So I purchased the CPP 6872CBK assembled front disc brake kit for my 1969 GS400. https://www.opgi.com/brake-systems/...a-body-stock-spindle-std-booster-m1790dx.html To make along story short, after bleeding the brakes, the pedal is good until it push it a couple times (like trying to stop, then go, then stop again). Then it keeps going farther down, unless I pump it a couple times. It doesn't just drop, it feels like it is very gradual, and the pedal is father down the next time I push it. I looked all over the brake system and there is no fluid leaking anywhere. When my lady helped me bleed the brakes, I did not see any air coming out. Just solid fluid. I have a feeling that the master cylinder is bad and was just looking for second opinions or tips. By the way, I did bench bleed the master cylinder before installing, too. Let me know what you all think.
Sounds like theres air. But Ive had bad new masters before....Are you sure she doesn't have short legs? She was pushing the pedal all the way to the floor and not letting up till the bleeder was tight?
Bad master cylinder. Sometimes another thing they will do is when you hit the brake, they will also slowly creep to the floor.
https://www.summitracing.com/parts/mvp-0105 This was a great investment. It really helped me. I could not get all the air out any other way.
Well, after doing some impromptu internet research last night, I may have figured it what the issues is. I saw this more than once, on different forums where people had the same problems with their CPP disc brake kits. Apparently, if the front caliper bracket is not perfectly aligned and the caliper is not free to move on the sliders, it can cause this exact issue. I'm pretty sure that this is the case with at least the right caliper. When I was torqueing the lower ball joint castle nut, I noticed that the bracket was flexing and bent a bit when it was up against the lower control arm (turned spindle all the way to the right, tie rods not connected). Both of the front calipers took some effort to get into the brackets, too. If the surface of the pads is not parallel to the rotor, and the caliper cannot move freely, it causes extra effort to grip the rotor, and the pistons to not return in the calipers. I must have read 4 or 5 posts with the same symptoms, issues, and solutions. I even found some instructions for bleeding that were not included with the kit I got. I'll post up later and let everyone know if this worked out. Thanks for the input so far!
I don't know if this will help but when I changed my system over (kit from Inline Tube) It took several master cylinders and combination valves to find a set that worked as intended and didn't leak. I even tried pulling a set out of the junkyard and just had terrible luck. In the end, I used a "new" master cylinder from inline AC/Delco but had to use the seals/pistons from a "new" Inline Tube Master. The bore on the "new" Inline master was .002" oversize and made the fluid bypass the seals. The "new" Delco seals were undersized and failed to build pressure (probably shrunk over time). It took 2 "new" masters to make one working. 2 of the first combination valves leaked out the back. I had to finally use the inline tube version combination valve that Todd sells. https://www.stage1restoration.com/product/distribution-block-1971-72/ Don't forget the aluminum bleeder tool that screws into the switch. After the parts finally worked in sync, I bled the brakes so many times and just couldn't get the air out. The bleeder fittings didn't show any bubbles but the pedal was never right. After using the Motive power bleeder...air bubble problem solved! I had bought a Wilwood combination valve with separate circuits to use, if this hadn't worked. I may still switch since I like the idea of separate circuits. Lastly I had to replace calipers recently because they were sticking. This was a real nightmare scenario, I think mostly because of poor quality/questionable overseas parts. I wasn't able to drive my car much for the 2 years it took me to figure this out. UGH. I miss the days when you could drive to the local parts store and buy American made parts. They rarely failed and the tolerances were right on. Rant over, hope you find some help in there somewhere. Putting disc brakes on shouldn't be so hard. FYI, thanks everyone for all the posts about swaping disc brakes and issues. I think I read them all.
Well, for future reference, when installing an aftermarket front disc brake kit, make sure that the calipers can move freely in the brackets. Mine were binding and not able to move, especially the right one. I make some minor adjustments to the brackets with a hammer and center punch (after some careful studying and measuring), squared the ends up with a file, put some caliper lube on the sliding parts, got my better half to help bleed brakes again, and it seems to be working much better now. The peddle stays firm through multiple applications with the motor running. I couldn't take it for a test drive though, due to the intense storm that rolled into the area a while ago, while I was putting the wheels back on. I'm supposed to get the alignment done tomorrow morning, so that will be the test drive.
Sometimes this little tool will help the Bleeding Process . . . . Not saying this is everyone's issue with Brakes but it helps the Bleeding Process. Brake Proportioning Valve Bleeder Tool can lock the low pressure exhaust valve to make your braking system bleeding easy and avoid the combined valve from tripping. APPLICATION — Compatible with various popular non-adjustable GM combination valves, Disc/Disc Disc/Drum PV2 & PV4, AC Delco 172-1353, 172-1371 brake proportioning valves. HIGH QUALITY — Made of aluminum (NOT PLASTIC) A must have tool for bleeding brakes. HOW TO USE — Remove the brake light warning switch on your Combination Valve and replace it with this tool. When Brakes are bled re-install the warning switch.. $10 - https://www.stage1restoration.com/product/brake-proportioning-valve-bleeder-tool/ .
Thanks Todd. I actually do have one of those and it worked well on the initial bleeding. I would definitely recommend it! I bought the one from CPP since that is the kit I have.
