Disc Brake Conversion Question

[dcramos72]

Hey All,

Just finished converting front drums to disc on my 64 C10. I bought the kit from Early Classics. All hooked up and lines bleed. I ran vacuum to an inlet on the manifold that is behind the carb (mid 80's 350). Started up fine, but brake pedal went right to the floor. When I turn the engine off there seems to be a bit more pressure in the pedal, but still goes right to the floor.

I read in the booster instructions that you are supposed to drill a hole 1" below original hole in the brake pedal. I didn't do this because the connecting rod coming out the back of booster aligned with the hole almost perfectly right out of the box. Booster diaphragm seems OK as I sucked on the vacuum hose and am getting no air through.

Please let me know what I am doing wrong. Is it a vacuum issue or is it the hole/angle off the pedal.

Thanks!

Dan

[Rich 5150 69]

Air in the master cylinder, did you bench bleed the master...and is the brake pedal rod long enough..( full stroke into master cylinder ) are the first things that come to mind....

[dcramos72]

Yes, bench bleed the MC before installing. Filled to 1/4" below edge and bleed till the fluid was about half way down in each cylinder.

Brake pedal rod long enough? You mean rod coming out back of booster? Currently brake pedal is in its original position when completely out.
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[luvbowties]

Originally Posted by dcramos72

Yes, bench bleed the MC before installing. Filled to 1/4" below edge and bleed till the fluid was about half way down in each cylinder.

Brake pedal rod long enough? You mean rod coming out back of booster? Currently brake pedal is in its original position when completely out.
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Did your kit have a plug (spacer) to put into the hollow end of the mc piston? This hollow may be in the mc piston where booster rod fits--some mc's are hollow here & require that plug for a spacer; other mc's are 'blunt' at this piston surface & do not need the spacer.

[dcramos72]

No plug or spacer came with the kit (just plugs for brake line inlets for bench bleeding). Can't remember if hollow space was blunt or flat.

Can't tell if brakes are applied (sitting in garage), but does not feel like it.
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[luvbowties]

Originally Posted by dcramos72

No plug or spacer came with the kit (just plugs for brake line inlets for bench bleeding). Can't remember if hollow space was blunt or flat.

Can't tell if brakes are applied (sitting in garage), but does not feel like it.
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One of 2 things is probably happening. (1) Your pedal is not pushing fully into the booster . or (2) Your booster is not pushing the mc-piston fully into the mc. Get someone to help you & see what happens when you try to bleed your mc via the leg-pumping method. If it bleeds & builds pressure properly, problem solved. If it merely pumps just a tad of fluid, or maybe none, then one of the 2 scenarios above exists. I'm betting the mc has a hollow piston that will require a spacer. BTW: This spacer can be made from a bolt you cut the threaded end off of--one whose diameter is just enough smaller than the hollow in the mc piston that it freely, but closely, "rattles around" when test-fitting into hollow. Cut off just enough length--approx. 1 inch +/-. Using a bench grinder, dress down one end to a blunt point, or cone, kinda like the end of a .38 bullet. Grind down other end about flat (or indented just a tad if you can drill the end ever so slightly with a big enough bit to make it into a very shallow well-shape: to accept a booster's push-rod), to make the length come about flush with the end of m-c piston's outer limit of travel in the cylinder--you will be filling the hollow. Again, some mc's have a flat-ended piston, against which which the orig. brake-rod pushes; these use no spacers. Others have a hollow piston, **into which the booster-rod enters about 1 inch+/-. **Here's where I feel you are "coming up short".
Did your kit come with a single-outlet, single-line mc like what came on your truck originally? or did it come with a dual-outlet, dual-line mc like comes on '67 and newer, which requires you to re-plumb your system to accept the dual-brake system?

[gimmy 64]

did you buy the booster and master from ece? i did not and had to put a longer rod on the booster

[dcramos72]

Yes, bought the booster and mc from Early Classics. They dug up my order this morning and confirmed I was shipped the correct parts and insured they should work together.
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[luvbowties]

Originally Posted by dcramos72

Yes, bought the booster and mc from Early Classics. They dug up my order this morning and confirmed I was shipped the correct parts and insured they should work together.
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If they indeed sent you the correct kit, and components were/are correct, then they may be correct. You have seemed all along that you know quite a bit about mechanics, and my evaluation of your abilities has not changed. But when we think about it, there is quite a bit of new, long, 'empty' tubing necessitated by converting to the dual brake system. When I installed my 'piece at a time' from various donor vehicles, I knew in advance that I would have a bunch of bleeding to do. So, I bought a full gallon to not only bleed the system's big volume, but to also run enough fluid thru so as to end up with all new fluid in my system. A good way to bleed front discs is to open both front bleeders and let it sit for 24-48 hours--this does a gravity bleed.

Now, there is always a chance you were sent a wrong part. To determine if booster and mc are compatible, remove mc from booster using only the 2 nuts--the lines will support the mc, and NO fluid will be lost. (1) Assume you have a deep-hole mc: Cut a 5/16 inch length of approx. 5/16 -3/8 inch diameter wooden rod(must fill most of deep hole mc's diameter) and slowly reattach mc to booster. If there is no interference, either booster rod is too short, or they omitted the spacer, or the rod needs adjusting longer if rod has the adjustable screw-on type(lengthening/shortening) rod. If you encounter any resistance pushing mc up flush with booster, that would indicate matching mc and booster. (2)Assume you have shallow-hole mc, watch when you reattach mc to booster. The booster rod should come to within approx. 0.030 inch of rear of mc's small-dimple piston. Any case: there should be no resistance mating mc to booster, else you would have partial-brakes applied at all times, causing a 'riding the brake pedal' condition.

I'd love to see a pic of your mc's piston-end and a pic of your booster's pushrod-end. I'd be looking for depth of mc-piston(deep-bore vs. shallow dimpled piston); and for booster's rod, whether short, whether it is long enough to reach bottom of deep-bore in mc piston, and/or whether it looks to be adjustable. See my email address in your private message box--IF I can determine how that forum-function works!

[dcramos72]

Bowties,

Sorry for the delayed response. I will take some pics tonight of the mc and booster rod and send your way.

Thanks so much for the info below. I will give this all a shot this weekend!

Thanks!!
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[jj1965]

I had the same issue and it was air in the system. Small leak I didn't notice and it caused the problem. I would bleed again and see if it helps. Does your MC rod have an adjustment. I extended mine until it applied the brakes and backed it off until they didn't rub a little adjustment made alot of difference.

[tincan1966]

Something else to remember- make sure the rear drum brakes are adjusted up correctly. If they are not, the wheels cyls will not bleed correctly,either, causing a spongy pedal.
Maybe I missed it, but in all the discussion about needing a spacer or not, did you seperate the booster and MC again and double check the rod depth? it's a pretty easy answer to the question of if the MC is getting depressed anough. If you already answered that question, I apologize for missing the response.

[dcramos72]

Here are pics of the MC and Booster rod. It is a deep bore (inserting a phillips it goes to a depth of 1-1.5". Rod looks to be that same length.

[gimmy 64]

try unscrewing the rod out more. looks kind of short.

[dcramos72]

The end isn't threaded. It just pulls right out, so no way to adjust length.
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[Captainfab]

If you are questioning the compatability of these two parts, first measure the length of the intermediate pushrod from the MC mounting surface, out to the end of the rod. Then measure the depth of the bore in the back of the MC piston, from it's mounting face. The depth of the bore should be just slightly more than the length of the intermediate pushrod.

[mark 66]

I had a similar problem in the past. I took a stainless bolt and cut it to fit inside mc to take up the space.worked good. mc bore size and different combonations can be somwhat trial and error. to get the right pedal feel

[dcramos72]

Measured both and booster rod is slightly shorter than piston bore depth, so I think I'm good. Must be air. Rebleeding everything now.
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