kalli

Hi all,
still in the process of stopping rearend vibration.
All parts are new, tyrtes balanced (including new balanced drievshaft, measured to size and u-joints)
it starts at about 70mph and gets worse the quicker I go (i usually stop at 80mph as it gets unbearable or frightening).

I will drop the engine with half inch drop mounts I have to get the angles better, however there's something I want to check first. Looking at an old picture of mine it seems it simply not straight.
How would I best go about ths? make sure that all is one perfect line, or make sure that everything is the same distance from frame?

brentamis

Im having the exact same issue as well. Makes highway driving sort of annoying...

OCHOHILL

Find center of the car between the wheels front and rear and pull a string across those points. Double check the wheel location to the spring perches and spring perch width. I hope the rear is correct for the car. Something doesn't look right.

groho

it looks like you've lower your car also. Is that the case? Pinion angle can cause issues also. If your rear is not square, then you're gonna see it in the wheel well, front to back and left to right. Quick check, find center of the crossmember by measuring between front frame rails, then measure from the tranny cross member back to each spring perch. As a precaution, also measure to the axle tubes in the event the the rear has shifted off the perch.

MonsterBilly

Kalli, In am dealing with the same shat! it is driving me krazy!

Here is what i have done:
replaced the T5 trans mount
replaced the drive shaft with one balanced to 10k rpm
replaced the entire rear end with a 8.8 exploder rear end
changed pinion angle up to 3* in both directions
replaced the T5 with a newer better unit

So this leaves two things, the clutch (centerforce dual friction) or the engine!

thats all i can figure!

kalli

well I have all new parts, so nothing should be out of balance and it's almost guarnteed it has to do with the angles simply for this reason.

- cruising on motorway 70mph is okish, slight vibration that I seem to ignore by now when you get slowly up to speed it starts vibrating around 80mph
- when i'm going baloobas and go from standstill 1st, 2nd, 3d WOT at some stage this vibration kicks in and it feels a bit later (90 ish), however when I let go off the pedal it seems to be even worse then and I coast safely back to 70ish.
from this
a) it feels worse at high speed on deccelleration than on accelleration-> this indicates the the pinion in back needs to be raised. is that correct or do I have that the wrong way round?

b) the angle at gearbox going down is like 6 degrees and the angle of pinion going up something like 4. that would be somehow ok (the 2 degree difference), but the main problem here is that the workign angle of the u-joints is too high. the angle between slipyoke (tailshaft) and driveshaft added with the angle of driveshaft against yoke is too high. you want that as little as possible. (i have to check my notes for what exactly it was, i just remember it was too high)

Now what I'd have to do is to raise the tailshaft at the back and the whole lot would be 'flatter'. if it came up by 2-3 degrees, all would be in the range it should be (or I could modify pinion angle then so it would be). I can't possibly raise it with the mount as the gearbox would hit the floor in front of the gearbox mounting
So the solution to that is too lower the engine, which will bring the gearbox way from tunnel and up at the back.
To add to all this angle stress I feel that the angles as seen from on top of the car are not right. it seems there's even more bends (see picture). this is guaranteed to not help either.
So I guess what I'll do is to use the drop mounts I have and at the same time move engine and gearbox side-side or twist so i get a better line.

I'll measure from wheels and frame. I don't mind if everything is offset to one side as long as the driveline is 'in line'

Monsterbilly: it's very easy to figure out if it's engine/clutch related. If the vibration is at same speed, no matter what gear you know for a fact that it's not engine/clutch
I can rev in 1st and 2nd to 6500 no vibration. vibration kicks in for me (i start to feel it) above 70mph and no matter what gear 3rd, 4th or 5th

groho: in the back there's a 5leaf mid-eye, that's the only dropping going on there and the rear axle is specificly made for this car (quickperformance racing. they sell hundreds of them ... )

67mustang302

Driveline angle is off. Check for worn u joints and play in the pinion yoke.

kalli

67m302: u-joints are about 1 month old (came with new driveshaft), with the pinion i rather hope all is ok (less than 3000 miles on it, wouldn't like swapping bearings). but I'll check. I'll meet a friend tomorrow for lunch and I'll try and straighten up whatever I can.
I'll see from there.

eZ

you know most people over torque thier U joints squeezing the bearings too tight. Ruins them almost instantly and creates the vibration you are describing. should be about 14-16ft lbs. Also when you have the wheels balanced sometimes the weights can fall off the first drive home. check to see if the balance weights are missing. Good way of checking is to run the car on jack stands with the wheels off to see if same vibration occurs.

Those are just simple checks that you should do before messing with engine mounts. But 6 degrees is a bit much for your tranny. rather see it about 2.

mikenkiki05

try checking your tires and rims and make sure they are dead nuts also most shops will balance them but when you ask them to speed balance them most shops wont do it because they havent been trained to speed balance rims, and most shops dont have the speed balance option on there machine

here is a example

1 a tire has 1/16 inch run out at x amount of speed

2 a tire at highway speeds has 3/8 run out at x amount of speed,

ask any professional drag racer and he will tell you they speed balance there tires for that reason

i used to circle track race and the winners every week had speed balanced there tires and rims and me we didnt balance at all and didnt win but 3 races while others was winning week in and week out.

it may be a pinion angle also but dont over look tires and rims also

not 1 single rim is 100% true round some are as close as 92% and some of your cheaper ones are around 78%


hopes this helps you a little bit and not to confusing to understand, i dont claim to know everything i just listen to alot of info on this forum and other forums also lol