There could be couple of reasons for this. First of all, it is possible to have air in the brake lines that goes to the rear brakes, or you could have a leak somewhere.
When bleed the brake do it in this sequence:
1. Right rear
2. Left front
3. Left rear
4. Right front
Here is a helpful video of properly bleed the brake system:
One of the most common leaking place is the rear wheel cylinder. Remove the brake drums to inspect the rear wheels.
I have attached diagrams for your reference.
Please let me know of any questions.
Images (Click to enlarge)
Saturday, October 9th, 2021 AT 11:21 AM