brakes issues, still....

[T77911S]

I am still having issues with brakes on the race car.
car is a late model circle track asphalt car.
It has dual MC's and a NEAL brake pedal
front calipers are HOWE and rears are wildwood. all have been removed and cleaned
MC's are the rectangle type. my pressure bleeder does not mount to them so I just ordered an adapter to fit them, problem may be the MC's are too close together to use it. I may have to unbolt one at a time.

problems start with
the MC's are mounted LOWER than the calipers.

problems:
1 cant get the system bled
2 I think the fluid may drain back since calipers are higher
3 brake bias.
4 seems like poor fluid flow to the rear's

1. last attempt at bleeding my son pumped while my wife sucked.(had to put that one out there for rawknees). I had my vacuum bleeder connected to the calipers although not a great seal at the nipple. the pedal seemed hard, best its been, after doing this. but on to problem 2
2. I got in it the other day and drove it down the street. pedal seemed spongy again, not as hard as right after bleeding. just read today about drain back and found this.

Proportioning and Residual Valves
and this
https://www.summitracing.com/search/part-type/residual-pressure-valves?cm_mmc=ppc-google-_-search-_-all-part-types-_-keyword&gclid=Cj0KCQjw_r3nBRDxARIsAJljleFF3-ce6j3gpB3pM_guLWRJso8piiL3qs0pnNeGqv5TwcP3PXaONv0a AqS7EALw_wcB

4. seems like the fluid flow to the rear is low. especially the right rear. the left rear did lock up on short test drive, not sure about RR.
it does have very old SS braided brake lines. not sure if they go bad inside like the rubber ones do

3. brake bias.
it does have the rod that goes between the to MC's BUT!! the center pivot does not move like it does on the wildwood so I am not sure of how the bias is adjusted other than perhaps rod length of each MC.

[Zeke]

Some so called SS brake lines are only rubber lines with a sleeve to look 'good'. IIRC, you got this from your FIL and he was a real racer. If that's the case I would think he'd avoid that kind of thing. Still, new flex lines are not expensive.

Thinking more about this, rubber lines are good. Maybe they are rubber wrapped with a SS sleeve simply to keep them from being cut by debris from the dirt track. I think you should stop with the bleeding and pull these off and see.

You shouldn't get drain back if there are no leaks.

Besides, you only need them to work for 15 minutes.

[John Rogers]

As for my experience and the other folks I raced with the only way to bleed the brakes is with a pressure bleeder and usually pumped to 5# which would even clean air out of a prop valve. If your m/c's do not allow the pressure bleeder to fit I would change them since air in the brakes can kill! Since you said dual m/c's are they connected with a bar so both move with the pedal, if so I would disconnect the cross bar and do fronts and then rears. Pumping the pedal should work with one end at a time after you make sure there is clearance so the m/c piston comes all the way back.

[porsche tech]

Once had a guy tow his Boxster in after he had R&R'd the calipers to paint them and couldn't get them to bleed after reinstallation. He put them on the wrong sides which put the bleeder on the bottom of the caliper instead of the top. Weird one.

[Jims5543]

Have you considered sourcing and installing speed bleeders?

Introduction - Speed Bleeders - Russell Performance Products

You basically crack open the valves and they act like check valves, no back flow.

Fill master, keep an eye on it and pump several times. I used to do the 2 backs then the 2 fronts on my RX7 with these. They worked great and saved a lot of time.

Also, once you have the brakes bled and sorted and you still have back brake lock up, can you change the bias? If not, then consider modifying the rear pads so they are smaller and bite less.

[T77911S]

i was looking at the speed bleeders. need to check the size of nipples I have now. (did rawknees hear that).

the car was built around 86. I assume the lines are that old.

checked them again last night. a quick pump hardens the pedal and seems to stay for a bit. going to track today to see what they do. will take it slow.

drain back does seem, odd. you would think it would be like putting your finger on the end of a straw when its in a glass of water and you remove it and it holds the water. but they do make a device specifically for that problem ,. go figure.

looked at the rear rotors. looks like they are actually working after my short drive. the corrosion has worn off. it wasn't bad, just a light rust.

[techman1]

Heard, but never seen / verified:

If the brake line rubber swells, it first becomes evident with a hanging caliper.
The thought is the pressure from the MC is enough to overcome the swelling, but when you release the pressure inside caliper will not release. Just check if it is binding after a drive.

[wayner]

Try bleeding at the Master cylinder first.

Sometimes air gets trapped

[cstreit]

You’ve already stated the cause.... can’t get the system to bleed... ...but how do you know this is the issue?

What symptoms are you experiencing that led you to this conclusion?

[T77911S]

if I first press the pedal it goes down a little further than it does the second or third pump.

took it to the track.
I had brakes, not confident in them though.
the track is shaped like a "D" so I am turning a little going into turn 1. about lost it a few times due to rear end coming around. it does not help I am learning left foot braking so I was very slow to come off the brakes once it started to come around. (kept it straight).
bias could be part of the issue there as maybe the left rear is locking up.
I did not have problems on turn 3 as I was braking straight line.

still getting up to speed
I am going to look at the bias adjustment again.
the ONLY way I can see the bias changing is for the pivot in the brake pedal to move from one side to the other. maybe it is stuck.

I need to change the bias and drive it again to see how they are.

[Jim2]

Sounds like something is not rigid at the caliper/rotor, perhaps wheel bearing.

[cstreit]

This could be pad knockback.

If a wheel bearing is loose or the hydraulics are losing a little residual pressure then that first pump moves the pad back into contact with the rotor. THe second applies the pressure.

If this mainly happens after a longer delay using the brakes or after an especially rough section of track then almost certainly is.

This can be solved by fixing the loose wheel bearing... ...adding anti-knockback springs or seals - or a residual pressure valve that holds a few psi of pressure in the system.

[T77911S]

i was looking at the residual pressure valves.
they say they are for brakes when the calipers are higher than the MC.

[Zeke]

Is the LR caliper set up to bite harder to help the car rotate? If so, that would seem to be a very difficult adjustment to maintain spot on. You might benefit from balanced brakes while you learn to drive the car. Did you tell us whether there were proportioning valves in the system? I know you have a weird set up pedal to both MC's. Would you consider yanking all that out and buying a stock car set?