. What would cause this, and how is it fixed????? Thanks RZ |
I think your motor is not balanced correctly. Does the shake come back at 4400 rpm? You did get the pistons balanced to one another, then the rods, then have the: crank, dampner, flexplate balanced to the bobweight of the piston/rod assembly, right?
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The rods came balanced to with in 2 grams and the pistons were staight out of the box.
I didn't balance the Flex plate or damper,... stock 28 oz. setup. RZ |
You need to take the pistons, rods, rings and rod bearings to the balance shop with the crank, flexplate and dampner. They calculate the bobweight for the pistons/rings/bearings. Then balance the crank/dampner/flexplate assembly to that.
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Unless you can feel a discernible engine vibration, this is probably just a "sympathetic vibration". The natural frequency of the shift lever is apparantly about 40 cps and it isn't well damped. Even a small engine vibration will add energy to the shift lever until it's going like crazy. %/
There are a couple ways to get rid of it: You can stiffen or loosen the lever or its mounting system until its natural freqency is out of range of the driver. You can add a damper to the lever to absorb the vibration energy. Maybe a heavy rubber sleeve that can be hidden by the shift lever boot. But I ain't guaranteeing anything... |
Thanks Guys,.....
Do you think maybe a Fluiddamper on the motor might help remedy this???? Just a thought.... RZ |
NO
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I can't figure out why this would happen. The crank, Flex plate and balancer were The same ones that I ran on the stock motor with no problems. The crank and Flex plate were not removed during the the rebuild (there was only about 500 miles on the Bearings)...... and the motor was still in the car.
The pistons were all exactly the same and the rods were within 2 grams of each other. ??????? I could see there being a problem if the crank, flex plate and balancer were new and had never been together before. But it was smooth before. Read: no shifter Viberation I am tending to think maybe theand added torque + HP may be the difference. I don't know???????/ RZ |
Can you actually feel an unusual engine vibration?
All engines vibrate a little. It's impossible to make an engine perfectly smooth because of the power pulses. Don't fix something that ain't broke... |
RZ,
The other guys have pretty well covered all but one thing that I have seen happen. A friend of mine with a MOPAR, excuse the non Cobra, had almost the exact thing happen and around 2800 RPM his shift lever would vibrate so bad it sounded like a snake buzzing. Then it would quite down as he got above that. It finally turned out to be his drive shaft had just a little twist in it. I seriously doubt if this is your problem but maybe it wouldn't hurt to look at your drive shaft and it's alignment. Ron |
What was replaced during your engine rebuild?
Does the vibration happen if the car is in park and reved up to 2200, does it come back at 4400? trying to find out if this is in your motor, or something in the drivetrain. |
Bob,
No, I can't feel any unusual vibration in the motor. It does not jump around or wobble on the motor mounts. Ron I will check out the drive shaft, but I doubt if this is the problem due to the fact that I ran the car for about 4 months prior to this engine teardown and rebuild. there was not a problem when the car was parked. Also it happens when the car is in Park as well as Drive. Mr. Fixit The block never left the Car. The motor was disassembled and reassembled while still in the engine bay. Flex plate was not touched, nor was the Crank shaft. Everything was changed except the Block, Crank, Flexplate, Balancer & Carb. I changed Pistons & Rings, Connecting Rods & Bearings, Heads & all valve train components, intake, cam, lifters, pushrods, waterpump, Yes the shifter starts viberating at 2200 rpm, both in Park and While in drive. >>>Stopped and/or while moving<<<<<< I don't notice it coming back at 4400 though. It might, slightly, but not as severe as the lower Rpm. Guys, I really appreciate your input on this. I am scratching my head here.... RZ |
"Everything was changed except the Block, Crank, Flexplate, Balancer & Carb.
I changed Pistons & Rings, Connecting Rods & Bearings," New pistons or con rods dictate rebalancing the crank, their bob weight is unlikely to be the same as the original parts. Since it happens while not moving, I would say it is in the motor. |
I agree with Fixit if the combined bob weight of Pistons Rings & Rods is not the same as the ones taken out there will be a harmonic vibration some place in the RPM range.
Ken |
Had virtually the same problem with mine. Started a slight vibration at 2000 and went away at 2200. Turned out that the pushrod between the clutch slave cylinder and the arm for the throwout bearing was too long (found the problem after the clutch slipped a little under hard acceleration). Apparently the clutch had worn some after 1500 miles and I hadn't left enough slop in the pushrod (had the slave cylinder piston all the way to the bottom). Removed the pushrod and shortened it about 3/8 of an inch and now everything is much better. Still vibrates a little bit if you're looking for it but otherwise not noticeable. I suppose that clutch linings can and will wear unevenly if you let them get out of adjustment. Just a thought :)
h dog |
He has an automatic tranny (C4) I had to reread the first post, I was hoping he just had a misaligned pressure plate.
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So..........
General verdict: ENGINE DISASSEMBLY? I guess I need to disassemble the motor and carry the pistons, rods, Crank, Balancer to a machine shop for proper balancing?????? I hate to have to do this, but if it'll cure the problem..... :rolleyes: Would the flex plate have to come out too???? Or can I use another one just like it. I assume to pull the Flex Plate, I would have to pull the whole engine out of the car..... :CRY: RZ |
Oops! :rolleyes:
h dog |
ZR I know on the first post said used the same flexplate by chance U picked up a 6cyl they will bolt on the 351W and are a couple af grams off and cause a vibration about 2000 RPM.
Another thing I would do is take the car to some one with a scope and make sure plug or wire or one is not crossed or at foul something is out of sink before tering things down. As a old man told me more than once stand back & just give it a KISS (Keep it simple stupid.) Ken |
Ron,
Hi, before you go and pull the engine,I would get a new harmonic balancer, an old one will move on it's hub and be outta balance or you could have damaged it putting it on. For a few bucks it's the simplest thing to try. Good Luck, Perry.:cool: |
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