u-joint replacement

RE: u-joint replacement

[div class="dcquote"][strong]Quote[/strong]
That said, i don't know about your specific vibration problem, but i've never known a u-joint to fail on one of these cars. The driveshaft runs in a pretty much straight line, so there's not much "u" ing for those joints to do.
[/div]

At 250,000 miles I developed a Vibration from under the car,
I immediatley thoought "U-joint", SO I got under the car and PUSHED/PULLED/TWISTED/ETC and no slop was found.

But.. the vibration remained...

Not too long after than while pulling away from the timeslip booth I heard the TELL TALE "squeaksqueaksqueak" that Ujoints make when they are going bad.

SO.. I got front and rear Ujoints and Proceeded the task of removing the driveshaft.
Once again while I was under the car I PUSHED/PULLED/TWISTED/WIGGLED/ETC on the drive shaft and no slop or looseness was found.

Upon removal of the driveshaft I was AMAZED to find the front Ujoint was FROZEN.. STUCK SOLID as if it were WELDED!!!

So...
1. just because you wiggled it and it was TIGHT
2. just because the driveshaft doesnt MOVE MUCH

Doesnt mean that your ujoints wont wear out.

My Guess is.. because the front of the shaft DOESNT move TOO much that over time the Ujoint decided not to be a ujoint any more.
 
RE: u-joint replacement

[div class="dcquote"][strong]Quote[/strong]
At 250,000 miles I developed a Vibration from under the car,I immediatley thoought "U-joint", SO I got under the car and PUSHED/PULLED/TWISTED/ETC and no slop was found.But.. the vibration remained...Not too long after than while pulling away from the timeslip booth I heard the TELL TALE "squeaksqueaksqueak" that Ujoints make when they are going bad...
[/div]

That's a common failure mode, i replaced both rear ujoints (both on the rear driveshaft) on my suburban when i got it as preventative maintenance, one was a little tight like you describe but not there yet.

But... 250k miles. that's a pretty good run.
 
RE: u-joint replacement

[div class="dcquote"][strong]Quote[/strong]
Has anyone actually taken a bad u-joint out of a FN10 or MN12 car?
[/div]

Yes.. My front Ujoint was SEIZED/ AKA BAD

It wasn't the typical type of failure where you could wiggle the shaft and say "OH LOOK, there's SLOP in that Ujoint".

Which is why it took me so long to track down the vibration.
It wasn't until later when I heard it squeaksqueak that I decided, "slop or NOT" I'm changing 'em.

That's when I found the front one was FROZED/SEIZED solid.

I'm sure 5000+ passes and 300,000 miles were a contributing factor.
 
RE: u-joint replacement

well I replaced them, no problem just took some patientce. I haven't had time to put everything back together yet because I've been putting in new trans poly x-member mounts, poly rear mounts, and repainting my exhaust. Neither u-joint was loose, but the front one did have a few rough spots on the bearings when you spun them. I'm kind of doubting that they were the problem but I'll know tomorrow night. I checked the tailstock for play and there is nothing at all. I talked to a guy that rebuilds these trans's all the time and he said that's should be the problem if there isn't any play. I'm starting to think the MAY be a problem with the dynotech shaft. Time will tell, possibly it was dropped during shipping and bent, who knows. I'll keep you guys updated.
 
RE: u-joint replacement

[div class="dcquote"][strong]Quote[/strong]
... I've been putting in new trans poly x-member mounts, poly rear mounts...
[/div]

Are you replacing the tranny mount as well?
 
RE: u-joint replacement

I did that last week actually :7 . I was able to get that out without dropping the exhaust. But when I tried to get the x-member out it wasn't happening w/o removing at lest the exhaust and possibly the d/s. I couldn't replace the carrier bushings w/o dropping the exhaust either. With the stock pipes it may be possible but not with the way mine is set up. So doing the u-joints allowed me to do a few other jobs that may help cure the problem. I also replainted my exhaust, looks like brand new again.
 
RE: u-joint replacement

yea it's the only one I could find and it's already solid rubber unlike the t-bird fluid filled units. It's also completely different than the t-bird mount which really surprized me. To tell you the truth the rubber on the trans mount I took out looked fine. It was still firm and not dried out. I still put the new one in. Now the x-member bushings were another story. Those were dry rotted to hell, they were soft and just needed replacing. I punched the center of the rubber out then burned the rest out with a torch. Here's something I though was strage. When I had the x-member out, the section under there the trans mount bolts to it sounds like it's filled with BB's ::wtf:: . I though this was strange but there must be some reason for it. ?? Anyone know about this?
 
RE: u-joint replacement

[div class="dcquote"][strong]Quote[/strong]
When I had the x-member out, the section under there the trans mount bolts to it sounds like it's filled with BB's [/div]

That thing is a vibration dampner.. it's got either "steel shot" or "lead shot" inside.
 
RE: u-joint replacement

Going to be putting the shaft in today. I noticed something yesterday, there is a white mark on the trans output shaft (index mark) and a missing spline in the yoke. Do I line these up? Anything special to know about this?
 
RE: u-joint replacement

Well I just got back from under the car. I kind of had a sinking feeling when the u-joints weren't in terrible shape, just a little rough in one spot. ;( There is definately an issue with the shaft. I brought the car up to 70-80 w/o the rear wheels on and there is still a vibration. Not a whole lot changed. I indexed it at both ends a few times, no change. I felt the shaft while it was spinning and there is definately a runout issue, I'm estimating >30 thou. I can't believe this whole time I've been chasing damn vibrations it's from the only thing that shouldn't be vibrating. I didn't look at the shaft before this because I didn't think it could be the problem. I'm going to talk to dyno tech and send it back. It sucks that it's going to cost me $75 to have it checked, fixed and rebalanced. The ONLY good thig about this is it has forced me to replace a lot of things that did need replacing.

*whole front end
upper & lower control arms
strut rod bushings
tie rods
steering rack

*hubs
*wheels hunter roadfoce balanced
*trans mount
*x-member mounts
*carrier bushings
 
RE: u-joint replacement

[div class="dcquote"][strong]Quote[/strong]
Has anyone actually taken a bad u-joint out of a FN10 or MN12 car? I haven't I have changed quite a few ,but never really had a bad one.Rear bushings and yokes well thats a different story. That has always been a problem with these transmissions. Personally I think you are asking for trouble running a 4.10 gear with no force lubrication. Ya it may be a pain to do for someone who doesn't have the equipment (bridgeport works great ),but I am sure if you ask around you can find someone who will be willing to do it for you.Alan
[/div]
My 93 had a vibration and you could not feel it when trying to wiggle the driveshaft and even when I removed them they didn't look or feel bad but I replaced them with new spicer joints and no more vibration
 
RE: u-joint replacement

I had a vibration in my 1998 Mark VIII LSC with stock gearing that started around 65 mph and got progressively worse the faster I went. At 85 mph the rear view mirror was vibrating enough that it was hard to see the rear image. I changed to a aluminum driveshaft from Reinhart Automotive, had it installed this week, and vibration gone. The driveshaft cost $480 and $300 to install. Expensive, but getting rid of the vibration was worth it. Good Luck, changing u-joints probably won't fix your problem.
 
RE: u-joint replacement

I don't think you fully read my post. I ALREADY have a mmx driveshaft, the dynotech unit dennis sells. Well I put new u-joints in, didn't change a thing. Put new u-joints in my stock unit and installed and it's way better. It's just the stock shaft hits critical speed. The mmx shaft I have must be bent or made t least improperly, while it's spinning slowly I can see ab30 thou of runout in it, while there isn't any in the stock shaft. I'm sending it back to dynotech to have them look at it. Possibly it was damaged in shipping or just made improperly..........I don't tknow. The saga continues.......x(
 
You must log in or register to reply here.
Back
Top