rg913

I have a 1999 gt with a ls3 th400. I have been chasing this violent vibration from the driveline for a while. It feels like wheel hop but much more violent. I had no problems before the swap. This issue that i am having is load dependant and has gotten worse as I flog the car trying to track things down. it does not shake the car when the tires are spinning. vibration is noticeable in all gears and especially on the gear changes. it feels like it is from the rear but i am thinking that the feeling is just due to the issue being transmitted through the driveshaft and rear end. the end result is the wheels hop. I have been through the rear end 3 times never have any sign of issue and the car drives at any speed just fine as long as its not wot. The converter is a precision industries with a sprag (i think may be broken). the trans is built with straight gears and every hard part you can put in it. was told it will hold 1k rwhp. This link is to a video of low speed what is happening. I believe that this issue is also what is going on at wot. the vibration is so bad it causes the windshield wipers to bounce off the glass about an inch lol. thanks for any insight that you guys may have.

https://www.dropbox.com/s/jktxnue8l0...20001.mp4?dl=0



Things that i have changed are

removed supercharger from car (was worse with more hp)
driveshaft- swapped with a friends car
all rear control arms and added solid bushings all around
gears, clutches, spider gears, everything in the rear end other than the pinion bearing race and the actual carrier which i bought used from a 2011 mustang to fit the strange 31 spline axles.
wheels and tires from et streets to some street tires on cobra wheels

had car on dyno, was able to make a full pass without the supercharger, not with it though.

no issue in reverse only in forward gears.

sorry for the long post trying to cover all the stuff i have been through.

DW SD

Couple thoughts:
Have you checked the pinion angle and engine / trans angles? There is an app, perhaps spicer makes it to check driveline angles.

I'll rule out u-joints since you said you swapped driveshafts.

Does the transmission yoke engage sufficiently deep enough? I believe you need several inches of spline engagement minimum. On my 6L80 + L92 swap, I initially used a TH400 yoke. It was much shorter than the 6L80 but of the right diameter and spline count, and I had significant vibration just running on the lift. I picked that off before getting on the road.
There is a bushing in the tailshaft housing that could be worn. The yoke rides against the bushing. If the bushing is worn, the driveshaft could wobble while spinning.

Doug

Project GatTagO

iTrader: (7)

Looking at the video I would say that you have an internal transmission problem, if as you say the rear end is in good condition.

Andrew

1981TA

iTrader: (7)

That yoke appears to be in a bit deep. Is it bottomed out in the trans?

rg913

DW- the yolk is within a half inch of the seal, I read that anything more than about an inch would be problematic. I added a drive shaft spacer to the custom drive shaft that i had built to have it engage further in the tailshaft. there was a small amount of slop with out it but you can clearly see on the yolk where the bushing is it is nice and tight with the spacer installed. I have not replaced the bushing it is a thought even though it only has a few hundred miles on it the seal is starting to leak a small amount from all of this. that should cover 1981 ta's question as well... i have tried multiple depths and 2 drive shafts. It is not bottomed out.

project- i agree that there is a problem forward of the drive shaft that is the culprit i am just trying to pinpoint that issue i am interested in your thoughts as to what internally in the 400 could cause this. I had my transmission builder over this evening showed him the video, he believes that this issue could not be from the trans or converter. I am not sold though. in his words the clutch style carrier can not hold the power... my argument is my old motor made more power than this one naturally aspirated and had no issue at all 100k miles and all stock. i have seen many high hp cars with nothing more than what i have in the axle. I am willing to bust out the cc but need some clarity on what i am working towards.

here is my plan buy a $450 ptc spragless converter to eliminate that as a possibility. if that is still not it i will buy another 8.8 axle or pull one from a friends car that has a spool 35 spline axles and is known good. please keep the ideas coming I have to make it down the track!!!

clinebarger

Sound like something is binding in the video? From what I can tell...It is Drive Shaft speed. I would seriously suspect it is in the Drive Line, Angles, U-joint bind, Pinion angle etc.

Old Geezer

iTrader: (3)

" I added a drive shaft spacer to the custom drive shaft that i had built to have it engage further in the tailshaft."

Been doing cars for a long time.. WTF is a drive shaft "spacer"??
What's that loud clunk noise? The vid only showed a few revs of the d/s, and I heard that clunk several times. If that's what we are looking to cure, I'd be looking for 2 parts slamming into each other, as the assy rotates.

superdave84

I agree, but the clunk happens when the driveshaft is in different positions. I think it may be getting bound up (from being too long of a shaft and/or being at some crazy pinion angle). My guess is that there is stress put on the driveshaft and U-joints, and when the U-joints do a rotation or a partial rotation, they probably hit the driveshaft or yoke out of sight. Careful inspection of the U-joints would show a mark if I'm right.

rg913

I have set the driveline angles, pinion angles everything has been verified multiple times by multiple people just to check my work. like i mentioned you can drive around all over town then all of the sudden this issue will start once everything is good and hot it is not all of the time just occasionally. I have had the driveshaft balanced and inspected 2 times i have installed a known good driveshaft from a friends car. nothing is bound up or making contact. I attached another video from the dyno you can see that there is a violent vibration at WOT

the loud clunk is something in the driveline like i mentioned i have rebuilt the axle many times as well as changed driveshafts

https://www.dropbox.com/s/762nli2xc9...R0026.MP4?dl=0

Item #ST-5557705 <--- google this. this is a driveshaft spacer... mostly used for swapping a c4 or tremec into a mustang.

rg913

check out the video at 1:30 and 4:00 you see that the vibration happens all is fine and well while driving through the gears.

I have inspected the u joints and you can not rotate the u joint to make it contact- the space between flanges is great enough this is not physically possible.

it feels like the issue happens between the flexplate and the tailshaft. something like the transbrake solenoind randomly clicking on and off/ during a wot pull it switches on off very rapidly that causes the trans to stop and start rapidly then transmit this through the driveshaft and axles the end result being the wheels hop.

Project GatTagO

iTrader: (7)

Video is not super helpful because everything happens very fast when it's at WOT. Can you replicate the vibration when you have the rear end up on jack stands?

Just looking at the video the driveline angles aren't that extreme. I still say it is something in the trans, but I don't know anything about automatic transmissions, so I can't really say what it might be.

Andrew

rg913

the issue is only there with load. you can make wot pulls nice and smooth on jackstands.

DW SD

You say the trans seal is leaking. That to me suggests an issue there. If the trans output shaft bushing has been worn, it will create a lot of vibration.
I might focus in there.

Doug

rg913

i agree and do plan to replace it... it does not vibrate at all no matter what the speed as long as it is below 90% throttle. it does vibrate at wide open throttle with load and the tires hooked.

cwylie

iTrader: (2)

I had an issue with my Duramax where it was doing something kinda similar. I would only get a vibration under 90+ plus throttle. Im not sure what rear suspension you are running but my issue was the aftermarket lift leaf spring allowing the rear end to rotate enough the throw off the pinion angle.

rg913

upr single adjustable lowers hpm double adjustable uppers spherical bushings on everything. the spherical bushings made the shake/wheel hop/vibration worse due to the no give from switching from poly bushings. the whole car feels like it is about to fall apart its so violent. rear view mirror steering wheel and windshield wipers are shaking like mad.

jmd

iTrader: (4)

It's very unlikely an on-off power application will transmit through the driveline and cause the wheels to hop. Wheelhop is usually just that; rear suspension.

The issue would crop up under WOT if it were transmission.

That right there tells you it's rear suspension.

Let's get to the point here. The rear chassis sucked since '78 when the fucksed-body was introduced; hence the need for quad shocks to control things. You're not accomplishing anything by going to solid bushings. When you want a car to actually handle worth a damn, you go to someone like Global West or Strano and talk turkey. Similarly, whomever that is for the SN-95, talk to them instead of firing off the shitty parts cannon of billet turds. It's not your transmission.

rg913

jmd- all good stuff - I was laughing reading your response to the control arms and bushings. I will keep working on the rear suspension until i can get it to stop doing this. I am lost as to what needs to be done though. I was going 1.50 60's last summer with 420rwhp in this car. Right now without a blower on it its probably less than that. I have never had a issue with it until I changed the engine/ transmission/ axle. It was my understanding that every drag car in the country ran team z, baseline, upr something like that.

I went to go get e85 last night in my car. it did not shake from a roll in 3rd on the highway, did not shake in first and actually hooked, only had an issue on the 1-2 gear change. it is so inconsistant it is frustrating.

jimmyg

It has to be drive line angles under load .that axle is tilting under heavy load and changing drive line angle .

Project GatTagO

iTrader: (7)

If you watched the first video, you can see that the there is a very loud popping noise at very low speeds.

Andrew