Jump to content

70 Monte Carlo Rear Disk conversion Woes


Recommended Posts

Helping a friend out with his 1970 Monte Carlo. Dropped a 383 Stoker in, Mild cam, Holley Sniper setup. Replaced all the brakes, new calipers, rear disk conversion. Put a new booster and master (stock) as well as a decent vacuum pump. (cam was only allowing for 8" of vacuum at idle. 

So now we know our mistake, we should of used a Corvette of similar master cylinder in place of the stock disk/drum setup. This also has the proportion valve on the side of the Master hooked to the front brake line only. Then it goes down to the distribution block with the brake light fail switch (no button there). 

Anyway with car off a few limos brakes are nice and hard, hit the key lump comes on, pedal drops to the floor.  So we know the issue. Not enough pressure is going to the back brakes as it has huge pistons in them, to balance the brakes enough to bias in the fronts. 

So Brakes are not my area of expertise. I'm a fabrication, and electrical guy. What do I need to replace. I know the master to a equal reservoir style, but what diameter bore?, Do we ditch the single prop valve, and replace with a later prop valve designed for 4 wheel disk and refab all the brake lines to the block, and due to the arrangement maybe have to redo the front lines? 

 

Any assistance in helping me out is greatly appreciated here.  I know enough from a prior job I assisted on to avoid CPP Crap. 

 

Thanks, 

 

 

Link to comment
Share on other sites

You need a new master and prop. Valve. I suggest one from a 80 trans am if your looking for easy stock stuff with rear disc brakes with at least a 1" bore but would suggest an 1 1/8" bore. You will also need a prop. Valve for disc/disc brakes that has a port for the front and one for the rear. Disc brake require a lot more fluid pressure and flow than drums. Good luck

  • Like 1
Link to comment
Share on other sites

I just completed a 4 wheel disc conversion using Baer brake parts. I researched a few different brands before settling on them. Like Kevin said, you'll need to get a master that is designed for 4 wheel discs, as well as a new distribution valve for 4 wheel disc. I installed an adjustable proportioning valve in the rear circuit, but probably didn't need it. Won't know until I really get the chance to bed the brake pads in properly and do a bunch of real hard stops, to the point of wheel lock-up. (they want a couple hundred miles of driving to get thru the rotor zinc coating before brake bedding procedure)

Regarding master cylinder bore size, 1 1/8" is the stock 2 W disc size. Baer recommends going smaller depending on your available vacuum & system. I went with a 1" bore m/c from 'the right stuff', purchased from Summit. I don't have a lot of miles on the car since the conversion, but the initial pedal feel, travel, and performance of the system is a huge improvement over the stock brakes. I almost went with the 15/16" bore m/c, but figured since I also have a vacuum pump, I would go conservative with the 1" and drop down if needed. It doesn't appear to be needed.

If you need part numbers, let me know & I'll find them.

 

 

Capture.JPG

  • Like 2
Link to comment
Share on other sites

Thanks guys. Looks like I've got some new lines to build to replace both the separated prop valve and distribution block into one unit.  I'll inform my friend of the news. Been digging thru the internet for a few days. Glad I joined up here and got a straight answer. Thanks again.. 

 

-DD

Link to comment
Share on other sites

 

****Looks like my friend found a conversion with the new prop valve included under the master. Will still need to build new lines and couple everything. Not a big fan of using couplings on brake lines but it will work. 

Link to comment
Share on other sites

  • 2 weeks later...

I installed the new Corvette Master Cylinder (it's huge) was able to mount the new proportion valve down where the old distribution block was.  I did bench bleed the new master, bled it again on the car before putting the lines back on. I used a vacuum bleeder started at rear pass side the rear diver side, front pass the front driver. Did that 2 times 2 full reservoirs of fluid without running dry as I was alone. Pumped the brakes a few times heard a pop I figured was the prop valve adjusting. Brakes are total mush can't pump them up. So I went back and sucked two more full reservoirs thru it. Got a bit of air nothing major. Pumped the brakes and they still won't pump up solid. Brake goes to the floor when the vacuum pump is turned on. 

 

No leaks and there is no button on the Prop valve. I did try stomping on the pedal to no help. 

 

Front brakes are dual piston Brembos and rears are these big single piston calipers I had to sit there and crank on the e brake lever to ratchet out the pistons.  No clue the name of them. Hard part is I've got the e brake adjusted with a old socket to get the tension right and the e brake still nearly goes to the floor but I have them adjusted to where the lever just leaves the stop like the manual says. 

 

I'm to the point of telling the customer he needs someone more versed in disk conversions. Or I've still somehow got air trapped someplace. Will try an old school bleed job when I get back on a few days from some personal business. Maybe the vacuum is missing some or sucking too hard. 

 

Thanks guys. 

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...