Transmission Story
GM Turbo Hydramatic 400
One of the really good thing in the Full Size Jeep design is AMC's choice of automatic transmission. The TH400 is one of the stoutest OEM automatics of all time, and putting this one in a truck the size of the FSJ is truly heavy duty. Remember, most of the bigger Chevy Blazer only came with the TH350. |
Quick Spec.
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One advantage with the TH350 is the lower 1st and 2nd gears but the TH400's superior longevity and ability to handle high horsepower applications makes this unessential. There is also a lower gear set available for the TH400 that brings the 1. gear ratio down to 3:1. It's a bit pricey, so it may be a better idea to do the gear change with the transfer case.
There were nothing wrong with the transmission in the Wag when I bought it except the usual sign of wear after the 220.000 ++ miles on the odometer. So when I installed the part-time conversion in the Q-Trac, I also took the time to overhaul the tranny. At this time I only bought myself a OEM overhaul set and a new stock converter. This was with the original engine still in the Wag so I did not at the moment see any use for an upgrade.
IT HAD TO COME
When I installed the new engine in the Wagoneer I couldn't leave the TH400 alone. I decided to convert my TH400 to a full manual/automatic so I exchanged money for parts (once again) and found myself the owner of a B&M TransKit. This kit, along with the suggested modifications converts the TH400 into a B&M-prepped street/strip automatic. Those transmissions are rated for 450hp applications so this maybe slight overkill for a off-road truck but now I sleep well at night.
The TransKit came with everything needed for the conversion together with one of the best instructions I have received. All the modifications where explained very well and together with the detailed drawing it was an easy installation. There were three levels of modification available: Street, Street/Strip and Full Race. I thought the street/strip option suited me best and did the required mods. I also changed the vacuum modulator to an adjustable one at the same time.
I had a TCI "Saturday Night Special" torque converter left over from some other project in the garage so when it turned out the new engine liked some more rpm's than the original (big surprise :-) I installed this converter instead of the stock one. This converter is supposed to have a stall-speed 300 - 500 rpm over stock. This should in my case turn out to be approximate 1500 - 1800 stall. This is maybe not the optimal converter but it makes the Wag move and it was free.
MY TORQUE CONVERTER CHOICE
The camp-fire talk about converters and stall-speed is a nearly never-ending story. One half of the automatic drivers says you should have as low a stall as possible for engine braking and to avoid overheating (more stall speed=more slippage=more heat), and the other half says that you must have the stall-speed located where the torque curve off the engine begins, so you have some available torque off line.
I find myself supporting the last alternative because I have not seen or driven many auto equipped 4x4 where there is serious engine-braking. Those few are equipped with extreme low gearing. On the other hand if your stall-speed is so low that your converter hooks up before the engine makes some useful torque, you will most likely never climb that hill. This will in the end result in not having to go down the hill at all, because you couldn't climb it due to your low stall-speed. (confusing isn't it)
I rather have to worry about going down a hill after I've climbed it, than standing on the bottom of the hill without being able to climb it !!
The shifter in the Wagoneer is placed on the steering column and connected to the transmission with a rod. This leads to unexpected shifting when the body moves in relation to the frame. So I installed a B&M Starshifter to correct this. The cable don't have this problem so I've also used morse cables on both the 4wd and the low-range.
Questions ?
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