I had many problems with al4 transmission , so i decided to overhaul it . After overhaul only one issue remained with the transmission , losing of first gear when the box is heated up . To pinpoint the problem , the box is unable to engage E1 clutch . And its due to the heat and loose of viscosity of the oil . Exactly at the top temperature of opening the oil cooler solenoid .
One approach was to check the pressure at idle , from cold to hot . It confirmed the loss of presure by 1 bar , so i decided to tighten the main pressure regulator cap , which located beside main pressure limiter . By tightening it 1.5 turn , oil pressure came back to normal range and abit higher than normal (2.7 bar at idle) . So i had kick engaging first and second gear at cold and no problem at Higher temperature . But after few weeks again the problem appeared again .
Since hydraulic valve block during overhaul just got cleaned , i can say its defenatly something wrong with valve block or type of the oil , because al4 dpo transmissions , got upgraded oil . First fluid used by PSA had Higher viscosity , but new oil type has slightly less viscosity . To solve this problem , i will change the main pressure solenoid , remove half a turn tightness on main pressure regulator cap . If problem didn't fixed , i will monitor oil temperature and engine temperature and functionality of one of two progression valves which i think responsible for oil cooler circulation . If i found irregularities with the valve i will change both progression valves (unbelievably there is absolutely no info on functionality of progression valves even in PSA rebuild manual ) . If all didn't help , i will do something i generally don't like , but it might help , i will add viscosity enhancer .