Alright guys, a little insight on the ride. I have a 1953 DeSoto 8 passenger sedan, mopar BB 400 with the 904 auto that has about 2000 miles on it from a different vehicle. Has all new brakes, went through the bearings and everything was in good shape, no metal shavings or chunks in rear end. So my problem is that when I take it out it has a minor vibration that one could say is tolerable but the longer you drive it the vibration gets worse, to almost intolerable. It has the minor vibration while cruising at any speed but once driving for a while, the bad vibration is only from about 45-50 and 57-62. With the brakes being new they are adjusted out a little to wear them in and are not dragging at all, the tires are balanced perfectly( I know this as I balanced them myself) and last off the vibration comes from the ass of my seat, not the steering wheel. I need to figure it out as there are only a couple weeks to BTT50's and I plan to attend. Any knowledge is much appreciated. it also has new u-joints and the pinion angle is almost parallel but offset. Posted from the TJJ App for iPhone & iPad
Doesn't a 400 use and externally balanced flywheel and harmonic damper? Were you able to reuse those if so? Tom
That I am not sure of. It was was my grandfathers motor that he had built for his 1983 ramcharger and had actually donated it to my project. He did however put roughly 2000 miles on it while in the truck and did not have any issues with either motor or transmission. Posted from the TJJ App for iPhone & iPad
I have 2 brand new bf Goodrichs on the back. All 4 are perfectly balanced. Defective tire maybe? Any way to tell if its bad other then actually changing them? Posted from the TJJ App for iPhone & iPad
Like the post above ^,every time I've had a vibration issue at certain speeds. It was a wheel or tire balance issue. Good luck let us know how it turns out.brice
You say the Pinion angle is almost parallel. Parallel to what? Is the new 440 sitting at the same incline as the stock motor? If not did you correct the pinion angle? The Wizzard
I would run it up to 65 mph then take it out of gear- if it still shakes when slowing down that would eliminate the engine and trans. At the speeds that its shaking at it still sounds like wheel balance
When you balance them, you should be able to see if a tire is out of round or seperated by watching it closely as you spin the wheel. Also, a bent wheel will cause bad vibrations but balance out fine. When you mounted the tires, I have seen people's air compressors full of water in the tank, filling the tire with just enough water to cause an awful vibration.... new brake drums can be out of balance, people can accidentaly drop a couple of needles out of a u joint when installing them. Or if the caps are pressed too tight and the u joint binds, instant vibration...just a few suggestions that I have personally seen.
My bad, the pinion angle is parallel to the engine transmission and output on the tranny but is offset so it is not in a straight line Posted from the TJJ App for iPhone & iPad
I put the wheels on the balancer to check them before mounting tires even tho they are brand new and they did not wobble. The tires while on the balancer also did not "swerve" or "hop" like they had a broken chord or out of round so I would assume not that. I did not think of a water situation. If that were the case, I would have to get the water our and rebalance them as it would have balanced them at balancer speed WITH the water correct? Also, I personally did the u-joints so I know I did not lose any needles. If I had an unbalanced driveshaft would it vibrate harshly at any speed or could it still fluctuate? Posted from the TJJ App for iPhone & iPad
I just solved a similar vibration problem that was driving me nuts...I could feel it in my butt; wheels balanced twice, then I found one rear wheel had a bad "wobble" from the factory (chrome smoothy) that was causing a sideways shake. Good luck, Frank
I am betting on the drive line being bent. It is almost impossible to get a driveline out of balance unless it is bent. Most driveline shops are lazy and just add washers to balance it. If it is truly straight it will be in balance. Also, how far off to one side vs length is it? Also some fords used a big harmonic balancer at the front yoke to eliminate vibrations.
When I built my car I had to have a driveshaft made because of the length. I hand picked the shaft Nd it did not have even a ding in it. I had a reputable shop weld my new end yoke on but I did not get it balanced. Now like a previous post states, obviously if it was the shaft it would get worse the faster you go but the vibration damn near goes away at about 70 mph. Posted from the TJJ App for iPhone & iPad
I chased a vibration in my 57 for most of one summer awhile back. Mine would come in at 65-70. I had converted it to a T5 trans and the pinion angle was off. I ended up shimming the axle about 2* to get the pinion up and it cured 99% of the vibration. As far as a tire vibration you could swap the tire/wheel from front to back & see if it changes in anyway.
I want to know how you got a 904 on that 400. 904's were only behind slant 6 and small blocks. Pinion angle should be about 1 1/2 deg up not parallel. i would also have the driveshaft balanced.
To get to the bottom of any situation, duplicate the symptoms. Drive the car, let the vibration get as bad as it can. Drive it in the garage, jack it up with a floor jack, under the diff. Place car stands under the rear axle, so the suspension is loaded...ride height. Block the front wheels, have a helper run the car in 'drive'...Crawl under, observe "WHAT'S SHAKIN' "! Repair. End of operation.
The 904 and 727 are essentially the same tranny. The early 904s were built stronger and can handle more power then the 727 can. They originally built the 727 for the slant 6 but eventually just used the 904 as it was used in more things and all around just tougher. I will have to take the shaft in and get it balanced. The shop that does them in my area will balance for around 135.00 Posted from the TJJ App for iPhone & iPad
Probably not but something to check, any slop in the pinion bearing? My o/t truck had the same problem, end up with a pinion bearing that was sloppy.odds are against it but something to check. (And yes it was mph specific , but only after deceleration) -Levi Posted from the TJJ App for iPhone & iPad
Anything is possible and I'm not weighing anything out till I know for sure.. When putting it all together I did not have any slop but I will check this out.. Thanks for all the ideas guys Posted from the TJJ App for iPhone & iPad
I had a similar problem with my 66 Chevelle. It was a long time ago but I recall that even though the u-joint was new it was the incorrect one. It fit the yoke on the driveshaft but the yoke on the 12 bolt was slightly different. I hope my memory is working right here. A friend finally found it a fashion similar to what the suggestion was above, car up on the jack stands and he flashed a timing light on the driveshaft. Sure enough it started to whip around at a particular speed. A little searching for the correct u-joint and that was the end of the problem. I sympathize with you, stuff like this just drives you nuts.
I think you have that reversed, The 904 will only work with a 6 cyl, and small block motor. The 727 is the stronger of the two and is probably what is in your car as it was used in all big blocks including the hemi.
Odd.. My grandpa is the one that said it was a 904 and h has been working on molars for over 40 years. Either way, they were both rebuilt my a reputable builder here and have only about 2000 miles on emm. Posted from the TJJ App for iPhone & iPad
Old wheels with problems in balance should be re balanced from the lugs and not the center hole. This applies only to bevel lug nut type wheels. Lots of shops have the lug center adapter for the balance machine but won't dig it out unless you tell them to.
I am guessing a drive shaft problem. How far out of the tranny does the yolk sit? If it is more than an inch your drive shaft is probably to short. Had this problem on my fairlane.
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