Low Brake Pressure, 67 Chevy Impala w/power brakes - Impala Tech
Brakes & Suspension Conversion Questions & more

 
LinkBack Thread Tools
post #1 of 11 (permalink) Old 11-04-2013, 11:19 AM Thread Starter
Member
 
Join Date: Feb 2012
Location: Florida
Posts: 88
 
Low Brake Pressure, 67 Chevy Impala w/power brakes

Low brake pressure I think. Have 700 psi at the new front upgraded calibers, and 600 psi at the stock rear drum brakes. Everything I have read states a minimum requirement of 1200 to 1400 psi at the front calibers and 600 to 1000 psi at the rear drum brakes.

Quick background everything is new except the power booster. Upgraded the front drum brakes with a Performance OnLine conversion kit, replaced all brake lines, rear wheel cylinders, and master cylinder and proportioning value (both designed for front disc and rear drum brakes). The reason I did not replace the power booster is based on the fact that it passed all checks as noted below, including tests for the power booster check valve. As an additional note, have 17.5 #s vacuum from manifold to the power booster. Hose not blocked and could find no leaks.

Booster checks performed:
1. Pump the brake pedal a few times with the engine shut off. Depress the brake pedal and hold it down. Start the engine. The brake pedal should almost immediately drop slightly, and the pedal should change from a high and hard feel to a normal feel. If it does not then this indicates a problem with the brake power booster, or possibly a low engine vacuum or plugged vacuum hose. 2. Run the engine for a few minutes. Turn the engine off and then immediately depress the brake pedal four or five times. The brake pedal should feel harder with each push, and it should come to a stop at a higher position each time. If the pedal returns to the same position each time then it indicates a problem with the brake power booster. 3. Run the engine for a few minutes. Depress brake pedal and hold it down. Turn the engine off and keep the brake pedal depressed for 30 seconds of so. The brake pedal height should not change during this time. If the pedal rises it indicates a problem with the brake power booster. As noted, all tests passed.

Any suggestions as to where I should look next or any additional tests will be appreciated. Thanks Bob
bfigueroa is offline  
Sponsored Links
Advertisement
 
post #2 of 11 (permalink) Old 11-10-2013, 09:32 AM Thread Starter
Member
 
Join Date: Feb 2012
Location: Florida
Posts: 88
 
It has been suggested that I use a master cylinder with a 1 inch bore vice the 1.125 inch bore that I have but have been looking for a smaller bore master cylinder, i.e., 1 inch vice the 1.125 that I have and all 1 inch bore masters are stated to be for 4 wheel drum brakes, not all discs or front disc and rear drum brakes as I have. Can I use an all drum brake master on my disc / drum brake system in order to get the smaller bore? Thanks Bob
bfigueroa is offline  
post #3 of 11 (permalink) Old 11-10-2013, 09:51 AM
Moderator
 
Join Date: Jan 2006
Posts: 12,456
 
Yes you can, you could even go as small as 7/8th inch. They are probably stating drum brake application as that is what the factory used and they are selling it as a service replacement part.

There are five different master cylinder bores made for GM vehicles that will all bolt up to meet the application needs of disc or drum, light or heavy vehicles. You can experiment by trying out various combinations of master cylinder bore and wheel cylinder size (there are different bores used at the wheels as well as the master cylinder).

Considering how dangerous it is to guess at the wrong combination; I always recommend contacting the vendor of your brake system to see what their engineers recommend you to use (This assumes you are buying a kit from a brake company and not your corner auto parts store). They can and will tell you what parts to buy to get your brakes to work.

Big Dave
Big Dave is offline  
 
post #4 of 11 (permalink) Old 11-10-2013, 10:00 AM Thread Starter
Member
 
Join Date: Feb 2012
Location: Florida
Posts: 88
 
Thanks Big Dave. Bought my conversion kit from Performance OnlLine and will call them as you have suggested. Bob
bfigueroa is offline  
post #5 of 11 (permalink) Old 12-08-2013, 11:40 AM Thread Starter
Member
 
Join Date: Feb 2012
Location: Florida
Posts: 88
 
67 Chevy Impala brake bleeding issue

When bleed my brakes all the air in the lines seems to be gone but the pedal only goes down about 3/4th of the way with the bleeder value completely open - same on all 4 brakes. Do I have a problem? Thanks Bob
bfigueroa is offline  
post #6 of 11 (permalink) Old 12-08-2013, 03:54 PM
Moderator
 
Join Date: Jan 2006
Posts: 12,456
 
If it is not going to the floor with the wheel's brake bleeder valve open then yes you have one of two issues. Mismatched linkage (mounting point on the brake pedal, combined with a brake rod issue), or your master cylinder's stroke is too short and you are hitting the end of the wall before your brake pedal hits the floor (you should hit the floor without bottoming out the master cylinder piston as it messes with the seal if you do so).

Once again there are many brake parts to match different applications (generally based upon the GVW of the vehicle). A lot of HD parts used in big cars are actually light duty truck parts. So once again there are lots of parts to mix and match as far as brake rods go (some are adjustable which really helps fine tune your pedal placement as some hate having a clutch pedal higher than their brake pedal). There are many different length and styles of brake rod that have to match your car and your master cylinder (which hopefully you know the application of the master cylinder so you can replace it with a service part after it eventually wears out).

The back of the master cylinder piston is also machined differently. Some are flat with a small conical shape divot, others have small tunnels machined into the piston with round bottoms to keep the rod in place.

Finally for years GM used to stamp two holes in the brake pedal (it is made of case hardened steel, so you really don't want to be trying to drill an extra hole). One for manual brakes and the other mounting point was for power assisted brakes. The top hole was for manual brakes which needed all of the mechanical advantage (lever arm) that it could get to build brake line pressure. The Power Assist pedal brake rod attachment point (hole) was lower so as to not over apply the brakes to suddenly.

I would also like to point out that manual brakes and power assist brakes both work equally well. Anyone from the frailest little old lady to a longshoreman off the docks of New York harbor could lock up the wheels of the car with equal ease.

Where power assist becomes a desirable option worth the added price that was formerly charged when it was an option, is that it allows you to effortlessly hold the car in DRIVE (implies having the optional automatic transmission instead of the STANDARD manual transmission) at a stop light or while waiting for a train to clear the tracks.

Manual brakes and a manual transmission are perfect together. You only need power assist if you have a big V-8 that wants to go when held in drive by your foot on the brake pedal. After a few minutes your leg starts to tire, so you either get power assisted brakes or greet the car owner in front of you as your car begins to creep forward as your leg tires.

Big Dave
Big Dave is offline  
post #7 of 11 (permalink) Old 12-18-2013, 11:58 AM Thread Starter
Member
 
Join Date: Feb 2012
Location: Florida
Posts: 88
 
67 Chevy Impala brake bleeding issue

Thanks Dig Dave. Been followinfg your suggestions and no luck todate. It may be the master cylinder. Per research on the internet I found an AUTOSPECIALTY / KELSEY-HAYES M82019 master cylinder with a 1" bore.
Per specs it should work on my 67. Maybe not. Are the any other suggestions for a master with a 1" bore for my application just in case the M82019 does not work with my 67 as implied? Thanks Bob
bfigueroa is offline  
post #8 of 11 (permalink) Old 12-18-2013, 02:45 PM
Moderator
 
Join Date: Jan 2006
Posts: 12,456
 
With brakes it is all about the gross vehicle weight. Similar weight vehicles share similar brake parts across the GM platform. Best bet is to get a Hollander Interchange number for all of the stock parts on your brake system (master cylinder, caliper, wheel cylinder, brake rod, brake pedal, and the booster) that will tell you what interchanges. To do this you need to either buy a Hollander Interchange catalog on line for your year vehicle; or buddy up to your friendly neighborhood recycler so you can look over his shoulder as he researches your car on his computer (I don't know when the last printed on paper Hollander Interchange catalog was published, but I suspect it was some time in the nineties).

I have several that cover the late seventies to the mid eighties that I bought for $75 to $120 each. To me they where well worth it. Price varies on the number being offered at one time and the condition of the book as some are moldy and water damaged with the pages you want all glued together (but you can find out ever thing there is to know about a Yugo that year). Others are pristine with only the occasional grease smudge.

Big Dave
Big Dave is offline  
post #9 of 11 (permalink) Old 12-19-2013, 02:45 PM Thread Starter
Member
 
Join Date: Feb 2012
Location: Florida
Posts: 88
 
67 Chevy Impala brake bleeding issue

Once again, thanks for the detailed reply. The problem I am having is any time I ID an alternative interchangeable master cylinder it is for the original / stock item, i.e., a unit with a 1.25 inch bore, and based on various research I need a cylinder with a 1 inch bore to increase the 700#s of pressure at the front calibers to about 1000#s plus as needed. Have been trying to stay away from the $400.00 plus units from the high performance / racing shops. Will just keep looking for an alternative cylinder. Thanks again, Bob
bfigueroa is offline  
post #10 of 11 (permalink) Old 12-19-2013, 02:48 PM
Moderator
 
Join Date: Jan 2006
Posts: 12,456
 
Most Mustangs use a 7/8th inch to one inch bore and I believe they bolt up but that needs to be checked out before you buy anything.

Once you have an interchange part the book tells you every car that has a part that will bolt up. Raybestose made parts for every one not just Chevy.

Big Dave
Big Dave is offline  
post #11 of 11 (permalink) Old 12-22-2013, 10:50 AM Thread Starter
Member
 
Join Date: Feb 2012
Location: Florida
Posts: 88
 
67 Impala SS - need master cylinder with specs

Have had a lot of good feedback which has lead me to the specific requirements I need for my replacement master cylinder, i.e., 1 inch bore, 1 1/2 inch deep pocket and front disc brakes with rear drums. Have visited more web sites then I can list, and have talked to every vendor that has a posted phone #. Problem: no where have I been able to ID a cylinder that meets all 3 specs. It amazing that no one knows all the specs of the parts they manufacture / sell. At best, I can ID a product that meets 2 of the 3 requirements but not all 3. The last master cylinder I bought had a 1 inch poor and was designed for front disc/rear drums but the specs did not note that it had a short / shallow pocket (i.e., Autospecialty / Kelsey-Hayes # M82019). Any help in locating a master cylinder that meets my need specs will be appreciated. Thanks Bob
bfigueroa is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Impala 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 for yourself.

Email Address:
OR

Log-in










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



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