1-2 accumulator and mechanical diode - TCCoA Forums
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post #1 of 2 (permalink) Old 08-14-2006, 12:26 AM Thread Starter
Join Date: Aug 2006
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1-2 accumulator and mechanical diode

Hello...found this site by searching and getting linked to the transmission tech articles...great stuff in there!

I lost 2nd gear in my 94 Thunderbird, 3.8L NA. After driving about 20 minutes it would finally start to grab and it seemed to shift normally. Eventually I also lost third.

I tore it down and found a small amount of carnage. The spring that presses against the 1-2 accumulator piston was broken. I figure that I need to upgrade the piston but it doesn't look like the new piston comes with a spring. Anyone have a Ford PN? Hopefully this caused my no 1-2 shift until driving around for a while.

Also my direct drum was slightly chewed up on the outside. The frictions in that drum were worn down to the steel and cupped. By slightly chewed up I mean there is wear but really not that much at all. In a different tech article I got linked to, they mentioned to check the wear on the inside of that drum. The inside shows no wear. Good, bad, indifferent?

Also the steel housing that people replace with the mechanical diode setup has about 1/16" wear on the retaining tabs. The sprag only turns counterclockwise but there is a mid-pitched hum/squeal when it does so. Time to replace or is that hum normal? I have seen pulled mechanical diode setups go for about $50 and new units for about $150. This is a stock daily driver.

This is my first Ford transmission...so far it seems much more user friendly than the 700R4's I have rebuilt. Thanks for advice and I can shoot some pics up if it'd help.
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post #2 of 2 (permalink) Old 08-14-2006, 07:29 AM
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Join Date: Aug 2002
Location: Camby, IN 46113
Age: 54
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Ok, if you can slide the steels up and down easily in the direct drum then it might be salvageable. If the steels hang at all or if the drum is discolored from heat, its scrap.
You just need to replace the reverse drum and intermediate one way clutch (sprag) with the mechanical diode setup. That old roller type setup is worthless in any situation. This isn't optional. Ford switched all cars and trucks to the mechanical diode type setup for a reason.
Now, on the springs, even if you are not doing modifications to the valve body I would still use a better spring setup. I would at the very least do a mild mod, but that is up to you. Get the F75Z-7F284-AA and F7AZ-7F284-BA springs. Make sure you get the accumulator bores smooth so that the new accumulators don't get torn or hang.
You also need to take the clutches completely apart to separate the pistons and fully disassemble the valve body so you can clean out all the contamination from the trashed clutch pack(s).
If you don't do every single thing I mentioned as the very minimum then you will be back in there doing it again in no time flat.
Good luck with it.

01 F150 5.4L 4x4 and a 98 Mustang GT vert sitting engineless and without transmission or converter

All my vehicles tuned by BC Automotive (me)

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