This paper is going to assume that you already have the transmission out of the car. If you can’t get that far on your own, you are probably in over your head trying to attempt a
This paper will be separated into sections:
Each of these sections will address work specific to those sections
If you are installing the transmission into a C3 that already has a manual trans, you have a
welded in crossmember. Unless you’re doing this swap as an engine/trans assembly, you
will not be able to install the trans without cutting the crossmember.
Mark the crossmember using a scribe and straightedge. It is preferable to make the cuts
on an ever so slight angle \ / so that the center section of the crossmember isn’t
locked in place and can be easily removed.
Using a reciprocating saw, cut along your marks as carefully as possible. This is a pretty
good trick to cut out the crossmember without poking holes into the floor pan of your car.
A steady hand and an assortment of different blades will get the job done though.
There are two basic ways to re-install the crossmember. One is to add plates to the sides
of the crossmember and bolt through to hold things in place. The other, and what I
prefer, is to use 4 plates welded to the cut-ends of the crossmember and frame to put it
back in place. These instructions will follow the second method.
Once the crossmember is out, you need to make it a little bit smaller so the plates will fit.
Using a grinder/sawzall/cutoff wheel/etc….trim the crossmember back by the thickness
of the plates you’re using. The plates I used were a little over 1/8” thick, so I trimmed
around ¼” off each end of the crossmember section I had removed. Now, trimming
wasn’t an exact science for me and involved all of the above and a good bit of grinding
under the car to fine tune the fit for the best weld conditions (minimal gaps).
Pair the plates together, tack weld them in a corner so that you have 2 double-thick plates, and then drill 4 holes around the plate for the bolts you’ll be using. Make sure you leave
enough room between the edge of the frame rail and the bolt holes to allow for welding
and a wrench to get in there.