7004R Conversion
[ Home ] [ Up ]

7004R Conversion

The 700r4 is an automatic 4 speed. 1st gear is 3.06:1 and 4th is 30% overdrive, so it is a wide ratio gearbox. It also has a torque converter lock-up clutch which has the effect of a 5th gear. It usually comes mated to the NP208 which is a planetary reduction chain driven case with a 2.61:1reduction. This gives a very favorable range of gears for a production drive train, and nicely compliments the torque curve of the I-H V-8 engine. Suitable donor vehicles would include GMC and Chevy 4x4 trucks and Suburbans from '87-'88 forwards. Older transmissions would have a smaller diameter input shaft. Most transmission shops are familiar with the common modifications for reliability and performance. The adapter for the I-H engine, which is a full hoop cut from 7/8" plate and a disc for matching the torque converter to the flex plate with short stand-offs, is manufactured, stocked, and shipped by Advance Adapters upon confirmation by Blackwood Labs of an order. It is of the best quality materials and manufacture. The price is $625+ shipping. You will need the 727 type flex plate, crankshaft spacer, starter spacer, and bell housing front cover. You will also need the lower cover for the 700r4 which will need to be cut down some to fit. It could be necessary to grind something less than 1/32" off the snout end of the stock starter housing if it does not bolt in without hitting the transmission, or the transmission bell housing can be relieved slightly in that area to ensure interchangeability of stock starters. If possible, the transmission and transfer case, along with the driveshafts, cross member, and mounts should all be acquired from the same donor vehicle at the same time. Any other associated items, such as shifters, wiring harness, bracketry, etc. should also be pulled. The kick down linkage is known as a "TV cable" and connects to a lower extension of the throttle arm. Some carburetors have this arm but no attachment pin, some have both, and some have neither. It is not a particularly difficult part to fabricate and replacement pins are available from aftermarket suppliers, but it is important to have the correct geometry. A mount for the cable can be made out of heavy gauge sheet metal or light plate by cutting a hole with about a 3/4" hole saw and filing it square, with a notch in one side, then bending the remainder as needed to attach to the intake manifold or carb bolts. Brackets are sold by Summit, JEG's and auto parts chains which can also be made to work. The best solution for a floor shifter for the transmission is the stock GM shifter or an off the shelf surface mount shifter from one of the major manufacturers specifically designed for the 700r4, although with a good bit of work, a Scout floor shifter can be made to work if original appearance is a concern. A column shift requires only a straight rod with spherical rod ends, a suitable lever for the transmission selector shaft, and whatever hardware such as bushings are necessary to bolt it together without binding or slop. The linkage can be adjusted so that on the stock gear indicator the drive and overdrive positions are equally spaced to each side of the "D"on the indicator, and the others are very close to the correct positions. This may require readjusting the neutral start switch. A suitable transfer case shifter can be made by bolting 1" angle iron to each side of the shifter hole with a bolt going through both of them for a pivot. Then any suitable piece of metal can be used for a shifter, with the linkage connection below the pivot. With about 2" or so between the pivot and the linkage, in 2-Hi the shifter is almost against the heater, while at 4-Low is almost flat against the floor. The boot would be determined by your particular arrangement but can be made acceptably compact. The speedometer drive should fit the existing cable. The cross member can usually be modified by cutting off the ends and welding on extensions made of channel iron or other structural steel or tubing. On late full sized trucks the block side mounts should be sufficient to control engine torque, however, on the earlier trucks with bell housing engine mounts a number of options exist. For example, Scout type front mounts can be adapted to the vehicle, supplemental mounts can be attached or welded directly to the adapter hoop, and or a torque arm can be fabricated between the transfer case and frame, or cable type torque links use between the frame and engine block. For an additional charge, bell housing type engine mounts can also be added to the adapter hoop. This will necessitate a shipping delay. The front driveshaft is very likely to have a Double Cardan joint, which can be very useful with a spring over axle. The rear output uses a sliding yoke which eliminates wear and wobble in the driveshaft, but can be converted to a fixed yoke with driveshaft slip joint if so desired, by using the output shaft and housing from a Jeep NP 208. The lock up clutch control circuit is a simple series circuit running from the transmission connector to a vacuum controlled switch (usually firewall mounted) then to the normally closed contacts of a brake light switch (use the Scout cruise control brake switch) and to fused power. A ground must be provided as well, and an external transmission oil pressure "delay" switch can be added if desired. The purchaser must accept responsibility for ensuring that the conversion is done in compliance with the usual and customary safety and performance standards, and is ultimately responsible for the safety of the completed conversion. The manufacturer and seller make no warranty or guarantee, either actual or implied concerning the product or it's use other than replacement or reimbursement for defects in materials and workmanship, not extending beyond the actual components of the purchased conversion kit, or such as is required by state law.

Reply-To: "Jim Blackwood" @ Blackwood@Foresight.cc

Subject: 700r4/I-H V-8 conversion detail sheet.