Gun Jam

Okay

Adding the 2 deg shim made very little improvement...although I do think it improved it a bit but not nearly as much gain as the 1 deg shim.

Right now the car runs smooth at 82ish and you can just start to feel the impending vibration. At this point the car is good enough to keep up with Ca traffic. To notice the vibration you would have to go 86 to 90. I never drive 90 for more than a few seconds.

But

Just for the sake of it I would be at peace if I never felt it start to vibrate....BUT
we hit a point of diminishing return adding a 3 deg shim might make no difference or start to make it worse again.

At this point Im starting to think maybe the DS is developing some harmonic and the effects of the harmonics have been reduced by a better pinion angle but cant be fully solved because the real issue is the DS.

1/2 critical speed is 4,000 rpm

at 87 the DS is spinning 4450 rpm (an yeah you can again hear and feel it vibrate at this speed and yeah it gets worse when you back off)

should i give up at this point?

Its not fixed but it is better and good enough most of the time....deep down it just bothers me to know that something still isn't right...

Hummm

-Gun

Cruzzar

Have you verified driveshaft length to be correct, if it is a little short it will cause a vibration.

Scott H.

.....

Gun Jam

Yeah Scott thats what I was thinking...Im sure by the time I can actually feel it its beating the hell out of everthing.

-Cruzzar
No I have not verified the DS to be the right length....Can anyone say that IF DS length is greater that x.xxx it will vibrate? I did post pictures of the actual spacing on page 2 or 3 of this post.

Thanks for your guys help

I'll try adding .50" of washers on the trans to raise it up and see what that does.

-Gun

Gun Jam

one thing I dont get...

we have been raising the pinion.

Now we are going to raise the transmission.

To me that sounds like we are undoing the job of the shims. Is the purpose of raising the trans simply to reduce the total angle so that Trans angle + diff angle is less. Is that the goal?

-Gun

kalli

Hi Gun,

with raising the transmission you will throw off the back again. Helping it or undoing it.
So for this it doesn't seem to be worth it.
But according to Scott if you have a gearbox pointing down by more than 4 degrees then you will have vibration as we're running short shafts.

So from all this get your angle finder out again (i remember you had one when you measured first day). Let us know the values (just like I wroite them down a few posts before). The we all know what we're looking at. and what your current situation is.

In my humble opinion the shaft you are running is cut too short (can someone confirm or is this my sole opinion?)

https://mustangforums.com/forum/5834565-post40.html


GUN: do not give up. remember? we're having a race!
at the same time you 'only' changed transmission. for this your problem has to be either
- ds length
- pinion angle
- transmission angle
- driveshaft vibrating (but since yours is balanced ...?!)

I measured my transmission to point down by over 6 degrees. what's yours at?

Kalli

Gun Jam

Thanks for the input kalli

my trans points down at 2.75 deg

Well then happy hunting to the both of us

-Gun

kalli

hehee ... honestly 2.75 degrees sounds perfect. so if your pinion is in the same 0.75-4.75 degrees up, then I'd personally start hunting down a driveshaft.
maybe the problem is that it's only cut too short. It seems that you don't have any general vibration any more as in only around 3000rpm or at 50mph.
Your vibration seem to be at very high driveshaft speeds only.
Since you have 3.8:1 gearing. assuming the following tyres you get the following driveshaft speeds at 90mph
25.5" tall ->~4700rpm
26.0" tall ->~4600rpm
26.5" tall ->~4600rpm

i think that's immense. So i believe when the shaft is balanced (as it is according to your cutter) I'd say it was just cut a tad too short ...
From what I hear the slip yoke should only be out by around 3/4". You have around double that. But i cannot see hof far you are actually able to push in the DS. I'm just guessing 1.2" or more

my vibrations are at driveshaft peak at around half your driveshaft speeds.
50mph (less vibr with 40 and 60) with 3.5:1 gearing and 26

67 evil eleanor

Gun, I just thought of something. What type of motor mounts and tranny mount do you have (things that have for sure been changed). Sometimes using a hard type on the motor and rubber on the tranny will yeild a viberation (I may have said this before). It seems that if its getting better with the angle changes, then you are close. I will say again that "road forcing" the tires and rims will eliminate a lot of guess work. You may even locate the problem as I have seen new tires and rims balance perfect on the "spin balancer" and be off by over 140 lbs on the forcer. It makes for a good wop at about 70 and get worse as the speed increases, often the car will be smooth at 55-60 and free of any viberations. A tire, new or old can change at "ANY" time.

Gun Jam

I can actually push the DS all the way in until it touches the rubber dust cover (maybe further) Yeah your calculations are correct I have the 25" tire. It spins the **** out of it.

Before I did anything I stuck in the stock DS and it nearly touched that dust cover about .20 gap (less than 1/4 inch) At that time the general word was an 1" shorter. A .20 gap is not enough to protect against the DS hitting the tail housing so 1" shorter sounded good to me (at the time)....crap

-Gun