yet another weird one!
 

fresh rebuilt transmission
had a stock 99 vb in it no mods..all worked great...
i couldnt leave well enough alone so i decided to j-mod it..(first mistake)..
drilled all holes as per jerrys updated 98 up vb drill specs. put it all back together n bolted iher up.. fired up the hand held tunner and raised pressure
extended shift points n headed out for a test run....wow... super hard firm shifts..im exited...(second mistake) i should'nt of been..

problem:

1-2 shifts hard under power , crisp n sharp under light acceleration
2-3 same as above
3-4 not as hard as 1-2/2-3 but noticably firmer n sharper.

while driving in overdrive once i start to slow down in traffic the computer commands a 4-3 down shift it neutrals no 3rd.. i can rev n rev to no avail..it will not engage 3rd .it will also not go back into o/d because speed is to slow.. if i manualy shift it into 2nd then back to 3rd it engages like normal..nice hard shift...

if i turn o/d off .i get firm shifts all the way up into third... i can cruise in third no problem as long as im under throttle..as soon as i let of the happy pedal and coast a little it neutrals again.. i try n turn o/d on but also wont catch.. bring it to 2nd then back to third all is well again till i coast once again...

any ideas what to check????? sensors,valves, pull trans out go through it??

tia,

My only input here is that the j-mod isn't designed for the truck VB. Weird ***** happens when you do that. Best advice is to get a car VB if you want to do that mod.

Other than that, not sure.

Darrin

he he he...did i forget to mention the transmission case v/b n internals came out of a 2000 lincoln town car.oh and that its installed in a mustang

fresh clutches put in ..all steels were lightly sanded but none had any blue heat marks on them ..all original stuff inside was reusable still had part numbers/black paint on some clutches but i decided to put new stuff in anyways.. all copper bearings inside tranny were scratch free n were reused.. every other seal was changed n air checked before build began. maybe i knicked a teflon seal or something on assembly.. im going to try n change all electronics on it n recheck the Accumulator bores n pistons to make sure everything is ok... if it keeps doing the same, time for a teardown..

ooops double post...

It REALLY doesn't sound like an internal issue because the gears work and hold until you try to do this one thing. If there was a problem with the clutches, seals or electricals you wouldn't only have this problem on a downshift. It would be there every time the part in question was called for use and that isn't happening obviously.

It's in the valve body. No need to pull the transmission.

i agree.. vb

thanks guys..ill pull the vb n see if i find whats going on?

swaped v/b out of an old 98 mustang gt tranny i had laying around.. performed j-mod to this one also. seems to have fixed problem.. ran 114 mph in the 8th mile track n its still shifting awsome..pulled pan to change filter n fluid no debris in pan... seems we can call this one ok.

thanks for feedback guys..

darrin did u ever figure out the problem with the tranny comanding od with the pa v/b???
im sending mines back as i eliminated all veriables n its definately the v/b.

I havent had any problems with my Jmodded 4R70w in my supercrew. Anytime i uplug the battery for a while it takes a few minutes of driving for the PCM to "relearn" the modded transmission