AOD sporadically jumps out of OD at 65+ for <1s

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Bludacious

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Nov 18, 2024
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Charlotte
Vehicle Details
'91 5.0 base, automatic
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Hi everyone! New here & will be sharing some mods I've already done to my bird that I haven't seen here or elsewhere, but for right now I'm in need of some assistance.

Had my AOD rebuilt plus mild shift kit first week of ownership by the race trans shop my boss uses for all our costumers hi-perf transmissions. Worked flawlessly 'til a few weeks ago when I replaced the plastic TV cable bushing due to it being cracked. Just so I'm clear: at no point did the cable detach from the throttle arm, I replaced the bushing to prevent this. I triple checked the cable adjustment before leaving the shop (I dailied a Gbody for a long time so I know TV adjustment is life or death for these OD autos). As I was leaving it kept trying to shift into OD by like 40mph, I stopped & again checked adjustment, when I started driving again all was normal.
Then I went to Florida & it started acting up from then onward. When I get on the freeway & apply light to mid throttle above 65-70mph it'll randomly pop out of gear (or into a lower gear?) for a fraction of a second, then continue as if nothing happened. Of course this bucks the entire car too which is rather alarming. Transmissions are the only thing I don't mess with personally on my rides so I'm at a bit of a loss. I don't have a pressure test gauge but I'm sure I can get one, & I have access to a lift to drop the pan if needed but I'd really rather not drop the V.B. as I don't want to risk losing springs or check balls.
 
If all this started after messing with the TV cable, I would definitely be looking at the TV cable adjustment as the most likely cause. If the old plastic bushing was cracked, then it’s possible the trans shop adjusted it to compensate for the play in the bushing, and now that you fixed that, it is adjusted too tight causing it to try to downshift too early.
 
MadMikeyL said:
If all this started after messing with the TV cable, I would definitely be looking at the TV cable adjustment as the most likely cause. If the old plastic bushing was cracked, then it’s possible the trans shop adjusted it to compensate for the play in the bushing, and now that you fixed that, it is adjusted too tight causing it to try to downshift too early.
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The previous plastic bushing was also installed by me after I had to remove the cable to remove the TB. The way it cracked didn't allow any slop in the linkage, it was splitting along the circumference (like slicing a sausage).

I adjusted the cable by opening the lock clip, holding the crimp with a pair of vise grips, gently pulling the cable to its maximum travel, then pulling the throttle to WOT & closing the clip. Is this the correct procedure? I will admit I didn't do diligence & ASSumed this was how it's done since that's how it works on the 2004R 😬
 
theterminator93 said:
Here is the tech article on adjusting the AOD TV cable: https://forum.birdcats.com/threads/adjusting-the-aod-tv-cable.340/
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Today I checked TV pressure & adjusted this per these instructions. Tested at ~35psi on a mechanical oil pressure gauge BEFORE adjustment.

When I left work today with the cable set at 'mid TV' shifting mimicked the first drive I made after replacing the bushing (rowing thru all gears by 35-40mph, severe bucking in all gears if any throttle applied). Stopped & put the cable back to 'max TV' (where it was before) & shifts got almost normal, still a bit too soon & a hair sooner than before I readjusted today.

It was still bucking with throttle til I stopped & floored it a few times in park to see if it'd maybe break in the valve or dislodge a blockage. This actually did seem to solve the throttle bucking at mid speeds (40-60) but haven't gone back on the interstate yet.

I forgot to mention in my initial post that I added a brand new 11 ton rated stacked plate cooler a while ago, I knew it was a bit overkill but it was free & the box said it had a bypass built in to let fluid pass thru when it's cold.

When I was omw back from Florida I went up i75 & as night came it got cold & the car started shuddering at 85, then 80, then 75. Didn't have any tools etc on me so I taped rags over the cooler & things improved a bit. Is it possible I'm over-cooling the trans? Would I have caused any permanent damage by doing this? It's still inline with the rad cooler so it should be getting SOME heat.... I really didn't think it was related to the bucking but now I'm not sure.
 
MadMikeyL said:
I’ve never heard of problems from the fluid being too cool. What fluid are you running? It should be MerconV in there.
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I have standard dex/Merc in it. I know merc V is supposed to supplant dex/Merc but I've heard at least as many problem stories as I have success cases for doing the same thing with dex3 to dex6 (not to mention there rarely seems to be a consensus), so I run what's been time tested. I do however run lubegard platinum in all my auto vehicles, it's worked many miracles for me before and I'm not entirely convinced dumping another 2-3 bottles in there wouldn't solve it, lol
 
Update, I've returned absolutely everything to the configuration it had when I initially installed the trans with exception of replacing the plastic bushing with the brass one that uses a hairpin clip. Problem is still persistent so I'm probably gonna send it back to the builders & eat the cost. I'll let y'all know what he finds when he cracks it open!
 
Changing from Dex3 to Dex6 is a whole different animal than changing Merc3 to Merc5. Dex6 is a much thinner viscosity than Dex/Merc or Merc5. The viscosity of Merc3 and Merc5 is the same. Putting Dex6 in an older GM trans is like putting 0w20 oil in a car that calls for 10w30. I actually use the Merc5 in older GM stuff that calls for Dex3.
 
MadMikeyL said:
Changing from Dex3 to Dex6 is a whole different animal than changing Merc3 to Merc5. Dex6 is a much thinner viscosity than Dex/Merc or Merc5. The viscosity of Merc3 and Merc5 is the same. Putting Dex6 in an older GM trans is like putting 0w20 oil in a car that calls for 10w30. I actually use the Merc5 in older GM stuff that calls for Dex3.
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Even if that's so, much like the dex 3-6 change the more I look around there doesn't seem to be a consensus on using OG Merc or V in the older units. The way I see it, V didn't exist when the AOD was designed so there's no possible way those engies could've accommodated any differences it may have no matter how small. If/when I have it sent to the builder I will ask him what he recommends, but I never got any explicit instruction to use V from him nor my boss (who saw me fill it with dex/Merc). Both of them have been in the hot rod game for decades so I'll most likely use whatever they recommend.
 
4R70s weren’t designed with Mercon V in mind either, yet it’s still recommended even by TSBs to use it. The AOD is mechanically the direct ascendant of the 4R70w, only key differences being in its electronic operation and the way the torque converter clutch engages, neither of which Mercury V would be a detriment on the older design
 
Update-
The erratic shifting was masking the actual issue which was the motor cutting out sporadically under load. The bucking was distracting enough that the loss of power went unnoticed, since I don't have the gauge package there was no falling tach or volts to alert me directly of these brief stalls.

Changed out distributor, cap, rotor, wires, plugs, calibrated TPS, adjusted idle. Asides from a rough idle in gear I have yet to nail down & it's running much better - bucking has stopped. Live & learn!

Thanks everyone for the help, I hope this thread can point others with a similar issue in the right direction.
 
Sounds much better than pulling the trans and sending it back to the builder. Nice find. Have you checked at all for vacuum leaks?
 
Bludacious said:
Changed out distributor, cap, rotor, wires, plugs, calibrated TPS, adjusted idle. Asides from a rough idle in gear I have yet to nail down & it's running much better - bucking has stopped. Live & learn!
Click to expand...

Now that you say that, I'm reminded of my situation a while back when I had a failing coil pack. I did erroneously attribute that to transmission shudder before identifying the true cause.

Glad you were successful!
 
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