I've sprayed wheel bearing/axle with WD 40. I now feel I need to add some form of grease (I don't want to remove the bearings-just try and work some grease in there somehow). That's when I spotted my graphite powder and thought that would probably work its way in with a few spins. (Giving an oldish pram a quick makeover before gifting it to my friend). My question is, do I need to try and remove the WD 40 before sprinkling the graphite. Don't want to clag it up. I have some good wheel bearing grease too, so whats your suggestion?
Simple answer: don't worry, there isn't any adverse reaction between the two.
Long answer turns into a quasi-religious debate, which is mostly irrelevant to your application.
Locksmiths have used a very light dusting of powdered graphite as a lubricant for a very long time. This works because graphite is both soft and shears nicely at the molecular level to form a slippery coating on the metal surfaces, which remains slippery when wet.
Unfortunately many people assume that if one light puff is good, more must be better.... and if you pile enough rock dust In there, you get mud -- slippery mud, but it can still gum up the mechanism. And since locks -- unlike your wheel hubs! -- can be sensitive to changes on the order of a thousandth of an inch, some locksmiths hate graphite on principle.
WD40 has its own pro- and anti- sects. It definitely does make mechanisms run more smoothly. But it isn't clear how much of that is because it gets things unstuck by displacing water )which is where the name comes from) and cleaning the parts, and how much it actually acts as a lubricant. This matters because a lube keeps parts from grinding on each other and keeps them running well over the longer run. However, a wet lube can also accumulate dust and turn into mud.
The one thing all these camps agree on is that the "silicone microsphere" lubes seem to be a bit better than either wd-40 or graphite for small parts. There are several brands; these basically go on wet but dry out to leave a dusting of tiny "ball bearings" -- and because they do have a liquid carrier, they're self cleaning so you can't make a mess by over applying them.
Having said all that ... for a more reasonably sized object like a wheel bearing, most lubricants will do a fine job, up to and including the proverbial axle grease.