Well, I think the inevitable has happened to the 3AT in my wagon. I took a 100-mile Memorial Day road trip from LA to Oxnard down Pacific Coast Highway, and it ran great as usual. I parked it while we ate at a restaurant, but as soon as I started driving back, it began slipping in first gear.

The fluid level is good and doesn’t smell burnt. I was able to manually engage first gear by shifting into first and then back into drive.

Where should I start troubleshooting?

• Transmission vacuum modulator

• Band adjustment

I want to go through some diagnostics and see if it’s something simple. Or is it time to bite the bullet and swap in a 5-speed manual with dual range?

The car has 111,000 miles on the odometer—14,000 of those were driven lifted with 27" tires

Mint looking MY! 

Auto… “just” manual swap it - you’ll thank yourself later. 

Cheers 

Bennie

Edited May 28, 2025May 28 by el_freddo

On 5/28/2025 at 5:35 AM, el_freddo said:

Mint looking MY! 

Auto… “just” manual swap it - you’ll thank yourself later. 

Cheers 

Bennie

I know swapping it is the ideal route, and I’ve got the whole parts wagon ready. But I think there’s still a bit more life left in this 3AT. It’s not grinding or making any weird noises. I pull out the good old service manual and run some tests this weekend.

Yeah I get that you want to run the auto until it’s proper dead. 

But you’re also wasting valuable conversion time - and when (or more importantly), where will the auto let you down again? It’s almost Russian roulette. 

My thoughts on the matter. If you’re keen on the auto keep at it. 

I’m no guru and I don’t know if this applies to just one or both autos in the MY and L Series - from reading on here common issues seem to be the pump shaft spline stripping out or the governor device on the side of the transmission under the dome bit giving issues. 

Cheers 

Bennie

Edited May 31, 2025May 31 by el_freddo

Update!
I discovered that the transmission modulator vacuum hose had transmission fluid in it, indicating that the diaphragm is likely failing—since there shouldn’t be any fluid in the hose at all. Fortunately, my local O'Reilly Auto Parts store had one in stock, so I swapped it out. Now, the transmission shifts through all three gears properly.

However, I’ve noticed a new issue: if I come to a complete stop and then try to proceed, first gear doesn’t engage. The only way to get it to engage is by shifting to Neutral ("N") and then back to Drive ("D").