foothilltom 33 Report post Posted February 6, 2022 Hello my brethren. Damn, it's been a long time since I posted here. I hope you're all alive and happy. My question is regarding "fitment" and compatibility of a 2nd generation C4 (1972 to be precise) with a 1969 coupe. Filling in some details... original 302 swapped out for a 351W, shorty headers some years ago original 1969 C4 stayed in car, was never super awesome, recently slipping bad, fluid smells burnt, etc. original C4 absolutely needs a rebuild For logistical reasons (son uses this as his daily), I decided to buy a tranny that aledgedly runs good with the plan to quickly swap out the ailing original C4, put this one in, and then buy some breathing room for me to rebuild the original C4. Hence my question about compatibility and fitment. Ideally, it won't require drive shaft alterations, but I do wonder if the different bell-housing, dipstick into pan type tranny may pose fit issues with shorty headers, for example. In summary, does anybody have any direct experience with this, knowledge of physical dimensions being mostly the same (or not) between the 1st and 2nd generation C4? Thanks very much in advance. My son and I restored this coupe when he was 14. He's 29 now and it's his daily driver. I'm 59 now and still learning. Tommy D Quote Share this post Link to post Share on other sites
RPM 1,190 Report post Posted February 7, 2022 Pretty sure they all bolt up, as long as it's a 6 bolt. In the future, I would look into getting a C5, it has better oiling. Look for an H or R servo. Quote Share this post Link to post Share on other sites
Vicfreg 773 Report post Posted February 10, 2022 The C-4s went to a larger diameter 26 spline input shaft in either '69 or '70, so you need a later model torque converter. If the trans is a "pan fill" then it will have a 164 tooth flexplate. If it is a "case fill" it could have a 164 or 157 tooth flexplate. The good news is that they are both 28oz imbalance. A C-5 is much better, I think they may be 50 oz imbalance, maybe RPM knows. The C5s also have a lock up torque converter. Hope this helps. I think the answer is that the '72 will work, but you will need to use the 26 spline torque converter. Quote Share this post Link to post Share on other sites
dcm0123 15 Report post Posted February 12, 2022 40+ years ago I put a C4 from a 71 full size into a 69 Mustang with a 5.0. Only problem was the bell housing hit the tunnel. My recollection was the converter was a larger diameter. Took a few hits from a 3# sludge hammer to add more clearance. Tire would chirp when manually shifting up through the gears. Not sure if this was just due to the difference in the converter diameter or a good rebuild. Quote Share this post Link to post Share on other sites
foothilltom 33 Report post Posted February 12, 2022 Hey guys, thanks for the responses. Like anything, you learn as you go and I just learned that buying what I thought would be a "straight up, bolt-up, replacement" to buy some time was probably not well thought out on my part. This C4 came with a torque converter, so at least I'm covered in terms of the spline difference in this generation C4. I was concerned about going with a C5 for fear of needing to do a lot of modifications, but it sounds like (from dcm0123's memory) I'll need to be doing some ahem, modifications to the tunnel to make the larger bell-housing fit. Maybe that'll go easy, but anytime the sledge is coming out, it's probably a sign of some bad planning. I understood the C5's have the lock-up converter, but I've also read that the early C5's had issues with the lock-up? Anyway, I got tunnel vision trying to get a straight swap to buy time for me to do a careful rebuild of the original tranny, but should have stopped long enough to think about all the improvements that have come Maybe I'll just unload this 1971 vintage C4 and start poking around for a C5 or open up the whole spectrum of AOD, etc. Thanks again. Quote Share this post Link to post Share on other sites
det0326 179 Report post Posted February 12, 2022 I used the AOD. If I was to go with an overdrive again I would go with the 4R70W cost more for the electronic shifter but a much better transmission. 2 RPM and Mach1 Driver reacted to this Quote Share this post Link to post Share on other sites
RPM 1,190 Report post Posted February 13, 2022 By the time you upgrade the aod to 4R70W specs the cost is a wash. 1 det0326 reacted to this Quote Share this post Link to post Share on other sites
det0326 179 Report post Posted February 13, 2022 1 hour ago, RPM said: By the time you upgrade the aod to 4R70W specs the cost is a wash. Yes u are correct. I got a 4R from a thunderbird and used for internals and Dan (Silverfox) helped me out with the valve body. He told me the tricks to do to it to make it shift properly. Then sold me the springs and governor parts for hardly nothing. It worked good I just never liked the nature of the AOD. 1 RPM reacted to this Quote Share this post Link to post Share on other sites
EastYorkStang 63 Report post Posted February 15, 2022 What mods can be done to the AOD to better it ? Already have the AOD. Quote Share this post Link to post Share on other sites
det0326 179 Report post Posted February 15, 2022 50 minutes ago, EastYorkStang said: What mods can be done to the AOD to better it ? Already have the AOD. First I would not do it, but if u go that route u need to look at the casting number. If it is not an E9 casting I would not waste my money. Quote Share this post Link to post Share on other sites
Her69fastback 3 Report post Posted February 15, 2022 The only thing I can add is. If you go with the C5 make sure who every is going to rebuild it they know what they are doing. My transmission guy said. The C4 & c5 look a lot alike. I was told if they use C4 stuff you will burn it up on the first drive. I’m not a transmission guy just passing on what I was told. Good luck Quote Share this post Link to post Share on other sites
foothilltom 33 Report post Posted April 29, 2022 Hey guys, just for "closure" (as often there is none in these threads), I chose to sell the 2nd gen C4 I had bought as a stop-gap (per my original description). Son limped the car up from LA and I set about re-building his original C4 first gen tranny over a 3 week period. Never had done that before, so I was quite uneasy. Took my time, took a zillion photos, and found at least 3 significant issues that would have explained the bad behavior. Anyway, C4 is back in, new servo, o-rings, bands, clutches, steel, thrust washers, bushings, seals, etc. and the Stang is back on the road. Only set us back the price of the master rebuild kit so I'm going to call it good for now. I'm sort of trivializing a rebuild that my hair standing on end at times, but it all worke dout. Thanks again for all your input. Tom 2 Mach1 Driver and lalojamesliz reacted to this Quote Share this post Link to post Share on other sites
Her69fastback 3 Report post Posted April 29, 2022 I put a C5 in the wife’s 69 bolted right up. I had to get a 164 tooth flex plate. Quote Share this post Link to post Share on other sites
foothilltom 33 Report post Posted April 29, 2022 Interesting...no mods at all? Bell fit in the cowel? Same drive shaft, x-member, blah blah blah? I suppose I'll keep that in mind if my rebuild fails me. Thanks. Quote Share this post Link to post Share on other sites
Her69fastback 3 Report post Posted May 1, 2022 I was told by the guy that rebuilt my transmission. That the c4& c5 look a lot alike. So make sure if you have a C5 rebuilt they know it’s a C5 not a c4. If they us C4 parts it will burn up Quote Share this post Link to post Share on other sites