Sliding side door very hard to slide open

[larch303]

This past year the sliding side door on my 1990 Astro has become hard to slide open. No problem with the locks or handle, its having it slide open.
Its definitely harder in the summer, but in winter its almost impossible now its colder. Its very hard to slide it open.
I tried lubing with WD40 in Nov, but it made hardly any difference.
Am wondering if something needs replacing?
Any suggestions? or is it just a matter of lubing better.
Thanks

[old_master]

Make sure all of the rollers are round and turn freely. Thoroughly clean the rollers and tracks, carb cleaner works well for this. Lube rollers and tracks with white lithium, not WD40. Lube them at each oil change and you'll never have a problem again.

[ericn1300]

there is a slot on the outside rear of the door about halfway up where the rear roller runs on the outside towards the rear that's often ovelooked. since it's exposed to the elements it gums up pretty fast. i got mine working good again by spraying inside the track with foaming liquid wrench first to clean the track and free up the roller, worked the door back and forth a few times, then applied white lithium grease with a Qtip to keep it moving freely. the front top and bottom rollers and traks are pretty easy to find

I don't know how old Old Master is but his advice is right on. my 1950 GMC manual specificaly recommends "oiling the door and hood hinges, a routine maintenance that service stations often overlook"

[Blue Bowtie]

I'll third that opinion. Cleaning is just as important as lubricating. Further, WD40 is not a lubricant, but is a water-displacing rust preventive. When it was first formulated, it was never intended to be a lubricant, but like the common screwdriver, has been abused into the role of a "do everything" liquid. Tracks get Lubriplate or a similar lithium grease, hinges and latches get 20W oil, lock cylinders get dry graphite. It's right there in the manual.

Once you get it cleaned and lightly lubricated, it will be easier to see any distortion or alignment problems with any of the three roller sets - Don't forget the upper, even thought the outer and lower tracks seem to gather the most debris.

[larch303]

Well that should help! I don't have a garage, so I may have to wait until the end of the winter to have a go at this.
I suspect the rollers are bunged up and now its cold it gets that much thicker and hence very hard to slide.
Will see if I can borrow some heated indoor space to have a go at this!
thanks for all the advice here!