Roll out

Mark, do you have any idea on most probable culprits for sudden hydraulic pressure drop during roll out? Does hydraulic pressure drop when control surfaces are moving or antiskid controls the brake?

After touchdown the only hydraulic systems that should be in use are ground spoilers and brakes. (I don't think 737-300's have hydraulic thrust reversers).

You have one electric and one engine driven pump for each system. That should be plenty of muscle for brakes and spoilers.

You could have a bypassing spoiler or brake actuator.

Measure brake temp with a laser gun . Are they equal temps? Raise the spoilers, is there one not coming up?

The crews shouldn't be pulling up flaps/slats until on taxiway. Make sure they are not.

Would you explain thoroughly what do you mean by "bypassing brake actuator" or "bypassing spoiler"?

Hydraulic fluid is going directly from the "in" port to the "out" port and it's not making the actuator go in/out or up/down (in the case of brakes.... not making it to the "out" port to compress the brakes.

Ruptured internal seals or physically broken pistons/rods.

A bypassing spoiler can be seen with the laser temp tester. The unit will be hotter than the rest. The output line will also.