Vibration 68 Runner 383 4 speed combo

[The Beep]

Hi

This is driving me crazy. I have had the car for 15 years with a few big block motor tranny combos. Never had this before with other combos. I recently swapped in a 383 (non drilled crank used bearing etc...) to replace a blown 400 and left in the existing 4 speed in the Road Runner with 4:10 rear gears and then this started. Normal driving no issues. If I bring the revs up in a lower gear it won't do it. If I walk it up to speed, no issues either. However run it hard and once it hits 55-60 mph car starts to shake hard. I cant really tell where but it seems mid body. Feels like something is coming off! Slow down it goes away but not instantly. Press clutch same deal.

Had the drive shaft balanced, swapped wheels and tires. New motor and tranny mounts. No luck. The car is currently tucked in for the winter but I can poke at it.... Any ideas?

 

[Sonny Black]

Hi

This is driving me crazy. I have had the car for 15 years with a few big block motor tranny combos. Never had this before with other combos. I recently swapped in a 383 (non drilled crank used bearing etc...) to replace a blown 400 and left in the existing 4 speed in the Road Runner with 4:10 rear gears and then this started. Normal driving no issues. If I bring the revs up in a lower gear it won't do it. If I walk it up to speed, no issues either. However run it hard and once it hits 55-60 mph car starts to shake hard. I cant really tell where but it seems mid body. Feels like something is coming off! Slow down it goes away but not instantly. Press clutch same deal.

Had the drive shaft balanced, swapped wheels and tires. New motor and tranny mounts.

it sounds like a carb or fuel problem.....clogged line , filter, float?:sad1:
.....

 

[67 coronet]

if you are saying it goes away when you press the clutch then it sounds like a bearing is going out under load.take a good look at pinion bearing and output of trans for any play.

 

[The Beep]

if you are saying it goes away when you press the clutch then it sounds like a bearing is going out under load.take a good look at pinion bearing and output of trans for any play.

I like it! Hope you are right.

 

[kiwigtx]

Check your tyres - I had one years ago with "wandering wires" the steel belt were not perfectly in line around the circumference, and showed up at higher speeds.

Also were checking this - did you align your bellhousing when installing the gearbox? You may need to install offset dowels at the rear of the block, and centre the bellhousing before the gearbox is fitted. Results of a misaligned bellhousing would show as a huge vibration at the higher speeds like you are saying.

 

[69Bee]

The 400 is EXTERNALLY balanced, where-as the 383 is INTERNALLY balanced, as long as the 383 is a steel crank. That is most likely your vibration problem. What year was the 383?

All 400's were Cast cranks (external balance), and all 383's were Forged Steel cranks (internal balance). The ONLY exception were late 1971 383-2bbl motors which were cast cranks.

 

[Hemi Rebel]

How are your shocks? Are you dribbling a tire down the road like a basketball? Drive line vibrations occur at slower speeds. 30 to 40 or so.
I had a wrangler once that was a trade in. Hit 55 and it would literally throw the car into the next lane it shook so bad. That was fun . The jackass that traded it in probably had oversize jacked up wheels and tires on it and didn't want to lose them so he threw in a set of stock wheels and tires. Maybe the originals or who knows what. All I know it the f-ing right front had water in it. Not something you see ever so its not something you would think of when trying to diagnose a death shake. That pissed me off. Bad

 

[Meep-Meep]

As pointed out by 69Bee - If you used the flywheel from the 400, where everything worked fine, and now put that same exact part on the 383, you will have a vibration issue. Look at the back side of the flywheel for a series of holes or a big cut out as to reduce weight. A few pecks with a drill might be to correct the balance, but you don't want to see a whole bunch of weight removed. What you want on a stock steel crank 383 is a "balanced" flywheel, meaning no offset weight.

The tire theory is also interesting and worth looking into. I recently heard a story of a car with a tire that came apart but luckily no damage was done to the car (old Chevy). Tires were "like new" tread wise but 16 yrs old. A big chunk of the rubber just came off presumably after being heated up from a 40 mile trip.

 

[The Beep]

I like it! Hope you are right.

As pointed out by 69Bee - If you used the flywheel from the 400, where everything worked fine, and now put that same exact part on the 383, you will have a vibration issue. Look at the back side of the flywheel for a series of holes or a big cut out as to reduce weight. A few pecks with a drill might be to correct the balance, but you don't want to see a whole bunch of weight removed. What you want on a stock steel crank 383 is a "balanced" flywheel, meaning no offset weight.

The tire theory is also interesting and worth looking into. I recently heard a story of a car with a tire that came apart but luckily no damage was done to the car (old Chevy). Tires were "like new" tread wise but 16 yrs old. A big chunk of the rubber just came off presumably after being heated up from a 40 mile trip.

Sorry for the slow reply..... Yep everything came off the 400. Once the weather breakers here I'm checking out the flywheel.