Power Brakes - low vacuum or bad booster? [Archive] - Team Camaro Tech

: Power Brakes - low vacuum or bad booster?


Batchman
Mar 13th, 01, 06:37 PM
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.

davidpozzi
Mar 13th, 01, 07:38 PM
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

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Check my web page for First Gen Camaro suspension info:
David's Motorsports page (http://ourworld.compuserve.com/homepages/David_Pozzi/)
First Gen Suspension Page (http://ourworld.compuserve.com/homepages/David_Pozzi/first_gen_suspension.htm)
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).]

dale68z
Mar 13th, 01, 09:01 PM
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?

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68 z28 ,68 rs 327 ,73 454 vette, 2 goofy kids

Batchman
Mar 14th, 01, 04:50 PM
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!

dale68z
Mar 14th, 01, 07:52 PM
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?

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68 z28 ,68 rs 327 ,73 454 vette, 2 goofy kids

Batchman
Mar 16th, 01, 03:45 PM
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
Mar 31st, 01, 04:08 PM
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.

davidpozzi
Mar 31st, 01, 05:30 PM
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 (http://ourworld.compuserve.com/homepages/David_Pozzi/)
First Gen Suspension Page (http://ourworld.compuserve.com/homepages/David_Pozzi/first_gen_suspension.htm)
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Can Am Vintage Racer

Batchman
Mar 31st, 01, 07:31 PM
No Dave It is an aftermarket booster - 9" from Stainless Steel Brakes.

my69gofast
Mar 31st, 01, 08:16 PM
<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.

Batchman
Apr 1st, 01, 08:47 AM
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.

my69gofast
Apr 6th, 01, 12:34 AM
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.

Peter
Apr 6th, 01, 12:35 PM
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

oger
Apr 6th, 01, 06:33 PM
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.

KED67
Apr 8th, 01, 04:58 PM
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.

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KED67
1967 RS/SS 350 4-Speed Convertible
1968 6 Cyl & PG/Console for the Wife & Son

davidpozzi
Apr 10th, 01, 09:42 AM
I take it your booster is mounted flat against the firewall and not using the stock type angled bracket like a stock booster?
David

------------------
Check my web page for First Gen Camaro suspension info:
David's Motorsports page (http://ourworld.compuserve.com/homepages/David_Pozzi/)
First Gen Suspension Page (http://ourworld.compuserve.com/homepages/David_Pozzi/first_gen_suspension.htm)
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Can Am Vintage Racer

Batchman
Apr 10th, 01, 04:25 PM
No David - the booster does have the angled brackets but it stll would not allow the brake plunger/piston? to fully seat. I had to add the nuts to each of the four booster studs between the booster and angled brackets to move the whole booster/MC assembly 1/4" away from the firewall.

my69gofast
Apr 19th, 01, 12:40 AM
<BLOCKQUOTE>quote:</font><HR>Originally posted by Peter:
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<HR></BLOCKQUOTE>
I know this is two weeks later, but I was looking through a catalog and came across a vacuum resorvoir. Remembered this topic and wondered why not get one of these instead (around 35 to 45 bucks)?



[This message has been edited by my69gofast (edited 04-19-2001).]

Peter
Apr 19th, 01, 05:45 PM
my69gofast:

the vacuum canister will only store the vacuum, so if you generate 14" of vacuum this is what you get, it will not double the vacuum. this is why you need the electric vacuum pump.

the vacuum canister is also a good idea to use with the electric vacuum pump if you do alot of city driving and the pump happens to fail, ( stored vacuum ).

Peter

my69gofast
Apr 20th, 01, 12:12 AM
Peter
I see. I was just wondering because I knew some guys run a canister when they have a big cam.

I am also considering my options because I have this same SSB kit in boxes and, from what you guys are saying, it seems like it is a little sensitive to low vacuum. I don't remember exactly, but I think my engine had 15 in when I was tuning the car last summer. I wonder if a another booster that is more compatible with this level of vacuum can be used with the rest of the kit?

Peter
Apr 20th, 01, 04:26 PM
my69gofast

i was thinking of this too, i was thinking of going with a 12" booster but from what i hear all boosters need a minimum of 16 to 18" of vacuum. www.mpbrakes.com (http://www.mpbrakes.com) is a great place for parts and information. david would know better, he's into the brake thing.

i called mpbrakes today to ask when they plan on shipping my electric vacuum pump, they said in a week or two. they also told me that they are not going to sell them any more because they are discontinued and there costomers are complaining to much because of the long wait. good thing i put my order in two weeks ago.

hope this helps

peter

[This message has been edited by Peter (edited 04-22-2001).]

Peter
Apr 22nd, 01, 04:28 PM
if your still looking for the electric vacuum pump, i think you can get one at rb's obsolete. www.rbsauto.com (http://www.rbsauto.com)

hope this helps

peter

my69gofast
Apr 23rd, 01, 01:15 AM
Hey Peter, thanks a lot. I will keep it in mind for when I finally get around to installing the SSB kit on my car.

Thanks again