Brake System and Combination/Proportioning Valve Diagnosis

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

coachdtierney54

Full Access Member
Joined
Mar 19, 2017
Posts
106
Reaction score
14
Location
US
First Name
Dan
Truck Year
1985
Truck Model
C30
Engine Size
454
A trailer brake controller. If the larger is for the front, then why did I fill that one when bleeding the rear brakes?

Sent from my XT1710-02 using Tapatalk
 

87V30

Junior Member
Joined
Jul 24, 2018
Posts
4
Reaction score
0
Location
USA
First Name
Kevin
Truck Year
1987
Truck Model
V30
Engine Size
5.7
@coachdtierney54 Is that a tee fitting coming out of your forward most port on your MC? On my hydroboost setup the front (smaller) MC reservoir is for the rear brake system like Blue Ox said.
 

coachdtierney54

Full Access Member
Joined
Mar 19, 2017
Posts
106
Reaction score
14
Location
US
First Name
Dan
Truck Year
1985
Truck Model
C30
Engine Size
454
Yes that leads into the cab and connects to trailer brake controller.

Sent from my XT1710-02 using Tapatalk
 

coachdtierney54

Full Access Member
Joined
Mar 19, 2017
Posts
106
Reaction score
14
Location
US
First Name
Dan
Truck Year
1985
Truck Model
C30
Engine Size
454
I have no clue what is going on with it
You must be registered for see images attach


Sent from my XT1710-02 using Tapatalk
 

Blue Ox

Turning Diesel Fuel Into Fun
Joined
Mar 27, 2018
Posts
4,831
Reaction score
10,633
Location
LI-NY
First Name
Derek
Truck Year
MCMLXXXV
Truck Model
K20HD
Engine Size
6.2L
Okay, so a brake controller should be a switch. I don't think it has any bearing on the truck brakes unless it is leaking.

On my truck the larger reservoir is in the front, but the smaller one is still for the rear brakes. Calipers have much larger displacement and need a bigger reservoir.
 

coachdtierney54

Full Access Member
Joined
Mar 19, 2017
Posts
106
Reaction score
14
Location
US
First Name
Dan
Truck Year
1985
Truck Model
C30
Engine Size
454
Found the leak. What is this?
You must be registered for see images attach
You must be registered for see images attach


Sent from my XT1710-02 using Tapatalk
 

Blue Ox

Turning Diesel Fuel Into Fun
Joined
Mar 27, 2018
Posts
4,831
Reaction score
10,633
Location
LI-NY
First Name
Derek
Truck Year
MCMLXXXV
Truck Model
K20HD
Engine Size
6.2L
Load sensing proportioning valve. Good luck finding a replacement. Most folks, and apparently GM say to eliminate it. But I had severe rear lockup problems on my 'burb without that valve. YMMV. Although I would replace that rotten lower pipe before I condemned the valve.
 

coachdtierney54

Full Access Member
Joined
Mar 19, 2017
Posts
106
Reaction score
14
Location
US
First Name
Dan
Truck Year
1985
Truck Model
C30
Engine Size
454
Lot of rust for a southern truck... How did you bypass yours? I thought about getting an adjustable valve from Jegs.
You must be registered for see images attach


Sent from my XT1710-02 using Tapatalk
 

Wes P

Junior Member
Joined
Dec 5, 2019
Posts
28
Reaction score
17
Location
Texas
First Name
Wes
Truck Year
1985
Truck Model
C20
Engine Size
406
Posting in all LSPV-related threads for reference:

LSPV delete on '85 C20 increased braking performance.

Basic procedure:
- Remove valve, post-LSPV hard line, hose, axle bracket
- Measure, measure again, cut, drill, tap, weld stop nut on bracket (or add a screw)
- Release axle hard line from clips
- Install bracket, brake hose (180 flip), zip ties
- Bleed brakes

Parts: 2 zip ties.
Materials: brake fluid
Time: 4 hours, leisurely, without experience, being careful.
Note: Be gentle with hard lines. Plug the hard line after disconnecting. Don't empty the master cylinder.

You must be registered for see images attach
 

Forum statistics

Threads
41,855
Posts
903,581
Members
33,368
Latest member
TheDuke
Top