nonameo

Well, I just recently did a auto->manual swap on a 90 gxl. I NEVER got to run the car before I did the swap.

here's the specifics

-vibrates badly under load in the shifter and the rest of the car, but not the steering wheel

-weird oscillating vibration when not under load. IT's like the vibration goes on and off... on and off... etc etc.

- seems to do it more when you turn left than right. <-- very noticeable thing.

-I can watch the belts on the car and see them oscillate with the vibration.


-tires all have good pressure

-engine got 70 front and 95 rear(all even) with ghetto compression test

-changed spark plugs

-driveshaft has clearance, also worked FINE in another car, as well as the differential and rear end(but it sat a while before it got used again...)

-TII rear end and tranny

-new lightweight ACT flywheel.

-previously I thought this problem was only under load. But now I noticed this other vibration and its strong enough to be pretty noticeable. I think they are related. Might not be.

-oh yea, BAC circuit is bad too, getting 2.5 volts with the circuit voltage test.

-and also - I think vac is somewhere around 15 in HG, but it was hard to get a reading because the needle likes to stick(have to thump it to get it to move)

Wyznewski

Ouch, 20 psi variance in pressure between front and rear rotors=rebuild time.

Kenteth

Crap its hard to quote all that right.. .so

quote with comments

Well, I just recently did a auto->manual swap on a 90 gxl. I NEVER got to run the car before I did the swap.

---> Least it runs now

here's the specifics

-vibrates badly under load in the shifter and the rest of the car, but not the steering wheel
---> Initial thinking: Out of balance drivetrain (missing bolt on the flywheel, flexplate, driveshaft, or halfshafts)

-weird oscillating vibration when not under load. IT's like the vibration goes on and off... on and off... etc etc.
---> Oscillating... I wish I could admit thats a good word to use when describing vibrations... but its not. If it goes on and off, its intermititent. If it vibrates on one side of the car, then the other, its oscillating. Oscillating in that case would be...weird

- seems to do it more when you turn left than right. <-- very noticeable thing.
---> Things to check: Front wheel bearings, lug nuts, tie rods, stearing column knuckles and rack, steering fluid.

-I can watch the belts on the car and see them oscillate with the vibration.
---> Again with the oscillate. Are the pulley misaligned? Is a pulley not true (bent or wobbly on one side)?


-tires all have good pressure
---> Sunny side of life.

-engine got 70 front and 95 rear(all even) with ghetto compression test
---> Not so sunny side. I wish I could tell you to count error rate of ghetto fabularity. Numbers are a bit low and a bit far apart. Remember each rotor would have three spikes on the compression test to get a good idea of what is going on.

-changed spark plugs
---> Those things get expensive

-driveshaft has clearance, also worked FINE in another car, as well as the differential and rear end(but it sat a while before it got used again...)
---> Some cars use internal and external balancing (where the driveshaft is balanced in the transmission-- something stupid like that.) Just keep in mind because something works in one vehicle, doesn't mean it will work in t next. BTW Driveshafts on our FC's are self balanced (usually a balance weight on one of the ends-- check to see if its there.)

-TII rear end and tranny
---> 430 gear ratio better than my 390 :/good choice though, heard our n/a trannies only last to about 200ish hp.

-new lightweight ACT flywheel.
---> You kept the flexplate/rear counterbalance attatched to the rear of the engine right?

-previously I thought this problem was only under load. But now I noticed this other vibration and its strong enough to be pretty noticeable. I think they are related. Might not be.
---> Clarification? Only under load, or at all times-- even idle?

-oh yea, BAC circuit is bad too, getting 2.5 volts with the circuit voltage test.
---> Meh, bac I ditched mine, but I also have no cold idle and winter will be a mother later this year...

-and also - I think vac is somewhere around 15 in HG, but it was hard to get a reading because the needle likes to stick(have to thump it to get it to move)
---> Consider buying a vac gauge ($20) to run into the dash of the car for constant monitoring while you're driving. Much easier to get decent readings. I plumbed mine into the same vac line as the stock pressure sensor.


Goodluck mate!


EDIT:

A strong idle vac BTW is around 20"Hg (yes.. small g!)
The highest vac I've gotten on my car at idle was right around 19-20... but if the car was cold, it would bounce anywhere from 12-18 until it was warm. Then it would sit around 15 until I gave the pedal a nudge to get the rpms up. The highest vac I've seen on the manifolds was 23" Hg. I've heard in pristine condition, 25 was about right.