Ok here comes the story. I'm getting a vibration from the rear end on my T-bird over 70 mph. It's been going on for a year or two but I had chalked it up to bad u joints and a out of balance drive shaft. The vibration feels like I'm driving over rumble strips on the pavement and vibrates the floor, seats, dash and steering wheel. How do I know it's not a front suspension issue? Well 1. The whole front end is less than a year old and 2. if I jack up the rear of the car and drive it to over 70 mph the sucker vibrates :hick:
So since I know for sure that the rear is causing the vibration let me tell you what I've done to figure out that it's the rear end:
1. I know it's not a wheel balance issue. The car vibrated with the old 8 holes as well as the Snowflakes it has now. Plus when I remove the rear wheels and just thread the lug nuts on to keep the drums on and drive it over 70 mph it still vibrates.
2. I had the u-joints re-placed, the drive shaft balanced, and the tail shaft bushing in the trans re-placed this year. No difference in vibration.
So I've spun the rear wheels and drive shaft by hand (with the trans in neutral) and everything seems to move freely with no noise. The axle bearings don't make any funny noises. Plus AFAIK the axle bearings won't cause a vibration. I doubt that it is a bent axle shaft because I would get some sort of vibration below 70 mph if it was. Also watching the wheels spin there is no wobble as far as I can see.
I'm starting to suspect the pinion bearing or gears. The pinion has no up and down movement as far as I can tell (I move the whole rear end when I wiggle it :hick:) but I can rock the drive shaft back and forth till it clunks slightly and starts to turn the rear. Also if I turn the rear wheels by hand the wheel I'm turning will start to move before the one opposite will. So any ideas?
Also I just remembered that yes the engine is not the cause. I can rev it to 6000 rpm in park and it's smooth as glass. I'm pretty sure it's not a drive shaft issue either as it's speed sensative NOT RPM sensative. It will vibarte at 70 mph+ in both 3rd and OD.
THAT is the issue I'm having !!!! Exactly.I also replaced the axle bearings and seals,same problem persists.
So we are both screwed :hick:
I'm going to take the car to the guy who put the 3.73s in 6 years ago and see if he can figure it out. I bet it's the pinion bearing. I mean what the hell else could cause it?
My thoughts exactly.I also went through everything you spoke of.Baanced the driveshaft,new wheels and tires,balanced.new axle bearings,swapped the tranny,swapped the harmonic balancer,new clutch and flywheel,new tranny mount.It sucks.
An out of balance driveshaft issue WILL be speed sensitive not RPM sensitive. Regardless of engine speed, driveshaft speed continually increases with vehicle speed.
I also, am experiencing a similar problem...although, mine doesn't sound nearly as bad as yours. When I swapped the 2.73 7.5 out for my 3.73 8.8, it continued to happen right around 70mph...I think I may just have had some wheel weights come off.
Good luck,
Don
True but the vibration always occurs above 70 mph, either in 3rd or 4th gear. The thing is the drive shaft is spinning much faster at 70 mph in 3rd than 4th. However the rear wheels/rear end are turning about the same speed in either 3rd or 4th gear at 70 mph, making me think it's a rear end issue. As I said I know it's not the wheels as it will still vibrate with the wheels off at 70 mph.
The difference in 3rd and 4th gear is input shaft speed...not output shaft speed or driveshaft speed. If the driveshaft were spinning much faster in 3rd than 4th, then vehicle speed would be higher. Driveshaft, pinion, differential, axle and wheel speed are all directly related to vehicle speed, not RPM. That's why a bad u-joint (just like a hub bearing) will get worse the faster you go, regardless of engine RPM.
Example, wheel speed is 70mph (gear selection is irrelevant), axles are turning the same speed, differential is turning the same speed. Assuming a 3.73 gear ratio, the pinion gear is turning 3.73 times faster than the differential/axles. The pinion gear has a on it which the driveshaft is bolted to. Do you see how engine speed does nothing to affect driveshaft speed while maintaining a constant vehicle speed? There is nothing between the tires and the driveshaft to allow it to increase or decrease speed independently of the vehicle speed.
Good luck,
Don
Ok after reading what I wrote I worded it all wrong:hick:. What I meant to say is that in 3rd or 4th (or any gear) the driveshaft and pinion are turning faster than the axles. Being that the drive shaft is balanced (it was balanced up to 4500 rpms) I'm fairly sure that the vibration has to be a rear end problem, speciffically the pinion bearing. The only thing in the rear that can cause a vibration like I'm feeling is the pinion bearing, unless the gear set is screwed, which I highly doubt.
I'm taking the car over to the guy who did the rear end a week from today. He's going to look it over and if everything checks out I'm back to the drive shaft. If it's the shaft fugg it I'm getting another one and having the new one balanced.
Let me know what you find out.
Error in communication...lol. Personally, I wouldn't think it would be a pinion bearing...That thing should make a lot of noise if it's loose enough to do that...and if the gear set isn't just right, it'll whine...usually there are some warning sounds that the rear will make before something gets loose enough to do that.
Best of luck, hope you get it figured out!
-Don
I hope so too. Hopefully the differential guy will find something :hick:
Hey Guys, I know I'm a little late but mine has been doing it too. Myself and a buddy of mine swapped my 7.5 with 2.73's for an 8.8 with 3.55's in it. It had disc brakes but I decided to stay with drums, I know it's not the normal thing to do but I couldn't afford new wheels and mine wouldn't work with the rear discs. So we put 92 mustang gt axles in, new seals and gear lube and friction modifier. After doing the swap my speedo is way off, I got the gear specified for the gears but it wasn't much different than the stock one, I recently bought the gear that goes in the trans to see if that helps, what I'm getting at though is I get that rumble strip feel like you guy's have but it also acts like it has a speed govener on it now. Top speed in my Fusion is 111 mph then the computer shuts it down, I know my T-Bird doesn't have this but it won't go past 90 mph. I know this because just for the hell of it I had it dyno'ed in june and that was top speed, it wouldn't go past it. I'm wondering if anyone else has had this problem? I only drive it on weekends to shows or occasionally I just take it for a little cruise so it's not as bad as it would be if it were my dd but it still sucks. Oh yeah if you're wondering, it didn't do too bad on the dyno, over 130,000 miles all original internals, minor bolt ons, and exhaust, it came with 155 hp stock, it put down 178 hp at the wheels. I know it's not a huge number but it went in the right direction, so I'm happy with that.
Sorry for high-jacking your thread, but it kinda fit.
Well the differential guy looked at the rear and it's fine. Nothing is loose and it's as tight as it should be. So now we're back to the drive shaft. The dif guy says it has to be the shaft. So now it's back to the guy who balanced the shaft on Tues the 28th to have the balance checked again. The shaft was balanced to 3000 rpms not 4500 as I previously thought.
I'm wondering at this point if the shaft could just be fubar and not balance out with 3.73 gears in the back. The shaft was originally balanced with the 2.73 gears but I'm guessing that perhaps the balance issue was always there but just not felt with the 2.73 stock gears.
I'm thinking the same thing for the Sport.I'll probably end up having a new one made.
Well it looks like your driveshaft is spinning at 3300 rpm to move your car at 70mph. ;)
thank you.
so when are you going to jack up the one rear wheel, get under there with the the car in N, grasp the yoke and twist / lift up and down.
you had the tail shaft bushing replaced,,yeah i know. now lets see if they really did it or not.
the best way is to drop the d/s from the rear and then do the above.
the last think i can think of is your d/s is out of phase due to the ujoint work.
or...get a second opinoin on the rear end.
I *think* I may have sticking rear drums. Here's why: I had the car up on jack stands with the rear wheels off and ran it up to 70 mph with the rear wheels off and the drums bolted on. Sure as shiznit it vibrated. So I stopped the car, put in in neutral, and shut it off. I went to spin the drive shaft and I could only rotate it so the rear wheels would move forward.I tried to spin the drums and they would only turn forward, not in reverse. I couldn't turn the wheels in reverse. So I put the car in park, turned it back on and ran the car in reverse. I then shut it off and put in in neutral. I went to spin the wheels by hand and now they went forward and reverse. Another thing I noticed this weekend when I had it out was it vibated like usual on the highway but after some stop and go road construction (ie hitting the brakes a lot) it stopped vibrating when I got to 70 after the construction zone. So when I get time this week I'm going to be pulling the drums apart to check for sticking.They might just need to be adjusted (hopefully :hick:)
now that sounds more like it.
if they are adjusted out too far, you should have trouble getting the drums off.
So I took the drums off today and it's not the problem. Everything checks out fine. So now we're back to the drive shaft/drive line/rear end. I'm going back to the shop that balanced the shaft Tuesday and he's going to pull it and recheck it along with checking everything else in the drive line. I'm going to stay in the shop so I can see what ever he finds. It should be a fun day :hick:
You know the more I think about it the problem has to be the drive shaft. If anything else in the rear was vibrating it would happen well below 68-70 mph. Since it starts at 68-70 mph, in 3rd or 4th gear, it has to be the drive shaft.
Post the findings,I still have the exact same issue.
Well I changed the transmission mount just for fun today and even though it was broke the vibration didn't change. At least I fixed the broken mount :hick:
I'm wondering if this vibration has something to do with the design of the drive shaft. I've noticed that a lot of Fox Mustang guys have this same problem going to higher (3.55 or greater) gear sets. It could be that the higher gears cause the drive shaft to reach it's critical speed. This seems to be solved among Mustang guys with an aluminium drive shaft. I'm thinking if the drive shaft shop can't get it to balance I might get an aluminium drive shaft from a Police Interceptor and have it shortened to fit my T-bird.
or an aerostar d/s
can you pull the yoke out of the tail end and post a pic?
did you check play in the axles when the drums were taken off?
not sure about your 3.55 theory as the problems should be pretty common with folks running 3.73 as well.
Axles are tight so that's not it. Yoke looks ok as I don't see any damage to it. I'd have to pull the shaft out again to get a pic but I won't have time to do it this weekend as I'm busy.
I'd do an Aerostar drive shaft but every one at the yard is bent:hick: The Police Interceptor shafts seem to all be fine though.
As for my theory: I've read a bunch of threads on Mustang boards about guys with Fox bodies switching to 3.55 or higher (3.73 & 4.10 included) gears having problems with drive shaft vibrations with the stock shaft. Since I have 3.73s and the stock shaft I'm thinking that it *may* be my problem. The common cure among Mustang guys is a FMS aluminium shaft. Since that wouldn't work for a T-bird I figure my best bet would be a cut down Police Interceptor drive shaft. I'll wait till Tuesday when I go back to the drive shaft shop. It should be a fun day;)
When you had it jacked up did you try running it without the drums? just something to throw out there. did you try the hose clamp trick? you just about covered everything else.
I haven't tried either of those. I should have tried the drums off when I had the wheels off the car:hick: Oh well. I really don't have time to mess with it this weekend so I'll have to wait till Tuesday. Like I said I'm staying at the shop on Tuesday till this is fixed.
I don't think it's the drums.I'm REALLY leaning towards the driveshaft.I think I'm going to just run to the yard and grab a cop car driveshaft,but,I'll have one problem,NO-ONE around here will touch an aluminum driveshaft.If that doesn't pan out,I may just have mine re-balanced.
The guy who "balanced" my drive shaft can make an aluminium one so I'm pretty sure he can cut down a cop car one to make it fit.
Just wondering but does anyone know if the 4R70W and AOD input yokes are the same? If so can I re-use the one from the cop drive shaft with new u-joints if I go that route? I figure the axle is the same as the 8.8 and 7.5 use the same axle ;)
Good questions.I'll have to look around for someone to weld mine up.
I think I'm going to go to the wreaking yard Monday and grab a Police Interceptor drive shaft. I think I'll bring it with me for shiznits and giggles if the stock shaft won't balance out. I just wonder if I can fit it in the T-bird :hick:
Let me know what you find out,and the details.I'll probably need them asap for the Sport.
I will. I'm still not sure how the hell I'm going to fit a drive shaft in the 88 T-bird's trunk:hick:
The last time I hauled one,I took an old sheet and wrapped the driveshaft up really good and layed down the passenger seat and had it from the front floor board to the back seat.Must wrap.You don't want road grime and everything else in the car.
That might work ;) What sheets work best Spiderman or Batman?
Personally,I'd go with Batman,but I don't want to push my super hero beliefs on you.LOL.
It's not the drive shaft. The source of the vibration is..........a bent passenger side axle:hick:. Some how the passenger side axle got bent. The weird thing is it doesn't really vibrate or wiggle noticeably till about 70 mph then you can really see it. The shop noticed it when they had it up on the lift running it trying to see what was causing the problem. So now I've got to get me some axles and bearings. I figure what the hell if I'm replacing one might as well do both if I'm in there:mullet:
Good to see you found your problem. Now you can enjoy it again.
I definitely wouldn't have thought of a bent axle...do you have an irregular wear pattern on the tire that's on that axle?
The funny thing is that the tire wear pattern is fine. I don't do a lot of expressway driving with it so maybe that's why. The axle is definatly bent. I could see it vibrating at about 70 when it was up on the lift. It really doesn't vibrate bad until that speed, then it goes nuts:hick:
Interesting.I don't think that's my problem,but,I may grab a set of axles when I'm out at the yard as a just in case.I have new seals and bearings,so,swapping the axles would take but an hour at the most if I take my time.
You never know ;). I didn't know mine was bent till I saw it vibrating.
The thing I don't get is how I bent it. I've never slid into a curb. Hell the closest I've come to a curb is bumping it at 3 mph parallel parking once in the last 2 years. Maybe I hit a pot hole just right or something at speed :dunno:
Oh the passenger side one is bent.....and it won't come out :hick: I can't push it far enough in to get the C clip off. I can get the driver's side one off easy if I want to but the passerger side, the one that has to be changed, is being a jerk. I spent 3 hours screwing with it today and almost got the C clip all the way off but not quite. I should be able to get it tomorrow when I have more time.
Old bent passenger side axle shaft out new axle shaft in and the problem is solved. It's smooth as silk at 70 and above :D
Glad to hear you got it taken care of! Watch out for those grand canyon sized pot-holes!
Oh I will. When I take the car out of winter storage in April there are still monster pot holes left over from the winter that haven't been filled yet:hick:
I think some of the worlds worst pot-holes have to be in South Dakota in the more rural areas(most of the state!). I was up there a few years ago and it was a 45 minute ride into town @65-70mph...not a thing around but pot-holes....dodging massive pot-holes on a crumbling road at those speeds isn't the best of ideas...especially in the explorer sport we were in...lol.
Sounds like I94 in the winter in Chicago:hick:
Yeah, it seems like the weather, plowing, and freeze/thaw cycles really eat up the roads FAST!