PS You probably knoe all this but.- The extra reverse pressure is for engaging the reverse brake band.

They are pretty high in the region of 250PSI for neutral to 300 odd PSI region for reverse. I have the pressure settings in PSI somewhere if you need them. ''The get yer home feature if the hydraulic pressure fails''.The hydraulic servo cylinder which disengages the forward clutch cone is located on the back of the box,near the prop drive flange or reduction box and is held in the gearbox body by i think 3 bolts.Once the piston in this has pushed out and disengaged forward gear when neutral is selected it remains under pressure holding the forward clutch cone out of contact with its mate while in neutral and also while reverse is selected and used.The pressure is only released when forward gear is selected. there is no pressure required to obtain forward gear. Hydraulic pressure is only used to obtain neutral and reverse. I doubt that unless the pressure is seriously too high. So,could it be that the pressure is too high? If the pressure is set too low,the ahead will be unable to disengage? The astern function is actuated by the 'blow-by' from the pressure control valve,if there is insufficient flow as a result of the release valve being set to high,astern wont engage? The suggestion i got was that the shims had possibly been increased already to increase the pressure for the ahead gear to release. Adjustments to this should be done with a pressure gauge screwed into the plug port on the boxes top plate,but for the small increase in pressure that you need just a calculated guess would surfice.Probably a weak relief valve spring,but add shims to increase pressure.There are O ring seals on the F&R lever unit behind which the relief valve,spring and shims are so go gently. The hydraulic pressure is adjusted by adding or deducting shims from behind the relief valve spring which is situated behind the forward and reverse lever unit on the port side of the box. Looks like the problem may be more complex than it first appeared to be. The reverse function engages sweetly sometimes,on some occassions it fails to engage without lots of revs and a few seconds delay.Ī kind and knowledgable chap who repairs and restores listers suggested altering the hydraulic pressure by shim adjustment. Brake band adjustment is correct,nipped down and 3 full turns back.ĭrained the oil and refilled with EP 80/90.

Lister lh 150 gearbox manual bmw