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Thread: converted to Explorer rear disc brakes - are brakes dragging? Pedal could be better

  1. #1

    Default converted to Explorer rear disc brakes - are brakes dragging? Pedal could be better

    Hi Everyone,

    I recently upgraded my 8.8 rear in 84 wagon to 31 spline axles, 9" housing ends etc and Explorer rear disc brakes. I think these brakes have a 1 7/8" piston. Looking at the specs gadget posted in a sticky, front stock calipers have 2 7/8" piston and the master cylinder is 1". seems like this combo should be good but my pedal is softer than before and I'm concerned that the stock master cylinder may have a residual pressure valve thus dragging the rear brakes....

    Any thoughts? I'm thinking a disc/disc MC would be better but would a smaller MC bore (say 15/16 or 7/8) give me a firmer pedal?

    Thanks!
    1984 Mercury Colony Park Wagon - gone to the darkside. 5.3 LS Turbo Swap with 4L80E. 6.62@106 in the 1/8 mile (low 10's in the 1/4), full weight, AC, no compromises! Rocky Mountain Race Week 2020 and Race Week 2.0 2020

  2. #2
    I post a lot...
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    Default

    More than likely you have a residual pressure valve. Also, and perhaps in the same device, a proportioning device. I can say in my old 89 wagon I opened up the device, which screwed into the master, removed the pressure holding component and reamed out the valve to reduce the proportioning effect. Then added an adjustable proportioning valve. I wound up after much testing leaving the adjustable valve completely open for best braking balance. The variable is i don't remember what size drill bit I used to ream open the proportioning valve so you may need to use the adjustable valve depending on how much you open the stock valve.

    84 may be have a different setup to do the same two things.
    "X" car 89 Colony Park LS Mods>Engine delete, SS duals magnaflow hflow cats, 2010 Must GT mufflers, auto air shocks, Posi, Tran cooler, big front brakes, 03+ rear disks, Large 3g alt, Tripminder, GS grill, 86 seats, 16" HPP wheels, winter boots=96 Cartier wheels, 215-65/16 Goodyear ULTRA GW3 snows, pi rear sway, alum driveshaft.
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  3. #3
    I'm an air-conditioned gypsy gadget73's Avatar
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    yes on the residual valve, and the proportioning won't be quite right either. You want a master and a prop valve from a 90s or later car with disc/disc. If you use the 90s booster that should also help somewhat with pedal feel. More assist possible, but its a better design. Smaller diameter too, which is the magic trick for fitting an extra pedal in one of these.

    Also be absolutely sure you have all the air out. Not sure where the bleeders sit on Explorer brakes when mounted to your rear end but you may have to dismount them, shove a board in between the pads and rotate them around to get that last little bubble out.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  4. #4

    Default

    Interesting. The guy I use for custom work sometimes suggested a 1 1/8" mark V master cylinder for more fluid push and stiffer pedal, which I would like. If you all think the 90s mc would be better I can go with that instead

  5. #5

    Default

    is the residual valve in line somewhere or it is housed in the prop valve that is mounted on the frame below the master cylinder?
    1984 Mercury Colony Park Wagon - gone to the darkside. 5.3 LS Turbo Swap with 4L80E. 6.62@106 in the 1/8 mile (low 10's in the 1/4), full weight, AC, no compromises! Rocky Mountain Race Week 2020 and Race Week 2.0 2020

  6. #6

    Default

    OK, I think the residual valve must be in the combination/prop valve that is on the frame rail. It's strange - has both brake lines from the master going in and 3 lines going out: one to each from caliper and a single line for the rear brakes that gets split to each side at the rear axle.

    I have a test n tune scheduled for this weekend about 90 miles away from home - is the brake drag from leaving the residual valve in the brake system bad enough to cause any damage to the rear disc brakes or will it be a problem for some drag racing? I suspect so, but I don't really know how big of deal this is....Thanks!
    1984 Mercury Colony Park Wagon - gone to the darkside. 5.3 LS Turbo Swap with 4L80E. 6.62@106 in the 1/8 mile (low 10's in the 1/4), full weight, AC, no compromises! Rocky Mountain Race Week 2020 and Race Week 2.0 2020

  7. #7
    I'm an air-conditioned gypsy gadget73's Avatar
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    I think all the valving is in that block on the frame. The late 90s cars with dual piston front calipers and rear disc still used the same 1" piston as the 80s cars with rear drum and small front disc. The pedal on my 86 with all late 90s brake parts is not spongy and doesn't have excessive travel at all.

    The 2 in, 3 out was just because it needs to get to 2 front brakes somehow. When the block goes away you can just install a tee to get that done.

    Probably not a real problem for racing but it will wear the pads a bit more quickly. Take it for a couple mile test drive. If the rear brakes aren't noticeably hot, don't worry about it. Just drive carefully if the brake pedal feels funky.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  8. #8

    Default

    Yeah, those brakes are definitely dragging, jacked up the rear end and it's tough to spin the rear tires in neutral and I can hear the pads scraping the rotors.

    It appears that the fittings in the combination valve might be different sizes? same size lines I think. Definitely have 2 different size fittings in the master cylinder. Does anyone know what those might be? I was assuming everything was 3/16" line with 3/8 24 fittings? Thanks!
    1984 Mercury Colony Park Wagon - gone to the darkside. 5.3 LS Turbo Swap with 4L80E. 6.62@106 in the 1/8 mile (low 10's in the 1/4), full weight, AC, no compromises! Rocky Mountain Race Week 2020 and Race Week 2.0 2020

  9. #9
    I'm an air-conditioned gypsy gadget73's Avatar
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    its all 3/16" lines. I've always recycled the original fittings because of the goofy sizes.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  10. #10
    Mazda5: the Anti-Van! 1987cp's Avatar
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    When I got tired of failing stock combination valves, I tried all new replacements from Speedway Motors. Starting with my stock master cylinder and stock brakes, I ended up adding:

    Front brake holdoff valve (has 2 outlets, so no T fitting needed)
    Rear brake residual pressure valve
    Rear brake adjustable proportioning valve

    I didn't end up driving the car a lot afterward, but from what I remember, it braked better than when the stock combination valve was still working, and heaps better than experiments using incorrect hardware (i. e. just a T fitting to the front and adjustable prop valve to the rear drums).

    Speedway lists their holdoff valve as being for disc/drum setups specifically. Perhaps disc/disc doesn't need a holdoff valve because the concept is to help overcome the return spring on the drum brakes? Anywhoo, what I think I remember reading was that disc/drum cars use a 10psi residual pressure valve, and disc/disc use either 2psi or no residual pressure valve. Thain may even remember that conversation, even though it was aeons ago.



    Edit: Found my post from fully a decade ago! Seems I found info from a website called The Brake Man. I don't see tech info offhand on their new site, but I mentioned a few things here at the time:

    http://www.grandmarq.net/vb/showthre...l=1#post548593
    Last edited by 1987cp; 12-28-2020 at 05:53 PM.
    2012 Mazda5 Touring | Finally working on the LTD again!

  11. #11

    Default

    THanks! That's good info. I'm living with "decent" braking now, it stops the wagon well and holds the rear brakes well enough for my 2 step at the drag strip. Would like better holding power though!
    1984 Mercury Colony Park Wagon - gone to the darkside. 5.3 LS Turbo Swap with 4L80E. 6.62@106 in the 1/8 mile (low 10's in the 1/4), full weight, AC, no compromises! Rocky Mountain Race Week 2020 and Race Week 2.0 2020

  12. #12
    Domestic Tourist Lincolnmania's Avatar
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    get the air out.
    i have 98 front brakes and 93 rear brakes on my 86 town car and i never changed anything else.
    works fine.
    car has been all over the east coast several times.

    1986 lincoln towncar signature series. 5.0 HO with thumper performance ported e7 heads, 1.7 roller rockers, warm air intake, 65mm throttle body, 1/2" intake spacer, ported intakes, 3.73 rear with trac lock, 98-02 front brake conversion, 92-97 rear disc conversion, 1" rear swaybar, 1 3/16" front swaybar, 16" wheels and tires, loud ass stereo system, badass cb, best time to date 15.94 at 87 mph. lots of mods in the works 221.8 rwhp 278 rwt
    2006 Lincoln Town Car Signature. Stock for now
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    1987 TriBurner and 1986 Alaska stokers keeping me warm. (and some pesky oil heat)

    please be patient, rebuilding an empire!


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