help needed olds350 w/373 rearend high rpm

[blitzcivic]

hi i needs some help. i have a 86 olds cutlass w/ a rocket 350 eng. and a turbo 400 3spd tranny running w/ 3:73 rear end posi. its really fast at the line but at about 60mph the car vibrates like crazy. and the rpm is howling at about 5000rpm. was wonder if i should swap trans to a th200r or 700r w/ adapter plate. or is there something else i shoul do. is it normal to have such a high rpm at 60mph.

any help would be greatly appreciated.

[niccaleb112602]

first i'd find out why its now only a two speed, sounds like u have no third gear

[blitzcivic]

well the tranny is switching through all 3 gears

[DrRocket]

Originally Posted by blitzcivic

hi i needs some help. i have a 86 olds cutlass w/ a rocket 350 eng. and a turbo 400 3spd tranny running w/ 3:73 rear end posi. its really fast at the line but at about 60mph the car vibrates like crazy. and the rpm is howling at about 5000rpm. was wonder if i should swap trans to a th200r or 700r w/ adapter plate. or is there something else i shoul do. is it normal to have such a high rpm at 60mph.

any help would be greatly appreciated.

Well, it looks like this is a conversion from the original V8 and tranny. Did you do the conversion, or did you buy it like this? Is the rear end original?

First of all, are you sure the speedometer is reading correctly? With the different rearend and tranny, it wouldn't surprise me to see some pretty big inaccuracies. Have someone follow you in a car at a pre-agreed upon speed to see how far it's off. I'll bet you'll find you're going a lot faster than you think. And try a variety of speeds. The error can change with an increase in speed. Some co-ordination with cell phones will help here.

Second, where did the driveshaft come from, and is it balanced, and what shape are the u-joints in? What about the length? Most clutch and u-joint places will do this work quickly, and it really isn't that expensive. The same shop will tell you what kind of measurements to take, and can tell you if it's the right length. If you've got it apart, have the flexplate and torque converter balance checked also.

The Turbo 400 trannies are good, but they have no overdrive. Are you going to race the car? If so, you might want to stick with the 400. If you'll mostly use the car on the street or highway, I'd consider an overdrive unit. There's lots of debate about the 200r vs. the 700r. I'll let you do some research on that one. They both have their adherents.

Are you sure the rear end is a 3.73? I've got a big block with a 4:11 and four speed in my car, and it doesn't hit 5 grand at sixty for sure. Unless you know for certain, it might be a 4:11 or worse. Don't rely on the seller's claims of "Yah, I'm sure it's a 3:73!" It isn't unusual for sellers to have NO CLUE as to what they really have. Also, what shape are the rear axle bearing in? They can make a LOT of noise, vibration, and racket when worn. I speak from experience with most of these questions. It wasn't unusual for Cutlasses from this era to have a 2.7 something ratio. Consider a 3.3 something ratio, expecially if you switch to an overdrive tranny. The reduction in noise and vibration will be dramatic. It'll be plenty quick enough to get your license yanked, yet pleasant enough for everyday driving.

It sounds like a neat car. I like these Cutlasses. I'll bet if you check some of these things out, you'll find some of the noise and vibration sources. These are some of my intitial thoughts. Hope they help.

[maxwedge]

Originally Posted by blitzcivic

hi i needs some help. i have a 86 olds cutlass w/ a rocket 350 eng. and a turbo 400 3spd tranny running w/ 3:73 rear end posi. its really fast at the line but at about 60mph the car vibrates like crazy. and the rpm is howling at about 5000rpm. was wonder if i should swap trans to a th200r or 700r w/ adapter plate. or is there something else i shoul do. is it normal to have such a high rpm at 60mph.

any help would be greatly appreciated.

There is no way 60 mph is 5000 rpms in second gear something else is going on, find out!

[blitzcivic]

thank you for your response, i appreciate it. i had the drive shaft custom made from ct drive shaft and it was balanced and has new u joints. the rear end is from a monte ss and i did check the gears and they are 3:73 and i check for play in the bearing they were good. i also did have some one drive next to me at 60 and i had a autometer tach in the car checking the rpm. ive tried putting a new trans module it made a small differance by adjusting the shift points. i did notice the motor and tranny are at a slight angle. when i installed the new tranny i had to move the cross member back. so i was wondering would this slight angle give a vibration.