trans shifting to late...... anyone know anything

[broncobuckinaround]

86 b2 automatic 206,*** 2.9l

just did an engine rebuild. and i went to go drive the b2 and it felt as if it was starting in second gear. well as i went down the street it shifted around 3500-4000 rpms.

ive checked the vac modulator and it holds pressure, tested for 20 mins. ive check the tubeing and found that one of the tubes was suffering from dry rot. so i bought some new vac hose and im still in the process of re-installing it. damn thing is a trick.

what else could cause this problem. oh and forgot to mention the b2 was sitting for 2 years before i got it. ive also did a fluid and filter change.

 

[SenorNoob]

Oddly enough my first thought on reading this the limp in mode for the transmission in the newer trucks. I wonder if there is something similar going on here?

 

[kimcrwbr1]

If you can get a vacuum guage at the vacuum modulator you want to see manifold vacuum to the modulator above 17 inches Hg at an idle. Can you shift into 1st manually? It wouldnt hurt to put a new modulator in just be careful when you pull it out have a drip pan ready and the new modulator ready to install. Carefully pull it out and transfer the pin to the new modulator and quickly put it in. Make sure the cat has cooled down you have the A4LD I know it is easier getting to the modulator on my C3 from behind and over the tranny mount there is no room between the cat,frame and tranny. Check your linkage adjustment and confirm it is in 3rd or drive.

 

[broncobuckinaround]

well i have an update.

i finally got it back in with the new hoses. and its shifting between 2000-3000 rpms.

but still not sure if its sometimes starting in 2nd. but yes i can manually shift and it shifts just fine.

is it normal for this to be shifting bwteen those rpms. about 30% pedal.

seems a lil gutless for a fresh rebuild on the engine. could that be trans related.

 

[broncobuckinaround]

oh and can a vac modulator be adjusted it has a allen head bolt screw thing on it.

 

[doorgunner]

sometimes the rubber ring on the fluid filter tube will stay in the hole that the filter came out of.....then when you install the new filter, it won't fit correctly causing the fluid pressure not to buld up enough to shift right....

or you may need to add more fluid

 

[broncobuckinaround]

thanks doorgunner. im pretty good at trans filter replacement never had a comeback in 7 years. lol. but it couldnt hurt to double check ones work. i do keep checking the level to be sure it always comes back at spec.

do you know if the vac modulator can be adjusted

 

[kimcrwbr1]

Engine vacuum has alot to do with shift points same as vehicle speed. The modulator is adjustable but you want to confirm it is getting manifold vacuum at the modulator first. Did you make any changes recently with tire size or gear ratio? With light pressure on the skinny pedal it should shift into 2nd around 12-13 mph. Re you sure the modulator is holding vacuum pressure low vacuum pressure will delay the shift points until the governor in the tranny takes over between 25-30 mph. To test the diaphram in the modulator hook a length of vacuum pubing up to it and suck on it until it stops, holding your tonge on the hole if it loses pressure the modulator needs replaced. I did find the threads for the adjuster may be leaking carefully put a dab of permatexaround the threads at the base and see if it holds pressure. What I did was count the turns out put the goop on the threads and turned it back in the same amount of turns. Focus on vacuum pressure and the oil level. GL

 

[broncobuckinaround]

well no that you mention it. i do have 32/11.50/15's on it. and i did do what your talking about, about sucking the air out of it. it help the pressure for 5 mins. with out loosing any. now you got me thinking it could be those big tires causing the late shifting. i was planning on taking those off cause i dont have the clearance for them. i found a set of 235/75/15's that are all terrains. ill try that too.

i think weve done everything we can with the modulator.

new hoses, great seal no leaks, tested pressure at modulator and manifold, cleaned metal tubing. no cracks in it. but havnt yet adjusted modulator. but we might want to wait til i can get these smaller tires on it first to double check to see if it the bigger tire making it shift funny.

 

[alwaysFlOoReD]

IMO the large tires have a lot to do with your lack of power. Stock size is ~ 27" and without new axle gearing 32" is like starting in second gear. Adding in more mass and inertia for the larger tires compounds the problem.

Richard

 

[broncobuckinaround]

i guess ill get those tires swapped out. and see if it helps. im sure it do what you say.

 

[alwaysFlOoReD]

Let us know.

Richard