Fox AOD Overdrive to 3rd Hard Downshift

Motorsport71

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Jun 3, 2020
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So my 1985 Mustang has the factory AOD with a 2400 stall converter and I put 3:73 gears in the back. When I purchased the car 3rd and 4th gear were out of it. I had a tranny shop do a complete overhaul including a shift kit that shifts hard enough to break the rear tires loose on the 1 - 2 shift during a hard acceleration. So here's my question. When It does a 4 - 3 downshift on its own (like passing other cars) it revs up a bit and slams into 3rd. I've done some research and some people say that is just the nature of the beast. You need to shift to 3rd manually (drive from OD) and wait the couple seconds for it engage into 3rd before passing. But I can pull it from OD to 1 (which puts it into second) and it shifts quick without the rev and slam. I know the 4 - 3 shift can snap a shaft which is probably why it didn't have 3rd and 4th in the first place. Is this actually normal? I mean all up shifts are awesome. Except for the 4 - 3 downshift all other downshifts are great. The tranny guy says its normal for that transmission but I really want to hear it from you guys. Any input would be great.

Thanks for looking,
Motorsport71
 
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Mustang5L5

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Mod Dude
Feb 18, 2001
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I can only speak to my stock AOD trans when I had it, but it was a low-mileage car driven by an elderly woman at the time. But, it did not behave anything like you described. The 4-3 downshift if I rolled on the gas to pass a car was almost like a smooth rolling down into 3rd gear. Nothing harsh about it. If anything it is very similar to how my modern daily driver downshifts on the highway.

I've since swapped to a T5 so no recent experience unfortunately. Still have the trans gathering dust for when I find a super clean GT convertible with a busted AOD for dirt cheap :)
 
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foxbodybill89

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Jan 19, 2020
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Mine doesn't do that, all the downshifts are as smooth as can be. Could be something to do with your shift kit, hard to say if you don't know how it was stock.
 

KRUISR

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Apr 16, 2015
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I have a stock AOD ('90) with a Lentech VB - so shift kit and shift pattern change (1-2-D/OD vs 1-D-OD of stock)

When I first put this setup on the road I set the kickdown cable to Lentech instructions. I found that setting too aggressive so I backed off the kickdown cable adjustment to slightly softer.

So what was too aggressive for me. 1st to 2nd and 2nd to 3rd were VERY fast, firm and hard. This by itself was not bad. I could not get to shift into OD in town unless I sped up to 50-55 mph and then got off the gas. It would shift to OD then. Not a great scenario when just easy cruising in town. Also what I didn't like was when coasting down from 50+ mph down to in town speeds it would VERY aggressively downshift (like slamming the gear down yourself) on its own from OD to D at about 35mph - no choice. I think this would be great if using for road course or very aggressive driving.

So I backed the kickdown cable setting off a little (less pull on the cable) and now I can drive and shift near factory points (if I want) or shift hard and fast enough to chirp tires going into 2nd and 3rd at WOT. The coasting issue is resolved and relaxed cruising can occur.

Your car may have a rod instead of a cable so adjustment may not be as simple.
 

junkyardwarrior

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Jan 10, 2011
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without knowing what they did internally it's hard to say

pretty common for shops to eliminate the wave plate in the direct clutch which will absolutely result in a harsh 4/3 downshift. I leave them in.

if you get a rpm flare on 4/3 downshift, theres possibility that the direct clutch clearance is excessive, or possibly an accumulator piston or even servo piston leaking. Again without knowing what they did or didn't do, it'd be hard to pinpoint it.

Many times a transgo shift kit solves this kind of thing IF everything else inside is up to par. Problem is, if it doesn't solve it, you may be looking at pulling it apart again.

some shops think that the B&M shift kit is awesome, and it shifts very hard, but it also destroys trans parts. I don't use them. Transgo only. Very well thought out kits for the AOD's among others.
 
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