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390 bad vibrations!
Help, I,m going to lose my mind! Just installed a new 390 and c-6 in my cherry '66 f-100 custom cab. There is a vibration that starts at around 1800 rpm. Truck is stopped and in park. The motor was the original 352 but was changed to a 390 with crank and rods etc. I also had it balanced and professionally rebuilt. Crank pulley and flex plate were included in the balancing. The motor guy says that it couldn't be the motor...the tranny guy says it can't be the tranny. What do I do next? I thought I had the sweet set-up but the old oil-burning 352 and fordmatic were much better!!!
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390 bad vibrations!
Make sure the firing order is right. I had the same thing happen on my 302. I had the 351w firing order and it ran but it was rough at 1800 and got worse at higher rpm. It was rough at idle but with a mild cam I kind of expected it. Sometimes its the simple things that make you pull your hair out
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From: taylor usa
390 bad vibrations!
Did you put a new torque converter in? I had one do this in a Jeep Wagoneer that I was converting over to small block shabby. My first thought was balancer but also had the engine balanced so that would not be the problem. Talked to the tranny guy and he said it couldn't be the trany. The only thing I didn't change was the torque converter (wife was making noises about the cost of the conversion), so I talked to the trany guy and he said I did not necessarily need to change the torque converter.
To trouble shoot the problem I unbolted the torque converter from the flexplate and it solved the vibration problem. This meant it was beyond the flexplate. Nothing large enough in the trany to do this but the converter. Was a hard lesson to learn. Either pull the engine or the trany and transfer case to get to the converter.
Anyway sorry to ramble but you might try unbolting the converter, sliding it back and see if the problem still exists.
S
To trouble shoot the problem I unbolted the torque converter from the flexplate and it solved the vibration problem. This meant it was beyond the flexplate. Nothing large enough in the trany to do this but the converter. Was a hard lesson to learn. Either pull the engine or the trany and transfer case to get to the converter.
Anyway sorry to ramble but you might try unbolting the converter, sliding it back and see if the problem still exists.
S
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390 bad vibrations!
I checked the firing order and that is OK. I guess I have to bite the bullet and get under the truck again to seperate the engine and tranny. I have an extra bellhousing to use so I can bolt the starter up. The big problem is....it is cold, wet and snowing here in Colorado and I don't relish the thought of grovelling around on my back again!!!! I'll keep you all posted. Thanks!
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From: Coal country
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Hey! Sgreen was simply saying to unbolt the converter from the FLEXPLATE, not take out the whole transmission! If you unbolt the converter, you can push it to the rear of the truck, into the transmission bellhousing. You should be able to push it far enough back to disengage it from the flexplate. (I recommend you put the nuts back on the converter studs, to protect them just in case, but be sure to screw them down to the top of the stud.)
Once you've made sure you can safely rotate the converter inside the bellhousing, and that you have enough clearance to turn the engine over without the flexplate hitting anything, fire it up! If you still have the vibration, it is an engine problem. If it doesn't vibrate anymore, its the tranny.
Man, don't stay out there any longer than you absolutely have to! I HATED getting icicles in my moustache! That's one reason I moved back home, in South Carolina.
Post back if you've got more questions.
Good luck!
Once you've made sure you can safely rotate the converter inside the bellhousing, and that you have enough clearance to turn the engine over without the flexplate hitting anything, fire it up! If you still have the vibration, it is an engine problem. If it doesn't vibrate anymore, its the tranny.
Man, don't stay out there any longer than you absolutely have to! I HATED getting icicles in my moustache! That's one reason I moved back home, in South Carolina.
Post back if you've got more questions.
Good luck!
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From: taylor usa
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Banjo was correct. I should have been more concise. That is exactly what I was recommending. I simply stated that it was a good lesson in having to removed the engine or trany and transfer case. In attempting to save a few bucks it cost me more than that in labor. Good thing I work cheap. Quite often I get what I pay for though...
S
S
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390 bad vibrations!
Here's an update on the 'vibrating 390'. I had the tranny (c-6) pulled out at a shop. They ran the motor and it still vibrated!!!! They are playing around with putting wieghts on the flywheel and finding a correct damper for a 390. The prevailing wisdom out here at 7000 feet is that the 390 had a different damper than the 352 ,which is the one that I used. However, I know that a 390 is internally balanced and that I am probably going to have to pull the motor and check the internal parts. Is this frustrating or what??
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all alone in the world
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From: oklahoma
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if you had the motor balanced, and they didnt find the damper wrong then, wellllll, i would take the truck back to them and make them fix it. you cannot balance a motor without the damper and flywheel. i would worry about what they did and didnt do now.
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From: Sun River St. George
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Sgreen, Excellent test! I learn something new every day on this site. About the Harmonic Balancer. These are neutral balance as is the flex plate on 390 engines. To balance the thing, the pistons must all be the same weight, same goes for the rods. Then the crank is balanced by itself (both sides). My machine shop includes the weight of the rings and inserts in the calculations for the balancing bob weights. This business about different harmonic balancers for a 352ci verses a 390 is not accurate. The 390 balancers are thicker than the really old ones on the 352s but that is the only difference I have observed. Ford balancers and drive pullies will drive you nuts! Your machine shop is blowing smoke and if they cannot or will not correct this situation I'd take my business elsewhere.
William in Atlanta
William in Atlanta
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From: Littleton, CO
390 bad vibrations!
[updated:LAST EDITED ON 15-Nov-02 AT 02:59 PM (EST)]Sir James:
Where in Colorado was the work done? I am about to undertake a similar journey and may have to re-think my avenues.
Where in Colorado was the work done? I am about to undertake a similar journey and may have to re-think my avenues.
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390 bad vibrations!
I know this may be a bit late but I had a similar problem with a 390 in a mustang that I had balanced. Turned out it was the fan clutch, it would create a very noticeable vibration at a certain rpm. Of cours if you dont have a fan clutch this won't apply but is something to keep in mind.:-X12
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390 bad vibrations!
As of this date I have made the truck "driveable" but it still vibrates...you can feel it in the steering wheel. Now there is another problem ; there is a slight shuddering when I am accelerating in ist and second gear (c-6). The engine guy says its the tranny; the tranny guy says it's the driveshaft; the driveshaft guy says it's..........! All new shaft...spicer u-joints and a new fancy, teflon coated slip-joint! Anyone have any suggestions? This whole project has been a big disappointment!! I hate vibrations!!!!! I once visited a small hydro-electric plant in the foothills of California many years ago. The chief engineer proudly showed me a nickel that was standing on its edge atop the running generator!!! Thats the way I want it!! The guy was beaming! The only vibration I can live with at this point in my life emanate from my 1981 Harley low-rider!
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From: Sun River St. George
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James, Take a deep breath! Relax! Grab a brew, drink it, (slowly). I think you are to close to the problem. I would start with tests, do the SGreen disconnect the torque converter and check for vibration. Un hook all the engine drive accessories (take off the belts) start the engine and see if things change. You can run it a while with out the water pump. You need to determine if the problem is drive train or engine related. If the problem is in the transmission it will get worse and eventually something will fail. No huge deal, transmissions are available and rebuilding one is not that expensive. The drive shaft can be checked for balance and run-out. The differential drive pinion angle can be checked. Spring wrap and spring shackle issues can be solved. You need to diagnose the problem. Chances are it is right under your nose. Please post back and let us know how this turns out!
William in Atlanta
William in Atlanta
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390 bad vibrations!
William...many thanks for the help. Here is where things stand....the tranny was disconnected..motor vibrates!! the 352 vibration damper was removed and substitued with one for a 390. That helped. Washers were added to one of the crank pulley bolts. that helped. Engine was run with without belts...no change. It's driveable but the steering wheel buzzes. I won't be wosrking on it until the spring so I hope nothing comes apart in the meantime. The shuddering problem is a mystery. No angles have been changed in the driveline. Could it be the slip-joint?? I know there is a solution for all this but right now I don't have the patience or money. It's Friday night tomorrow and I'm going to do it up proper (as I usually do on Fridays)....plenty of Sierra Nevada pale ale and carousing at the local C and W bar!!!!! Despite all these problems, I love my FE. I wish I could ride behind it to hear that mighty engine roar!!!!
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From: Sun River St. George
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James, Man I hate to be the one to say this but it looks like the balance of the rotating assembly is off. The machine shop that did the work the first time around should re do it (free). Each component (pistons and rods) must weigh the same this weight plus the weight of the inserts and rings is calculated to provide the weight of the bob weights that are then added to the crank and used to balance the crank. The crank must then be balanced on both sides. Sorry man! Looks like that puppy gotta come out! The giveaway is the change brought about by adding a washer to one of the drive pully bolts on the harmonic balancer. It is unlikely but is it possible that you have a flexplate from a 410 or 428? These are externally balanced components and will really screw up an internally balanced motor. Random thought! You can tell by looking at it when the engine comes out.
William in Atlanta
William in Atlanta