Not So Good Vibrations

jikelly

jikelly

20+ Year Stangneter :roc</strong><span class=
Jul 9, 2003
872
53
99
Lubbock Tx
#1
So I'm enjoying driving the stang again a heck of a lot. Course the 3+ dollar a gallon gas prices have my eye twitching a little. Anyway, I got on it today to get around this jack hole in a truck and I felt heavy vibration under acceleration. :shrug:

What the heck?

I'm not sure why that vibration is there. I first remember feeling it when I got my car out on the loop and up to 60 MPH. I think it might just be my u joints, but could it also be my drive shaft needs rebalancing? Do they fall out of balance?

My drive shaft was modified when I installed my Tremec 3550. It was shortened. It's been years since I regularly drove my car but my memory tells me that on the highway there was vibration around 65-75.

Anyway what do you guys think?
 
#2
You need to check the pinion angle.
With the tranny change and the driveshaft mod, you may have altered the angle the rear pinion aligns with your driveshaft.
I'm not sure about a 73' Stang, but the fox mustangs(79-93) should be between 2 and 4 degrees 'nose down'.
That's the pinion pointing to the ground slightly. When you accelerate, and load the rear end, the pinion will straighten, being parrallel to the drive shaft.

Here's a link to help you.

http://www.steeda.com/news/tech_articles/pinion_angle.php
 
#3
Yeah, I keep meaning to look at that. Probably should have done that after the tranny install years ago. I don't have one of those gauges, but I do have a protractor and a TI-89. I'll see if I can figure out where it's at tonight. I know the angle the engine is at changed when I installed that roller block.

Thanks!

Um, how do I change the pinion angle?
 
#6
Checking pinion angle is pretty easy - if you have a 4 post drive on rack that will allow you to climb under the car while the car is resting on it's own weight.

If the angle of the output on the trans is -4 you need to get the input of the rear end to +4. If it's off more than a degree or so, you (might) have problems.

It's really easy on a 4wd!

Here's some more tech:

http://www.drivetrain.com/driveline_angle_problem.html
 
#7
I have a TKO in my 65 Fastback and it has a similar problem. I have heard that it is common with the Tremec swaps due to the the angle the trans gets into due to the over sized trans having to be dropped down a bit to eliminate hitting the trans tunnel. It is not the pinion angle but the other end. I have an aluminum drive shaft and it was supposed to make it better, but in really looking at the angles after I had the problem seems that the problem is the TKO. Also check your trans mount. I moved mine up so the trans just touches the tunnel (In the front where it hits) and backed it down a tick. I got the kit a long while ago from Dark Horse Performance I think. An easy way to tell is look at your Fan, you can usually see it if it is a problem as it was pretty pronounced on my install.

I can tell you it gets scary at the track when you running it hard at 130-140mph. I have a T101A from Tex Racing transmission that will solve that problem and the tough shifting of the TKO (In road racing to qualify that).

Sandy

[edit] I just caught your avitar, you may have more room on the later year cars, but not sure...
 
#9
To make it work you would have to move the pinion angle some serious amount and not sure that would even do it. It is also to the point where you have issues with other things (fan, mount, oil pan). The angle is just bad, fixing it by messing with the rear end is not the way to go if that is what your saying but I guess you could... In any case, I'm sure people can get it working but I'll solve it by replacing the gear box with something that is better for my application. I went with the TKO as I thought I might drive on the street and the 5th would have been nice. When I put the car together that was the idea, but that plan was a compromise so back to a T10 variant and problem solved. The TKO swap is a good one, I just didn't realize it as I was tossing it together that I should have cut or bump out and fixed the tunnel when I could have and it would be a really good street package, but if going to that much trouble you can get a T56 in without much more work.

Good stuff.

Sandy
 
#10
Have you ever climbed under a street rod and looked at the driveshaft? The output of the transmission is 3" offset from the input of the rear end. They don't have a vibration problem - because the angles are complementary.

You are making this too complicated. With the TKO you lowered your output shaft, what, 1" probablly less? That makes it like an extra 1 or 2 degrees of angle at the most. You add a shim between the spring packs and the rear end to get the angle of the rear end complementary. It takes about twenty minutes to figure out what angle you need and change it. It takes longer to find the correct shim!

Or.......you can cut the floor up and raise the output shaft of the trans to get the angle right. Either way.............you are mechanically changing the angle of the trans to the rear end.

Here's a picture of what I'm trying to describe:

2joint_angle.gif


I grew up on a farm between Fresno and Bakersfield. We use stationary power (diesel engines) via driveshafts all the time to run wells. It is a farily standard deal to figure out driveline angles and get them right. Driveline vibrations are downright dangerous in this application as they tend to shake things loose or wear out bearings. This is not a big deal, but it can be if you get it wrong. A misinstalled drive shaft like this killed my grand dad in 1968 when it came apart on a brand new well. He was standing roughly 150 yards away when it failed.
 
#11
Sure, I guess just moving the angle of the diff around would help, but it is really not just that problem. The rest of the engine is pretty tilted back, to the point that headers, oil pan, fan in my case are all a bit (tech term) out of whack. I would rather try to clean all that up with getting the trans back to the correct height so my pan will not be angled back from the pick up (would be fine for a chevy I guess), header suck back under the car, motor mounts (TCP style) fit better, etc.

One question as you seem to know a good amount about the drive line, as both sides of the drive line get more severely angled, even if both correctly set up, how does that impact vibrations or high speed operations?

Sandy
 
#12
sganz said:
Sure, I guess just moving the angle of the diff around would help, but it is really not just that problem. The rest of the engine is pretty tilted back, to the point that headers, oil pan, fan in my case are all a bit (tech term) out of whack.
Click to expand...

Did you measure it from stock? How much did it change? Mine was fine until I put mid eye springs in (which changed the pinion angle, and not for the better).

I would rather try to clean all that up with getting the trans back to the correct height so my pan will not be angled back from the pick up (would be fine for a chevy I guess),
Click to expand...

You should be running a baffled and sumped pan on your car anyway. You can uncover the pickup in 8-9 at Willow pretty easy and starve the engine for oil.

header suck back under the car, motor mounts (TCP style) fit better, etc.

One question as you seem to know a good amount about the drive line, as both sides of the drive line get more severely angled, even if both correctly set up, how does that impact vibrations or high speed operations?

Sandy
Click to expand...

I found this chart which seems reasonable:

http://www.4crawler.com/4x4/CheapTricks/Driveline-101.shtml

I know that there are also minimum angles as well as maximum angles. The driveshaft has to have some angle so the universals will rotate on the bearings. I've read that 1/2 degree is enough.
 
#13
Craig -

I don't have a before and after. I am going to look at it this weekend and see how off it really is. The car has regular position eye leafs, so that hasn't changed, but that is not to say it is angled any thing close to what it should be. I'll look and see how it is.

The pan is a good Aviaid 9.5 Qt pan, but seems not a oil pick up problem but likely when it blew a pump shaft, but have not pulled the motor, and oddly it was the sweeper onto the straight at WSIR that the motor died. That is another thread for later :(

I know if the min angles, someone mentioned that on the angles of half shafts for CV joints for the same reason, need some movement for lubrication. But I would imagine that being a far less of a problem then the bad pinion angles I'm likely having.

I'll do some homework and see how bad the pinion/trans angle is. I think it could be fixed a lot from just fixing the pinion angle, but the TKO is still going away :D

Sandy
 
#14
sganz said:
Craig -

I don't have a before and after. I am going to look at it this weekend and see how off it really is. The car has regular position eye leafs, so that hasn't changed, but that is not to say it is angled any thing close to what it should be. I'll look and see how it is.

The pan is a good Aviaid 9.5 Qt pan, but seems not a oil pick up problem but likely when it blew a pump shaft, but have not pulled the motor, and oddly it was the sweeper onto the straight at WSIR that the motor died. That is another thread for later :(
Click to expand...

I'll be interested to see what happened. I heard stories from older mechanics about oil pump shafts twist off when mechanics would use wire wheels to remove gaskets and "lose" a wire. It would get in the oil pump and sheer off the shaft. If you have an ARP shaft and you busted it........wow.

I know if the min angles, someone mentioned that on the angles of half shafts for CV joints for the same reason, need some movement for lubrication. But I would imagine that being a far less of a problem then the bad pinion angles I'm likely having.
Click to expand...

You can get vibrations either way.

I'll do some homework and see how bad the pinion/trans angle is. I think it could be fixed a lot from just fixing the pinion angle, but the TKO is still going away :D

Sandy
Click to expand...

I hear you.

I watched your videos (the one from Streets, anyway). When you gas it in some corners (right handers, on the gas, over bumps), it sounds like you have a tire rub. Do you? Where is it and how bad?
 
#15
Alright, I've just finished measuring my transmission, driveshaft, and pinion angles. I've also read 12 or so different articles on determining you pinion angles. I think this one has the best explanation http://www.vibratesoftware.com/html...pshaft_Angles.htm#Calculating working angles:

So here is what I found.
Transmission output shaft is 8 degrees up, according to the article.
Driveshaft angle is 3 up.
Pinion angle is 5 up.

That means I've got a front ujoint working angle of 8-3 = 5.
And a rear ujoint working angle of 5-3 = 2

The difference between the two is working angles is 3 degrees. Everything I've read says that is right at or just outside the limit.

Now I've got to figure out how to fix it. I could easily place a shim under the transmission cross member to move it up, but I think I only have 1/4 of an inch to go before the top of the tranny touches the tunnel.

I know I could also shim the rear, but it is already pointing upward and I've read that was bad too.

What do you suggest??
 
#17
The 5 degree working angle at the front is too much, and the difference between the two is too much.

The working angles should be 2-3 degrees ideally, with absolute max of 4. The working angles should be within 1/2 a degree of each other.

Have a look here:

http://www.vibratesoftware.com/html...pshaft_Angles.htm#Calculating working angles:

And you (and anyone else) can download software which makes it all easy here (goto downloads, then download "Vibrate 5.0"):

http://www.vibratesoftware.com/
 
#20
I discovered yesterday that there is not enough room in the tranny tunnel to make any difference at that end.

I guess I'm stuck with those operating angles. Unless I cut into tunnel or find a way to drop the engine down.
 
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