Power Brakes - low vacuum or bad booster? - Team Camaro Tech
Brakes, Suspension & Steering Conversion questions, Steering & Handling

Reply
 
LinkBack Thread Tools Display Modes
post #1 of 23 (permalink) Old Mar 13th, 01, 06:37 PM Thread Starter
 
Join Date: Mar 2001
Location: Oceanside, CA, USA
Posts: 12
Unhappy

I finally finished installing a power disc brake conversion (from Stainless Steel Brakes (Super Duty A123-6)) on my 69 RS but have found that it does not produce enough brake line pressure.

I put a pressure gage on the aftermarket proportioning valve (for the front to rear brake line) to ensure I have the right amount but get very little reading on the gage even with the pressure increased all the way.

I checked the engine vacuum and found 16.5 Hg initially but once the engine warmed up and the automatic choke eased off so did the vacuum pressure - down to 10 Hg.

I added a vacuum canister but still no improvement (pretty sure I hooked it up right - carb to valve fitting on canister and pipe fitting on canister to valve fitting on booster).

Not sure what to do now! Please help. Thanks.
Batchman is offline  
Sponsored Links
Advertisement
 
post #2 of 23 (permalink) Old Mar 13th, 01, 07:38 PM
Moderator
David Pozzi
 
davidpozzi's Avatar
 
Join Date: Nov 1999
Location: Central California, USA
Posts: 9,685
Post

What diamiter booster?
What is the front brake line pressure reading with around 100 lbs pedal pressure, and where exactly are you measuring it?
I allways hear 16 inches vaccum is minumum.
Pull the vaccum hose and do the brake line reading pressure again. Let's see what the difference is.
Oh, and make sure you haven't blocked the rear of the booster. Air needs to get in there to press on the diaphragm. A lot of guys when swapping from manual brakes re use the old rubber boot which should be left off.
David

------------------
Check my web page for First Gen Camaro suspension info:
David's Motorsports page
First Gen Suspension Page
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Can Am Vintage Racer

[This message has been edited by davidpozzi (edited 03-13-2001).]
davidpozzi is offline  
post #3 of 23 (permalink) Old Mar 13th, 01, 09:01 PM
Senior Tech
Dale
 
Join Date: Sep 2000
Location: Glendale,AZ.U.S.A.
Posts: 918
Post

After you shut the engine down,the booster should hold vaccum.Wait 5 min.then pull the vac hose to booster.There should be vaccum.Start the car up,have someone pull the vac. hose off the booster,while you are pressing on the brake pedal.The pedal should move,up or down,I cant remember which way.Then,reinstall the vac hose,again,the pedal should move,the other way. There should be a check valve on the vac. hose to the booster.Do you hear any vac. leaks,inside car?

------------------
68 z28 ,68 rs 327 ,73 454 vette, 2 goofy kids
dale68z is offline  
post #4 of 23 (permalink) Old Mar 14th, 01, 04:50 PM Thread Starter
 
Join Date: Mar 2001
Location: Oceanside, CA, USA
Posts: 12
Post

Tonight I took out the canister and connected the vac line from the carb to the booster. I ran the car for about 5 minutes, shut it down, let it sit for about 5 minutes. I pulled the vac line off - no whoosh of air.

I checked the vac pressure again by connecting a vacuum gage to the vac line coming from the carb - started the already warm engine and got 15" this time - not sure why I had 10" the other day.

David - the booster is 9". I'm measuring the brake line pressure using a gage screwed into the inline after market proportioning valve which I installed on the front to rear brake line near where the parking brake routes through the subframe. I have pressed on the brake pedal while looking at the gage but get very little reading - 100 psi maybe. The replacement MC/booster came with a rubber boot - I looked under the dash where the pushrod comes through and saw the spongy material (about 1/2" diamter around the rod) you have described in your other posts. Last night I pressed on the pedal, after the car had been run and sitting for about an hour, and did hear a small bit of a whoosh from inside the car.

I called the company - they suggested an electric vacuum pump considering only pulling 10" but tonight its reading 15" - will spend the money but want to be sure the booster is not bad which is my hunch based on the lack of whoosh when removing the vac line.

Thanks for the replies - this brake conversion has been one hurdle after another - can't wait to get on the road again!
Batchman is offline  
post #5 of 23 (permalink) Old Mar 14th, 01, 07:52 PM
Senior Tech
Dale
 
Join Date: Sep 2000
Location: Glendale,AZ.U.S.A.
Posts: 918
Post

Do you have a 1 way vaccum check valve in the vaccum hose,is it good?The lack of a woosh when removing the vac. hose,tells me the booster is bad.I would think,yhough,that you would be able,even with a bad booster,to have more than 100psi.I dont understand the plumbing of the brake lines.Are you saying your front and rear brakes are working off the same master cyl. bore?(single reservoir master cyl)I will assume,you're using a dual master.How far does the pedal travel?What are the front brake pressures?When you bleed the system,does alot of fluid come out with each pump?

------------------
68 z28 ,68 rs 327 ,73 454 vette, 2 goofy kids
dale68z is offline  
post #6 of 23 (permalink) Old Mar 16th, 01, 03:45 PM Thread Starter
 
Join Date: Mar 2001
Location: Oceanside, CA, USA
Posts: 12
Post

The MC does have two reservoirs. I have not measured the pressure on the front brakes.

The conversion kit I bought included a proportioning valve that must be installed on the front to rear brake line after the stock proprotioning valve. This aftermarket valve is used to regulate the pressure to the rear brakes which are stock drums - too much pressure would cause them to lock up from what I understand. I put a gage on the aftermarket proportioning valve to measure the pressure to ensure the rear drums would get enough but not too much pressure.

But the problem is the lack of pressure - and I agree that I think the booster is bad. I'll have to take it and the MC off and send it back to the company. Once it comes back I'll bench bleed the MC, install it and the booster, rebleed the system, and cross my fingers.

[This message has been edited by Batchman (edited 03-16-2001).]
Batchman is offline  
post #7 of 23 (permalink) Old Mar 31st, 01, 04:08 PM Thread Starter
 
Join Date: Mar 2001
Location: Oceanside, CA, USA
Posts: 12
Smile

Well I finally found out what the problem was. The booster is not bad and I'm pulling enough vacuum (barely - 15"Hg).

The problem was that when the MC/booster was fully mounted into the car the booster piston was hung up on the firewall - it would not fully retract after pushing the brake pedal to recreate a good vacuum seal - it just kept leaking. I tried making the hole larger but could only go so far so I added one nut per mounting stud to give me about the extra 1/4" to 3/8" spacing I needed to move the booster off the firewall.

Good to go now - reading 500 psi on the proportioning valve to the rear brakes. Would still like more but better than the nothing I had before.
Batchman is offline  
post #8 of 23 (permalink) Old Mar 31st, 01, 05:30 PM
Moderator
David Pozzi
 
davidpozzi's Avatar
 
Join Date: Nov 1999
Location: Central California, USA
Posts: 9,685
Post

I take it you don't have a stock booster?
What is it?
David

------------------
Check my web page for First Gen Camaro suspension info:
David's Motorsports page
First Gen Suspension Page
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Can Am Vintage Racer
davidpozzi is offline  
post #9 of 23 (permalink) Old Mar 31st, 01, 07:31 PM Thread Starter
 
Join Date: Mar 2001
Location: Oceanside, CA, USA
Posts: 12
Post

No Dave It is an aftermarket booster - 9" from Stainless Steel Brakes.
Batchman is offline  
post #10 of 23 (permalink) Old Mar 31st, 01, 08:16 PM
Senior Tech
 
Join Date: Oct 2000
Location: Long Island, NY
Posts: 269
Post

<BLOCKQUOTE>quote:</font><HR>Originally posted by Batchman:
- this brake conversion has been one hurdle after another - can't wait to get on the road again!<HR></BLOCKQUOTE>

Batchman
I have this same kit in boxes and am about to start the install. I would really appreciate it if you would let me (and anyone else with this kit) know what problems to look out for during the install and what you did to overcome them. Thanks.

my69gofast is offline  
post #11 of 23 (permalink) Old Apr 1st, 01, 08:47 AM Thread Starter
 
Join Date: Mar 2001
Location: Oceanside, CA, USA
Posts: 12
Post

my69gofast:

I can't blame all of the hurdles on SSB - some were my own. Biggest hurdles I ran into included the following:

- I had to replace the front brake lines because the heads on the pipe nuts? that screw into the brake hoses were stripped. If you do this remember that you need to order the lines for NON power brakes. I figured I was now using power brakes so I ordered replacements for power brakes. Would not fit because the conversion does not use the stock proportioning valve. Had to send them back (oversize of course) and wait for the correct standard brake line to come in. NOT SSB's fault.

- The super duty large sized calipers rubbed on my rally wheels - had to have the centers cut down about a 1/4". SSB says these calipers will fit on 15" wheels which is correct but not on 15" rally wheels without the above modification.

- The last problem was that the booster piston would not fully retract after applying the brakes because it hit the firewall. Solution was to add nuts to the four mounting screws on the booster to move the booster off the firewall. SSB should have had some sort of warning about the possibility of this or thier tech support should have suggested this.

BTW - SSB uses the same calipers that Baer uses manufactured by PBR.

Now that it is all working properly and stops pretty well - still have to stand on it a bit - but this is due to the still somewhat low vacuum I have - 15"Hg - but at least it now stops.
Batchman is offline  
post #12 of 23 (permalink) Old Apr 6th, 01, 12:34 AM
Senior Tech
 
Join Date: Oct 2000
Location: Long Island, NY
Posts: 269
Post

Batchman
Thanks a lot for the info. Hope you enjoy your new brake kit. I'm really looking forward to getting rid of the manual drums...they're pretty scary.
my69gofast is offline  
post #13 of 23 (permalink) Old Apr 6th, 01, 12:35 PM
Tech Team
 
Join Date: Oct 2000
Location: U.S.A.
Posts: 46
Post

hi batchman

i too have the same kit from ssb, real nice kit.

i also have the same problem your having with low vacuum, 14 to 15". with poor braking. i just ordered a electric vacuum pump from master power brakes. GM # 22034995, i should be getting mine in a week or two, due to the fact they are backordered.hopefully this will solve my problem and maybe yours.

peter
Peter is offline  
post #14 of 23 (permalink) Old Apr 6th, 01, 06:33 PM
Senior Tech
 
Join Date: Feb 2001
Location: Concord Cal. USA
Posts: 2,664
Post

14to 15in is not low vacumn. A stock setup will work fine with 8in of vacumn I think you problem may lie in the small diameter booster it just doesn't have enough area to really help your breaking.

oger is offline  
post #15 of 23 (permalink) Old Apr 8th, 01, 04:58 PM
Tech Team
 
Join Date: Apr 2001
Location: *SoCal*
Posts: 74
Post

I kinda agree with the last post
I'm gonna be using stock gm issued ones. Just rebuild them.
How do I test, with these outta car, to see if they do not need a rebuild?
More than happy & kinda figure I need a car to test, tho.

------------------
KED67
1967 RS/SS 350 4-Speed Convertible
1968 6 Cyl & PG/Console for the Wife & Son
KED67 is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Team Camaro 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 we receive a lot of registrations with bad email addresses. IF you do not receive your confirmation email you will not be able to post. contact support and we will try and help.
Be sure you enter a valid email address and check your spam folder as well.



Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



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