You may have remembered my original thread entitiled 3.9FD questions. Well, here's my situation:

About 2 months ago I got a brand new set of 3.9 FD gears installed in my car, which droned while holding at a constant 3000-3500 rpms in 6th gear (ie all the time on the freeway). My installer has tried several diffrent shims and got it much quietter, but couldn't ever get the noise to be completely reduced. So, he decided that the gears would need to be replaced, assuming that they were bad from the get-go. So we start trying to talk with 350evo about getting them replaced. The offer that I've been presented with is that they would take the old ones back and give me basically 1/2 price on a brand new set. That's great, but I'm feeling like I'm getting screwed out of a bunch of cash here. And what if it WAS my installer's fault that they old set got screwed, do I pay an additional $300 to go to a diffrent shop and have them installed there? Well, that means I'm out even more money. Do you guys have any recommendations about what I can do other than bend over and take it?

 

Tell them if they don't warranty the part and replace it for free you will show up in person to discuss it with them.

 

That'a a delimma I've worried about in the past as well - buying a product one place and having it installed at another. Fortunately, I've been lucky. As for your gears, I've had mine for over a year now (installed at 350evo in Cincy) & after reading numerous posts about 350evo's gears, I've yet to hear about a set "being bad" from the start (not that it is impossible for this to occur). I do know that when it comes to modding diff gears, you better have a shop that specializes in gears & has experience doing them - it's a touchy area for sure. After initially reading your post, my first response was "Sure the tech is going to blame the part...not the install" - that path of least resistance, you know? I have read several posts in which an owner has had the gears re-installed due to diff whine by a knowledgable shop & the re-install was successful. IMO, if you're going to do the re-install, I would go to a different shop with your existing gears - assuming the gears were ok from the start, 2 months of use with the "loose lash" (making the gears run cooler, but with more noise) is not going the ruin the gears to the point of needing new ones. I would take this stance initially & go to another shop - ask around here on the forum for locations in your area where the 3.9 gear has been installed successfully & go from there. Explain the situation to the shop & ask if they are willing to guarantee their install work with the assumption that the existing gears are ok.

I don't know the details of the level of whine you're experiencing nor who did your install....but trying to help before you fork out more $$ on new gears if you go that direction. As for my gears, I requested a slightly looser lash in order for the diff to run cooler - has the RPM whine, but I happily live with it - ha!

 

Yea, I'm thinking I want to go to a diffrent shop and get them to take it apart and see if they can fix it, if not then have it sent out to 350evo... I am in talks with BJ over at 350 evo to see if we can work out some sort of a reduced price for the part if something is wrong with it.

 

Good move....keep us filled in on the results. Best of luck!!

 

Okay, my original installer upon putting my car back together noticed something. Here's the email that I got from him:

Here are the pics showing the what was causing the bearing to howl... Basically
the larger diameter spline section was stopping the flange from pushing against
the front tapper roller bearing. So the bearing would start to push away from
being seated properly and start to howl. I machined the flange to clear that
area and now it sits against the bearing. Sorry the pictures are blury, but the
light kept reflecting off the the metal. You can at least see the wear marks of
where it was contacting each other. I am now going to be on my way....

And the pictures as well.

 

thats great...from an engineering standpoint, especially to something like this..its hard to machine something 100%...there will always be standard deviations of error. For something thats not mass produced, its not like they can just throw a batch out. Sorry for what happened, but looks like ur problem can be fixed. Thats teh good thing about metal :-D

 

Yea, there is still a verrrry slight noise, something you wouldn't know is there unless you went through what I did. I'm happy enough with the final result, it is unfortunate for everybody involved that this part wasn't machined right from the start, but oh well. I guess that is what you've got to expect from this kind of a mod... lesson learned, very well.