Front disc brake conversion - Pontiac GTO Forum
User Tag List

 1Likes
Reply
 
LinkBack Thread Tools Display Modes
post #1 of 14 (permalink) Old 02-09-2019, 01:49 PM Thread Starter
 
gtoearl's Avatar
 
Join Date: Dec 2009
Location: ROSEVILLE, CA
Posts: 194
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 22 Post(s)
Front disc brake conversion

Hopefully you guys can help me with an issue. Just replace the upper and lower control arms with new front springs. Also was able to score a disc brake conversion from a 66 Chevelle. Everything bolted on correctly. The items I purchased Included the master cylinder but without the proportioning valve and booster. I still have the rear drum brakes. Which I refreshed with new shoes springs and drums. Got a proportioning valve from C PP . The booster I purchased from Summit. Hopefully this is enough background for you to answer my question.
I can’t seem to get the adjustment on the rear brakes to the point where they will not lock up . Seems to not lock up if I’m fairly easy on the brake. If I put the slightest increased pressure like a hard stop the rear brakes will lock up.
A friend of mine from a local restoration shop told me they never put a combination proportioning valve on their brake conversions. They simply run the front reservoir to the front brakes and put an adjustable proportioning valve to the rear brakes. I’m not questioning their procedure but my question is why do all these kits out there have a combination proportioning valve for the brake conversion. I’m wondering if I have something wrong with the mechanical issue on the rear brakes, adjusted too tight, emergency brake adjustment or some other mechanical issue. I do not have any gauges to check the pressure to the front and rear. I’m wondering if I have a defective combination proportioning valve where it is not centered. I’m sure there’s many reasons why my brakes are locking up on the rear. But I would like to get some input from all you guys. Thanks for any help.
gtoearl is offline  
Sponsored Links
Advertisement
 
post #2 of 14 (permalink) Old 02-09-2019, 06:14 PM
 
Join Date: Oct 2017
Posts: 668
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 162 Post(s)
The master cylinder needs to have the different valve for drums, otherwise it will send too much pressure and lock the rears (what you are experiencing).... You can get the correct valve at CPP if Summit won't fix for you...

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
cij911 is offline  
post #3 of 14 (permalink) Old 02-09-2019, 06:35 PM Thread Starter
 
gtoearl's Avatar
 
Join Date: Dec 2009
Location: ROSEVILLE, CA
Posts: 194
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 22 Post(s)
Appreciate very much your response. I did not buy the master cylinder from a retailer. This was the master cylinder that came with the deal I got from the guy that owned the 66 Chevelle. I understand after calling the restoration shop where I got the stuff that the master cylinder was for a disc/Drum system.
gtoearl is offline  
 
post #4 of 14 (permalink) Old 02-09-2019, 09:53 PM
 
Join Date: Oct 2017
Posts: 668
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 162 Post(s)
Quote:
Originally Posted by gtoearl View Post
Appreciate very much your response. I did not buy the master cylinder from a retailer. This was the master cylinder that came with the deal I got from the guy that owned the 66 Chevelle. I understand after calling the restoration shop where I got the stuff that the master cylinder was for a disc/Drum system.
Hmmmm....assuming the plumbing is correct, then I would check pressure at the rear.

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
cij911 is offline  
post #5 of 14 (permalink) Old 02-09-2019, 10:33 PM
 
PontiacJim's Avatar
 
Join Date: Dec 2012
Location: Gastonia, NC - Born & raised in Connecticut - 31 years
Posts: 3,739
Mentioned: 1 Post(s)
Tagged: 1 Thread(s)
Quoted: 404 Post(s)
Garage
Quote:
Originally Posted by gtoearl View Post
Appreciate very much your response. I did not buy the master cylinder from a retailer. This was the master cylinder that came with the deal I got from the guy that owned the 66 Chevelle. I understand after calling the restoration shop where I got the stuff that the master cylinder was for a disc/Drum system.
Purchasing a "deal" from another does not mean you got a "deal" let alone the correct & matching parts.

Are the items brand new and unused? If they were used, maybe the guy with the Chevelle was also having problems and decided to get rid of the system and go with something different. Seeing the '66 Chevelle did not have disc brakes and the dual master cylinder did not appear until 1967, what exactly do you have - factory GM parts or aftermarket add-on?

We have had posters on the forum buy a new set-up that was for their car only to have problems and not seem to get it to work correctly. It is very important to match all parts. Maybe something incompatible that doesn't match?
1968gto421 likes this.
PontiacJim is offline  
post #6 of 14 (permalink) Old 02-11-2019, 03:55 PM
 
iharting's Avatar
 
Join Date: Oct 2018
Location: Venezuela
Posts: 10
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Can you post pictures of the Master Cylinder and Proportioning Valve? One of them should be the wrong part for that set, because it seems too high fluid pressure is going to the rear brakes.
iharting is offline  
post #7 of 14 (permalink) Old 02-13-2019, 11:30 AM Thread Starter
 
gtoearl's Avatar
 
Join Date: Dec 2009
Location: ROSEVILLE, CA
Posts: 194
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 22 Post(s)
Hopefully this helps. The proportioning valve is from CPP. The master cylinder was from the 66 Chevelle set up.
Attached Thumbnails
Click image for larger version

Name:	AA215406-B50E-4ED8-BE9F-8468EA0540AD_1550075287372.jpeg
Views:	92
Size:	979.5 KB
ID:	117633   Click image for larger version

Name:	C83C6CAE-4AFD-44F2-9493-A70ADB836B9D_1550075316758.jpg
Views:	91
Size:	1.05 MB
ID:	117635  
gtoearl is offline  
post #8 of 14 (permalink) Old 02-13-2019, 11:34 AM Thread Starter
 
gtoearl's Avatar
 
Join Date: Dec 2009
Location: ROSEVILLE, CA
Posts: 194
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 22 Post(s)
This is how I received it from the purchase I made. You can see that there’s a small I think adjustable proportioning valve plumbed in. I’ve been told this is not a proportioning valve.
Attached Thumbnails
Click image for larger version

Name:	F4AD609C-4F58-481F-887F-64F2EA041A70_1550075654518.jpg
Views:	87
Size:	1.52 MB
ID:	117637  
gtoearl is offline  
post #9 of 14 (permalink) Old 02-13-2019, 06:30 PM
 
Join Date: Oct 2017
Posts: 668
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 162 Post(s)
Quote:
Originally Posted by gtoearl View Post
Hopefully this helps. The proportioning valve is from CPP. The master cylinder was from the 66 Chevelle set up.
That is what you want and you HAVE TO MAKE SURE IT IS FOR REAR DRUM SETUP. You many have received the wrong Part #.

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
cij911 is offline  
post #10 of 14 (permalink) Old 02-15-2019, 08:34 PM
 
iharting's Avatar
 
Join Date: Oct 2018
Location: Venezuela
Posts: 10
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Ok. If proportioning valve was not centered, you would have a red brake light at your instrument panel ,so I would do this:

- Check if the rear drum brake shoes are in the right position (shorter shoes towards the front)
- Check if parking brake adjustment is not too tight (First adjust shoes with parking brake loose)
- If problem is still there, check booster rod is not preloading the master cylinder piston
- Finally, try how the system works without the rear brakes residual pressure valve that is seen under the M/C

My '71 Chevelle had disc/drum brakes with proportioning valve and no residual pressure valve from factory and it worked perfectly. Then I converted it to disc/disc brakes with a new proportionig valve and no problems.

Work with patience.

Hope this info helps too:

https://www.brakebleeder.com/rear-br...p-drum-brakes/
iharting is offline  
Sponsored Links
Advertisement
 
Reply

  Pontiac GTO Forum > The 2004-2006 GTO > Drive train, suspension, alignment and brakes.

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Pontiac GTO Forum 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











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Thread Thread Starter Forum Replies Last Post
SSBC front disc brake conversion problem!!! 66problem 1964-1974 Tempest, Lemans & GTO Exhaust, Suspension, Alignment, Fuel Tank and Brakes. 25 10-29-2015 10:59 PM
Front Disc Brake Conversion on a 65 poocher 1964-1974 Tempest, Lemans & GTO Exhaust, Suspension, Alignment, Fuel Tank and Brakes. 3 10-08-2014 09:24 PM
1966 front disc brake conversion Tony Arnold 1964-1974 Tempest, Lemans & GTO Exhaust, Suspension, Alignment, Fuel Tank and Brakes. 5 05-08-2014 05:43 PM
Front Disc Brake conversion Kingfreeze21 1964-1974 Tempest, Lemans & GTO Exhaust, Suspension, Alignment, Fuel Tank and Brakes. 13 02-25-2013 06:30 AM
Front Disc Brake Conversion Jim 1964-1974 Tempest, Lemans & GTO Exhaust, Suspension, Alignment, Fuel Tank and Brakes. 11 07-01-2012 09:14 PM

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