How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Tim's Auto Repair Your Own Question
Tim's Auto Repair
Tim's Auto Repair, mechanic
Category: Chevy
Satisfied Customers: 15762
Experience:  Have owned a repair shop for 25 yrs.
14541291
Type Your Chevy Question Here...
Tim's Auto Repair is online now
A new question is answered every 9 seconds

I replaced the right rear wheel cylinder and brake line and

Customer Question

I replaced the right rear wheel cylinder and brake line and vacuum bled both rears and now i have no pressure to the rear brakes
JA: Have you checked the fluid? How old are the brakes?
Customer: Fluid level is over half, shoes are over 50% left and front were just done two months ago
JA: What is the model of your '50 Chevy?
Customer: Its a 1997
JA: Are you fixing your vehicle yourself? What have you tried so far?
Customer: Yes fixing it myself, and havent tried anything yet
JA: Anything else you want the mechanic to know before I connect you?
Customer: The red park/brake light is on also and wasnt before
Submitted: 6 months ago.
Category: Chevy
Expert:  david craig replied 6 months ago.

Hi Im David, when you vac bled the rear brakes did you get fluid out?

Customer: replied 6 months ago.
got fluid out of both wheel cylinders
Expert:  david craig replied 6 months ago.

did you also bleed the fronts?

Customer: replied 6 months ago.
No
Expert:  david craig replied 6 months ago.

do you have a dual master cylinder or a single bowl?

Customer: replied 6 months ago.
Single reservoir, divider about 1/3 inside reservoir, two brake lines coming out of master into abs module
Expert:  david craig replied 6 months ago.

ok. bleed the brakes again. rr rl fr fl. do it with the engine running.. if there is still no pressure to the rear brakes, then adjust the shoes up with the thumbwheel and see if they improve.

Customer: replied 6 months ago.
Rear shoes are adjusted as tight as possible, and if it makes a difference with brake pedal pressed front brakes work correctly cannot turn Tire but back can be turned with ease
Expert:  david craig replied 6 months ago.

4 wheel abs?

Expert:  david craig replied 6 months ago.

if it was me, i would bleed them the conventional way with a second person. engine running. bleed those suckers 4 or 5 times if you have to. i have had to bleed a few vehicles brakes 8 or 9 times... doesnt make sense, but it worked.......

Customer: replied 6 months ago.
3 channel to my knowledge, 3 lines come out of abs module one goes to back, two go to the fronts
Expert:  david craig replied 6 months ago.

oh yea, thats right. the rear runs off the axle for both. if bleeding them conventionally the way i described doesnt help, you will probably need to take it to a shop and have the abs module bled. the system is bled with a diagnostic scan tool with abs module bleeding capability.

Customer: replied 6 months ago.
just to be certain bleed rr then lr then rf then lf with engine running. Then restart at rr and repeat 4 or 5 times?
Expert:  david craig replied 6 months ago.

yes, or until you get pressure

Expert:  david craig replied 6 months ago.

hows it going?

Customer: replied 6 months ago.
Finally got a chance to bleed brakes, couldn't get any fluid out of the rr wheel cylinder no matter how many times pedal was pumped. I suspected the master cylinder was bypassing before but now I know it is. So I'm going to replace it and go from there unless you think it could be something else?
Expert:  david craig replied 6 months ago.
The master should do it
Customer: replied 6 months ago.
Replaced master and bled entire system till no air coming out of bleeders, have hard pedal with truck off. When Appling brake pedal, pedal does not fall by itself but I can continue to push pedal further through travel is this normal?
I started truck and red brake/park light went out, but pedal is not firm travels through stroke with little resistance. I know this is not normal but don't know what to do next
Customer: replied 6 months ago.
Why is this closed? My questions haven't been answered, and I'm still without brakes and a truck.
Expert:  david craig replied 6 months ago.

BECAUSE IT TIMED OUT. I DIDNT CLOSE IT. THE SITE DID

Expert:  david craig replied 6 months ago.

With the pedal pumped up with vehicle shut off start the vehicle. does the pedal sink?

Expert:  david craig replied 6 months ago.

hello?

Customer: replied 6 months ago.
Hi, I can't always respond right away cause truck is at my work and I don't have access after business hrs. So I can only test stuff during my 8 to 5 and only if I have time between my bookings.But just tried what you asked and with pedal pumped up, no pressure on brake pedal, and truck running, pedal doesn't move.
With pedal pumped up, truck running, and brakes applied pedal fades until it makes manual contact with Master and your using manual brakes.
Expert:  david craig replied 6 months ago.

pump the pedal up up with engine off. keep your foot on the pedal with pressure. start the vehicle and pedal should sink.

Customer: replied 6 months ago.
Did that and yes it sinks down till it brake rod contacts master cylinder plunger
Expert:  david craig replied 6 months ago.

how much travel would you say?

Customer: replied 6 months ago.
Over 3/4 of the entire travel. It stops falling once you've run out of booster travel and are pushing directly on the master cylinder plunger
Expert:  david craig replied 6 months ago.

that sounds like a booster to me

Expert:  david craig replied 6 months ago.

ckeck the check valve that goes into the booster. make sure its seated all the way and that you cant blow through it both ways.

Customer: replied 6 months ago.
Removed check valve from booster could here vacuum releasing from booster so in theory booster diaphragm should be intact and working correctly, check valve is working as it should as I can suck on hose side, but not blow and can blow on booster side but not suck.
Expert:  david craig replied 6 months ago.

ok....let me think

Expert:  david craig replied 6 months ago.

do the back wheels still turn with the brakes applied?

Customer: replied 6 months ago.
No, brakes hold all tires from spinning
Expert:  david craig replied 6 months ago.

what model chevy and size engine?

Customer: replied 6 months ago.
1997 Chevrolet Silverado extended cab short box 5.7l vortec
Expert:  david craig replied 6 months ago.

ok. im going to see if it has an accumulator or proportioning valve. gimme a sec

Customer: replied 6 months ago.
Any luck?
Expert:  david craig replied 6 months ago.

i got really busy at the shop.. sorry. ill get on that now.

Expert:  david craig replied 6 months ago.

its a combination brake proportioning/modulator assembly. you may need to have the system bled by the dealer with a scan tool.

Customer: replied 6 months ago.
Did the abs bleed procedure 4 times already made no difference.
Expert:  david craig replied 6 months ago.

then all i can tell you is adjust the back brakes up a little more. if that dont help, theres nothing left other than to replace that unit

Expert:  david craig replied 6 months ago.

im going to opt out and seei f anyone else has any ideas.

Expert:  Tim's Auto Repair replied 6 months ago.

Hi, My name is ***** ***** for the delay.

I will do my best to assist you.

did you bleed the brakes using a scanner to operate the ABS solenoid?

Expert:  Tim's Auto Repair replied 6 months ago.

first,,be sure the rear brke shoes are adjusted up against the rear hubs.

then use a scan tool to bleed the abs system

Expert:  Tim's Auto Repair replied 6 months ago.

PLEASE COPY AND PASTE the link below to your browser, I have uploaded more info on this there please copy and paste the link below to your main browser[INTERNET EXPLORER or FIREFOX]

.

https://www.dropbox.com/s/co7wohhzj6zygls/1015-chevy-abs-ANTILOCK%20BRAKE%20SYSTEM.doc?dl=0

.

if the link doesn’t work that way, try it this way

thanks

.

www.dropbox.com/s/co7wohhzj6zygls/1015-chevy-abs-ANTILOCK%20BRAKE%20SYSTEM.doc?dl=0

.

Customer: replied 6 months ago.
Rear brakes are adjusted as tight as possible to still allow drums to be slid on and off.Scanner was used to bleed the abs which we did 4 times.And both of your links won't open.unless I install an app
Expert:  Tim's Auto Repair replied 6 months ago.

you shouldnt need to install an app..pate the link into your main browser,,it should open up

Expert:  Tim's Auto Repair replied 6 months ago.

if you have already tried to bleed with a scanner and you still have no pressure,,

i would think your problem here is the ABS module itself..

there is nothing else left

Customer: replied 6 months ago.
Got the link to open.And I wouldn't say it's a lack of pressure. Currently with truck not running pedal will pump up hard and stay hard and hold all wheels from turning.
With truck running pedal with travel through its stroke until brake rod makes mechanical contact with Master Cylinder plunger and you then have manual brakes, it's like there is no power assist on the brakes. But I have checked for vacuum on the hose that goes to the boosters vacuum is present. Checked the check valve into the booster it is working correctly. Also removed check valve out of booster and heard strong vacuum escaping. So I left the vacuum hose unattached from booster, but plugged to not have vacuum leak and started the truck brake pedal pumped up hard and stayed hard almost holding tires from spinning couldn't overcome power of engine. Only reason I bring it up is cause if the abs is bypassing or leaking off internally shouldn't it do it every time the truck in running? Or only with vacuum assist cause it's a high pressure internal leak?
Expert:  Tim's Auto Repair replied 6 months ago.

still sounds as if the rear shoes are too loose or it still has air in the abs..

Expert:  Tim's Auto Repair replied 6 months ago.

i dont think there is anything wrong with the booster itself

Customer: replied 6 months ago.
The pedal is not spongy at all and the rear drums hold the wheels from turning.
We used scan tool to bleed abs 4 times and never got any air out of any bleeder screw on any of the 4 abs bleeds.
Expert:  Tim's Auto Repair replied 6 months ago.

do you hear a vacuum loss near the booster?

Customer: replied 6 months ago.
No, i have checked for vacuum leaks none present. Like I said before when I removed the check valve from the booster to test it I heard the vacuum escape then which proves the booster is holding vacuum
Expert:  Tim's Auto Repair replied 6 months ago.

ok,,

i know you have replaced the master,,but if it has no air in the system and from the way you explain,this still sounds as if the master is bypassing the fluid and loosing pressure..

Customer: replied 6 months ago.
I thought that too so I replaced the master again, rebleed everything and still no change.I'm going to swap the bpmv assembly hopefully soon and see if anything changes, as that's the only thing left in the system that hasn't been changed.
Expert:  Tim's Auto Repair replied 6 months ago.

yes,,it is possible for it to be bad causing the fluid to loop back

Expert:  Tim's Auto Repair replied 6 months ago.

Parts InformationOEM Part #Price

Brake Proportioning/Combination Valve

Hydraulic System, Brakes

Pressure Metering Valve

12548265 $290.16

Order By Description.

.

PLEASE COPY AND PASTE the link below to your browser, I have uploaded more info on this there please copy and paste the link below to your main browser[INTERNET EXPLORER or FIREFOX]

.

https://www.dropbox.com/s/dzum9qa6983vuai/1018-chevy-Combination%20Valve.doc?dl=0

.

if the link doesn’t work that way, try it this way

thanks

.

www.dropbox.com/s/dzum9qa6983vuai/1018-chevy-Combination%20Valve.doc?dl=0

.