Vonda and All, Lets look at some pictures of the stock factory exhaust=
system that is behind the mufflers until the turn going down the exhaust p=
ipe. The system from the exhaust manifolds to the mufflers are 2.25inches =
in diameter. Muffler exit to the =E2=80=9CY=E2=80=9D is also 2.25 inches i=
n diameter. For the rest of the factory stock was 2.5 inches diameter. =
http://www.gmcmhphotos.com/photos/g7045-factory-stock-25-inch-exhaust-sy=
stem.html The pictures show how the exhaust pipe and =E2=80=9CY=
=E2=80=9D are layout. The =E2=80=9Cmuffler bearing=E2=80=9D which to d=
egrade over the years are a 3=E2=80=9D size which is why the 3=E2=80=9D sle=
eve is used on the 2.5 inch system. This piping is a factory stock system =
that had failed with pin hole leaks its length to the end on the 77 Eleganz=
a II with 403 motor. It was at that time (2006) that I redid the system to=
a 3=E2=80=9D from the mufflers back using Jim K parts to the 90 going bac=
k and the side exit tail pipe end. I had previously put the Thorley header=
s on the coach when the CI exhaust manifolds were leaking badly. Muffl=
er Bearings
http://www.appliedgmc.com/prod.itml/icOid/1180 You ma=
y only need the Silicon rubber piece if your bracket can be cleaned and pai=
nted. You can use all or parts of a 2.5=E2=80=9D or 3=E2=80=9D system =
from Jim K as I have done for both my 2.5=E2=80=9D and 3=E2=80=9D installs.=
http://www.appliedgmc.com/prod.itml/icOid/667 http://www.appliedgmc=
.com/
prod.itml/icOid/666 3 years ago I replaced the 3=E2=80=9D exhaust=
system on the Stretch coach to a mostly SS setup. Stainless from the head=
er pipes to the 90 degree turn going to the rear and an SS tail pipe end as=
sembly on the end. I chose to use 3=E2=80=9D aluminized exhaust pipe that =
runs to the rear tail pipe, typical you can buy them from a muffler shop in=
8 foot sections and they do fit into the coach from the rear. To remove t=
he old stuff cut it into pieces to ease the removal. Use WD40 or other to =
remove from the muffler bearings. DO NOT use any tubing that has been bell=
mouth on one end to run from front to back as the bell mouth will not fit =
thru the muffler bearings. I use only SS band clamps to assemble the entir=
e setup. The only bell mouths sections are one side of the 90 going back a=
nd the SS tail pipe assembly. The important thing here is to tighten the b=
and clamps to 60 ftlbs (as per Jim K) when using them. If you don=E2=80=
=99t the system WILL at one time or another separate at one joint or anothe=
r (Don't ask me how I know). Jim K has the best pricing for the SS band cl=
amps as you will need several 2.5=E2=80=9D clamps (4) and a number of 3=
=E2=80=9D clamps (6), even beat my local pricing. I also recommend the=
Remflex Gaskets if you also redoing the headers or manifolds. http://=
www.appliedgmc.com/prod.itml/icOid/670 I again say get them from Jim K=
as he buys in bulk and they can be considerable less from him that from bu=
ying directly from Remflex or my local supplier which typically you get no =
real discounts. You can hunt up the SS stuff locally or online, but yo=
ur best bang for the buck is buying all or part of the SS kit either in the=
2.5 inch version or the 3=E2=80=9D version and the cost will be similar to=
buy from Jim K and it will fit the first time with doing any fiddling. No=
n of this is really hard to do, just get the coach up on jack stands and ge=
t the old out and the new fit in. I used a sawzall to cut it into pieces =
for easy removal. You can get a cheap one from Harbor Freight that will wo=
rk just fine cheap. and some blade=
s too Just what has worked fo=
r me, your results may vary! JR Wright GMC Great Laker MHC GMC =
Eastern States Charter Member GMCGL Tech Editor GMCMI 78 GMC Buskirk =
30=E2=80=99 Stretch 1975 GMC Avion (Under Reconstruction) Michigan =
> On May 31, 2017, at 9:59 AM, Keith V wrote: > =
> Good choice Vonda, > > Reading your posts I have no doubt you can=
do your own exhaust, it's not all that hard. > > The hardest part is =
removing the old stuff usually. > > I got all my tubing and clamps fro=
m carquest they had lots of 3" and mandrel bends > > > BTW before b=
uying the silicone donuts, my 75 came with the 3" donuts even though it had=
2 1/2 inch exhaust. > > > Lastly the rear muffler is the way to go=
if you can swing it. I put a flowmaster 80 back there and I'm happy. it CO=
ULD be a tad less rappy, but meh. > > ________________________________=
