Vibration in 4th gear

[J's98Snake]

I got a vibration that comes up through the shifter and makes a noticible amount of noise when present.

I don't have the vibration in 1st, 2nd, or 3rd when spinning high RPMs. only in 4th from 90ish to 125ish.

My d/s angle is good (-10 degrees), all motor and tranny mounts are good (polly mounts). D/S is FMS al that's been on the car since 03.

I never noticed the vibration before I put my new motor in. I'm pretty sure it has nothing to do with the motor since 6500 rpms is 6500 rpms not matter 1st or 4th gear.

Could the gears in the tranny be so beat up in 4th gear? Tranny is a TKO 500 that's been eating 500+ rwhp since 03 and a lot of track time.

Fluid leves are good, rear end is same combo for the last 4-5 yrs.

 

[CJK440]

There is no gear in the tranny for 4th gear since it is 1:1. All that happens is the syncro slider locks the input and output together. The other gears are in mesh but just are along for the ride.

Does it change between under power, coast or float?

What about 5th gear at those speeds?

 

[DVJ38]

My car used to groan/grind/rumble at the top of 4th and at those same speeds in 5th. I have heard that it could be caused by the tailshaft bushing/bearing going bad, but I do not know for sure. It did go away after my transmission was rebuilt however.

 

[Bad99SVT]

I got a vibration that comes up through the shifter and makes a noticible amount of noise when present.

I don't have the vibration in 1st, 2nd, or 3rd when spinning high RPMs. only in 4th from 90ish to 125ish.

My d/s angle is good (-10 degrees), all motor and tranny mounts are good (polly mounts). D/S is FMS al that's been on the car since 03.

I never noticed the vibration before I put my new motor in. I'm pretty sure it has nothing to do with the motor since 6500 rpms is 6500 rpms not matter 1st or 4th gear.

Could the gears in the tranny be so beat up in 4th gear? Tranny is a TKO 500 that's been eating 500+ rwhp since 03 and a lot of track time.

Fluid leves are good, rear end is same combo for the last 4-5 yrs.

I have the same exact issue going on with my 95 cobra..let me know if you fix yours and ill try it on mine and ill do the same if i figure it out!!

 

[Ciotti]

I have this problem too, the top of fourth gear at 110 or so I get a NASTY vibration as I shift into fifth and I never really have the balls to keep my foot down and see if it will go away. It keeps shaking as I put the clutch in and pull it into neutral and I think it also keeps shaking as I put it into fifth but I'm not %100 sure since I always lift when it starts and it slows down quick that those speeds.

I've been through 1 trans rebuild and 1 whole new trans and it's done it with all of them. New motor mounts didn't fix it, nor did building the rear diff but I haven't touched the trans mount or drive shaft though. I've always sorta assumed it was the drive shaft and since it only happens at over 100 it's never been a priority.

 

[crr084]

Not sure if this is the same vibration, but ever since I installed my MGW short throw shifter I have a buzz in 4th gear around 60 mph, since the author of this post said it was coming through the shifter that was my first thought, doesn't do it in any other gear, could be something to do with short throws, or this may be completely unrelated, good luck, just my 2 cents.

 

[CJK440]

I have heard that it could be caused by the tailshaft bushing/bearing going bad, but I do not know for sure.

Even more of a problem than the bushing is what nobody considers, the inside of the slip yoke. Bushings wear and might cause some slight misalignment of the output yoke but what people don't consider is all those miles of the slip yoke splines stroking the output shaft with every movement of the rear suspension. Eventually those splines wear and allows for a slight wobble of the slipyoke on the output. While it may seem minor, it only takes a slight bit of slop to throw the u-joint yoke off center and allow the front end of the d-shaft to orbit instead of stay central.

I had a similar issue with an vintage musclecar and went nuts until I replaced the slip yoke. There was no comparison between the fit of the old and the new on the output. I could even feel it with my finger.

Just one other thing to consider however new shaft in '03 doesn't seem like it would fail that quickly unless there was lots of miles.

 

[J's98Snake]

Even more of a problem than the bushing is what nobody considers, the inside of the slip yoke. Bushings wear and might cause some slight misalignment of the output yoke but what people don't consider is all those miles of the slip yoke splines stroking the output shaft with every movement of the rear suspension. Eventually those splines wear and allows for a slight wobble of the slipyoke on the output. While it may seem minor, it only takes a slight bit of slop to throw the u-joint yoke off center and allow the front end of the d-shaft to orbit instead of stay central.

I had a similar issue with an vintage musclecar and went nuts until I replaced the slip yoke. There was no comparison between the fit of the old and the new on the output. I could even feel it with my finger.

Just one other thing to consider however new shaft in '03 doesn't seem like it would fail that quickly unless there was lots of miles.

Great insight, my D/S does have 70,000 + miles and a lot of track time w/ slicks and plenty of "aggressive street driving" which is a nice way to say street racing.

I assume it has to do with the speed the D/S is spinning at 100+ mph under a load (WOT), since there are no vibrations in 1st, 2nd, or 3rd. I haven't tried 5th gear at those speeds but I will.

I'm going to inspect my u-joints, if they're solid I'll look into the yoke and report back.

 

[DVJ38]

Even more of a problem than the bushing is what nobody considers, the inside of the slip yoke. Bushings wear and might cause some slight misalignment of the output yoke but what people don't consider is all those miles of the slip yoke splines stroking the output shaft with every movement of the rear suspension. Eventually those splines wear and allows for a slight wobble of the slipyoke on the output. While it may seem minor, it only takes a slight bit of slop to throw the u-joint yoke off center and allow the front end of the d-shaft to orbit instead of stay central.

I had a similar issue with an vintage musclecar and went nuts until I replaced the slip yoke. There was no comparison between the fit of the old and the new on the output. I could even feel it with my finger.

Just one other thing to consider however new shaft in '03 doesn't seem like it would fail that quickly unless there was lots of miles.

Interesting point. I can definately see this being true.

I should note that with my old transmission the driveshaft would slide in and out without much of a problem. Then on my new transmission the clearances were so tight I had to lube up and tap tap tap in the same driveshaft.

 

[Wynn]

Sounds like a common problem. Mine did the same thing. Paid $100 to have my driveshaft balanced, and it still did it. Replaced the tranny (bad synchros anyway) and the problem dissappeared.

 

[F8L BYT]

Mine started doing the same thing after I had the gears put in/ rear end built. I dont worry about it too much since I only see those speeds at the track which is rare. I had someone tell me it was most likely my driveshaft since it was/is a stock one

 

[DVJ38]

Mine started doing the same thing after I had the gears put in/ rear end built. I dont worry about it too much since I only see those speeds at the track which is rare. I had someone tell me it was most likely my driveshaft since it was/is a stock one

Did you try rotating the flange on the rear end? I know after I replaced the rear end in my car I got a vibration at around 100 mph, and thought about doing this.. but then again I'm rebuilding the stock one and putting in an aluminum one this spring so I didn't worry about it.

 

[J's98Snake]

It's def a speed thing that comes on around 90-100, both in 4th and 5th gear. I'm going to instect the u-joints and rotate the D/S 180 degrees on the pinion gear just to see.

 

[Ciotti]

I realized this week that it actually only happens on mine at 120 and above... Thank god I didn't get caught, sorry occifer I was just testing a vibration problem I've been having

 

[Bad99SVT]

I had the same vibration in 4th at 100+ also. I rotated my driveshaft 180* and took care of the vibration now. Smooth as ever now.

 

[thesource]

Aluminum driveshafts are well worth the money for cases like this.

 

[PACIFICGREENSVT]

My upper cont arm bushings in the little ears on the rear axle went bad. I had a bad vibe from 60& up,
I put in all new bushings upper & lower arms & it went away.