C5 brakes - 15/16" manual master - high effort & travel in pedal

[bochnak]

70’ chevelle originally all drum car
Swapped in C5 discs/calipers all corners
Prop valve installed on rear line after distr block
77’ Malibu manual master 15/16” bore
Push rod correctly adjusted AFTER bleeding brakes (push rod was pre-loading master piston during bleeding of brakes)
Bench bled master



Took the car out the other night after finishing the swap. The brakes work, but not to my liking. Pedal travel is several inches. If I look under the dash and push on pedal with my hand, master piston depresses into bore about ¾”. I have to stand on the pedal with both feet in order to get the car to stop in a hurry. I can't get brakes to lock up.

Either I have air in the system, bad master?, or I need a smaller bore size. Thoughts?

[Apogee]

Matt, what are you running for pads? Are these new rotors or take-offs? What did you do for bedding in the pads and rotors?

I think the first step should be to verify that you don't have any air in the system and that your master cylinder is not failing. If you can apply the brakes and hold them, the pedal should not sink at any rate. If it does sink, that means that it's internally bypassing fluid and needs to be rebuilt or replaced. Since it's probably a remanufactured unit, anything is possible there. When you bench bleed the MC, did you plug both outlet ports and confirm that is was indeed fully bleed? It should hydraulically lock once the seals clear the compensator ports inside the reservoirs when you try to stroke the piston...if it doesn't, then it still has air stuck inside the MC somewhere.

A smaller bore master cylinder will provide more pressure at the calipers, however it will come at the expense of more pedal travel assuming that everything now is fully bleed. Your pedal travel now sounds a bit excessive. There are a lot of guys running the 7/8" bore Wilwood units on here with good results, although even with that master cylinder, we'll typically recommend running at least a "FF" rated coefficient of friction pad, if not something more aggressive like a "GG" pad (Hawk HP Plus, EBC Yellowstuff, etc).

HTH,
Tobin
KORE3

[jtm311]

I agree with Tobin sounds like air still in the lines or the master. I bought one of those power bleeders for $70 best thing I ever purchased

John

[bochnak]

Matt, what are you running for pads? Are these new rotors or take-offs? What did you do for bedding in the pads and rotors?

Pads and rotors are take-offs. I did my best to match the pads to rotors as the seller did not label them. I did nothing to bed the pads. I simply took a few spins around the block and did not like the feel of the pedal.

I think the first step should be to verify that you don't have any air in the system and that your master cylinder is not failing. If you can apply the brakes and hold them, the pedal should not sink at any rate. If it does sink, that means that it's internally bypassing fluid and needs to be rebuilt or replaced.

Pedal does not sink at all.

Since it's probably a remanufactured unit, anything is possible there. When you bench bleed the MC, did you plug both outlet ports and confirm that is was indeed fully bleed? It should hydraulically lock once the seals clear the compensator ports inside the reservoirs when you try to stroke the piston...if it doesn't, then it still has air stuck inside the MC somewhere.

Yes, it's a reman unit. I simply bench bled the unit with tubes running back into reservoir. Unit came with plastic plugs, I'll take the master back off and use these to confirm whether it will lock or not.

Thanks for the response. I'll have some time this weekend to mess with it.

[bochnak]

I agree with Tobin sounds like air still in the lines or the master. I bought one of those power bleeders for $70 best thing I ever purchased

John

Thanks. I have used a power bleeder in the past, nice tool to own. For the moment my power bleeder is a 12 pack and some neighbors

[bochnak]

Here is my best description of pedal feel: Pedal travels several inches. First couple of inches I guess you can say it's spongy, and pedal gets firm and stays firm during last 1/2" of travel.

[bochnak]

I was able to work on the car last night. I pulled the master off, plugged the ports, and verified that it would hydro lock. It was in fact “locked” once the piston depressed about 1/8”. I re-installed the master and power bled the entire system this time versus the 2 man manual way the first go around.

The pedal now has way less travel, is firm after 2” of travel. I was unable to road test due to rain. I’ll try and take it for a spin tonight.

I noticed when manually bleeding, the fluid from rear bleeders trickled out, while fronts moved quite a bit more volume. With power bleeding at 20psi, I was able to get way more air out of the rear lines. I bet this was my problem.

Now I think I am faced with another problem: bore size. The 77’ Malibu manual app calls for a 15/16” bore size. The master I bought was a cardone 10-1639, and bore size is not listed on MFG’s site, and autozone lists it as a 1”. I bought it from O’Reilly and the site and parts guy do not know the size.

Thanks for all the responses.

EDIT: Emailed cardone regarding bore size. I received a response confirming 10-1639 is 15/16".

[Gitter Dun]

Try running without distribution block.

[bochnak]

I test drove the car last night. Pedal is great now. I was able to lock up the brakes with 1 foot no problem.

The 15/16” bore provides great modulation, is a bit on the firm side (pads are probably still not bed in), travel is good. I noticed brakes started to bite better once I got some heat into them.

I’m satisfied

Thanks for all the help, guys

[bochnak]

Try running without distribution block.

What would I gain from this?

[Apogee]

Running with a distribution block/combination valve is one way to remove some variables, although none of your symptons were really pointing towards an issue like that. If/when you're at your wits end, removing components from the system one by one can be a last resort to isolate a problem, but you can usually reason your way through hydraulic issues fairly well if you take your time and don't jump to premature conclusions.

In any event, congratulations on getting it figured out and solved. The initial bite of the pads is going to largely be a function of the pads themselves, so you can usually go to a more aggressive street compound if you don't like the current feel and would like more initial bite. Since the pads and rotors are take-offs, I wouldn't expect them to need to be bedded-in, although putting the different pads on different rotors can require the pads to conform to the new rotors due to the difference in wear patterns.

Tobin
KORE3

[bochnak]

The initial bite of the pads is going to largely be a function of the pads themselves, so you can usually go to a more aggressive street compound if you don't like the current feel and would like more initial bite. Since the pads and rotors are take-offs, I wouldn't expect them to need to be bedded-in, although putting the different pads on different rotors can require the pads to conform to the new rotors due to the difference in wear patterns.

Tobin
KORE3

At some point I will upgrade to better pads. I tried my best to "match" the used parts. I'm just glad to get rid a 4 wheel manual drums.

I'm going to take a break from suspension and brakes and focus on a new powerplant.

[Gitter Dun]

What would I gain from this?

I dont and never have run a distribution block. Rear brakes are plumbed from MC to proportioning valve to rear brakes, front brakes direct from MC to brakes. Thought it might help but looks like you got it fixed.

[Vicinity]

I dont and never have run a distribution block. Rear brakes are plumbed from MC to proportioning valve to rear brakes, front brakes direct from MC to brakes. Thought it might help but looks like you got it fixed.

Odd, I thought the way you have it is the way it was supposed to be done. My LS1 brakes are plumbed exactly the way Gaetano explained, I have no problems.

[bochnak]

My chevelle was originally a drum/drum car, so the distrubution block is a 50/50 valve with the dummy light feature. I did not have to touch it for this swap. I chose to install the prop valve further downstream to retain the brake light feature.

[Pete68]

Matt, FYI Im running the C5 master cylinder with my C5 rotors and calipers. Brakes feel excellent, great feedback, good control and modulation. Effort is very good, not too hard or too over boosted. I bought the master cylinder and booster on ebay used for around $150. Something to consider.