Before you try what Robert suggested, take a look at your rear brake cans. There are two different types of parking brakes used on buses, DD3 and Spring. Spring brakes were not an option on 4106s, but DD3s became optional long about mid-year of 1963 production. A previous owner may have installed either type, so you need to determine what you've got, because the release procedure is different between the two types!
How can you tell what you've got?
Simple - look at the rear brake cans. How many air lines do you have coming off the cans - 2 or 3?
If two, you have spring brakes.
If three, you have DD3s.Release Procedure - Spring Brakes
1. Build coach air pressure up to governor cut-out (approx 120 psi).
2. Lightly cover service brake with foot - do not apply, just cover.
3. Push in on parking brake knob until it seats. Wait 3 -5 seconds.
4. Put coach in gear and away you should go.
Coach should roll after #3. If not, then pull knob back out to reset brakes and repeat steps 1 - 3. If coach still doesn't roll when put in gear, something is wrong and needs to be looked at. Make sure coach wheels are properly chocked, preferably front and rear, before doing any investigative work.Release Procedure - DD3 Brakes
1. Build coach air pressure to governor cut-out (approx. 120 psi).
2. Lightly cover brake pedal - do not apply, simply cover.
3. Push in parking brake knob to release parking brakes.
4. AFTER pushing in knob, apply a FULL service brake application (FLOOR IT) and hold for 3 - 5 seconds.
5. Release service brakes, coach should roll when put into gear.
6. If coach doesn't roll, lightly cover service brake again (do NOT apply - just a light touch).
7. Pull knob to reset parking brake.
8. Repeat steps 1 - 5.
As stated above with spring brakes, if the coach doesn't roll after steps 1 - 5 are repeated, there may be a problem that needs investigation.Setting Spring Brakes for Parking
1. Once parked, lightly cover service brake sufficiently enough to just keep coach from rolling.
2. Pull parking brake knob to set brakes.
3. Release service brake - coach should not move.
4. If coach will move with parking brake set, have brakes looked at immediately!Setting DD3 Brakes for Parking
Procedure is basically the same as for Spring Brakes, but the critical point
here is that you LIGHTLY hold the coach with the service brakes before pulling the knob to set the parking brake. You should ONLY apply enough service brake to keep the coach from rolling, no more. The harder you have the service brakes applied, the more difficult it will be to release the DD3s.
FWIW & HTH. . .