Hi,

I have some problems with my breaks in my Impala 1970, all drums.
The wheels dont lock, even while break very hard, and I have a bad pressure. Afer some miles the breaks are becoming better, but they are still bad.
Meanwhile I have changed the master cylinder and have checked all wheel cylinder, none is leaking, all air is removed.

I heard that some cars have a proportion valve. What is it for?

I attached a pic. Is this the valve?
http://i303.photobucket.com/albums/nn132/Impala-1970/k-P1050328.jpg
Could this cause my problems?
I could nor find it at rockauto or summit. Where can I buy it?

Thanks
Tom

Yes. That is the DISTRIBUTION BLOCK. You can get one here..ss396.com (http://www.ss396.com/mm5/merchant.mvc?Screen=PROD&Store_Code=chevellecamino&Product_Code=FPR-107&Category_Code=VALVES)

Could this be my problem? How could I check it?

What is the sense of it?

It splits the pressure front to back. Then if it detects low pressure for a leak. It will send all the pressure to the end (front or back) that is still working. Its a safety thing.
Is the Brake warning light on the dash lit?? If not, It's probably not the distribution block..

No, the warning light on the dash does not light