Brake Issue

[Les Gibson]

Hi all. Had Friday and Saturday Races this weekend at New Oxford Dragway in Oxford, Maine. Had a great Friday night taking the win Top ET ( Super Pro). Saturday I was running two classes, Box and 5.80 index with the Gassah Guys Club. Took the win in the 5.80 class but had to bow out after 3 rounds in Box. I had noticed in the round before that when getting on the brakes after the finish line that the pedal felt firm initially but then would get soft and eventually get really soft. After the 3rd round in Box I thought I was going to go into the sand trap but had enough brake to get slowed down enough to make the turn on the return road.

The basic info on my brake system is a Wilwood tandem master cylinder, and Aerospace Components brakes front and rear. Being a full chassis car, the master cylinder is mounted on the left frame rail just forward of the drivers seat. I replaced both residual pressure valves and the manual bias adjuster this past winter, along with new pads front and rear. Brakes felt and worked great prior to Saturday. Did some troubleshooting today and it appears that the master cylinder isn’t moving much fluid. If i pump the pedal three or four times it is firm initially but if I continue pressure on the pedal it goes all the way to the firewall. I checked for leaks and there are none. I’m thinking the master cylinder has gone bad. Anyone have any other ideas?

 

[Inertia]

If there is no fluid loss from the reservoir, the fluid level isn't dropping, but pedal goes to floor, I'd be looking at the Master. (by-passing internally)
Make sure pedal pushrod is adjusted to allow the m/c piston to fully return to its stop .

Nice work at the track,
Good luck .

PS, was this round-robin ?

 

[Les Gibson]

If there is no fluid loss from the reservoir, the fluid level isn't dropping, but pedal goes to floor, I'd be looking at the Master.
Make sure pedal pushrod is adjusted to allow the m/c piston to fully return to its stop .

Nice work at the track,
Good luck .

PS, was this round-robin ?

No loss of fluid. When I took the cover off the MC this morning to check the level both sides were full. Pedal pushrod adjustment is correct.
No, it wasn’t round, but I didn’t have much time between rounds as the run order was Box, No Box then Gassah Guys, followed by the other classes being run.

Thank you, it was the best weekend of racing that I’ve had in a while.

 

[Inertia]

Heat and pad composition are a consideration, but you been doing this a while. lol

 

[MOPARMAGA]

Hi all. Had Friday and Saturday Races this weekend at New Oxford Dragway in Oxford, Maine. Had a great Friday night taking the win Top ET ( Super Pro). Saturday I was running two classes, Box and 5.80 index with the Gassah Guys Club. Took the win in the 5.80 class but had to bow out after 3 rounds in Box. I had noticed in the round before that when getting on the brakes after the finish line that the pedal felt firm initially but then would get soft and eventually get really soft. After the 3rd round in Box I thought I was going to go into the sand trap but had enough brake to get slowed down enough to make the turn on the return road.

The basic info on my brake system is a Wilwood tandem master cylinder, and Aerospace Components brakes front and rear. Being a full chassis car, the master cylinder is mounted on the left frame rail just forward of the drivers seat. I replaced both residual pressure valves and the manual bias adjuster this past winter, along with new pads front and rear. Brakes felt and worked great prior to Saturday. Did some troubleshooting today and it appears that the master cylinder isn’t moving much fluid. If i pump the pedal three or four times it is firm initially but if I continue pressure on the pedal it goes all the way to the firewall. I checked for leaks and there are none. I’m thinking the master cylinder has gone bad. Anyone have any other ideas?

Les, I had a master cylinder go bad on my charger I had in highschool.
Only thing different than your case was when I didn't have brakes it was 0, no warning, had to do some serious offensive driving to not get into several wrecks. So that is what it sounds like to me. Only other thing I can think of is try bleeding the brakes and see if somehow a air pocket got in the lines
Good luck & good job!

 

[Bewy]

Agree with others, from the description, most likely m/c.

 

[MoparLeo]

And also complete brake system flushout with a sealed bottle of brake fluid to eliminate any excess moisture in the system.

 

[Les Gibson]

I've settled on replacing the M/C, now my next question is what bore size do I need? There are no part numbers visible on the present M/C, but I'm thinking 1" bore?

 

[MoparLeo]

For the proper Master cylinder, contact the original caliper manufacturer.

 

[71Demon540]

I've settled on replacing the M/C, now my next question is what bore size do I need? There are no part numbers visible on the present M/C, but I'm thinking 1" bore?

Did you try and bleed the brakes manually to see if there is any air in the lines someway/somehow? I have a master on my floor with anti residual valves as well. Sometimes mine will be stiff then soften up. But I never lost brakes. I also had a stupid anti proportioning valve that I had adjusted wrong years back. But that’s another story. I would personally try and bleed them manually and see if any air is trapped in the system before replacing the M/C. Those wilwood master cylinders ain’t cheap. Just my thoughts though.

Something else that may be possible is one of the anti residual valves are sticking since you replaced them last winter. Wouldn’t be the first time something brand new either is junk out of the box or fails shortly after some usage.

 

[Les Gibson]

Did you try and bleed the brakes manually to see if there is any air in the lines someway/somehow? I have a master on my floor with anti residual valves as well. Sometimes mine will be stiff then soften up. But I never lost brakes. I also had a stupid anti proportioning valve that I had adjusted wrong years back. But that’s another story. I would personally try and bleed them manually and see if any air is trapped in the system before replacing the M/C. Those wilwood master cylinders ain’t cheap. Just my thoughts though.

Something else that may be possible is one of the anti residual valves are sticking since you replaced them last winter. Wouldn’t be the first time something brand new either is junk out of the box or fails shortly after some usage.

After inspecting for the leaks the next thing I did was to try to bleed the brakes. Had the wife working the pedal and the M/C was barely moving any fluid both front and back. I could see one of the residual pressure valves being bad, but what are the chances both would be bad? This was my fifth race of the season and the brakes were totally fine at the previous 4.

 

[71Demon540]

After inspecting for the leaks the next thing I did was to try to bleed the brakes. Had the wife working the pedal and the M/C was barely moving any fluid both front and back. I could see one of the residual pressure valves being bad, but what are the chances both would be bad? This was my fifth race of the season and the brakes were totally fine at the previous 4.

Ya I’d agree with others that the master is bad then.

 

[Johnny Dart]

After inspecting for the leaks the next thing I did was to try to bleed the brakes. Had the wife working the pedal and the M/C was barely moving any fluid both front and back. I could see one of the residual pressure valves being bad, but what are the chances both would be bad? This was my fifth race of the season and the brakes were totally fine at the previous 4.

Ah yah ..... The ultimate marriage test, bleeding the brakes.
"Pump, pump, pump, hold"
"Holding"
"Pump, pump, hold "
"Are you holding ?"
"Yes, I'm holding"
"Are you pumping? "
"You didn't say pump ! "
"Well pump ! "
"I am ! "
"Well not yet ! "
"Did you say pump or hold ? "
"Oh Jesus, what's for dinner ? "

 

[Inertia]

I would personally try and bleed them manually and see if any air is trapped in the system before replacing the M/C. Those wilwood master cylinders ain’t cheap. Just my thoughts though.

There is an easy test to check for air in the brakes.

With the emergency brake applied to move the pads or shoes into contact with the disc/drum.

With the Master cylinder cap on, have the brake pedal pumped a coupla times and hold down.
Remove the cap off the master cylinder, watch the fluid surface and have the pedal released.
Any air in the system is being compressed by the pedal, - when released, the compressed air will force fluid back into the reservoir.
There should be very little return to the master, cuz, with the emergency on, - the springs can't compress the wheel cyls, - the pads (front and rear) only "relax" displacing nothing,
It would be expected to see a slight "roiling" of brake fluid in the reservoir, but any volume of return indicates air.
I have had a literal geyser of fluid shoot violently back after customer swore he bled brakes.

Brake fluid is an excellent paint remover, so if any fluid gets on paint, have lotsa water nearby to flush liberally .

No volume of fluid return, - no air,

Experience .

 

[furrystump]

Does the peddle slowly sink with normal steady brake pressure on it? Yes, MC is bad. Internally bypassing.

 

[71Demon540]

There is an easy test to check for air in the brakes.

With the emergency brake applied to move the pads or shoes into contact with the disc/drum.

With the Master cylinder cap on, have the brake pedal pumped a coupla times and hold down.
Remove the cap off the master cylinder, watch the fluid surface and have the pedal released.
Any air in the system is being compressed by the pedal, - when released, the compressed air will force fluid back into the reservoir.
There should be very little return to the master, cuz, with the emergency on, - the springs can't compress the wheel cyls, - the pads (front and rear) only "relax" displacing nothing,
It would be expected to see a slight "roiling" of brake fluid in the reservoir, but any volume of return indicates air.
I have had a literal geyser of fluid shoot violently back after customer swore he bled brakes.

Brake fluid is an excellent paint remover, so if any fluid gets on paint, have lotsa water nearby to flush liberally .

No volume of fluid return, - no air,

Experience .

I don't think he has an emergency brake or stock master cylinder location. But I understand how that would work on a stock setup.

 

[Inertia]

I don't think he has an emergency brake or stock master cylinder location. But I understand how that would work on a stock setup.

Lol, I didn't really think so, but it applies to all, I was just covering all the bases.

Was using it as a teaching opportunity for general consumption, lol

Cheers

 

[moparstud440]

If I were you I'd replace the master cylinder and see what happens. I had one go bad on the starting line of all places one time. It was a stock one. Brakes were fine all day, I staged the car and I was waiting for the tree to come down. I thought I felt the peal slowly move towards the floor as the tree came down. I left like normal, my opponent went red luckily so I decided to lift and make sure I had brakes and as I wasn't 100% sure if my pedal went soft or it was in my head. My pedal was WAY soft, like go to the floor, so I'd slowly pump it and on about every 5-6 pumps it would sorta work. I made it back to the staging lanes creeping along. I ended up having a .003 light, that got me the bye into the finals. I sat out the bye and had to run my sister in the finals. In between all that we checked things over and couldn't find any leaks or anything wrong. I think I dialed like 19.99 in the finals against here and had to idle when I staged as the brakes wouldn't hold. Made a slow pass in the finals that I lost, but ended up replacing the master cylinder and it fixed the issue. Not sure what the chances are both it a 1973 style master cylinder with 2 ports, so something took a crap, I'm still thankful to this day it I felt it on the starting line, because it would been ugly to find that out 1/4 mile later going about 115 mph than.

 

[Les Gibson]

Does the peddle slowly sink with normal steady brake pressure on it? Yes, MC is bad. Internally bypassing.

That's exactly what it's doing.

 

[Inertia]

If I were you I'd replace the master cylinder and see what happens. I had one go bad on the starting line of all places one time. It was a stock one. Brakes were fine all day, I staged the car and I was waiting for the tree to come down. I thought I felt the peal slowly move towards the floor as the tree came down. I left like normal, my opponent went red luckily so I decided to lift and make sure I had brakes and as I wasn't 100% sure if my pedal went soft or it was in my head. My pedal was WAY soft, like go to the floor, so I'd slowly pump it and on about every 5-6 pumps it would sorta work. I made it back to the staging lanes creeping along. I ended up having a .003 light, that got me the bye into the finals. I sat out the bye and had to run my sister in the finals. In between all that we checked things over and couldn't find any leaks or anything wrong. I think I dialed like 19.99 in the finals against here and had to idle when I staged as the brakes wouldn't hold. Made a slow pass in the finals that I lost, but ended up replacing the master cylinder and it fixed the issue. Not sure what the chances are both it a 1973 style master cylinder with 2 ports, so something took a crap, I'm still thankful to this day it I felt it on the starting line, because it would been ugly to find that out 1/4 mile later going about 115 mph than.

If you had line lock, it would have held any pressure you could pump up.
You prob know that with the line lock applied, you can keep pumping to increase pressure without releasing button .

Nice light, good job.

 

[Les Gibson]

I have a new Wilwood M/C on order, should be here tomorrow or Wednesday. I'll let everyone know if it fixed the issue. Appreciate everyone sharing their thoughts and ideas with me.

 

[Les Gibson]

Received the new Wilwood M/C yesterday. Got it bench bled and installed. Good brakes now. Old M/C was definitely the issue.

 

[Demonx2]

Glad you got it fixed but I didn't want to pass by on the opportunity to say CONGRATULATIONS on your weekend!! Wow - just another reason I don't want to live (and race!) in Maine: might have to race you and get sent home. Way to go, well done!!

 

[Les Gibson]

Glad you got it fixed but I didn't want to pass by on the opportunity to say CONGRATULATIONS on your weekend!! Wow - just another reason I don't want to live (and race!) in Maine: might have to race you and get sent home. Way to go, well done!!

Thank you for the kind words! I don't know about the getting sent home part! Even a blind squirrel finds a acorn sometimes. I'll get a good dose of humility at Maple Grove this weekend when I go down for the annual Independence Showdown big money bracket race. This will be my third time participating in this race and I only have one round win to show for it! Last time I participated the ol powerglide gave up the ghost on the very first run of the weekend! Went through the car with a fine tooth comb this past weekend so it's as ready as it's gonna be!