Been distracted over the winter and spring, but now busy lowering the seat platforms to allow installation of 2004 GT front buckets. Still want to try shimming the axle to change the pinion angle. This is the ONLY thing left to try, and it only costs a couple bucks. Will try this soon as the seat platforms are finished. All the experts say pinion angle should be 1 1/2 degrees or less. Not sure what it is right now, but will give it a try anyway...

 

I would still look at the drive shaft and yokes. http://www.armorb.procarcare.com/inc...04/4fig15.html

 

what does actually happen when you lift the car on it's frame and drive that speed jacked up ?
so that the rear wheels are free. do you still get the shakes ?

Kalli

 

Have you run it up on a dyno? That would eliminate the front and allow you to observe the rear under load.

 

I think that vibrations associated with pinion angle may get more severe depending on the rear ride height (the anti-squat geometry forces pinion angle change as the suspension moves). Have you checked this, back to back, driver only vswith a couple of large rear seat passengers?

Norm

 

I think Kalli's idea is your next step. Put the car up on jackstands and run it up to vibration speed. If no vibration, then it must the front end, but I doubt it, at this point. Remove the driveshaft and stick a yoke in the trans and run it up to vibration speed. If no vibration, you have it narrowed dow to the driveshaft on back, although it sounds like you're there already.

 

I just read an article regarding the same problem. It might have been in one of the Ford magazines - don't know that for sure though. Seems the fellow only got this problem when he loaded the trunk down with stuff while he was on the HotRod Power Tour. All that weight changed the angle of his driveshaft and started the same type of vibration. Answer to to install a small spacer underneath the trans mount to put 2-3 degrees on the u-joint. The article would be worth hunting down - I just looked through all my magazines but couldn't find it but I'll keep looking. With all that you have tried I bet its the angle on the driveshaft that needs massaging.

 

The article I was talking about is the July 2007 issue of Car Craft pages 66 & 68. If you can't get it then let me know and I'll copy it and mail it to you.

Tony V.

 

I just wrote a very long reply and it got lost in the system--Will not repeat it--You have been given some very good hints and suggestions--What you describe sounds like wheel and tire--As you suggest driveline is turning 3 times as fast and produces a roar not a shake---The only thing that has not been mentioned is a situation where eitherrear spring might have a bind and be transmitting shake that they (or the shocks) should absorb.

 

I have been going through a similar issue. 66 Fastback, with 93 5.0 and a T-5 with 8" rear. End up getting a new "Quality" $350.00 drive shaft solved everything except for a vibration at around 60-65 mph. Faster it is gone, slower it is gone. FYI, I had a brand new $115.00 drive shaft from a reputable mustang outfit nearby, and as it turns out, you get what you pay for! that driveshaft was junk. Nearly 20 thousand out of round at the rear, 6 thousands out at the front (using a dial indicator).

There is one thing im working on. Years ago I had a vibration problem (same car but way before the rebuild and all the new parts) and i found out that the original drums i was using had a large weight on one side. If I made sure that weight was on the same side as the axle hole (the hole you use to unbolt the wheel bearing caps through), the the vibration was gone. If not, the vibration was pretty bad. Now after rebuilding everything and using many many new parts, including new drums with no weights on them, I have been dealing with the vibration problem again. the new axle took care of half of it. I decided that I am going to fill the axle shaft access hole by making up a set of round discs that are 1" in diameter, with 5/16 fine threads in the center. These plugs (for a lack of a better word) will be just smaller than the 1 1/8" access hole in the axle. The new brake drums have smaller holes between the stud holes that are perfectly centered with this access hole. So I can just bolt this weight to the drum (using some red locktight on the threads)at one of the smaller hole locations. This will allow the brake rum to be installed only one way, with the plug dropping into the axle access hole on the axle flange to balance out that void of missing steel.

I figure, that 1 1/8" hole that is 3/8" on one end and 1/2" on the other (flange changes thickness as it nears the outer edge) must weigh a few ounces. I dont see why this huge hole in the axle wouldnt cause a small balance problem. (there doesnt appear to be any additional metal on the axle to counter this large void).

I hope this works, but personally, I think these balance problems that just happen at one speed is more harmonics due to a group of very slightly unbalanced parts. A combination of the engine, trans, driveshaft and axles rotating at just the right speed can cause a combined imbalance that you cannot measure easily on any one part (At least thats what I have read).

Especially when using the 5th gear of a standard T-5 (5th is .68 to 1). From articles I have read, low RPM's at higher speeds usually spells trouble for vibrations. Thats what I believe since it goes away at higher speeds. Perfectly smooth from 75 to 95+ mph.

Changing Engine and Trans mounts also helped. Im having good luck with the urethane engine mounts that wrap completely around like newer mounts (unlike the old rubber ones that can seperate). Had really bad luck with the urethane trans mount (much vibration transfer). I keep changing crap around after I fix something to see how it reacts with the hopes that 60-65 will be smooth.




[IMG]local://upfiles/83310/A88B89A2F9124E17952DDF7135E6ECAA.jpg[/IMG]