Manual brake system parts interaction.

Chassis, Suspension and wheels

  1. Locomotion

    Locomotion Well-Known Member

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    Hoping some brake knowledgable people can answer some questions & help me figure out some ideas I have. Open to ideas, suggestions and/or constructive criticism

    On my Aspen wagon I have a lot more pedal travel than on my Dart Sport. (race cars) with the same manual disc master cylinder (1.03" bore). Aspen doesn't have a proportioning valve & Dart Sport does. Aspen apparently had a "Z-bar" lever for the brakes that the previous owner eliminated. Pushrod is at an angle which can contribute to more travel, but it has worked well for him for years and for me so far (Just the extra travel bothers me.).

    1) Is there a way to tell if any extra travel is due to air in the system or because F-body calipers are bigger than A-body calipers (2.75" vs 2.60")? Or can the proportioning valve or lack of have an effect on travel, in addition to the angled pushrod?

    2) Should a bigger bore master cylinder provide a slightly quicker release of the brakes than a smaller bore/longer travel M/C.? (Think drag racing RT's.)

    Thinking about adding a truck/van master cylinder with a bigger bore (1.125") to compensate for the bigger F-body calipers and pushrod angle.

    Probably should get a non-Z-bar pedal & pushrod, but finding one plus installation time makes it impractical at the moment.
     
    Last edited: Feb 25, 2018
  2. Oldiron440

    Oldiron440 Well-Known Member

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    The larger bore will firm up the pedal as far as drag racing with a foot brakes the best tip I can give you is to install a line presser gage and use a constant presser to stage the car. Stock class cars can't use trans brakes so they use a line lock on both axles and leave off the line locks using a gage to set presser when engaging the line locks.
    This is for consultancy and reaction times.
     
  3. Oldiron440

    Oldiron440 Well-Known Member

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    A line lock can and will release the brakes faster and more consistent than you can with your foot.
     
  4. Oldiron440

    Oldiron440 Well-Known Member

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    I'm setting up the Ford and I will my Plymouth with a two step and the four wheel line locks using a MSD-6AL-2 with programmable timing to help the small tire cars hook. The Plymouth has 10.5 /30 or 295/60/15 the Ford 275/60/15 drag radials.
     
  5. Locomotion

    Locomotion Well-Known Member

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    Thanks, but line-locks are only allowed on non-drive wheels in NHRA Stock and don't believed they can be used to release/launch the car. Cars are allowed to use 2-steps, pressure gauges and brake switches to release the 2-step. But you still have to release the brake itself with your foot. I've considered this, but after 40 years of footbraking, and a new car now, I'm trying to avoid getting use to a new routine. Hoping I can make enough mechanical changes to reach that "comfort zone" without bumping in. Already have shorter tires, high air pressure & minimized wheel stagger.
     
  6. AJ/FormS

    AJ/FormS Well-Known Member

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    >If the rear drum brakes are out of adjustment,the pedal will go down further until the shoes hit the drums.This is a normal consequence.

    If you get a hard peda
    l,sometime/anytime, before it hits the floor, then there is a very low likelihood of air being in the system.
    > If the pedal does NOT get hard, this does not absolutely indicate air in the system.The bouncy pedal could originate elsewhere; like; old hoses, flex in bent pads, seized sliderpins,misalignment of the pads to the rotors, loose wheel bearings, rear shoes that do not contact fully the drums,cracked rear drums , etc. But the C-valve,by itself, has nothing to do with it.
    > if the pushrod travels down towards the m/c, then it's probably a non issue., as it will straighten out somewhat during brake application. As far as I know, the pedals are all the same. P-rods, IDK
    The Front brakes will not apply until the the fluid in the rear system presents resistance inside the m/c.This is because the front system is supposed to be activated by hydraulic pressure...not mechanical. But if the rear system fails,then the pedal will travel much further down, until, inside the m/c, the rearmost piston mechanically hits the front piston, and then front braking can begin.
    On older cars or cars with failed self adjusters in the back, I always know when it's time to adjust them.....by how low the pedal travels.
    >Also, it may just be a matter of pushrod length adjustment,to bring the C-port into proper relationship.
    >If you make that pushrod too long, the piston will move to the wrong side of the compensating port. With the rear brakes properly adjusted,you will get a hard pedal very early in the pedal travel........for a few hundred miles. Then as the rear shoes wear, the pedal will fall lower and lower over time..because the C-port is no longer functioning.
    > If the rod is too short, the early part of the pedal travel is spent in forcing the fluid out of the piston chamber, and back into the reservoir.
    >If the rear shoes are properly adjusted;
    the larger bore m/c's, in your application will just reduce the pedal travel and increase the leg-effort..... The factory front calipers will/should work fine with any m/c, and you can use the sizing to tune those two parameters to fit your liking. I happen to like the 15/16. Being a streeter,it gives me a good amount of modulation range, and is easy on my leg.
    >as to release time; it's a pressure system; the pressure drops to zero instantly after you release the pedal. There is however some time involved in the retraction of the caliper pistons and brake shoes. You however, can compensate for this at the tree, by leaving those few nano-seconds earlier.
    >I leave my front wheel-bearings ever so slightly loose. This allows the rotors to "knock back" the pads during the first revolution. I do this for a different reason however, in my streeter; to reduce drag and decrease fuel consumption.This does however, lead to slightly more pedal travel.
    > to my way of thinking,on a proper working system, and in a drag-race application,with an automatic trans;pedal-travel, if reasonable,would mean nothing to me. It's a one time concern; right on the start-line, and before the clock starts. After that,I for one, wouldn't give it any more thought. That's my opinion
     
    Last edited: Feb 25, 2018
  7. Oldiron440

    Oldiron440 Well-Known Member

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    I have friends that run an E/AS I will have tell them they can't use a rear line lock, after all they told me about the setup.
     
  8. Locomotion

    Locomotion Well-Known Member

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    AJ/FormS,
    I manually adjust the rear brakes on both cars after every race weekend to keep things consistent while eliminating any chance of the self-adjusters causing any drag. The Aspen does slow down ok from 104mph (for now) even though race weight is over 3,930. Holds ok on the line at 3,000 or below also, if that offers any clues.

    Pedal rests loosely with the pushrod in the bore. Not sure how to determine proper pushrod length, especially with the altered geometry without the z-bar, or whatever it's called. Pushrod at a slight up angle.
     
  9. Locomotion

    Locomotion Well-Known Member

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    Do you mean E/SA (E/Stock Automatic)?

    If you all want to double-check: Section 11A, Page 7 of the NHRA rulebook says no 4-wheel or rear wheel line-locks allowed. By "rear wheel", I'm sure they mean rear wheel drive vehicles, not FWD.
     
  10. AJ/FormS

    AJ/FormS Well-Known Member

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    Comments inside the Quote
     
    Last edited: Feb 25, 2018
  11. Oldiron440

    Oldiron440 Well-Known Member

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    IDK, I had asked how they left so hard and thats what I was told.
    I will be talking with them soon to go over this topic.
    But I know they leave of a line lock and a two step, front tires four feet in the air. Car runs 10.60s legal.
     
  12. Locomotion

    Locomotion Well-Known Member

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    On the Aspen the self adjusters have been eliminated and there is no proportioning valve. it's plumbed direct.

    Based on what I remember from diagram that BudW may have posted, the previous owner kept the pushrod attached at the original point where it was with the Z-bar which is below the centerline of the M/C bore. But he eliminated the Z-bar and lengthened the pushrod, so the pushrod is angled up into the M/C. Looking at under the dash, it "appears" that the actual pedal pivot point is in line with the M/C and the pushrod pivot is below that. The diagram appeared to show a different pedal arm with different pivot points of everything.

    The pushrod & M/C have the o-ring retainer set-up and won't come out without some force. But I modified the o-ring so it goes in easier during assembly. The pushrod is firmly engaged, but there is a little slop at the pedal end of the pushrod.

    It brakes ok, just the travel is longer than what I'm use to. It's seems to be at normal height and goes to about 2" from the floor. But I suppose I could touch the floor with enough effort. I thought there might be some air when he re-did all the lines (including pedal geometry), thinking that the M/C could be bigger to reduce travel & firm it all up. I already have braided front lines to the calipers, which helped on my Dart.
     
  13. AJ/FormS

    AJ/FormS Well-Known Member

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    Oh, wow, I never thought of that! I guess I'll go order me a another line-loc...for the rear wheels,now. I'm a streeter, no restrictions apply. Maybe I'll trigger the off button by an adjustable attitude-switch. As soon as the front end rises a set amount, it will release the rear brakes. I guess I'll' have to figure out how to install bigger brakes back there.
     
  14. AJ/FormS

    AJ/FormS Well-Known Member

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    Well then, check for firewall flexing.I don't recall the pedal ratio but it must be at least 7 to 1,maybe closer to 10/1. So even a little flex makes a huge X-fold of difference on the pedal-travel.
    A bit of slop between the P-rod and the pedal arm is normal.
    I guess I should check my p-rod angularity now,lol.

    Your thinking is correct; a larger bore m/c will firm up a pedal and reduce pedal travel....at the expense of effort, which on a drag-car IMO is a fair trade. But now you will be pushing yet harder, and so firewall flex,if it exists, will be even more of an issue.
     
    Last edited: Feb 25, 2018
  15. Oldiron440

    Oldiron440 Well-Known Member

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    I worked for a Co. that a mechanic before my time with the co. when replacing rear brakes would leave the self adjusters disconnected. Over time there were soft pedals with long travel, some I was able to adjust and hook up adjusters others took parts. I never understood his thinking.
     
  16. AJ/FormS

    AJ/FormS Well-Known Member

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    Make-work

    I've seen that kind of flim-flam. Customer returns with the complaint. Mechanic returns the system to normal, charges customer for new parts, plus labor,claiming faulty cable, thinking no harm no foul, and everybody is happy;Especially the mechanic making easy money.
    Now I'm not saying your guy was like that, Only that in 40 plus years in the business, we have seen chit that shouldn't be going on.
     
    Last edited: Feb 25, 2018
  17. Oldiron440

    Oldiron440 Well-Known Member

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    nope, the man did not believe in self adjusting brakes....
    These were all co. truck's.
     
  18. AJ/FormS

    AJ/FormS Well-Known Member

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    Yeah, I got that vibe in the earlier post.
    As for me, I don't believe in crawling under my car every 5000 miles,or less, to run the adjusters out,lol. Call me lazy,s'ok
     
  19. BudW

    BudW Moderator Staff Member

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    I’ve been to the Tulsa dragstrip a few times – a long long time ago.
    I like to go fast – but just not into racing . . . full time.


    I do not see any reason or purpose to disable the auto adjust functionality of drum brakes – but if it will shave a few milliseconds – then I guess someone else can go do it (but not me).

    On a similar note, I wouldn’t drive a car on the street without a combination valve (referred earlier to a C-Valve and sometimes also referred to a proportioning valve) either.
    For track use – then I don’t see a problem – for if brakes go out, you got time to stop (somewhat) before hitting people, cars or other hard objects.


    Power brake cars do have a Z-bar apparatus that quickens the brake rod motion at master cylinder, because of the vacuum brake assist. That way the driver has less brake petal motion (and effort) to achieve the same brake distance.

    The brake petal (item # 8, in picture below) is the same on manual brake and power brake cars (they are different between automatics or manual transmissions, though). Because of the Z-bar apparatus, and because brake boosters need more space away from engine, the brake push rod (on manual brake cars) and brake booster input pushrod are in different locations by roughly two inches (higher for power brakes), or so.

    Both manual and power brake cars have a firewall stiffener place (not sure what everyone else calls, it, though) – Item #1. The power brake booster has four studs that go through the firewall stiffener (Chrysler calls it a Reinforcement) and into the brake petal bracket (Item # 5). That bracket has six holes in it, the middle two holes are not used with power brakes.
    77 FPM pg 5-24 a.JPG

    If you look at the manual brake master cylinder, it has four studs. The bottom two studs go into the same holes the bottom two brake booster studs go into. The top two master cylinder studs (marked in red in lower picture) go into the middle holes. The stiffener plate (reinforcement) has two studs that go into the top two holes.
    77 FPM pg 5-24 b.JPG
    Purple = all (power and manual brakes). Red = manual brakes only.

    That manual brake stiffener plate (reinforcement) is hard to find. A person could make one and possibly an aluminum version might be lighter than steel, - maybe. By placing the master cylinder back into its original holes – will make the pushrod level, again.


    I don’t think that is the only problem you have (pushrod angle).
    AJ/FormS is correct, the combination valve (proportioning valve) is designed to engage the rear brakes first, sense it takes more motion to do so, once that occurs, it then applies the front brakes - in roughly 50/50 braking.

    Factory sizes:
    Brake caliper piston diameter 2.75” (same if pin-type or slider type calipers)
    Rear wheel cylinder diameter 0.937” (15/16”) (note: one can get these in different sizes)
    Master cylinder diameter (Manual or Power) 1.031” (1-1/32”)


    On an unrelated note: my ’97 ¾ ton 2*4 diesel pickup (same for '94-97 2*4's) came with 0.937” (15/16”) rear wheel cylinders (as well).
    The 4*4 versions came with 1.06” (1-1/16”) rear wheel cylinders.
    In the case of my pickup, by installing the larger diameter bore wheel cylinders, it improves the braking ability and feel, drastically.
    Logically it makes no sense – sense two wheel cylinders with different bore sizes, the smaller diameter cylinder will move further than the larger diameter one will. With disk/drum brakes, the combination valve will not apply the disk brakes until the drums make contact, first. In this case the braking ability is greatly improved. Matter of fact, the next year truck ('98), the rear wheel cylinder are the same sizes (so why the difference – IDK).

    I do know that by playing with different diameter wheel cylinders, racers can get the brakes to work for you instead of against you, with some trial and error.

    Now, with the problem with excessive petal movement – I’m not sure yet. I wonder if it is a problem with a hose expanding under pressure (a bad thing) or air, maybe.
    BudW

    Hopefully this helps some.
     
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  20. Locomotion

    Locomotion Well-Known Member

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    I appear to have the power brake set-up on the left and the wagon was originally a stick car. It looks like I may have more "leverage" than normal with the linkage removed. It was converted to manual brakes with an adapter, but the pushrod angle is angled up from the pedal to the M/C. I doubt any firewall stiffeners were removed and the front brake lines are braided steel. The only rubber in the system is the hose connected to the splitter on the rear axle housing. I will be trying a big truck manual brake M/C to reduce travel and increase firmness. I can always go back if I don't get the desired results. The Gainesville, FL NHRA divisional event next weekend will have a test & tune Thursday. Can't stay for the Gatornationals because I didn't have the "grade points" to enter a national event (Previous year divisional entries.) Orlando last weekend was the first NHRA race on the car.

    Self-adjusters can cause some drag and removed they don't need much after the races. But I'm also swapping the slicks from side-to-side after every weekend to maintain even wear and prevent directional feathering on the tires.





    brake-stepup-linkage-jpg.jpg
     
    Last edited: Mar 1, 2018