69 PDB Problem - Chevelle Tech
Brakes, Suspension & Steering Conversion questions & more.

 
LinkBack Thread Tools Search this Thread Display Modes
post #1 of 14 (permalink) Old Feb 12th, 20, 1:52 PM Thread Starter
Tech Team
 
Join Date: Aug 2018
Posts: 921
Really hard pedal, shop replaced booster w rebuilt booster, no better, replaced master cylinder, no better, replaced hard line across rear axle, better. Every time I mash brakes hard, brake warning light comes on.
Brakes not great, just OK.

I take car to Chevelle expert who I trust. I ask him to change proportioning valve on frame while he’s doing other work.

He says bad booster. He says rebuilt boosters very problematic. He says has replaced 3 rebuilt on same car, only uses new now.

Any comments ?

Is there a way to check my booster ?
Reelysalty is offline  
Sponsored Links
Advertisement
 
post #2 of 14 (permalink) Old Feb 12th, 20, 9:17 PM
Senior Tech Team
Bruce
 
Join Date: Jun 2006
Location: White Bear Lake, a northeast suburb of St. Paul, MinneSNOWta
Posts: 5,049
Garage
Re: 69 PDB Problem

In this particular case, the Brake Warning Light indicates low brake line pressure -- that's a bad thing.
Is your system originally Power Brakes?
Are the lines original?
Are the lines the correct ones?
Have you bled the entire Brake Line System (the first time I bled my 'Bu's brakes I found that the rear line was plugged)?
Do you have the brake rod (between the Brake Pedal and the piston) in the correct hole (the lower hole as I recall for Power Brakes)?
Are you using the correct Brake Fluid?
What is the age/condition of the Wheel Cylinders (Don't even mess with a Wheel Cylinder Repair Kit, just get new ones, if you need them).
How about the Calipers?
Parking Brake/Emergency Brake hook up?

Personally, I'd go with a new Booster. I'd drain all the fluid out and then blow out the lines. Then I'd install a brand new booster (making sure to follow the instructions), I'd refill and bleed the system, making certain that the Caliper and Cylinders work "as advertised." Careful with the Brake Fluid -- that stuff is excellent paint remover!!!

"If your Brakes don't stop you, something else will."

Our You Tube Vids:
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

NickeyChevelle is offline  
post #3 of 14 (permalink) Old Feb 12th, 20, 10:05 PM Thread Starter
Tech Team
 
Join Date: Aug 2018
Posts: 921
All work done by popular hi volume shop chain

Yes factory PDB

Some new lines are obvious

I can’t do brake work, no second person for bleeding

You would change out almost new booster ?

I read something about warning light reads “pressure imbalance”

Parking brake seems fine.
Reelysalty is offline  
 
post #4 of 14 (permalink) Old Feb 12th, 20, 10:23 PM
Lifetime Premium Member
John
 
Join Date: Apr 2019
Location: North Idaho
Posts: 52
Garage
You mentioned a proportioning valve on the frame. I believe 69 had a distribution block on the frame with a hold off valve attached to the master cylinder, at the booster. Do you have one if these valves on your car?
Attached Thumbnails
Click image for larger version

Name:	20200115_061009_1581560609336.jpg
Views:	15
Size:	53.9 KB
ID:	616388  
Johnny Bravo is offline  
post #5 of 14 (permalink) Old Feb 12th, 20, 10:36 PM Thread Starter
Tech Team
 
Join Date: Aug 2018
Posts: 921
Thanks,
Doesn’t look familiar,
I’ll have pics tomorrow
Reelysalty is offline  
post #6 of 14 (permalink) Old Feb 13th, 20, 3:09 PM Thread Starter
Tech Team
 
Join Date: Aug 2018
Posts: 921
Here’s the 2 distribution centers I have.

Engine has 15” at idle,
20” at 1250. Kicked idle to 1250 and drove around block, no difference in pedal.
Attached Thumbnails
Click image for larger version

Name:	422CC877-AC25-44F5-AECC-79B1E81079ED_1581620933307.jpg
Views:	8
Size:	35.8 KB
ID:	616458   Click image for larger version

Name:	3FF74328-A3F7-4AD2-9CE0-5B9447D07586_1581620960252.jpg
Views:	8
Size:	57.0 KB
ID:	616460  

Last edited by Reelysalty; Feb 13th, 20 at 3:34 PM.
Reelysalty is offline  
post #7 of 14 (permalink) Old Feb 13th, 20, 10:49 PM
Lifetime Premium Member
John
 
Join Date: Apr 2019
Location: North Idaho
Posts: 52
Garage
That's the correct stuff. Maybe. Check your vacuum hose and see if it's either cracked, or possibly collapsing under vacuum. I don't know what your hose is plumbed into for a source, but check that too. It could be something simple like that. Does the pedal feel the same when the car isn't running?
Johnny Bravo is offline  
post #8 of 14 (permalink) Old Feb 13th, 20, 11:13 PM Thread Starter
Tech Team
 
Join Date: Aug 2018
Posts: 921
Vacuum hose plumbed into stock manifold port. Pedal feels about the same engine running or not.

When brake warning light plugged in, it glows brighter as I mash brake.

I can drain vacuum, keep foot on brake, crank engine and pedal will drop a little.

Good mechanic says I replaced booster with new, defective one. Could I, or rather could shop have replaced with new defective booster ?
Reelysalty is offline  
post #9 of 14 (permalink) Old Feb 13th, 20, 11:37 PM
Lifetime Premium Member
John
 
Join Date: Apr 2019
Location: North Idaho
Posts: 52
Garage
I guess it's possible. I have no experience with defective boosters, so I'm no help there. Have you checked to see if the Clevis on the rod coming through the firewall is in the lower hole on the brake pedal?
Johnny Bravo is offline  
post #10 of 14 (permalink) Old Feb 14th, 20, 1:12 AM
Lifetime Premium Member
 
Join Date: Jul 2000
Location: In the Shadow of GIANTS stadium,N.J.
Posts: 7,938
Garage
Re: 69 PDB Problem

Was the brake warning light on when you first complained of the hard brake pedal ? and before any parts were replaced ?

John
71 El Camino SS
406 SBC M21 3.31 12 bolt
"Quality is always remembered,long after the price is forgotten"
71350SS is offline  
post #11 of 14 (permalink) Old Feb 14th, 20, 1:56 AM
Dennis
 
Join Date: Nov 2019
Location: Quad Cities, Iowa
Posts: 27
Garage
Re: 69 PDB Problem

There is an adjustment screw or nut inside the booster. If that isn't adjusted properly that pin will be pushing the master cylinder plunger in and your brakes with always be engaged. I believe they call for about a 1/16" clearance. You might want to start there. But if that's a pro shop they should have already done that.

Too soon old and too late smart.
Progress is not always forward.
Sludge is offline  
post #12 of 14 (permalink) Old Feb 14th, 20, 8:33 AM Thread Starter
Tech Team
 
Join Date: Aug 2018
Posts: 921
Quote:
Originally Posted by 71350SS View Post
Was the brake warning light on when you first complained of the hard brake pedal ? and before any parts were replaced ?
Oddly enough, no
Warning light started coming on, just a faint glow at first after rear axle hard line was replaced and I got some braking restored.

I’m gonna check that rod position next

Thanks for all comments !
Reelysalty is offline  
post #13 of 14 (permalink) Old Feb 14th, 20, 12:41 PM
Lifetime Premium Member
Ed
 
Join Date: Nov 2012
Location: San Diego
Posts: 1,018
Garage
Re: 69 PDB Problem

Have you replaced the rubber lines over the rear axle and front discs? Anything over 10-15 years old are suspect.

Ed

70 El Camino SS 396
68 GTO (Thanks Mom)
06 Silverado
07 SRX
OO52 is offline  
post #14 of 14 (permalink) Old Feb 14th, 20, 7:10 PM Thread Starter
Tech Team
 
Join Date: Aug 2018
Posts: 921
Quote:
Originally Posted by OO52 View Post
Have you replaced the rubber lines over the rear axle and front discs? Anything over 10-15 years old are suspect.
I think they were replaced.
Reelysalty is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Chevelle Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address. Note, you will be sent a confirmation request to this address.

Email Address:
OR

Log-in










Thread Tools Search this Thread
Show Printable Version Show Printable Version
Email this Page Email this Page
Search this Thread:

Advanced Search
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome