Dodge RamCharger Central banner

Soft pedal fixed...now i cant get rid of the brake/abs light

12K views 52 replies 14 participants last post by  Slednx440 
#1 ·
My 90 RC has been losing brake pressure while sitting at stoplights. It feels like the brake pressure bleeds off while I'm sitting there and then the truck starts creeping forward. It has new front brakes and the rear brakes are good. The fluid is topped off. Is it the master cylinder?
 
#2 ·
If the brake pedal is "falling away" its a leak.  Most likely is the master cylinder.  Sometimes the wheel cylinders leak in the rear as well.

Be sure to get a new MC, not a used. 
 
#3 ·
Ditto, you have a leak somewhere.  Look for fluid at the bottom of the drum backing plates, on the bottom of the calipers, the frame around the fuel tank, the hoses that drop to the axles and at the front knuckles.  If it's not leaking in those places, it's most likely leaking out the back of the master cylinder.  You can take the master cylinder loose with the lines attached if you are careful to see if there is fluid on the back of the piston.
 
#5 ·
For the pedal to go to the floor, it has to be the master, or a leak on both the front, and rear systems.
 
#8 ·
Usually a bad booster causes a hard pedal- no vacuum assist. Easy to test though.  Regardless, keep your OEM booster unless you are sure its trash.  The rebuilt ones are absolute junk.  Expensive junk.  The OEM ones are sought after especially the 3/4 ton and up ones- every month this comes up on the diesel sites.
 
#9 ·
The brake booster is easy to test. with the engine off, pump the brakes until they get hard to push, then with your foot putting medium effort on the pedal, start the engine. If you feel the pedal go down, and require less effort, then the booster is working. A booster going bad, will either go out completely, causing the brakes to be very hard to apply, or intermittently causing the brakes hard to push at random times.
 
#10 ·
The good news, I changed the master cylinder and it fixed it. The bad news, I bled the brakes today and now I have a brake light. I didn't remove any brake parts besides the master cylinder and the fluid is topped off. Any ideas?
 
#11 ·
miller6323 said:
The good news, I changed the master cylinder and it fixed it. The bad news, I bled the brakes today and now I have a brake light. I didn't remove any brake parts besides the master cylinder and the fluid is topped off. Any ideas?
Only two things gives the brake lights - parking brake on, and the proportioning/distribution valve slid while you were bleeding the brakes.
 
#13 ·
miller6323 said:
Parking brake is off so that limits it. Never heard of a prop/distribution valve...how do I fix it?
re-bleed the brakes. Sometimes the switch will stick on these old trucks. Then you need to pick a side, and have someone hold on the brake pedal, and slowly open the bleeder to see if the light will go out. If not, try the other side (front/ rear that is, not left/ right).
 
#14 ·
When you have a fluid leak, the proportioning valve has a piston that slides over due to the pressure difference of one side of the system to the other.  You'll find it under the frame, somewhere near the driver's seat. You can try stepping hard on the brake pedal to recenter it, may need to bleed the side (front vs rear) opposite of the direction the piston went, or you have to open and recenter it manually with something like an awl.
 
#16 ·
Not really.  If the valve is tripped, it means it has shut off flow to either the front or rear brakes and that's all you have.  A panic stop will usually result in the working brakes locking up, greatly increased stopping distance and a high potential for loss of control and/or collision.
 
#17 ·
The two side are separated. There is nothing that will shut off flow to either side, under any circumstances. The valves that also operate as a proportioning valve, will bypass that part if the front system fails.
 
#18 ·
Finally got around to bleeding the brakes today and it did almost nothing. I bled the back first and they seemed to have plenty of pressure. The front were the same way. When I drive it and slam on the brakes only the front lock up. Could it maybe be something in the drum causing the light? Now the abs light is on as well as the brake light. I've replaced the front brakes but haven't done the back ones yet.
 
#19 ·
DODGEBOYS said:
if your NOT looseing fluid the the master is bad
You can loose fluid and it still be the master, leaks into the booster and is consumed by the engine
 
#21 ·
I'm more of a diesel guy but perhaps did you crack or cause a vacuum line to leak?  Low vacuum on a diesel can cause those lights
 
#22 ·
Not that I know of. It's all metal lines around the master cylinder and all I did was open valves on the bottom to bleed them. The brake light didn't come on till a few days after I did the work and the abs a few days after that.
 
#23 ·
oem repair manual in bold letters  " THE VALVE SHOULD NOT BE DISSASEMBLED TO RESET THE PISTON " That said , have someone operate the pedal while you look at the valve inside frame rail under driver foot area . Not the little nail like thing sticking out , as the pedal is depressed it should move out slightly . DO NOT attempt to push it in . Movement is showing operation of hold off portion of valve . Adjust the rear shoes , top off fluid , step hard on brake pedal to RESET the light . DID you hold up on parking brake release and the actual p/brake pedal while checking that light? The last little return of that p/brake pedal shuts of the light if the p/brake was the cause of it being on . When you bled the brakes did you get a good flow from both front and rear systems ? If one end ( front or rear ) had a weak flow , the valve has shifted .  That valve is meant to shuttle if you blow a line limiting the loss of fluid to the blown 1/2 of the system "protecting" the remaining 1/2 so you have some
  ( either front or rear ) brakes but that's all .  The nail head pin can be held OUT gently while bleeding , oem has a tool , it is just a flat spring steel to hold it open , don't use vice grips . . Adjust , check and re-bleed system .Don't feel bad as far as I have seen yours is a common problem. Fix it before you drive it .  P/s so ya know  a dual master can be bad and have NO external leak .  :)
 
#24 ·
When I initially bled the brakes after I changed the master I got a really weak flow from the rear brakes. Now... when I bled them it had a strong flow to all 4 brakes. Now that I think about it I'm not sure the back brakes ever really worked. Anytime I've had to slam the brakes the tires would squeal and slide but I thought that was just am older truck with no abs. The previous owners didn't take good care of it so who knows when the back brakes were changed last. Could it be something in the drum? I'll look at the prop valve tonight.
 
#26 ·
If you have rear wheel ABS, there is a module above the rear axle, on the drivers side frame rail that also needs bled.

That also explains why the rear wheels also lock up.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top