Rear end vibrations

[dutchy351]

I'm curious if anyone has run into this issue before.

I've got a ba xr6T that we've doesn't a c4 conversion on. I recently pulled the box to have it looked at (replaced clutches ect) really just a maintenance sort of thing. We noticed when we pulled the tailshaft that the center bearing was torn, so took it to a reputable drive shaft shop in sydney replace it. While we we're there we replaced 2 Universal's and had it rebalanced. I also replaced my flexplate to a Yella Terra unit while the box was off

 

After all of this I now have a decent vibration especially evident from around 30-40 at light acceleration. I can accelerate through it and not feel it but parking lots ect are pretty horrible. I noticed today after reaching highway speeds that I have a "rumble" accelerating from 60-110 and almost like a pulse (my rear view vibrates to it) when cruising. I had my diff bushes/blade bushes ect replaced a few years ago with super pro gear aswell

 

Any thoughts? I definitely feel like I did everything to avoid any issues like this but yet, here we are haha.

[k31th]

gearbox mount is properly rubber mounted?

[dutchy351]

Yeah man, it's rubber mounted. It was in the car previously with no problems at all.

[k31th]

got no other good ideas

[dutchy351]

Does anyone else have an idea on this? I had someone suggest that the centre bearing height on the Hardy Spicer centre bearing could be different to standard and that I might need to space it. I used a few washers to bring it down roughly 4.5mm and it seemed a little better but I wasn't sure if I could keep going on the spacing. 

[JETURBO]

I’ve had C4 conversion BA’s in before and they didn’t need any spacing by the CB 

that said they still ran the rear CV onto the diff 

 

if I were you I would get everything re balanced “on car”, it’s called static balancing and not all ford dealers have the equipment to do so. This issue was huge in the early days on the BA’s so dealerships had to splash out on the equipment as regular balancing wasn’t cutting it 

[dutchy351]

I am still running the standard CV to the diff.

 

The thing I'm finding odd is in my experience an unbalanced tailshaft would present itself at higher speeds and you normally wouldn't feel any difference around the 30-40kh/h mark.

 

I might call Hardy Spicer and find out if their centre bearings are a different offset height to standard.

 

Any clue on costs of static balancing?

[JETURBO]

An unbalanced tailshaft can typically have x2 zones of unsettled throughout a speed range 

 

coupla hundred iirc but this was a while back I needed one done 

 

The HS units are typically F100 CB’s and do have a larger OD so every chance possible it needs a better “angle” 

[dutchy351]

Where would you start with the better angle? I have spaced it around 4.5mm and it did seem a little better (although could be a placebo) 

 

Where would you cut off your spacing in mm to say "this isn't gonna a work"