Chasing 100mph vibe and running out of ideas...

[9746Cobra]

I was told by a ford service writter that one of the shafts in the tranny isn't balanced.

:lol: He (the service writer) has no clue what he's talking about.

I didn't have a vibe until I changed gears. Turns out the pinion flange I used was bad. Put my old one back in and only have a very slight vibe between 80-110mph. It might there at higher speeds but with the exhaust and road/track surface I can't tell if it is or not.

If your vibe is slight and you can still see out of your rear view mirror your better off just living with it. Otherwise you'll have lots of headaches, spend money, and most likely it won't be any better. Might even make it worse.

 

[silvercoffin]

...

I had my stock tires balanced by a shop that had a HIGH SPEED BALANCER it turned out that the vib i had around 95mph was caused by defective tires. They couldnt be balanced any better. I had a bad vib noticed mostly in the steering wheel.

New tires...BFG G FORCES and no VIB

 

[snkepit]

I have this problem

 

[03 DSG Snake]

What about a CF DS from www.pstds.com? It fixed my vibe, and a bunch of the other NE guys have had luck as well. If nothing else, you might give them a call and talk to Mark (one of the owners), and talk with him. From my experiences, he's a "straight shooter" and won't try and sell you something you don't need.

How long have you had yours?



I've been wanting one for quite some time after dealing with the vibe for a few years. The aluminum diff mounts from MM took care of pretty much all of it, I just have a little minor one now at really high speeds, but it doesn't bother me.

Still want to get a Carbon D/S for weight and the rest of that vibe epper:

 

[RoyWoods]

How long have you had yours?



I've been wanting one for quite some time after dealing with the vibe for a few years. The aluminum diff mounts from MM took care of pretty much all of it, I just have a little minor one now at really high speeds, but it doesn't bother me.

Still want to get a Carbon D/S for weight and the rest of that vibe epper:

Almost 2 years. I think it's a great product and it definitely helped alleviate/cure my problem. The only thing I might do differently is order it with the optional aluminum yoke tubes. There is nothing wrong with the steel ones, but might as well get the best, and save a little bit more weight.

 

[cbr repsol]

I have a little vibration at speeds over 100. I was thinking it was the driveshaft but I wasnt sure if it is the culprate.

 

[Juruense]

Driveshaft, pinion angle, or pinion bearing.

 

[Dallas03Cobra]

OK this is going to sound weird but this worked for me. I started having a bad vibe over 95mph. This just started and I was like oh great I can't go to the track cause my car will shake apart.

So I noticed that my left front tire was low on Air. I did a quick check and all 4 tires were at different pressures. 24,29,35 and 31 psi. I put them all at 32psi and took the car out. No vibe even at 115mph. So I thought no way this was the problem, so I changed the tires back to their different pressures and vibe was present again. Put tires back to 32 and no vibe again. I know it sounds weird but hey give it a whirl and see if it helps.

 

[Juruense]

I believe you it is amazing how much better the car drives with proper tire pressure. I run 32.5 in all four tires myself.

 

[Avenger]

Update. Took the car out for a spin last weekend after installing differential bushing kit and the damn car still vibes !! Not exactly the same vibe as I had before though. It seems a bit worse and spread over a wider range of speeds.

I suspect it could be the tires. I have 2 months old ones in front but worn out DR at the back. For some reason, one of them shows more wear than the other but both DR were at 26psi with the front tires at 32psi.

I'm having a hard time believing a simple pressure adjustement will solve my issue... Could DR develop flat spot over a 5 month storage on a concrete floor ?

I'd like some opinions as I can't test anything until a few mores days. Tell me it's not gonna end up being my transmission / differential !

 

[Avenger]

You're the first one I've heard that can't get enough angle out of the front diff mounts. :shrug:

Good luck with it! :thumbsup:

I "think" we installed the rear differential bushing bracket upside down when we installed the MM poly kit. I can't confirm that bracket can even be installed upside down as I haven't tried to reinstall it completely but, from the looks of it, it is possible. Having it upside down would bring the back of the diff about an inch higher than if the bracket had been installed correctly. I think that's why we were hitting the subframe...

It makes a lot of sense but brings a few observations...

1) Why did I measure the typical -1.5deg pinion angle that everybody else is seeing ?

2) Did I damaged the halfshafts by running around with a messed up driveline geometry ?

3) Why did MM tell me their rear bushing actually lowers the back of the differential to allow for steeper upwards angle ?

:read:

 

[ac427cobra]

I "think" we installed the rear differential bushing bracket upside down when we installed the MM poly kit. I can't confirm that bracket can even be installed upside down as I haven't tried to reinstall it completely but, from the looks of it, it is possible. Having it upside down would bring the back of the diff about an inch higher than if the bracket had been installed correctly. I think that's why we were hitting the subframe...

It makes a lot of sense but brings a few observations...

1) Why did I measure the typical -1.5deg pinion angle that everybody else is seeing ?

2) Did I damaged the halfshafts by running around with a messed up driveline geometry ?

3) Why did MM tell me their rear bushing actually lowers the back of the differential to allow for steeper upwards angle ?

:read:

Alex:

A couple of things from the top here. I've learned the '03-'04 Cobras have a lot different issues setting the pinion angle than the '99-01's do. Due to the engine/trans combo. They come with mismatched angles from the factory and it's a challenge to get them aligned perfectly.

IMHO what MM is referring to is their solid aluminum rear diff mount is the one that lowers the rear end of the diff. It sounds like you put their rear poly mount in?

I don't think you damaged the halfshafts.

If you're having trouble getting the front of the diff high enough and it's hitting the subframe, get a grinder or small belt sander out and start removing some material from the subframe where it's hitting. Most likely it's hitting on those two upside down "U" pieces that are welded onto the front top cross tube that support the front of the diff.

I still would get somebody to swap a full set of wheels and tires with you first to see what happens with that!?

Good luck!

:thumbsup::coolman::beer:

 

[Avenger]

I installed their poly kit last year (rear bracket possibly upside down) and switched to their aluminium kit over the winter. I can easily get the required angle now.

Will try a whole new set of wheels this weekend. In the mean time, anyone think DR could develop flat spots ??

 

[03 DSG Snake]

I installed their poly kit last year (rear bracket possibly upside down) and switched to their aluminium kit over the winter. I can easily get the required angle now.

Will try a whole new set of wheels this weekend. In the mean time, anyone think DR could develop flat spots ??

Possible.

Take the wheels to a tire shop that can do a Road Force Balancing. That applies pressure to the tire and shows balancing problems that a 'standard' machine wouldn't. :burnout:

 

[Avenger]

Yeah, had my previous set of tires Road Force balanced last summer. Problem is the place I went to only knew that they were charging $50 for a set a tire, do not ask them to explain what they are doing...

Anyway, will swap another set of tires this weekend.

 

[Goodlife]

Its the driveshaft. Find a place to spin balance it or replace it.

 

[Avenger]

Driveshaft has been spin balanced

 

[hotcobra03]

mine started to viberate after changing the diff.mounts.i went to ford but they wanted an arm and a leg.but next time im using thiers,,strange though they do have two different bushing for the rear cover..even funnier one is for viberations under 35 and the other is for viberations over 75....i had thier parts blow up cant seem to find it..call ford parts

 

[Avenger]

Alright, here's a progress report. As you all know, the factory bracket was installed upside down when I did urethane bushings last year. I did not bother turning the bracket to see the improvement as I already had the aluminium bushing kit in hand and changing the rear bracket is quite a job.

So I installed the aluminium kit and started with around 2.5deg of pinion angle. Vibration was still present but car definitely felt better. I then went to 3.0deg and noticed another improvement. So I finally ended up having the spacer stack as per the MM instructions, which gives me around 3.50deg of pinion angle. Went for a test drive and noticed yet another improvement but it's still not what I would call smooth. Even though it has been balanced, I will try indexing the driveshaft and will report back my results.

For those of you chasing a drivetrain vibration, I strongly suggest buying an angle finder and measuring transmission / pinion angles. Bet you will find they are messed up...

hotcobra03, thanks for the heads up, I didn't know that. However, I am determined to get rid of the vibration issue while retaining the rear MM bushing.

 

[Avenger]

Yet another update. Removed the wheels and let the car rest on wood blocks placed under control arms. Brought the car up to speed and could easily feel the whole thing shaking. Tried indexing the driveshaft and it got better but nowhere near perfect.

Measured 0.003" of pinion flange runout and confirmed factory yellow dot was indeed located at point of maximum runout. Went to Ford and confirmed the factory spec is 0.010". I'm pretty sure I can rule out the pinion bearing at this point. Tell me if you think otherwise. Ford tech told me about a TSB for 03 Cobras with 65+ mph vibrations that calls for a driveshaft replacement.

I then called a friend with an 04 and borrowed his driveshaft. Lined up the yellow dots and brought the car up to speed (still on wood blocks). Felt a bit better but not much. Tried indexing that one but turns out I started with the best matchup. Put the car back on its wheels, loosened transmission crossmember and motor mounts and drove 10ft back and forth a few times.

Retightened everything and went for a real test drive. Car felt really smooth all the way up to 100mph with a slight vibration at speeds above that. It definitely has never felt that good but I'm still not exactly satisfied.

Today, I will try my original spin balanced driveshaft and see how it behaves. Needless to say I learned a lot of stuff doing that. I've been chasing this vibration for a long time and people around me think I'm crazy but I WILL get rid of it !! I can't wait for the day I put my car in 6th gear after a pass and don't feel any vibration during decelaration...

Will report back.