Vibration
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500, 472, 425, 368 Discussion, Vibration in Cadillac Engine Technical Discussion; I've noticed that sometimes if I drop my transmision (Turbo Hydromatic 3 speed) into low or second past the normal ...
  1. #1
    Sasquatch's Avatar
    Sasquatch is offline Cadillac Owners Fanatic
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    Vibration

    I've noticed that sometimes if I drop my transmision (Turbo Hydromatic 3 speed) into low or second past the normal shifting point and give it gas to gain speed and then return it to the drive position that I experience a tremendouse vibration of some sort. Almost like the tires are out of balance. I know that is not it but that's what the viration feels like. Is this something to do with the transmision. Is there a manifold vacume to the transmision for shifting. I think I read that somewhere. On the back of the Q-jet there are 2 vacuume ports one for the power brake unit and the other appears to connect to a tube that runs down to the transmission. I recently changed the tranny fluid and all looked well as far as no metal bits in the old fluid. I have had it happen 1 time just while driving but the other couple times have been when manually running it through the gears. Thanks for any input.

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    Angela Desmond is offline Cadillac Owners Fanatic
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    Re: Vibration

    Vacuum hose goes to the modulator on the transmission. I'm not sure exactly what it does, 'cause I don't know much about transmissions, but if the modulator isn't working right, the tranny usually bangs into gear instead of a smooth shift.Why are you holding the gears past the normal shift point? Do you have engine modifications that will produce more horsepower at higher than stock RPMs? And does the vibration occur only at the higher than normal RPMs or does it still vibrate after the shift and the RPMs drop? Out of balance tires usually vibrate the car at about 60 MPH. Driveshaft balancing will produce vibrations at all different speeds.What year is the car and how many miles are on the drivetrain?

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    Sasquatch's Avatar
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    Re: Vibration

    69 Hearse with 133,000 miles. Don't always run it manually through the gears just ocassionally for the fun of it. Shifts smoothly between gears. Probably should just let it do the shifting itself. Doesn't happen all the time just when I run the tranny at high RPM's ............above it's normal shift point. No mods to the engine. Got her up on jack stands right now with the wheels off. Waiting on a master cylinder so I took the wheels off to make brake bleeders easier to get to. While I was at it went ahead and removed all 4 shock absorbers and am going to replace. MC won't be here for 7 to 10 days so figured I'd tinker around with some other things. When I noticed the MC going I got mad and really ran it through the gears the other day and noticed the return of the vibration. Stupid I know but sometimes even the best of us get frustrated.

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    Angela Desmond is offline Cadillac Owners Fanatic
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    Re: Vibration

    You realize that you just answered your own question, right? You're spinning that driveshaft a lot faster than it's used to. If you're shifting at say 5000RPM in first and second, you'll never fell that vib. on the highway because in third at 5oooRPM you'd be flying!!! Probably you'd be doing about 120MPH or better. Let it shift itself, even if you're standing on it, and I'll bet you never get that vibration...Besides, do you really want to let go of a driveshaft just because you were pissed at the master cyl.? You'll be a lot more pissed after that...

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    Re: Vibration

    That still doesn't explain why I experienced it once while under NORMAL driving conditions cruising down US 1 at about 50 MPH. Could feel it start and began to slow. It gradually increased into a pretty good vibration slowed and pulled over into a gas station waited a couple of minutes and resumed my drive with no more vibration. Just put a new Flowmaster muffler on the car. Could the heat being generated by the muffler be causing the driveshaft to wobble? I doubt it but thought I'd throw it out there. Checked all the U joints and they are tight and so is the driveshaft. It's a 2 piece drive shaft as this hearse is built on the commercial chasis and is over 20 feet long. Thanks.

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    Angela Desmond is offline Cadillac Owners Fanatic
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    Re: Vibration

    You didn't mention the 50MPH thing earlier. Let's throw this around: driveshaft angles can also produce weird vibes. You have a 2 piece shaft, you say. What if, the rear springs were shot and that in turn makes the car sit a lot lower and changes the shaft angle; especially since it's so long that it's a 2 piece design. I've swapped rears (GM to Ford) and have gotten vibes and I know the angle isn't much different than it was originally. That's something I know other people swapping rears have also experienced....Also, brake drums that aren't true can also produce vibrations. Naturally, they produce it more when braking, but the shoes on drum brakes are always in contact with the drum, even while not braking...After I swapped rears and noticed a vibe, I had a shaft made up for me that was larger than stock, because I'm dropping the modified 425 in the car and it needs the strength. That got rid of most of the vibe but I still have some; I think that's something I'll have to live with...Bottom line: How's your rear springs? Try adjusting the rear brakes differently and see if that changes anything. You're just going to have to do some trial and error stuff. I don't think there is an easy solution.

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    Re: Vibration

    Ok cool. I was thinking along the same lines that's why I'm replacing the shocks. They were totally shot. Picked up my new ones today and will install tomorrow. Can't drive it yet because I'm still waiting on my MC to get here. Either way the shocks should make a huge difference. I wouldn't be surprised if the ones I took off were the originals they look that old and worn. I tell ya finding parts for these older cars can be tough. Took a while to locate shocks that would work due to the old design. They have the threaded stud top and bottom in rear and finding ones with the proper travel was tough but got some Rancho's that will work and they're heavy duty. Had to go with monroes in the front. Sens-A-Trac heavy duty. They don't match but who cares you don't see them anyways.:coolgleam

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    Angela Desmond is offline Cadillac Owners Fanatic
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    Re: Vibration

    Worn shocks put a terrible strain on the springs 'cause it makes them do all the work...

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