Brake pedal "pivot"

Chassis, Suspension and wheels

  1. Locomotion

    Locomotion Well-Known Member

    Messages:
    129
    Likes Received:
    14
    Joined:
    Apr 22, 2012
    Location:
    Florida
    Does anyone have diagrams and/or a parts list showing the brake pedal through the master cylinder? The person I got my wagon from eliminated the pivot. The brakes work, but braking is soft and the pushrod is at an obvious angle. Trying to figure out what's there, not there and what I might need to fix it and hopefully improve braking. All OEM brakes and it doesn't have a proportioning valve. '78/'79 wagon and race only.

    I've already replaced the manual M/C, rear brake assemblies, brake hoses and thoroughly bled them several times.
     
  2. volare 77

    volare 77 Well-Known Member

    Messages:
    1,383
    Likes Received:
    184
    Joined:
    Jun 12, 2014
    Location:
    maryland
    out of my 77 book

    aba.jpg
     
  3. Aspen500

    Aspen500 Well-Known Member

    Messages:
    5,296
    Likes Received:
    1625
    Joined:
    Feb 14, 2015
    Location:
    Rib Mountain (Wausau) WI
    Manual brakes don't have the extra pivot. The pushrod goes directly from the master cylinder to the pedal. Maybe I'm misunderstanding what you are saying and you've got power brakes??? Without a proportioning valve, you're going to have too much rear braking and wheel lockup, regardless if it's rear drum or disc.

    As for the angle, did the originally have manual brakes? If the master is mounted with the wrong firewall plate, it could be too high. Speculating thereo_O
    Maybe these will help? Pics of my '79 Aspen, original manual brake car.
    DSC00511.JPG DSC00512.JPG DSC00513.JPG
     
    Last edited: Dec 31, 2020
  4. volare 77

    volare 77 Well-Known Member

    Messages:
    1,383
    Likes Received:
    184
    Joined:
    Jun 12, 2014
    Location:
    maryland
    Oops, I didn`t read the manual part
     
  5. Locomotion

    Locomotion Well-Known Member

    Messages:
    129
    Likes Received:
    14
    Joined:
    Apr 22, 2012
    Location:
    Florida
    Thanks for info. Now I have a better perspective.

    It will be a few days before I can actually look again, but I believe that it may have had power brakes before. That would explain the up-angle of the pushrod. The wasted motion which decreases efficiency - kind of like the angles associated with a Mopar small block's lifter/pushrod/rocker arm relationship.

    I'm hoping the rear brake bias won't be too much. After all, skinny front drag tires can lock up easier than 9" rear slicks. As mentioned, it works and I can stop the 3,930+lb car from 106+ in the 1/4, but it takes some getting use to and concerned if it gets faster.

    So you're saying that a manual set-up has a different mounting plate which positions the master cylinder lower? I recall the aluminum 2-bolt MC mounted to a home made 5/16" plate. It's offset upwards from center. Bigger than the adapters I've seen for converting A-bodies from power to manual aluminum MCs.

    1) Do you know how much lower the centerline distance is between power and manual?

    2) Are there more differences under the dash between the two besides the pivot?

    3) I guess I'll have to double-check the pushrod length if I figure out how to lower the MC.
     
  6. Aspen500

    Aspen500 Well-Known Member

    Messages:
    5,296
    Likes Received:
    1625
    Joined:
    Feb 14, 2015
    Location:
    Rib Mountain (Wausau) WI
    I'm not sure about the difference in power vs manual height. There is a different firewall plate for each type. Basically, from the top of the cowl to the center of the outer master stud is 6 1/2" and the pushrod is a straight shot to the pedal, level with no angle.

    Under dash,,,,,,,,,,,,,it's all the same, IIRC. The pedal is the same aside from manual or auto trans (pedal width). The pedal in my car is from an automatic with power brakes (the car was originally a 4-speed O/D), and it was a direct swap. Pedal bracket is also the same for power or manual (or automatic and manual trans).

    Yeah, you're probably fine with those tire sizes and no prop valve, lol:D

    With manual disc/drum there's been a couple times I was glad I swapped to the wider pedal because you can use both feet at the same time, a.k.a. "panic stop" (friggin' deer............). I'm not exactly built like Arnold after all, lol:p
     
  7. Locomotion

    Locomotion Well-Known Member

    Messages:
    129
    Likes Received:
    14
    Joined:
    Apr 22, 2012
    Location:
    Florida
    Hmmm.
    But if the manual brake pushrod goes directly into the manual master cylinder, and is level, it would be a one piece pushrod as opposed to the multi-piece pushrod with the pivot/lever, as shown in the diagram. The pedal side pushrod is above the pivot while the power brake side pushrod is above the pedal side.

    I'm hoping I just need to re-do the home-made aluminum plate to lower my MC so it will be parallel with the existing pushrod.

    I'm assuming there is an oval hole in the firewall to accommodate either height?

    I'll try to get some pics in a few days so we can both see what's going on in my car.
     
    Last edited: Jan 1, 2021
  8. Aspen500

    Aspen500 Well-Known Member

    Messages:
    5,296
    Likes Received:
    1625
    Joined:
    Feb 14, 2015
    Location:
    Rib Mountain (Wausau) WI
    Correct, only power brakes have the pivot lever set up. Manual consists of the master, the pushrod and the pedal only. The hole in the firewall is sort of an oval shape so, with the correct plate (or fabbed one) the master will be where it should be.

    Pic of my car from about 12 or so years ago. The master cyl studs go through the lower 2 ROUND holes (just above the oval holes).

    2e31ecc9_118099.jpg




    .
     
    Locomotion likes this.
  9. BudW

    BudW Moderator Staff Member

    Messages:
    4,390
    Likes Received:
    1175
    Joined:
    Mar 4, 2012
    Location:
    Oklahoma City
    There are a couple of things to keep in mind. The '76-77 FM's used a cast iron master cylinder (with 4 bolts). The '79-89 FMJ's use an aluminum master cylinder (with 2 bolts). I'm not sure about the '78's FM's and think it was a mid year change (but could be wrong).

    The Firewalls are slightly different between the two master cylinder types, as well as the brake boosters or firewall plates.

    The upper most and lower most firewall holes are in same position – no matter what year FMJ. The middle 2 bolt holes in different location depending on the year (see above).

    Manual brake cast iron master cylinders, the lower set of bolts/studs use the same lower (firewall) studs that brake boosters use. The upper set of master cylinder studs are about in a mid way position on firewall.
    Manual brake aluminum iron master cylinders, the bolts/studs only use the middle firewall holds – which are a short distance (an inch?) above the lower firewall holes.

    The picture (above post) is from an '79-89 (aluminum master cylinder) firewall.
    This is a picture of the '76-77 firewall:
    100_1271.JPG
    100_1271c.jpg

    It was made to be not too difficult to switch over from manual to power or power to manual brakes. I did a lot of manual to power brake changeovers while working at a dealership.
    The same brake petal was used on both setups. The use of the “Z” raised the booster up on firewall a couple of inches

    BudW
     
    Locomotion likes this.
  10. Aspen500

    Aspen500 Well-Known Member

    Messages:
    5,296
    Likes Received:
    1625
    Joined:
    Feb 14, 2015
    Location:
    Rib Mountain (Wausau) WI
    Good to have you back BudW!
     
    Sub03 likes this.
  11. BudW

    BudW Moderator Staff Member

    Messages:
    4,390
    Likes Received:
    1175
    Joined:
    Mar 4, 2012
    Location:
    Oklahoma City
    Glad to be back.

    My workplace disabled access to our website. I would get online when things were slow, but now I can't.
    With that said, I've been working from home so have two computers to access - but had to do a lot to get there.

    We got hit hard with Ice in late October. Had ice a lot of times, but first time when leaves were still on trees. Had no electricity for almost 3 weeks (had a generator from before, though) and had no internet for almost 2 months. I have 1 acre within Oklahoma City limits with 140 huge trees (more than a dozen trees over 30 inch (760 mm) in diameter) mostly White Oak. I think maybe ½ are lost (lost too many limbs lost to recover). I need to get an tree expert out to mark what can be saved and what needs cut down. As is, I have enough “new” White Oak firewood to fill a couple of semi trailers and limbs to fill another couple of trailers.
    Hint, Hint, if you want to travel to OKC and looking for firewood, I can make it worth your trip.

    Wife (not I) has been fearing widespread looting, rioting government bombings and such, for over a year, so been upgrading my armory and food stores – so been busy there, as well. I got that completed just before power got knocked out (which was also just before our election).
    Wife is finally happy, so now I can resume my long automotive upgrade list.

    I have spoken to @slant6billy and to @Justwondering over the phone (both while I had no power or internet), which was nice.
    BudW
     
  12. slant6billy

    slant6billy Well-Known Member

    Messages:
    2,925
    Likes Received:
    619
    Joined:
    Dec 21, 2011
    Interesting enough, my workplace blocked this site as well. "FMJ" or "bodies" must trigger the alarm for some reason. I was looking into WiFi drive ups- Like a Drive-In, but a localized WiFi hotspot. Especially with the new 5G, the need for alternative connectivity is key. My local cable company sucks, but owns the 35 yearold coax in the area. Local phone Company service too is not too inspired to upgrade the service to FIOS. So the need for some competition is way overdue.
     
    Justwondering likes this.
  13. BudW

    BudW Moderator Staff Member

    Messages:
    4,390
    Likes Received:
    1175
    Joined:
    Mar 4, 2012
    Location:
    Oklahoma City
    I have a (somewhere . . . in my garage) a late '78 manual brake (aluminum) master cylinder reinforcement plate (like the item in black on Aspen500's picture, above) part number 3766120 - that I can take pictures for you, and/or measurements - if wanted. I have a use for the reinforcement plate - but looks like a person could make a new one out of aluminum pretty easily, if needed).
    BudW
     
    Justwondering likes this.
  14. BudW

    BudW Moderator Staff Member

    Messages:
    4,390
    Likes Received:
    1175
    Joined:
    Mar 4, 2012
    Location:
    Oklahoma City
    I found a couple of pictures of the above mentioned master cylinder reinforcement bracket (taken April of last year):
    20200407_162757r.jpg
    20200407_162803r.jpg
    20200407_163016r.jpg
    BudW

    Edit: I stumbled across these pictures by accident.
    Note, the reinforcement bracket is made of steel
     
    Duke5A likes this.