So what kit do you use? Especially for an 8 hole Mopar pump? The diaphragm do get hard and crack. Same with pulsator/air dome gasket. You could make that, but making a diaphragm isn't going to happen. I have seen other kits for the Ford 6 hole, and I tried exploring them to make an 8 hole, but no one has stepped up. Not even Carter. They point you to now and then. So your only option is an New Old Stock pump.
i don't think there are any good options for rebuild. i know the kit i bought was a cheap band-aid at best; waste of money. what got me into playing with these pumps was trying to chase a lack of performance with one of my cars.
i'll try to layout here what i did and you guys can critique all you want. i had a 6pak engine with cam, good heads and good exhaust . power wasn't terrible just not where i thought it should be. a pretty smart friend (site member ) suggested i do some fuel pressure test while driving and opening the carbs as i suspected a fuel issue; so i did. i was 2lbs, maybe a little less, at WOT; now i knew something. i didn't want to add an electric pump because i don't think there are any continuous duty aftermarket pumps out there and i'm not getting stuck along side the rode. next option was high pressure mechanical pump with a regulator. i nixed that idea because of finding a modern regulator that will work with a 9lb pulse pump. i decided to work with 6903 pumps, had several, and did drive and "bench" testing as i did modifications. i had four 6903 pumps, one 4862 pump, one edelbrock pump, an original 375hp 440 pump, and a mancini hipo 440 repop to play with. i had a spare block, installed a cam, fuel pump and rod. hooked all the stuff up, spun it with a variable speed electric motor and did pressure and free flow tests on the pumps i had. i also did in car tests with modified 6903's. took some time but a pretty good learning exercise. i ended up keeping the 6903's in my cars, but i opened the feed side to .31 (factory is .25) to match the 3/8" line from the tank and also opened the pressure side to .31 (probably don't need to do this if using 5/16" line on the pressure side, edelbrock pumps have this mod.). i worked on the mating surfaces of pump to give a better seal and to make sure the cast parts were flat. i found it's possible to add shims to the pump diaphragm stem well to pick up pressure on the 6903's. doing these mods on the pump for the 6pak engine gave me 6.5-7lbs driving pressure and about 3.5lbs at wot. 3.5lbs at WOT isn't perfect, maybe a minimum, but it sure did help. an OOTB 6903 is around 5-6lbs driving and may go into the high 4's with heat. the 4862 wasn't installed in the car but it did do 9lbs and i was amazed at one gallon of fuel in 30 seconds. i played with the 4862 a little to see if different orifice return sizes would help regulate pressure. that ended up kind of a yes and no. i could get a stable 7lbs at a simulated 2000rpm but low rpm pressure swings were 1-9lbs. i did find that return orifice sizes do make a difference in WOT pressure but not a big effect at normal driving speeds. 6903's, all of them, would do about 3/4 gallon in one minute. the 375hp pump would do 8-9lbs pressure and supply 1/2-3/4 gallons of per minute. the edelbrock pump did 11lbs pumped about the same as a 6903 but was considered unusable because of pressure. a lot easier to add pressure that remove pressure. the manicini pump was 16lbs and totally unusable. i came to the conclusion that the 6903 has limits with a streetable pressure and i think i'm at that point. i know some folks have had some good track results with them and they may be over achieving,..
i got to the rebuild thing by looking at a pump that i'd had on one of my cars for many years. on the outside the rubber was looking ratty so i'll rebuild it. bought the kit disassembled the pump, looked the parts over. the kit diaphragm was a little too large, very flimsy compared to the carter, but i stuck it in anyway. did the bench test, said nope! (glad i didn't install the pump), did my mods to the old pump, put the old diaphragm back in and happy motoring. what i did find was the carter bowl gasket/seal actually gets in far worse shape than the diaphragm. those diaphragms are pretty tough. the only things i used out of the kit was the bowl gasket and pump gasket. i'd been better off taking that $50-$60 and putting it towards a new pump.
