6 Speed conversion
Here's the lowdown on my 6 speed swap.
Why: Two reasons - First, my 195K mile car fell victim to the "C50 transmission pops out of 5th gear" problem. Second, I have a lot of motorcycle experience and since the 4AGE engine in the MR2 is
essentially a 1600cc motorcycle engine, it made sense to me that it should be geared more like a bike than a car.
Economics of the swap.
First, the C50 is the least desirable transmission. The C52 (found in 87 -89 MR2's) shifts better, and is much less prone to have the pop out problem. Either way, it's a good $1500 to re-build (properly) a
C-series transmission due to parts and specialized tools cost. Also, you'd still have the same 5 speed gearing.
The C160 6 speed transmission used in the 20V Blacktop powered mid 90's JDM Corolla is one of two 6 speed transmissions available to swap into the AW11. The C60 used in the later model Celica
is available in the US in junkyards or on E-bay, however you have to swap out bellhousings with a C-series trans (which means tearing down the transmission and buying the required tools to do that and
re-assemble it correctly), plus you need to replace the axles with a set from a 93 NA MR2 - another expense. You also have to mod the shift linkage so that it points out of the "front" of the transmission
rather than the "rear" as used in the FWD Corolla.
The C160 BT transmission only requires the shift linkage mod, bolts right up to the 4AGE block, uses the same axles, front and rear mounts, and the same clutch. This makes it a much easier and more
cost effective swap.
I bought mine from an E-bay seller in Canada for $780 including shipping and spent about $100 more on all the little things need to complete the installation.
Step 1: Take care of the shift linkage requirements.
I was fortunate enough to have a spare MR2 transmission that I could pull parts from, so that made it easier to do the work and still drive the car. So, I pulled the main shifter mechanism out of both
transmissions and compared them.
The hole in the AW11 shaft near the C-clip and the c-clip itself are not used with the 6 speed parts. NOTE! The AW11 shaft is HARDENED (the Corolla shaft IS NOT!), so drilling this shaft must
be done on a mill with a carbide bit. The sprung roll pin is designed for a 5MM hole, so the hole should be 4.97 - 4.98MM in diameter. Mine was right at 5MM, but still had tension and seems to work
fine so far.
Step 2: Drill the case for the AW11 shift shaft
Since the shift linkage has to point out of the front of the transmission, this is one of those things that MUST be done with any non-AW11 trans case you have. I used a sprung center punch and
eyeballed the place to punch since I didn't have access to a LONG 15MM drill bit. I was pretty damn close, so the rest was easy. I packed a rag in from the back side, then sprayed sticky motorcycle
chain lube on the outside to catch shavings and drilled the hole with a multi-step bit. I then used a grinding tip to make up for the slight miss in the original centering hole, knowing that the welded seal
retainer would still cover the extra opening.
Step 3: The rear shaft seal
Removing the Celica shaft and replacing it with the AW11 shaft also creates another problem unique to the 6 speed. The rear seal housing from the 6 speed must be used because it is spring loaded
and acts as the "reverse lockout". The problem is that the AW11 shaft is too short to contact the seal when in 5th and 6th, but it pokes out of the seal when in reverse. Rather than more welding, I chose
to use a 40MM freeze plug to cover the hole. JBWeld holds it together and the original Celica bellows covers it completely.
Step 4: The front shaft seal
With all the other major items out of the way, I did the front seal retainer next. I bought a new seal from the dealer, then bought a short length of aluminum tubing. I had a local machine shop lathe the
tubing so that the seal would fit correctly. I then trimmed it to fit the slight angle on the front of the case, using the installed shaft and seal as guides. Once it was all lined up, I used my spring punch to
mark the case and retainer, then had it welded up.
Step 5: Assorted small stuff
With all the major items done, I took care of the remaining things to do. One was to swap out the larger Celica ball stud and clutch fork for the smaller 200MM clutch that I use. Second was to build a plate
to mount the shift linkage bar. This was more involved than I thought it would be. I used a piece of 1/8" stainless since I couldn't find the 1/4" aluminum plate that I wanted to use. The stainless was very
difficult to work with since it is very hard. I wasn't very happy with the final result, although it does work fine so I'm going to re-do the plate in aluminum when I have some spare time. I also had to trim away
some of the material for the transmission mount. I did this by best guess and it doesn't line up quite right, so again, this is another little project to take care of soon. It works for now, but I want it to be right.
Ready to install!
Here are a couple of pictures of the "end" of the trans case - you can see how different the 6 speed cover is. It's ribbed and about an inch taller than the 5 speed cover.
I wrestled the thing in, in place of the 5 speed by myself (which made me feel like I'm getting old!) in one 12 hour day. I took some breaks in there, got lunch, etc., so it was probably about 10 hours of
"casual" work. It would probably have been half that with a helper.
I did find two things that were slight problems. I forgot to ask the seller for the engine plate, so I have an exposed starter ear behind the block (towards the rear of the car) and also forgot to ask for the
matching inspection cover. The other problem was that the water pipe coming out of the water pump and crossing the back of the engine had a SLIGHT interference, so when I build the new engine, I'm
going to make sure to use a pipe from a car that has the rear mount starter.
Other than that, it was your basic "remove and replace" swap. Of course, the big question is... "How does it drive?"
AWESOME is the answer! It has completely changed the car. It's MUCH quieter - so much so that I can now hear the "whistle" of the lightening holes in my under drive water pump pulleys as the engine
revs, can carry on a normal conversation at freeway speeds, and even had to turn down the stereo to about 70 instead of 85 - 95 used previously. Aside from that, the car now feels like it's READY to go
- any time, any place, any speed. With the deeper differential gearing (4:53 instead of 4:31) and the slightly deeper 2nd thru 5th gearing, acceleration is significantly better and more responsive.
Dropping in to 6th results in about a 200 RPM drop compared to the 5 speed at 70 MPH - just 3300 RPM at that speed. Shifting at near red line results in an RPM drop of about 2000, which is about half
of what it was before in the mid gears. The result is much better response and an overall feel that is much more like the close ratio transmissions found in Japanese motorcycles.
If you have an NA powered AW11, this is THE best thing to change in your car. I don't have telemetry reports on acceleration, but from the before and after videos, the car now appears to do 0 -
60 in about 7 seconds (about 1/2 a second slower than a Supercharged model) and is quicker in 0 - 80 by 1.5 - 2 seconds. I didn't launch the car too hard during the 6 speed videos since the trans mount
is still not right, but I look forward to running it at Sears Point in 2008 to get some official 1/4 mile times out of it.
Obviously an NA AW11 is not a drag car, but it's a good comparison between my car and stock so that I can see how my performance mods have improved the car. The real joy in the trans conversion is
always having the right gear available in corners. No more "do I over rev, or do I lug it some?" - now it's just choose the right gear and go.
Videos are on the MR2 movies page found in the navigation bar at the top left of the page.
Remember - I did all of this by myself in my garage and only had the aluminum welding and the lathe work done for me. It's really not a difficult swap, just pay attention to what you're doing and you'll be
|Videos of the 6 speed
in action are on the
MR2 movies page
|1986 MR2 AW11 4AGE NA 0-85-0 6 speed