HELP..Converted Lark to Disc Brake and can't get bleed pressure

Sounds from your description that you are trying to bleed the M/C with the cap off! Else, how could a stream of brake fluid hit the hood? Did you bench bleed the M/C before you installed it?

Get yourself a good self-bleeder kit, the one with a line of plastic hose, a jar and a pump. Leave the cap on the M/C during this process. RR, LR, RF and LF lines done in that order.

Brooksie

I did bleed it with the cap on but same problem, no pressure and no air in the lines at the bleed screws....so..... I took the cap off to see what the H%$^ was going on...Cap on or cap off, with another guy pumping and my bleeding the calipers and cylinders it would not hold pressure...now this system does not have a booster so we can leave out that senario as my 63 GT took forever to bleed with that damned HydroVac unit......still, this system won't hold pressure and I can't figure out why.... thanks for the response, though. Myuch appreciated greg

I was having a similar problem, I have replaced my old m/c with a new dual m/c to a disc brake equiped car. I decided I was not getting enough stroke on mine so I put about a 3/8" spacer between my brake pedal rod and the plunger in the m/c. Filled the m/c up with brake fluid and stepped on brake pedal and had a little over half of a pedal. Now I am going to remove the spacer and make my brake pedal rod adjustable so I can make up this difference.

I am not sure but I d>> Sounds from your description that you are trying to bleed the M/C with >> the

Yeah, that is what I was reading at the

website (provider of the 2 lb) RPV I bought...they said I only need a RPV when the MC is below the calipers horizontal plane.....so, with that that case I think I've deduced that my MC has gone south. Might I ask what model MC you purchased so I can replace mine with the one you used? I know I will have to run some new lines down to the junction blocks as the stude lines have these large threaded nuts going into the stock MC Thanks!

On Debbie's Marshal, I used a '71 MOPAR disc brake master cylinder. Bolted directly in the car and has been working perfectly for 6+ years.

The only 'mod' I had to do to it was to remove the piston and drill the end of the M/C for the brake light pressure switch. You could also simply install the brake light switch at the splitter block on the frame.

Lee DeLaBarre Daytona62

Go to the Turner Brakes website.. Click on the Instruction button and scrooll to the bottom of this link to find the list. I bought the one for the early Corvette. Simply because it was there and I knew it was for a front disc brake car. Here is a link to the Turner website.

I think you may still need the 10 lb. RPV in the rear but the 2 lb. RPV in the front is generally only required for underfloor MC installations. Not sure if the "rear" section of that MC has a built in RPV or not. Are the rear shoes adjusted properly?

nate

You can run a residual pressure valve in both situations.

2lb is for disk brakes. 10 lb is for drum brakes. These do two things. (1) To prevent siphoning of a master cylinder that is mounted lower than the caliper or wheel cylinder. (2) To keep a slight pressure in the line to prevent air from migrating back into the line and bringing moisture with it. Remember, brake fluid is hygroscopic. (absorbs water or moisture from surrounding air) 2psi for disc's because they have no return springs. 10psi for drums because the return springs pull the shoes (and w/c pistons) back in. A residual pressure valve will NOT prevent your system from being bled. Bleeding brake systems is always a challenge. Couple questions. Are your residual pressure valves the 'inline' type, or are they built into the master cylinder? Did you change your master cylinder from the stock drum/drum setup? Is the master cylinder a drum/drum, disc/drum, or disc/disc master cylinder? If you added disc brakes (to the front only), you need to put a disc/drum master on, or your pedal effort will change dramatically. Did you bench bleed the master cylinder? Remove the lines from the car and make up two short loops to run back into the master cylinder resevoir. Pump the master to remove all the air from the piston area. Is your brake pedal adjusted 'properly', with a little free play in it? If the m/c piston does not get fully retracted in it's bore it may not be uncovering the return port completely. This will hold the brakes on a bit, but can make bleeding a pita. Did you bench bleed the calipers? Did you loosen the caliper from the mounts and hold them up as high as possible (with the bleeders facing up). (put a c-clamp on the piston to keep it from pushing out) Then open the bleeder screw and pump the master...slowly... Watch for air purge. Sloppy. but effective. When you do get good blleding occurring, then start with the longest brake line first (usually the LR) Progress to the shortest line last. Are you running a proportioning valve? Is it the correct one for your setup? Is it adjustable?

Your brake supplier should have provided you with all of this information with the conversion kit.

For the 2lb rpv on the fronts, does that still apply if the MC is frame mounted but has the remote reservoir on the firewall??? The reason I ask is that when I put Turner's in my 63 hawk, I chose not to put the 2lb in after talking with Jim because I'm not sure anyone ever has... The single line goes from the hydrovac down to a brass fitting that splits out the 1 to the rear and 2 to the front. If you were going to put in a 2lb for the front, you'd have to put in 2 of them, or change the distribution system ( i.e. split front and back - 2lb rpv - split rf and lf. I searched through the archives and couldn't find indication that anyone had ever run across ( or mentioned) that quandry. I guess you could put the 2lb between the hydrovac and the

3:1 split...

I've also never been happy with getting the hydrovac fully bled - what's the secret?

thx, Jeff

Yep, the switch on pre-suspended pedals was located near the splitter block. At least that's how it is on the '55 Prez sedan.

JT

Lee wrote:

On Nov 6, 12:36 pm, Grumpy AuContraire wrote:

Thanks for all the information guys. Dave Levesque doesn't say much about what aftermarket MC's kinds would work on a Stude. Still, I made the setup work fairly cheaply, although it took me a month to get all the parts since the rotors were backordered....luckily it all came in as I was starting to worry. I have to say that the system bolted onto the spindles of my Lark without a hitch. Only thing I had to buy separate were the rims and hoses since he uses big GM calipers in his setup. I have the NAPAhose and Banjo bolt part numbers if anyone chooses to go this route, give me a hollar and I will save you some time as DL didn't pass along any part numbers for the hose conversion as well. Today, I went out a bought an aftermarket disc brake master cylinder based off the information Henry gave me here

off what JT says, one can use an MC out of an 84 T-Bird.I went to autozone today and got this unit 8 cyl T-bird had front disc/rear drum brakes from the factory sothe RPV's needed are built into the MC and I don't need to installinline rpvs which saves me a lot of double flaring and fittingfinding. Still, I imagine I am going to have to cut and double flarethe existing Stude line where they meet up at the MC ports. I justhope that the new MC mounts to the firewall correctly.Also, I am going to have to rewire the brake light switch. I'd liketo use one that you mount on the pedal....someone a while backmentioned which part number to use so if anyone knows what that isit'd be great if you can pass it along.Thanks Greg already built into the master cylinder

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or here or search ebay for "universal brake light switch"

they work great

Mark