Vibration in 6th gear

[DSGNator]

I just bought a 2003 Cobra coupe this week. The car is beautiful, only got 33k miles on it, clean car fax (for what it's worth) 2 owner car. It already had a pretty good bit of mods done to it, nothing that I wasn't already planning to do myself. The car is 10 years old so I understand it's not going to be on par with new car quality. (My last mustang was a 2012 GT. But that's another strory.) My biggest concern with it at the time is a pretty noticeable vibration that occurs when I shift into 6th gear. I can tell that the tires either have flat spots or are out of balance so I'm going to get that issue fixed this weekend. But the vibration when I shift is more noticeable than the tire vibration, it feels like it's coming more from the rear of the car. It does have the solid axle swap in the rear, and the previous owner had the 4.10 gears removed and 3.73 gears installed in place of them. The vibration only seems to be prevalent if I'm in 6th gear traveling 70mph or below. Once I get up to 75+ it goes away. One theory I have, aside from tires being unbalanced, is that I'm simply not used to this car yet. Maybe 70mph is too slow for 6th gear and it's simply just riding rough because I'm shifting into 6th too early. Hopefully getting the wheels/tires balanced with help the issue, and hopefully I'm just not used to how this car drives (Never driven anything with 3.73 gears before this.) Has anyone experienced anything similar to this?

*I apologize if there's already a similar thread to this. I looked through the "Before you post" list of threads and didn't see anything. Lot's of great info in there though.*

 

[Bigggy]

I had a similar problem when a bought mine. Right around 65mph, engine was about at 2200RPM and there was that "cycling" like vibration. Ask a shop and they rebalanced the Driveshaft, it was still there. Couples days later I found the problem, it turned out to be the lower tie-bar of the MM Tubular K member that was missing a spacer and was hiting the oil pan.

Yours might be something completely different, but look at stuff like this. Drive-shaft, axles, bushings, engine mounts...etc

 

[DSGNator]

Wow, that's pretty crazy. If balancing the wheels/tires doesn't work, I was thinking of getting trying the drive shaft next. The car has numerous suspension mods, especially in the rear. I'll get underneath and inspect everything the best I can if the problem continues. Thanks for your input!

 

[DSGNator]

Just an update,

I took the car in to get the tires balanced and the tech decided to put the car up on a lift and inspect a few things that could cause the vibrations before he even took it for a test drive. What he found made me want to kick myself in the head. He let me come into the shop to show me that there's a good bit of play in my front wheels, which means my wheel bearings are bad. I'm not too worried about that, it looks like an easy fix I can do in my garage, just frustrates me that I forgot to check the wheels for play when I was originally inspecting the car. The part that really worries me is my rear end. My rear diff isn't locking. You spin one tire, the other just sits there. It's got an Eaton Detroit True Trac limited slip differential and 31 spline axles. But from the looks of it the diff isn't doing it's job. I plan on replaing my front wheel hub/bearings this coming weekend, and maybe getting the car into a shop sometime during the week to inspect the rear end. I honestly don't know much about rear diffs so it's not something I'd be comfortable fixing, I don't even know what I'd be looking for. I still love the car and don't regret my purchase, just wish I would have caught these issues before hand and talked the price down. I've had the car for about a week and it's already becoming a huge money pit. I'll get it running right eventually!

 

[Bigggy]

For your front wheel bearing, you wheel need a 36mm socket, a new hub nut from the stealership and a torque wrench that can go to 258ft/lb.

Good find for the diff!

I know exactly how you feel when you say "money pit", it was the same with mine.

 

[ashleyroachclip]

^^Are you sure about those torque specs for the front ?
Seems high.
I am pretty certain that is not correct , more like the rear , if you have the IRS.

 

[Bigggy]

100% sure about the torque specs, yes its high but that's what recommended by Ford.

How to: Replace Front Wheel Bearing/Hub Assembly - MustangForums.com

http://www.svtperformance.com/forum...aring-replacement-recommended-parts-list.html

 

[DSGNator]

**New update, I dropped the car off at a local shop to have the rear end inspected. It kills me to know that I'm paying someone for an hour of labor ($99 + tax) just to take the diff cover off and inspect it. But I'd rather an ASE certified master tech figure out a repair for me than me just go in there and make a bunch of guesses. I just have NO experience with rear diffs, especially ones with aftermarket parts installed. I should find out what's wrong tomorrow sometime. Hopefully I can get it repaired by the weekend, because I want to do the hub/bearing swap this weekend as well as install new pads and front rotors.**

Thanks for the info about the front bearing/hub assembly swap. All the write ups I've read so far have said the torque specs for the 36mm hub bolt are 256 ft/lbs. I picked up a torque wrench that goes up to 250 ft/lbs so I should be able to work with that. As far as the car being a money pit, I'm doing my best to stay positive and not regret my purchase. It really is a beautiful car, and they're getting harder to come by with such low mileage. I still feel confident that after a bit of troubleshooting, repairs, fluid changes, and detailing, this car will be a top notch cobra that hauls some serious ass! It's a lot of money at times, but this is my hobby and it's what I love!

 

[Bigggy]

250 should be fine, mine only goes to 250 like yours. I'ts really an easy job (the front bearing).

I'm sure you will love the car when it will be up and running!

 

[DSGNator]

I got the car back from the shop today. Thankfully nothing is wrong inside the rear end. They took the cover off and did an inspection. The only thing they found wrong back there was a few loose bolts in the solid axle suspension. They also put a slightly heavier weight gear oil in the rear. Since driving it, the car does seem quieter, probably from tightening the suspension bolts. I haven't taken the car on the highway yet, to see if the vibration in 6th gear is still there, but at this point I don't think I can trouble shoot any further until I get those wheel bearings in. I've already got them on order and they should be here by Friday, so that's this weekend's project. I'm pretty excited! Once I get this vibration issue figured out, I want to figure out what's causing this squeaking/whirring sound when I try start moving from a dead stop while in first gear. It only happens when I don't give it quite enough throttle. Not sure if that's a slipping clutch or not. Thankfully that's something I've never experienced.

 

[DSGNator]

Here's another update:

Started changing out the hubs today and what a head ache it's been. I guess I was just really unprepared. I thought I had all the necessarry parts and tools, but man was I wrong. I started off the morning by discovering that my car sits too low to get a floor jack anywhere near the jack points, so I went and bought the lowest set of ramps I could find. My car was too low for those too. So then I went and bought some wood and got it cut into smaller pieces so I could drive on that to gain extra clearance for the jack. That actually worked. Once I got the lug nuts off, I found a fun little surprise, a second set of lug nuts underneath the first set, that were a different size. A size that I didn't have a socket for, so back to the parts store. Once I got the new socket and got back to work on the car, I discovered that I did have the right size socket and I'm just an idiot. Got the wheels off, break calipers (I broke the little clip that secures the pin that holds the caliper in place, got the rotors, and hub bolt caps off (think I'm going to have to replace those as well), and I finally got down to the hubs. Throughout this process, rust around the hub had been causing me some pain, but the hub was completely stuck. I beat on it with a hammer for probably an hour before heading back to the parts store to rent a hub puller. The hub puller got MOST of the hub off. The inner cone of the wheel bearing and rear bearing shield decided to stay on the spindle. They are still there and they are stuck like no ones business. I've been on them, sprayed them with PB blaster, and even tried using my Dremel to cut them off. Nothing. I've given up on them for the night, but I went and bought a propane torch. I'm gonna try to heat them up and knock them off tomorrow morning. I feel as thought re-assembly will be much smoother. Got new rotors and pads to put on as well.

 

[Bigggy]

Wow so much PITA! On mine it wasn't difficult maybe because the bearing wasn't worn so bad. It came out with only one hand.

As for the second set of lugs, sounds like you have bolt-on spacers.

 

[FiveOhJoe]

It's your pinion angle most likely. Only way to fix it is with a FTBR milled Ford racing cover and their front and rear solid diff mounts.

I have everything FTBR in my IRS and my pinion angle is perfect. I have zero vibration at any speed.

 

[DSGNator]

It's your pinion angle most likely. Only way to fix it is with a FTBR milled Ford racing cover and their front and rear solid diff mounts.

I have everything FTBR in my IRS and my pinion angle is perfect. I have zero vibration at any speed.

Does it matter that I have a Ford 8.8 instead of the IRS? I'm sure pinion angle is still an important factor, just wondering if those parts will still work with my rear.