When I did them on a gen 2, i used rail blocks under the counterweights so when I used falls to lift the car it was exactly where I wanted it to reach shackles and get on/off top.

Go by Walmart, get thick sewing needles, threader, and go to fishing aisle and get 65 pound test braided fishing line.

I did one belt at a time, drill 1/16" holes across the end 10 or so, a 1/8"-1/4" in from end. Butt ends of belts together or up to maybe a 1/8" gap, now sew the ends together with the braided fishing line. Now you can use the old belt to pull through the new belt with zero worries of scarring up or damaging the sheaves.

Do NOT use a bracket for hanging a car. It can get you hurt or killed. Those brackets are for preventing car movement when its still roped up etc, like your adjusting a brake.

Adjusting tensions, im not sure on the 3300s If you can see Individual load cell info or not. The gen 2s all shackles are on springs. I adjusted till even tension compressed springs evenly. Felt by hand, was good as far as I can tell. Normally I would use a real tension gauge on ropes to verify each rope one at a time. Just another fun thing you can't do with belts.

The Otis belts have pretty much zero constructional stretch, I'd imagine the schindlers are the same. Verify before roping, if you stay up closer to your max cwt run by you shouldn't have to ever shorten them

When you lifted car, what did you connect the chain fall to? Bottom of car?

On a gen 2 there's hoisting points on top of sling. It was underslung but they extended the sling stile up past cartop and put a big hole in it for a clevis. I am unfamiliar with the 3300s but they have to have somewhere to hoist from

EElevator when you do the Otis belt Tensioning you can plug the blue tool in and read tension. you want to get them within 10% of each other is what i was told. Also you have to run the hoistway with the car after making adjustments. As for marring the belts to pull through on the small belts I only do 2 holes big belts 4 holes on the end of each belt like you do and I use 2 wraps of seizing wire instead of fishing line. Once I'm done with the seizing wire I put it on the handrail and give it a few taps with a hammer and Then I use the filament stranded packing tape and run a 6" piece on the top and bottom of the belts splitting 3" on each belt.

The Schindler belts also have a twist in them so don't for get to consider that when re belting

I do 10% max from most to least tension suspension member too. What menu numbers do you view the individual load cell values on?

The Otis documents say to use seizing wire like you do, but to wrap it with tape afterwards, they are very worried about scratching up/damaging the sheave surfaces. I use braided line because I don't have to worry about it damaging the sheave and its much more flexible, making it easier to pull through the tight bends with these small diameter sheaves.

I believe it's M-2-1-7. It's been a long time since I've done it.

Use rail blocks at the top of the rails with appropriate chain falls attached. Remove oilers from each car top bracket (these brackets are designed for hanging car, just do 1 belt at a time and it wont be an issue) and install long reach clevis to each side. Land counterweight at a height that is comfortable for car top work. Pick car just enough to create slack on the belts. Drill small holes in ends of old and new belts and use seizing wire to "marriage" the belts (This is what EElevator and Rooster mentioned above) I also use wide gorilla tape about 8" above to 8 " below the marriage and keep it from coming apart.
Be very careful when pulling belts around so as to not get too much slack down at the counterweight. thats where it will get hung up and come apart of its gonna happen.
I've done alot of these over the past few years, so if you have any other questions, be sure let me know.
After the belting process is completed, the new belt data must be programmed into the LDU.

Can you program the new belt data from the on board cpu ?

I have a customer that is having a few 3300s installed. They were sold as non proprietary. I am suppose to put together a list of documents and service tools necessary to service these things for the GC on the job to pass along to Schindler. Does anyone have any suggestions

As far as the belt programming, yes that is done thru the on screen menu.
The non-proprietary thing is a load of crap. It's 100% proprietary equipment. Unless you work for Schindler, you won't have access to manuals or tools for the most part. We all know the other companies reverse engineer the controls just as Schindler does to them.
Even with me working for Schindler, its hard for me to navigate the controllers in these units because I don't do it on a regular basis.

Thanks for all the help. We ended up doing one at a time and using the fishing string with a wrap of electrical tape to keep line from getting snagged. The mcp showed to tension by getting the springs within 1mm of each other. Reset the belt info in controller and was up and running. The mcp referenced a temporary crosshead that could be bolted in to the plates on top of car and the using single beam clamp and hoist to pick car up. I didn’t hang car I tightened up middle shackle to carry the weight then changed outside belts one at time then lowered middle shackle to put weight on outside 2 Changed middle and tensioned.

Nice job!
In the beginning, we were told to tighten one belt to create slack for the others like you did. I started hanging the car just a bit after doing several the original way because I noticed that we were starting to ruin the threads on the shackles by overtightening them and never had replaclacements on hand. By lifting the car slightly, I don't put the strain on that cheap all thread used for the shackles.
The way I do it now, I don't even loosen the springs or nuts.
I pull the cotter and take the wedge itself off, remove the old belt, then screw the wedge back on and reinstall the cotter pin.
Always looking for a better and more efficient ways.