You do not have to remove the cat to replace the vacuum modulator, it can be reached from the rear over the cross member along side between the transfer case exhaust pipe, not the easiest thing to do but is do able. But before you replace it disconnect the vac line from the intake and connect a hand vac to it and see if it will hold a vacuum, if it does its probably still good and working.

If it does leak down make sure its not just the hose/tube assembly supplying it, get under it and connect the hand vac and its hose directly to the modulator itself and test being sure of tight connections. If you don't have one take it to a service center and pay them a couple bucks to vac test it for you.
Just don't want to see you go through the time and expense of removing the cat and changing it just to find it doesn't help.

If you do change it be sure and swap over the pin, take it out of the old one and put it in the new one. Otherwise it will do nothing, that is if the new one doesn't include it. From what I've seen they do not but may be a "by manufacture" thing.

IIRC its a 10mm bolt, remove it and the hold down clamp then pull the modulator straight out with a slight twisting motion.

I doubt its the problem, sorry to say but "no shift to drive and or OD" has to be the number one first sign a A4LD is dead and dieing.
If you dropped the valve body you'd likely find metal shavings/pieces laying on top of it in three places in small piles. May even find a piece/chunk or two in the pan that made it under it.
I really hope your not to that point but "history" is not in your favor.

 

thanx for the info, i will try to reach it that way..lol..i have a hard time even seeing it..gonna be a feel thing to check it...BTW.. i can shift to drive and OD.it just has to warm up first, then it runs just fine..weird huh?

 

You want see it but laying on your back and sliding your arm up there you will feel it. Using a 10mm small wrench you can get to the bolt but have a small bucket ready when you remove the modulator for the tranny fluid that will hit you in the chest ( I learned the hard way). I replaced mine in 10 minutes. Now for the test drive.

-Let Bronco warm to temp and checked tran fluid;added alittle
-Backing out of garage reverse felt smoother when engauged
-first time letting it shift through gears was no change; stayed in 1st
-stopped and shifted to 1st manually
-started again and manually shifted from 1st to OD; worked perfectly
-stopped and started again and let tranny shift automatically
tranny shifted through all gears smoothly and nothing odd felt
drove for 15 minutes while starting and stopping frequently and
tranny shifted correctly with no hesitation

I'm not convinced my problem is corrected so I'll test further tomorrow when I drive to work (40 mile round trip) and post again.

 

From house to work (20 miles):


-started off shifting manually;shifted OK
-at stoplight started off in D;shifted OK
-interstate driving at 70mph in OD;OK
-exiting interstate and starting in OD;shifted OK
-entering parking lot;reverse slipped and hesitated for a moment before
engaging

That's the 1st half of my test drive to work (outside temp 30 degrees) and I'm not convinced anything is fixed. I will see how the trip home reacts this afternoon. The Bronco isn't my daily driver but with gas at $1.85 here and diesel $2.79 I'd like to park my 7.3 powerstroke this winter.

 

My trip home was alittle different than this morning. I didn't let it warm up and leaving the parking lot it wouldn't come out of 1st. Pulled over and shifted manually to 1st and around 2500 rpm shifted manually to 2nd;shifted OK. I drove through town like this and when the engine reached 185* the tranny shifted OK automatically and I hit interstate and drove home. I am noticing my shift points are off (adjustment on new modulator should correct). Also backing into my driveway reverse is slow to engage but I'm going to continue to drive it unless my problem gets worse or tranny just lets go. I will say again that it was rebuilt 20,000 miles ago and fluid is red with no burnt smell.
I'll go by Ford soon and order a governor housing,spring and pin and find a Sonnax 35mm weight online and maybe after the holidays install. If this doesn't correct my problems I'll look into a 302 conversion that I've always wanted to do with upgraded tranny, lift kit and larger wheels.

 

Thats what I may do to my B2, a 302/aod install as week after replacing the tranny with one out of a explorer, that tranny went dead too! That is with a new torque converter and brand new OD input basket,one-way clutch and bands,clutch packs. I havn't even attemped to drop the tranny again to find out what happened. Its now shut down as I play with the new "toy" a 96 E350 bus! Bummer as I rebuilt the engine only 15Kmiles ago too. Once the holidays are over I'm going to tackel it again. As it is/was a daily driver for my wife and 302 option is not on the top of the list for her.... 302 with lead foot, small truck with the weak 7.5 rear end.....

 

problem solved..running smooth again..so, new filter/new fluid/lucas tranny helper and new vac mod....

 

That's great you got it fixed; my problem is still with me. I haven't got around to changing filter/fluid yet but replaced vac mod and added lucas tranny fix. After I added the lucas shifting got worse so I parked it and haven't tried fixing. Shifting got very erractic from changing correctly to changing from 1-2 at high rpm only to changing from 1-2-3-OD very quickly at low rpm. Reverse will ingage sometimes OK and then it will hesitate. I'll change filter/fluid soon and see what happens.