C4 Atlas Install
The cable assembly is ready and we will have two options for the main shifters – re use our previous cable shifters or go the mechanical route we will look at both and how they fit under the Jeep.
Al Vandervelde
I’ve been wheeling the silver flame TJ for almost 6 years. I think that’s the longest I’ve stuck with a single project since I started wheeling. It’s relatively unchanged since the first stage of the build when Jeep Thrills in Maple Ridge put it together. I was set on what I wanted and with experience I had from four full, from-the-ground-up builds before it, I got this one right the first time. I had planned on a V8 swap from the get-go but that underpowered little four banger just would not die. After the first two years, that V8 found its way under the hood in the form of a 1991 Ford 5.0L which I mated to the AX 15 Jeep tranny via Advance Adapter conversion parts. Alas, the AX15 might be perfectly fine in front of the four cylinder (or a six cylinder) but it is not quite tough enough for my driving style and the synchro’s came apart last year. This left me with a “now-what” situation.
I’m a die-hard stick shift guy. Almost every wheeler I’ve had, except my Cherokee, has been a stick. I guess I’m a bit old school, but I’ve never had an issue climbing whatever I wanted to and the standard transmissions generally work better in the snow.
However, with my choices limited in the stick department to get the strength I wanted - in a package that fits how I wanted it to fit - I had to make the leap to an automatic.
Making this change raised a lot of issues I’ve heard about from other wheelers, like excessive heat and stall for the converter. Issues that I didn’t want to run into myself. Many of the solutions I found are applicable to any automatic install.
With the 5.0L, I had more conversion options than you might think, but after speaking with lot of racers, mostly pavement and strip guys, I was confident a C4 could be built to suit my needs. The C4 is one of the smallest automatic transmissions on the market and with the Advance Adapters super short output shaft conversion; the entire transmission is only 18 1/2 inches long including the adapter. This opened up another option for me and that was swapping in a 4 speed Atlas T-case. I already had a 2 speed with a 3.8:1 low ratio that I loved, but going to a 4 speed would give me more mid-speed gearing options. The combination of the super short C4 and the Atlas 4 speed actually gained 3/4 of an inch of rear driveshaft length over the two-speed/AX15 combination.
On to TCI and the C4. TCI has several versions of the C4. My unit is based on the Streetfighter version capable of up to 550hp. However to suit my application and match the super short AA conversion I went with a full manual valve body in a reverse pattern. This isn’t for everyone. It basically turns the automatic into a full manual shift, I call it a standard trans/automatic hybrid – Ha Green Peace, I drive a hybrid. The reverse pattern puts first gear rather than third gear beside neutral. This gives the ability to “rock” the Jeep from reverse to first – something I need for snow wheeling and if you have ever watched extreme rock crawling, its what’s needs for some of those spectacular “saves” you see when you are sure a rig is going to go over backwards but at the last second the driver slams into reverse and backs out of the obstacle. I’ll get into modding the shifter next issue.
Stall. This turned out to require more planning than I expected. We all hear about high stall converters i.e. ‘I’ve got a 3500 rpm stall in my drag car’, but understanding stall and the heat a high stall converter can generate needs to be considered. Also going too low a stall speed, say under 1500 rpm, means that you can lock up the converter almost off idle - not great if you are bombing down a hill in a low gear and your rpm’s stay high – you could literally overdrive your brakes. To understand stall in a simple way, think of dragging your clutch in a standard. You rev the engine up a little, lift your foot slowly off the clutch as the rpm’s build, dragging it slightly for a smooth start then you take it completely off once your rolling and speeding up. That’s what a torque converter does. It needs to slip so you can hold the brakes at a light and not stall the engine. The stall speed is where your converter stops slipping to make for that smooth start - your converter is spinning at the same speed as your engine. Up until that stall speed, consider that your “clutch” is slipping and this generates heat in something that uses fluid to couple it together. High stall converters are great for drag strips – it stops the tires from roasting off the line. When you hit 5000 rpm in just a few feet and only go a 1/4 mile at a time, heat is not a big deal. These types of converters are not great when you spend almost all your time below that stall speed crawling around in the rocks. For my C4 I went with a custom converter with a 2200 rpm stall speed, it’s the rpm just above where I noticed I revved the engine and dragged the clutch most of the time - to take off from a stand still with the AX15. Not so low it will over power the brakes, not so high as to build up too much heat.
Atlas 4-speed. I love the Atlas T-case. This 4 speed will be my third, the previous two being a 4.3:1 in the Kandain Krawler and a 3.8:1 in this TJ. As part of this swap I had to change the current Atlas to fit the C4. With the short tranny, I gained enough room to install the Atlas 4 speed and still maintain a good driveshaft length. The 4-speed has a reduction box placed in front of the regular transfer case. This planetary gear set gives you a low ratio of 2.72:1 (stock non-Rubicon Jeep). The main case can be ordered with a range of low gear choices. The plan was not to make the Jeep a walking speed machine but to gain back some mid-range speed for snow play and to gain a little more low ratio for crawling. Keep in mind you don’t need as much low ratio with an automatic, as you can two foot and control your speed easier than with a clutch.
The final ratio choices of the unit I ordered were 1:1, 2:1, 2.72:1 and 5.44:1. I also chose the super short output this time. Mike at Advance Adapters generally doesn’t recommend this choice for those who drive their rigs on the street daily. The bearings are closer together restricting oil flow slightly and places the output bearings very close together, in my case I was happy with that compromise to keep everything as short as possible, and I do not daily drive my Jeep. I’ll stop here for now, there is just too much info to pack into a single article – catch up next issue when we get everything stuffed in and running.