My symptom is just no power. Brakes have almost no grab and what I do get seems to happen too far into the stroke (with the pedal too near the floor). Pedal does not pump up like it would with air in the lines, and does not sink when held down as it would with a leaky master. The hardware is: Pedal with 4:1 ratio GM 11" dual(!) power booster (New) CPP 1" disc/disc master cylinder (New) Front 2006 Crown Vic calipers 48mm dual piston (new) Rear 1997 Grand Cherokee calipers 48mm single piston (new) All new hard lines & rubber lines. All new pads & rotors Proportioning valve from an unknown 1990's disc/disc Jeep donor. Both of the caliper donors would have had 1" bore masters, so the master bore should be good, but I also tried this with a 1 1/8" bore master and it seemed a bit better in terms of the brakes starting to work higher in the pedal stroke, but you still wouldn't have wanted to stop quickly from freeway speeds with it. This is all in a '59 Dodge 1/2 ton pickup. Since everything else seems like it ought to work, I'm eyeing the prop valve. If it was off an abs equipped vehicle could that cause my problem? Am I overlooking something obvious??
Ok, that one I posted has an internal proportioning valve, metering valves and brake switch. I have had some issues making it work.
Yes- though the calipers may be new rebuilds as they were on there before I got it. The m/c & booster for sure are new new, not rebuilds.
I have used CCP for several cars, besides good products they do have an excellent tech line. I'd pose this question to them and have them send you an adjustable proportioning valve that will work with your components.
Pedal ratio sounds a tad on the low (numerically) side and the master probably a bit small on the diameter. I know changing those together is arguably self cancelling but if there's insufficient fluid volume you'll need to sort that and them deal with getting the pressure up. Having said that a duel 11" booster should add more power than you'd ever need. Hmmm. Need to look that up somewhere. Chris Edit; info I have suggests boost assists as follows:- 7" = 50% 7"d = 70% 8" = 72% 8"d = 101% 9" = 101% 11" = 138" 11"d = ???? assuming your booster is good you've got plenty of help! Edit 2 I calc a 1" with 4:1 and say 150lbs input with additional 138% assistance will net you about 1800psi which is a lot of line pressure. Booster not working then?
How are the MC and pedals mounted? Old tin flexing can change dimensions as you apply pedal pressure.
Is that not the usual way? Pedal & Booster mount are stock to the truck- it had power brakes from the factory- so I the whole assembly is tied into the dash as well as beefed up at the firewall. I'm not seeing it flex. Yes, I wondered if the bigger bore, but with a higher ratio might help, but wouldn't that mean more travel at the pedal? Seems like I want less travel (with more bite), not more travel.
If all you changed was the ratio then yes, you'd have more pedal travel, but increasing the master bore works the other way, so there's a balance going on. But if your booster is doing what it should be, especially given its' size, you should have more than adequate line pressure anyway with what you've got, so should stop well even if the pedal seems a bit low. A pressure gauge at the caliper would tell you what's really happening. Chris
Typically prop valves are used on disc/drum systems because of the size difference between caliper pistons and wheel cylinder pistons. In my world of truck repair, trucks with hydraulic four wheel disc brakes do not use any kind of prop valve. The only type of valve between the master cylinder and calipers is a pressure differential valve to monitor the front and rear brake circuits for pressure loss. Sent from my iPhone using H.A.M.B.
I had a similar problem on my COE......new GM 11" booster was bad right out of the box. Replaced and works great. Was scary to drive without the booster working properly.
When I start the engine with my foot on the brake, the pedal sinks like you'd expect of power brakes. Is there some other way to tell if the booster is...boosting?
A few things to verify. Your master cylinder's full stroke 1- the master cylinder stroke of the 2006 CV - front calipers My little bit says they have a 40mm stroke with 1" bore. That will cause you a lack of sufficient volume to the calipers. 2 - the master cylinder stroke of the 1996 GC - rear caliper. Your Master Cylinder stroke , the CV MC and the GC MC need to match so that the displaced volume is equal. 3 - that your master is receiving the full stroke from the booster out put rod. That rod is adjustable. You really need the master to be fully bottomed out before the pedal bottoms out on the floor board.
** RE #1 Hmm. This may be it: I believe the stroke on the CPP master is just a tad over 1". That is a pretty big difference from 40mm. So if this is the case, at full stroke the volume of fluid pushed would be only about 60% of the volume pushed by the CV master. That sounds huge. Might also explain why the 1 1/8 MC felt a little better than the 1". ** Re:#3 The pin between booster & master seems the right length, and both are GM style, but I wonder what Ford does with the booster/master connection to accommodate the much longer stroke of the master?
Hey 31Vicky- Where did you find that 40mm stroke measurement? I've been all over the web and can't find a stroke number for the G Cherokee master? Regarding vacuum- That's a good question. Since it is not an especially radical cam I assumed I had plenty, but I should check it to be sure.
My money is on pushrod length, I just went thru the same stuff. I lengthened by 3/16 adjustable rod. Brakes came on too soon, so shortened it a little. Seems good now
hello, I thought the grand cherokee used a 1 1/8'' what is the part number on your COMBINATION valve is it X 1KH2817 you may have a disc drum valve? could you not simply fit the grand Cherokee booster, brake master and valve complete unit ?? I know the brake master from a Cherokee doesn't fit the gm c3 vette style stuff.............
I can only remember a couple of disc/disc vehicles that did not use a proportioning valve, either external or part of the ABS system. The reason was/is the same as with disc/drum systems-to keep the rears from early lockup, for safer braking and meeting DOT stopping distance requirements.
I looked just a little bit, quickly found one reference amongst the entire interweb and it was right here on the Hamb. -Just one and the first one. That's why I said to verify it.
4woody, As mentioned earlier, your 4:1 pedal ratio is on the low side for power assist; normally closer to 3:1. You want to measure the master's full strokes to know for sure, but ones I've worked with (mostly Ford) are well over 1". Check the booster output rod (pin) for about 1/32" clearance, (or whatever the spec is for your booster) with full vacuum applied to the booster, normally about 20" Hg. I would remove the Jeep prop valve and only use an adjustable proportioning valve. Verify the pedal can full stroke the master. Very important! Bleed the system slowly and repeatedly with no vacuum assist, ideally with a pressure bladder. When you have a pedal, pressure check for leaks by "standing" on the pedal, with about 150-200 lbs. effort. If no leaks/weeps, finish bleeding. This should result in a firm high pedal with no assist, and medium pedal with vacuum.
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