The backbox fell off of my focus estate last week so I got a replacement from ebay. I assumed I would need to completely remove the old pipe before fitting the new piece but having done that, the new piece seems to fit really loose like it was designed to go over the lopped off old piece. So now I am wondering how to get the new piece to fit? Should I cut the old piece down and try and slip it back on ( it has a gash down the side though where i cut it loose), or cut the new piece back to where it is thinner and try and get that on? Any suggestions?

 

A replacement one will normally be flared at the end to allow it to slide onto where the old one has been cut off (should be a sliding fit, not really loose), then you clamp where the two overlap with an exhaust clamp (u bolt clamp is simplest) and maybe use some exhaust sealing paste.

Are you saying you've cut too much off the old system?
If that's the case the mounts will probably still fit but if the pipe exits through the bumper it will look wrong if it's too short so you might have to get a length of pipe welded on to match it back up.

 

I haven't cut off any of the middle section pipe. I put a cut in the remnants of the old back box pipe to help it slip off. so it is completely removed. The opening of the new back box is much larger than the diameter of the mid section pipe, not a snug fit at all, the u bolt clamp pinches the end but doesn't tighten it to make a seal.

 

I see, yeah I guess you could cut the flared part off the new backbox pipe and cut some lengthways slots at the end so it has some movement to be able to clamp... just measure the outside diameters first to be sure