May 2001
The choices for OEM replacement mufflers are:
1. Boysen (factory original on my car)
2. Eberspaecher
3. Bosal
A good reference for other options can be found on AGP's site.
I chose the OEM Eberspaecher ($370 US, delivered, for both front resonator & rear muffler from Zygmunts) because I wanted the quiet of the OEM system & was not looking for the added performance of a freeflow system. Cost of the Eberspaecher system was within $5 of Bosal & it is reputed to outlast the Bosal. Fit & finish are excellent & almost indistinguishable from the original Boysen unit. Removal is intuitive. If you don't have access to a lift or a pit, then putting all 4's on jackstands is the next best alternative. I find it easier to remove the hanger brackets instead of dealing with stretching the rubber donuts off of the brackets. The exhaust is heavy, approx. 70 lbs. but it balances nicely on a floorjack & the entire assembly comes out as a unit, Ref. Photo-1. Replacement front resonator & rear exhaust are no longer available as a single unit, but now come as two separate pieces Ref. Photo-2. For ease of handling the single unit assembly, I welded the two together at the socket fitting, Ref. Photo-3, I never have cared much for those cheesy stamped steel half-clamp/u-bolt fittings, this way I know it won't leak & is as strong as the original for lifting back in place.
The Eberspaecher replacement is complete & needs no additional hardware unless the copper nuts or rubber donuts need replacing. I dropped the catalytic converter, but it's not necessary to do that for removing the muffler. I wanted to replace the O2 sensor while I was at it (Autozone "rents" a nice O2 sensor socket & crowfoot set for a $15 deposit, fully refundable, but yours to keep if you don't return it). I put the car on jackstands the night before & soaked all the nuts with "Liquid Wrench". I soaked the O2 sensor with Liquid Wrench & heated the dickens out of the threads with a propane torch, don't worry about getting it too hot, it sees plenty of heat in normal driving & it's being replaced with a new one anyway.
If you're only replacing one of the two mufflers, take time to make careful measurements in situ before cutting the old system apart. I laid the new one side-by-side on the floor next to the old one. With the resonator held flat on the floor with a 25# weight, the rear muffler lifted off the floor by about 1-1/8 inches so I shimmed it with a block. I duplicated the same layout with the new one. This established the vertical & torsional alignment. I "triangulated" the axial & lateral alignment by measuring the distance from the tips of the hanger brackets on the resonator to where the pipes enter the rear muffler. It took a little tweaking to get it right-on & then I tack-welded it & checked again & welded it full around. If it ends up a little off once back on the car, it can be tweaked by applying some judicial pressure by blocking & prying with a lever or bottle jack. If it's way off you can heat the pipes with an oxy-acetylene torch to a medium red & they'll flex readily.
The Eberspaecher rear muffler comes with the tips painted black. A quick check with a magnet confirmed they're really stainless steel, so with some paint stripper & a little polishing, they end up nice enough to not need any enhancement, Ref. Photo-4.
Replace the rubber donuts with new ones if the old ones are cracked & rotted. I also replaced the bracket which supports the catalytic converter, part no. 11 76 707 417 7, $50.53 list at the dealer, $34.20 at Circle BMW. I aligned the rear muffler supports per Bentley's with about 1/4" forward offset. I installed the cat. support bracket fully neutral, it's slotted laterally & vertically & the stud provides axial adjustment.
gale, 92 735i
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