Hello, I am wondering what the general opinion is regarding the lifespan of using the original c4 in a 6 to V8 swap. The 6 cyl transmision shifts very well now (no shift flare). Searching previous posts I realize there are fewer clutch disks in the 6 cyl c4. If driven gingerly on the street would I expect to get years of service life or would it destroy itself in a very short period of time? Thanks,
I been told the 250 uses the same C4 as the 302, only a different (tighter) stall converter were used on the 6 cyl. I also heard both ways on the 170-200 has one less clutch disc and different drum & pistion.
The C4s used in the 70s (late model C4s) have three versions (internally only). The four cylinder units have the least number of clutches in the packs with 1 or 2 being common. The small six version of the C4 was used with the 170 - 200 and it has 3 clutches in the direct pack. The 250 and all the V8s used the same one with four clutches in the direct pack and 5 in the forward pack. This last one is the only one tht should be used behind a V8. It can be made to handle up to 350 hp or so by installing a TransGo reprogramming kit #40-2. Adding a cooler will extend the life at that power level but for more power then modifications must be made to add more clutches, cooling and lubrication for long life.
Paul S, What I'm considering doing is swapping out motors between my 77 4 door 289 (original 302) with my 76 2 door 250. I think both transmissions are original for the cars. From your comment both transmissions are the same internally and the 6 cyl trans is capable of handling the extra torque of a V8? The 289 is a stock rebuild with minor bolt ons (dual exhaust, 4 bbl). If both transmissions have the same modulator (stripe and type)valve, will the shift points be the same for each engine? I would perfer not to swap transmissions as the 6 cyl 2 dr C4 now shifts perfect where the 8 cyl C4 has the shift flare. This is something that has been there for years. I have tried adjusting the bands slightly as per your previous recomendations. It's certianly would be liveabe behind a 4 dr driver, but I would like the 8 cyl 2 dr to be a smooth shift for driving with only the ocassional heavy acceleration. Thanks,
The transmissions are totally compatible. The question of shift points is one of vacuum. Vacuum is what controls the modulator and the modulator controls shift points through modulator pressure. No one can guarantee that the shift points will be the same when you swap engines but they should be fine. Addressing the 2-3 flare - this is not normal for a stock C4. something had to be changed in the valve body or servo (intermediate, front) that is causing the release of the band before the direct clutches apply. I do sell a kit that can be installed to remove the flare in the C4. It is a restrictor that slows the release of the intermediate band. The swap should not influence the operation of either C4 so putting the V8 into the two door and keeping the transmission that you like in it should be fine. Putting the six into the 4 door isn't likely to change the transmission flare but if it becomes a problem that you want to address then shoot me an e-mail and we can discuss a couple of ways to approach the correction.
Thanks for the reply PaulS. I spent today taking the v8 out of the 4door. It is possible that transmission had previous work which resulted in the 2-3 flare. However I had always assumed it was a wear issue from a previous owner. I had a discussion with you a couple of years ago about band adjustment. the flare decreases with band adjustment but you recommend against this due to heat issues on the band and drum. What does you kit involve? Thanks Kevin
The kit is a restrictor that slows the release of the intermediate band that is adjustable, drill guide, tapping guide and a clamp to hold the guides in place. It comes with pictures and full instructions.
