? for the pros

Lee Thompson

New Member
I have a fully built, up to, but not including billet shafts. (Alto clutches and wide band, built pump, clearances set exactly to Chris manual) My ? is why do I have a large pressure drop on the 1-2 shift only. Let me explain. With a pressure gage installed, any throttle angle producing under 150 psi, the 1-2 shift is VERY quick and Snappy. As I increase throttle and pressure goes over 150 the shift deteriotes, and the pressure always falls back to 150 on the 1-2 shift.180 falls back to 150. 280 falls back to 150. The higher the pressure the more the shift goes away. The shift is quick @ higher psi but not as firm as @ under 150. On all other shifts pressure only drops 15-20 psi @ any throttle angle. BTW @ full TV I have 280-290 psi. Min. TV ,90 psi. Best shifting trans. I have ever seen except for the pressure drop. Have not tried another VB, did install a stock BR servo--no change. I am open to any and all suggestions. Thanks
Did you change the spring mentioned in the paragraph under Figure 6C-36
in Chris' rebuild manual? It is on page 108 or 109 ( my manual is the first
edition). It discusses softer upshifts with more throttle angle.
there is a leak in the circuit.pressure drop indicates the more pressure applied the easier the leak is to be productive to dropping line pressure.at half throttle when the shift feels ok how much drop occurs?
Thanks to all

Did not change the spring--have been using a TCI shift kit--does not call for changing any springs--has always worked before on other trans, so don't think that is the problem, but worth a look. Chis, on the less then 150 psi shift is good and pressure only drop 15-20 psi. Just a blip on the shift. On shifts above 150 the pressure drops back to 150 but instantly goes back to what ever it was before shift. Also a blip. I have changed servo, it appears the leak is not there. Could you point me in some sort of direction as to what to check or look at. Could it be in the VB? Do have another VB but have not changed it out. Thanks
if it drops that much there is a leak somewhere.check and retorque valve body,accumulator housing etc.at wot on a 1/2 a drop more than 40 actually 25 indicates a proble.at the drop what does the engine do?the normal drop is due to another circuit puling oil from the source reducing psi until the extra element is applied.

What does the eng. do? I assume you want to know if it revs or trans flares--neither---Eng. does nothing unusual. The shift happens as it should and is quick--does not slip--just not as firm as under 150 psi. Once the shift happens the pressure goes back to whatever it was before the shift. I had the trans out to check the band---just as when installed--no burn marks--I am afraid it won't live like that. Would it be worth while to switch VB. Thanks for your time.