Finally bought my dream truck...but came with this problem. From park, I can't downshift or go straight to drive as if it's not there. Only way I can drive it is to put the gear in either 1 or 2, then drive up to 25 MPH or so before I can upshift it to drive. Sometimes, I have to repeat this a few times before I can upshift from 2 to drive. This happens each time I put the gear in park. The truck has 135K miles with a 351 motor.

Thanks for all your help!

86 Bronco XLT
6" Lift

 

Sounds internal to the transmission , but I'm no expert.

 

I have an 86 351, C6 as well and had similar problems. Not quite as severe as yours. I adjusted the linkage (I should say had it adjusted) and then put in an adjustable Vacuum Modulator ($13.99 at NAPA) Took all of 15 minutes to install and adjust. Problem is completely gone. The modulator has a rod which will engage the tranny internally via vacuum to allow the unit to shift b/w gears. Give it a try, it is cheap enough it may be worth it.

Scott

 

 

Scott,
Is the modulator valve located above the trans oil filter? Might as well replace the filter and change the trans fluid. Anything else I might need? Prefer to buy everything from the parts store before I drop the oil pan. Hate making side trips if you know what I mean. I'll work on it first thing tom/Sat morning.
Thanks!

 

Scott,
Disregard my question below (still searching the internet). Thought modulator valve and intermediate accumulator valve is one of the same. Found out the modulator valve is located or mounted somewhere outside the transmission (bell housing) while the intermediate accumulator valve is inside the transmission above the trans oil filter. Thought they were the same part. I'll buy an owner's manual too when I get to the parts store after work.

 

If you lay under the truck and look at the tranny, you cannot miss the valve. It is sticking into the side of the rear next to the output shaft. Should be a zinc coated round deal with a vacuum line attatched. Only thing in that area that you can access. Should be a little "U" type bracket with one 9/16 or 1/2" bolt holding it in. Remove the bolt and pull gently to free the modulator. Remember to keep track of the rod that should come out with it. You will need to clean this and reinstall into the new modulator. Make sure to drain your tranny first or, like me, you will forget and pull the valve only to wear about 3-4 quarts of ATF across your chest!! It is a pretty easy job to swap, though I have not figured the adjustment part out yet. Works fine out of the box, but maybe better with adjustment.
One other note: There are different type of modulators. The one you have now should have a colored strip around it. Supposedly, you need to replace it with the same color. My original was a red stripe, but there were only green and black to be found. Acording to a local mechanic, it really does not matter as they are basically interchangeable. I opted for the black stripe and it works fine.
If I can be of any more help, let me know.
Sorry it is so long winded, just wanted to help as much as I could.

Scott
1986 Bronco 5.8L 4x4
-also in the stables-
1985 F-250 S/C Diesel 4x4
1967 Bronco 289 4x4