The Rodding Roundtable
Motorhead Message Central => Rodder's Roundtable => Topic started by: 40 on October 15, 2005, 11:58:33 PM
Did I mention before that I HATE brakes??I'm trying to finish up my 36 and drive it a bit before the snow flies and am having trouble getting a good pedal.It is an under floor,4 wheel disc set-up with a 7" single diaghram power booster.I have 16 to 18 inches of vaccum,the correct residual valves,have bench bled the master cylinder and bled the system 3 times...once manually and twice with a power bleeder...once from the m/c outward and once from the bleeders in.Have I ever told you guys how much I hate brakes :x With the motor off,I have a great feeling/firm pedal but the moment I start the car....The pedal softens and goes ALMOST to the floor.I have adjusted the push rod to the point that I have just a slight touch of drag on the brakes.When I engage the pedal,all of the calipers seem to be moving the pads etc correctly...I can stop the wheels but it just barely holds the car still at idle and the pedal is within a 1/4" of the floor.Have I said before how much I HATE brakes! I am not totally sure of the bore size...I think it's an inch and an 1/8.I am also not real sure of the manafacturer as this setup came with a project I purchased...it was new in the box but had no info with it.It is the typical Corvette style setup sold by ECI,Master Brake etc.I am not a big fan of single diaphram boosters...I always order a dual but I have seen this identical set up used many times with good results and am thinking I may have a defective booster or M/C? Any thoughts or help will be greatly appreciated....Man,I HATE brakes :roll:
Two possibilities
One, there is air in the system yet
Two, you have a bad residual check valve
Quote from: "40"With the motor off,I have a great feeling/firm pedal but the moment I start the car....The pedal softens and goes ALMOST to the floor.
If you can apply the brake with the engine off and get a hard pedal, keep your foot on the pedal while you start the car. (Not sure if this is what you did.) ....Does the pedal drop as far?
If you pump the brakes rapidly, does the pedal get hard again? ...If yes, I agree with Enjenjo.
Quote from: "40"I have adjusted the push rod to the point that I have just a slight touch of drag on the brakes.
If all the pads are in contact with the rotors with your foot off the brake, then there would be very little fluid moved by the m/c upon brake application, so the pedal should remain firm. ....I don't think a faulty rpv would apply here, but trapped air, or a bad booster may be at fault.
Which push rod are you adjusting? ...The rod between the pedal and the booster, or between the booster and the m/c?
Quote from: "40"When I engage the pedal,all of the calipers seem to be moving the pads etc correctly. ...I can stop the wheels but it just barely holds the car still at idle and the pedal is within a 1/4" of the floor.
Possibly not enough assist from the booster?
TOO MUCH travel of the brake pedal? ......Many cars with power brakes required less travel of the brake pedal, and reduced the pedal ratio by moving the push rod closer to the pivot.
Could it be possible that the rod from the booster to the m/c needs to be longer, and the rod between the pedal and the booster needs to be shorter? ....(I'm not sure about this, just thinking aloud!)
One time I got triped up on something like this and it turen out that I had the calipers on the wrong sides,It was on a mustang and it looked like I was bleading out of the top of calipers ,but WRONG,look close.
Russ
Well...I had another go at the brakes last night.I replaced the residual valves with the ones from the 37 chassis I'm building and re-bled the entire system....same result :x I also removed the booster and varified that I had about 3/32" clearance on the rod between the booster and M/C.An old timer told me to push the plunger in on the booster,hold my thumb over the hole and see if the pressure bled off...If not,he says it's definately not the booster....I did this and it held so am thinking the booster is probably OK.In response to the questions above....I have a firm pedal,with my foot holding the brake,it softens and goes nearly to the floor when the car is started.Pumping the brakes seems to have little affect on the pedal.I can hold the pressure on the pedal for a good length of time with no pedal fade whatsoever...to me that seems to indicate that the M/C is OK ?I didn't accomplish anything in regard to correcting the bad brakes but out of frustration.... I did manage to put a nice dent in the hood :roll: Did I mention I HATE BRAKES!!Guess after serving my 24 hour cooling off period....I'll have another go at it.Maybe I should farm this one out before I have to rebuild the entire car :roll:
Daryle, One of the magizines last month had a article on this same thing. I'll see if I can find it. If you useing the a 1" piston master cylinder, it maybe to big. They also talked about the booster.
On my stude I went from a 1 1/8" bore to a 1" bore master cylinder and
it made a big difference.
I think the 1" is 78 Corvette, after they got rid of the big piston Delco
calipers. It took 3 tries to get the proper M/C at my Parts Plus store.
Worked very late last evening to finish up a home we're building up on the river and didn't get back after the brakes.Since I don't feel real confident with the componants used in the set-up,I am leaning tward scrapping the entire system.I will replace it with the dual diaphram booster and go to a 1" or possibly a 7/8" bore cylinder....this will require revamping the mounting bracket and re-routing the brake lines but should give me the brakes I'm looking for.....I HOPE :roll:
Mike,If you can recall the mag and month that brake article is in I'd appreciate it.....I probably have the mag as I subscribe to nearly all of them....that said,they are stacked on the floor in the corner of my office,I haven't even looked at one since probably last February!
Daryle, I found the article but I forgot which one it was again. I did leave it laying out. As long as the dog doesn't eat it today, I should be able to tell you tomrrow. It was not the same problem you are having but did suggest using a 1" MC and at least a duel 9" booster.
If you pump the pedal do you get a higher pedal?
Good problem solving brake post and perhaps should be included in the tech forum for furture reference once all gremilns are worked out successfully.
I just recently had a car with a similar problem, with every thing right, it just didn't have enough brakes. In this case, it had a 7" single booster, and a 1 1/8" bore master cylinder. After changing the booster, and master cylinder, with no improvement, I changed to a 7" dual diaphram booster, and a 15/16" bore master cylinder. that solved the problem.
by the way, if you have Wilwood residual valves, I have yet to see a 2 psi valve that would work at all. I will no longer use them.
Daryle. The dog ate one of my parts books but spared the Nov 2005 Car Craft. On page #62 is the article that I think might help. The dog is a good hunter......really. Check your vacuum, at idle, in drive, with your foot on the brake. The article talks about a different problem than your but may shed some light on it for you. Do the the rear caliper have 2 bleed screws each? I have garage space if you get tired of it :lol:
Thanks Mike...I've got that mag around here somewhere....I see Streetrodder did a multi-part article on brakes that seems to be well written and informative also....Now,all I need is the time to read them!!Also...Before I forget...I'm planning a surprise birthday party for the wifes 50th....I have rented the Knights of Columbus Hall near our house.It will be on Saturday,October 28th.I'll shoot you an e-mail with more info....it just popped into my head so I thought I'd mention it in case my "OldTimers" kicks in :roll:
Daryle, Thats that opening day in Iowa and I've put up with this dog all year. I would hate to disappoint the dog but will see. Anita said her birthday was coming up. We were going to send her a half a dozen cards, just to remind her.
Quote from: "40"Did I mention before that I HATE brakes??I'm trying to finish up my 36 and drive it a bit before the snow flies and am having trouble getting a good pedal.It is an under floor,4 wheel disc set-up with a 7" single diaghram power booster.I have 16 to 18 inches of vaccum,the correct residual valves,have bench bled the master cylinder and bled the system 3 times...once manually and twice with a power bleeder...once from the m/c outward and once from the bleeders in.Have I ever told you guys how much I hate brakes :x With the motor off,I have a great feeling/firm pedal but the moment I start the car....The pedal softens and goes ALMOST to the floor.I have adjusted the push rod to the point that I have just a slight touch of drag on the brakes.When I engage the pedal,all of the calipers seem to be moving the pads etc correctly...I can stop the wheels but it just barely holds the car still at idle and the pedal is within a 1/4" of the floor.Have I said before how much I HATE brakes! I am not totally sure of the bore size...I think it's an inch and an 1/8.I am also not real sure of the manafacturer as this setup came with a project I purchased...it was new in the box but had no info with it.It is the typical Corvette style setup sold by ECI,Master Brake etc.I am not a big fan of single diaphram boosters...I always order a dual but I have seen this identical set up used many times with good results and am thinking I may have a defective booster or M/C? Any thoughts or help will be greatly appreciated....Man,I HATE brakes :roll:
What kind of calipers do you have on the back?
Quote from: "enjenjo"I just recently had a car with a similar problem, with every thing right, it just didn't have enough brakes. In this case, it had a 7" single booster, and a 1 1/8" bore master cylinder. After changing the booster, and master cylinder, with no improvement, I changed to a 7" dual diaphram booster, and a 15/16" bore master cylinder. that solved the problem.
Frank...I can't understand why you would have brakes with a smaller master cyl. as it wouldn't move as much fluid when stepping on the binders :? :?
John
QuoteFrank...I can't understand why you would have brakes with a smaller master cyl. as it wouldn't move as much fluid when stepping on the binders
In this case, the master cylinder was too big to give an effective multiplication of force, which combined with the 7" single diaphram booster, also not know for good force multiplication, even standing on the brakes, you could not apply enough force to stop the wheels. The smaller master cylinder bore multiplied the force more, and the double diaphram booster, increased the force multiplication enough to make the brakes effective.
Mike...It is opening day in Nebraska as well....Katie is very excited as well.Worse than that,the Huskers play Oklahoma in Lincoln that day....my tickets are laying on my desk...unfortunately,I fear I may not be the ones in my seats come the 28th :evil:
Decided to revamp the entire system and go with a 7/8" bore M/C and an 8" dual-diaphram booster if I can fit it into position without to much modification. There is an extremely well written,very informative 2-part article entitled "Brake Time" written by Ron Ceridono in the August and September issues of StreetRodder Magazine and a follow up on boosters in the December issue.It is full of illistrations,charts etc explaining clearly how an entire brake system works....one of the better articles in StreetRodder in a long,long time :shock: It is well worth the read....I learned a lot! I still HATE brakes but after reading the article....perhaps not as much :roll: The article Mike eluded to in his previous post is also a good read.Perhaps one of the Franks could include this info in the Tech section for future referance??
Quote....it just popped into my head so I thought I'd mention it in case my "OldTimers" kicks in
Before I forget...I'm planning a surprise birthday party for the wifes 50th....I have rented the Knights of Columbus Hall near our house.It will be on Saturday,October 28th.
Worse than that,the Huskers play Oklahoma in Lincoln that day....my tickets are laying on my desk...unfortunately,I fear I may not be the ones in my seats come the 28th
Daryle,
Think the "OldTimers" already kicked in :lol:
You might want to check your calendar as the 28th is on a Friday. The game is on Saturday the 29th. :( Just had to give you a hard time. If you want to sell the tickets I have 2 son inlaws that would be interested in buying them from you :D .
later
bob
One of the biggest mistakes I have seen on brake set up is the lines are reversed on the master cylinder. Make very sure that the large resevor is hooked to the front!!!!!!!!! I did this wrong and I have fixed other cars that were wrong. For a while Speedway motors had a picture of a setup in their catalog that was wrong!!!!!!!!!! this is an easy fix before you go throwing everything away.
Don
Quote from: "40"Decided to revamp the entire system and go with a 7/8" bore M/C and an 8" dual-diaphram booster if I can fit it into position without to much modification. There is an extremely well written,very informative 2-part article entitled "Brake Time" written by Ron Ceridono in the August and September issues of StreetRodder Magazine and a follow up on boosters in the December issue.It is full of illistrations,charts etc explaining clearly how an entire brake system works....one of the better articles in StreetRodder in a long,long time :shock: It is well worth the read....I learned a lot! I still HATE brakes but after reading the article....perhaps not as much :roll: The article Mike eluded to in his previous post is also a good read.Perhaps one of the Franks could include this info in the Tech section for future referance??
Stacey on the HAMB just posted what her problems (issues) were. She just figured it out after quite a while and lots of flustrations. Quoted from her:
"Here's what was wrong..
#1 we had to reverse the lines on the master cylinder
#2 we had to make a threaded rod to take up the gap between the plunger rod and master cylinder.
Everything is GREAT with these changes, I can slam on my brakes and leave awesome skid marks!
Stacey"
Hope it helps
Quote from: "enjenjo"QuoteFrank...I can't understand why you would have brakes with a smaller master cyl. as it wouldn't move as much fluid when stepping on the binders
In this case, the master cylinder was too big to give an effective multiplication of force, which combined with the 7" single diaphram booster, also not know for good force multiplication, even standing on the brakes, you could not apply enough force to stop the wheels. The smaller master cylinder bore multiplied the force more, and the double diaphram booster, increased the force multiplication enough to make the brakes effective.
Yes, i understand that, but it seems that the brake pedal went to the floor when the engine was started, ASSUMED that a larger bore master was in order, not smaller.
John
You;re right, my pedal didn't go to the floor. It was just ineffective.
This goes back to air in the system, or bad residual valves, or maladjusted linkage. When you eliminate every thing else, the unlikely is the only thing left.
Bob...You're right....I think the "OldTimers" has already got me! Her Birthday is indeed Saturday the 29th not the 28th.I have a friend who has asked for my Oklahoma tickets but is unsure if he can get away....If he can't,I'll shoot you an email if they are available.Should be one heck of a game :shock: GO BIG RED!!!
I am thinking about using a remote fill for the M/C...mounting it fairly high on the firewall.....this will get it above the M/C and wheel cylinders and hopefully create a little additional line pressure.Any thoughts or experiences ??I have very little clearance under the floor so if nothing else...It'll make checking the fluid easier :roll:
Quote from: "enjenjo"You;re right, my pedal didn't go to the floor. It was just ineffective.
This goes back to air in the system, or bad residual valves, or maladjusted linkage. When you eliminate every thing else, the unlikely is the only thing left.
That was one of the things about Daryle's problem which I couldn't understand.
I can understand a smaller m/c bore generating higher fluid pressures, which in turn creates stronger holding power.
However the original post said the pedal was firm with the engine off, and the pedal would drop almost to the floor when the engine was running.
Assuming all the air had been bled from the system, how would the m/c bore be a factor here? ....Daryle also said he set the pads against the rotors so the brakes were dragging slightly. ....Unless the booster applied more force to compress any air to a higher pressure, why would he lose the firm pedal, and where would the m/c move any additional fluid? .....Ballooning brake hoses??
Please know I do not disagree with anything Frank said above.
Under the conditions described, I don't see how decreasing the bore of the m/c would keep the pedal from dropping near the floor. If anything, the larger bore will displace more fluid with less pedal travel, but will result in a lower fluid pressure at the calipers.
From what I have been able to learn, it doesn't really matter which port the brake lines are connected to, UNLESS there is an rpv or proportioning valve built into the master cylinder, or UNLESS a combination valve is used. ....This is assuming the m/c has a straight bore, and is not a stepped-bore design.
GENERALLY, but not mandatory, the front brake circuit is connected to the m/c port closest to the push-rod. .....On a disc/drum system, the discs are usually connected to the larger reservoir.
Master cylinders for a disc/disc system should have TWO large reservoirs. ....According to law, the reservoirs must be large enough to hold enough fluid for a specified number of brake applications. ....Disc brakes (generally) require more fluid volume than drum brakes, so the reservoir capacity is usually greater.
Laziness has its advantages! ...I won't change parts without knowing why! :D
its easy to bleed all the air from the lines but should the calipers be swaped side to side during the build it puts the bleed nipple to the bottom leaving a huge resivor of air up behind the piston
you can bleed three bottles of fluid through the system and if the air pocket is trapped above the nipple it wont expel with out
1 swapping them back to their original position / or
2 unbolting the caliper placing a block of wood between the pads and rotate bleed nipple to top dead center then get a friend to help bleed each one then refit
using a piece of fish tank airline attached to the bleed nipple and a glass bottle is a great way to see what air is being removed
i have also seen guys get caught out buy swapping brake callipers from rear of front axel to frontof front axle when fitting rear rack and pinion this also orientates the nipples to the bottom
it easy to see why air gets trapped once you have a caliper apart and the piston out of it
A quick test to eliminate the calipers. Clamp the front and rear brake hoses and see if you still have the same problem when you press the brake pedal.
I assure you that I have made nearly all of the mistakes mentioned in these earlier posts but in this case.....nothing appears to be amiss....everything is mounted correctly and I'm convinced we have all of the air out.I did manage to get a somewhat better pedal with the current set-up but nowhere near the braking ability I have with other cars I've done.Going from the current 1 1/8" bore to the 7/8" bore will increase my pressure at the wheel cylinders from somewhere around 450 PSI to nearly 750 PSI and I'm told the 8" dual diaphram booster will increase that pressure by another 15% or so.The M/C I'll be using has equal sized reservoirs and are somewhat larger in capacity than the current one.I am learning that disc/disc setups not only require more pressure but more volume as well.On my 40 coupe with a similar setup,I can touch my toe on the brake and lock up all four wheels.....that's what I'm after with the 36.When I get the parts and get it all assembled,I'll report back with the results.....In the meantime,I'll try and figure out what to do about the front wheels turning into the fenders :shock: Aren't cars fun :roll:
Got the brake system revamped.....couldn't fit the 8" dual diaphram booster under the floor so I opted for a dual 7" and replaced the 1 1/8" m/c with a 15/16" unit.I also added a remote fill mounted to the firewall.They work super but I believe they could have been a bit better yet with the 8" booster.....I will modify the chassis I'm building for my 37 Sedan to accept the 8".While bringing the car home from the shop,going about 70mph down the interstate,I look in the rear view mirror just in time to see the soft top flying thru the air like a frizbee after getting sucked out of the top of the car.....we hadn't put the rubber seal in place yet as we wanted to buff and wax it before we installed it.The top insert had a cloth-like backing attached to the rubber/vinyl...the glue held great,the two layers separated leaving a nice white 1" strip of material attached to the roof :roll: Naturally,it was rush hour traffic so the top got ran over a zillion times and destroyed :( Waiting for the UPS man AGAIN!!
What difference does it make that the lines may be hooked up backwards? The answer to this question may alleviate a problem I have been experiencing.
If the lines are hooked up backeards, it may, or may not cause a problem. If the master cylinder had built in residual check valves, the rear drum brake valve, 10 psi, hooked to the front brakes, may cause the brakes to drag.
[quoteWhile bringing the car home from the shop,going about 70mph down the interstate,I look in the rear view mirror just in time to see the soft top flying thru the air like a frizbee after getting sucked out of the top of the car!![/quote]
Reminds me of 1966 and I had a '55 T-bird. It was running particularly well one Sunday afternoon. Construction was nearly complete on a new 4-lane highway south of town, but not open to the public yet. I took the car to the end of a long stretch and opened it up. The tach was reading 5000 rpms when I heard a noise like a giant beer can being opened (swwwish). I looked in the rear view morror to see my rear glass doing flip-flops high in the air. When it hit the pavement it exploded into a million little pieces. I went back to where it hit and found every piece of the stainless trim and the gasket.
I am also having brake problems, but I really think mine is the Willwood residual valves. I had good pressure and it would hod for about two-three days but would get soft and I would have to pump th epedal up again.
I really didnt worry about it (as it would pump up and hold fine), but after I pulled the entire front suspension off to move the MII crossmember back an inch to center the wheels up in the wheel-well, I cannot even get the pedal to pump up and get hard.
I am wanting to change out the valves, but havent put much into it since I have finally gotten more parts and the truck is not ahead of me.
Frank, what is a good residual valve to use that will fit in the lines where I have my willwood ones? I dont want to have to cut and re-flare the lines.
Thanks.
I have been buying them from Stainless Steel Brakes. No problems with any of their valves so far.
Frank....Do you have contact info for them??Thanks!
http://www.ssbrakes.com/
Thanks!! 8)
Thanks Frank, I ordered two fo the two pound ones and will toss my Willwood ones.