I would start troubleshooting in the Down circuit.

^ What E-man said. Check your lower final limit and even the high-speed cut-out switch. Will it run down on inspection from the terminals on the controller?

put your helper on the car top. have him hold in the down and safe button. meanwhile you are in the MR with your meter on DCV. put the black lead on HL1, put the red lead on the down inspection button, etc etc etc till you see voltage.

21 UCLS is a geared unit with a 6850DK Selector(No Advancer Panel). To run on Inspection you need DX-HX which picks D and H. If the relays are picking you have another deeper problem in the Generator Leveling Field Circuit. If they are not picking when you press safe button and Down check the bottom limits on 6850DK selector. The bottom most limit controls DX. The limit above will drop FE. These limits on the DK Selector are the NTS System for the Unit. The switches top and bottom mounted in the Hoistway which causes an Emergency Stop if FE is still in when it is hit at either Terminal is the ETS System. Those selector limits are weak spots and get covered with oil or dirt. My advice is to check them first.

As per above but I would also ask if the lift runs on normal in the down direction? If so then you would think the controller flexes, leads and any generator windings are ok. If this is so then look at supply coming from the car ie buttons and travelling cables. Get your mate to try it while your in the MR and test for it. If the car does not run on normal then its most likely the reverse ie a flex or lead issue.

elevator does run down on automatic but a little slow on leveling H , D , and DM all pull in and the same from car top insp. and machine room insp.

So if you can place the car on inspection from the controller, you can test to see what isn't working. Does this work and the top of car not? Is ins1 and 2 dropping out? Are you getting 125v to the inspection buttons? Are you getting 125v to the main up or down main reverser circuits from the inspection buttons? If you say that indeed H D DM (DX?) in then you will have to check the volts going to the levelling field circuit.

None,

Is this Original equipment? Any modification?

On normal operation!
When an up call is placed. When a down call is placed.
Does the elevator step up in speed correctly?
Does it step down in speed correctly?
How many speed relays are there?
Does it stop at the floor correctly?
What are your motor voltage and amp readings?
If it is a 6850 selector does the carriage lift correctly?

None, are you certified elevator mechanic? If you are and you have prints, coming on this forum for help with a car that will run on inspect one way but not the other is kinda making me wonder...

i think he is saying that all the direction relays are coming in when he inspects down, but the car does not move, i.e. stalled. is this correct? if it is then there is trouble in the generator field circuit, or a compounding problem.

Yes everything is coming in for it to run down on insp. thanks i will check more into the generator field circuit

i would suspect a compounding problem, make sure your SF relay is working correctly. if you are getting the same voltage across the generator leveling field in the up and down direction, then you will need to adjust the bedspring for more series field, or adjust the taps in the generator.

It certainly could be compounding. Does this happen at high and low points in the shaft indicating a counterweight issue? I would as you say test your levelling field volts first.

look at the section of the print that shows up and down contacts effecting generator fields. Before I call it compounding are there any contacts failing or are you getting voltage to the generator shunt field and getting a dc output from the generator.
I wish I could see the drawings, I don't remember the details off the top of my head. I always like to work with drawings in front of me.