Close



Page 1 of 3 123 LastLast
Results 1 to 25 of 59
  1. #1
    FEP Power Member fgross2006's Avatar
    Join Date
    Sep 2014
    Location
    Freeport NY
    Posts
    2,024

    Default Rear brake drum performance

    I opened another thread about shoe size and that I had found 2 slightly different rear shoe sizes listed on multiple websites.

    I determined that the 9 x 1.71 was the correct one and replaced my rear drum brakes earlier in the week. They can be tricky so I took my time and bought new spring kits etc. After I got both sides assembled and adjusted I put the tires on and since I had the car on stands I checked the rear brake function and was surprised to find that while engaging the brake pedal both tires continued to spin, even with the pedal pushed as hard as it could get it the tires still spun.

    I tightened up on the adjustment some more but honestly if I tightened any more I would have cracked the shoes. I took the car to my mechanic and had him go over the whole set up. The only thing we found wrong visually was the self adjuster cable hook fell out on the driver side. Regardless of that, it would have affected self adjustment, not braking function. So I bought new self adjuster kit fpr the driver side only since the passenger side was assembled OK.

    The wheel cylinders appeared to be functioning when stepping on the brake pedal and there was no fluid leaks in either side. We determined there to be poor pressure to the rear so we replaced the master cylinder. Now he had trouble bleeding the rear passenger side. They spent a better part of the day and it kept producing air. We tried putting the disconnected brake line into a large cup of brake fluid and pumped the brakes until bubbles stopped coming up and there was definitely a bled line. Reconnected the line, tried to bleed out the minute amount expected from reconnecting to the wheel cylinder and now the line is filled with air again.

    He tells me he suspects the wheel cylinder is sucking air so I say if I'm changing one, I'm changing both. So off with everything and now a pair of brand new wheel cylinders. This time the system blead easy and the pedal is firm and high as it should. Drove the car and has great stopping power. The only thing, the rear tires still spin when the brake is engaged. This cant be normal. The car has great stopping power and doesn't feel as though I'm only using front brakes. I know that feeling when only the fronts are braking. Yet, why is it that engaging the brake while the car is off the ground results in the rear tires slowing but not stopping?

    My mechanic suggested I look for a proportioning valve. Has anyone here had this issue or seen of it? Any links to the correct proportioning valve or even an upgrade that allows adjustment of pressure between front and rear?

    Also, this whole mess allowed us to find the rear driver side axel seal was leaking oil so I also ended up pulling the diff cover, replacing the driver side seal and dropping 2 fresh quarts of gear oil and a bottle of friction modifier. I just rebuilt the 8.8 rear about 5 or 6 years ago. I'm surprised one of the seal leaked so soon considering the car isn't driven much.
    Last edited by fgross2006; 07-15-2023 at 08:04 PM.

  2. #2

    Default

    How old is the soft line from the brake line to the rear housing lines? I would replace it if you don't know how old it is.... These can collapse from the inside..... Check all of your metal brake lines too,, If any look questionable, replace them all.....

  3. #3
    FEP Power Member fgross2006's Avatar
    Join Date
    Sep 2014
    Location
    Freeport NY
    Posts
    2,024

    Default

    Quote Originally Posted by Bentley View Post
    How old is the soft line from the brake line to the rear housing lines? I would replace it if you don't know how old it is.... These can collapse from the inside..... Check all of your metal brake lines too,, If any look questionable, replace them all.....
    the soft lines were replaced about 6 years back when I did my single to dual exhaust conversion. Part of the process was switching the rear brake line setup to match an 86 and up. I'd suspect the steel lines from proportion valve to the rear before the soft lines at the drums. They are not old enough and haven't been used enough.

    I'm having no luck finding a proportion valve for an 84 even used. I see a few for 84-86 SVO but their must be a difference.

  4. #4

    Default

    When you have them perfectly adjusted they should drag ever so slightly. My rear drums (7.5) work great. When you say they won't stop the wheels is it when the engine is running? If you depress the brakes do the shoes move with the drum off?
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    K&N filter in a stock dual snorkel, GT40 heads, Edelbrock 3721 intake, MSD 8456 Dist., MSD 8227 coil
    Comp cams XE254H, hypereutectic pistons
    Hooker Super Comp Shorty Equal Length Headers, catted BBK H-pipe, full custom duals
    Maximum Motorsports caster/camber plates and strut tower brace, 3.73 rear, dura grip (both Yukon)
    Ford Performance Springs, Firehawk A/S 225/55r16 on LMR TRX r390 wheels (street)
    Federal 595 rs-rr 245/40r17 and 255/40r17 on OE cobra r wheels (race)
    AOD rebuilt with a 6 clutch direct drum, Koline steels stacked with 8 clutches, Kevlar band, superior shift kit, new torque converter. --Everything else stock and fully functional.

  5. #5
    FEP Power Member fgross2006's Avatar
    Join Date
    Sep 2014
    Location
    Freeport NY
    Posts
    2,024

    Default

    Quote Originally Posted by emerygt350 View Post
    When you have them perfectly adjusted they should drag ever so slightly. My rear drums (7.5) work great. When you say they won't stop the wheels is it when the engine is running? If you depress the brakes do the shoes move with the drum off?
    With the car on a lift or Jack's and the rear wheels off the ground, putting the car in drive and spinning the wheels, applying the brake does not stop the rear wheels from spinning. They are adjusted as tight as possible.

    And we checked wheel cylinder function with drums off. They do move when brake is applied. So why do the rear wheels not stop or lock even when the brake is pushed as hard as possible?

    I'm thinking adjustable proportion valve may be needed?

  6. #6

    Default

    Quote Originally Posted by fgross2006 View Post
    I'm having no luck finding a proportion valve for an 84 even used. I see a few for 84-86 SVO but their must be a difference.
    I had a really hard time finding a proportioning valve for my 84, it was full or crust and the front line was completely plugged. Car had no stopping power at all even standing on the pedal and any force was coming from the overadjusted rear to compensate.
    I wound up with an expensive nos one that was mislisted for another vehicle because it was either that or some janky adjustable thing i didnt want to even get into messing with that.

  7. #7
    FEP Supporter
    qikgts's Avatar
    Join Date
    Jan 2010
    Location
    Rockledge, FL
    Posts
    1,461

    Default

    Quote Originally Posted by fgross2006 View Post
    With the car on a lift or Jack's and the rear wheels off the ground, putting the car in drive and spinning the wheels, applying the brake does not stop the rear wheels from spinning.
    How much throttle are you giving it in the above example or is this at idle with no throttle input?


    If it comes down to needing the prop valve rebuilt, that can be done too.

    https://www.musclecarresearch.com/va...-E0ZC-2B328-AA
    '85 GT

  8. #8

    Default

    When it works it works well, autocross yesterday I was noticing when and how the rears would lock. Very progressive, I think it was a well designed system. Where is the proportioning valve?
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    K&N filter in a stock dual snorkel, GT40 heads, Edelbrock 3721 intake, MSD 8456 Dist., MSD 8227 coil
    Comp cams XE254H, hypereutectic pistons
    Hooker Super Comp Shorty Equal Length Headers, catted BBK H-pipe, full custom duals
    Maximum Motorsports caster/camber plates and strut tower brace, 3.73 rear, dura grip (both Yukon)
    Ford Performance Springs, Firehawk A/S 225/55r16 on LMR TRX r390 wheels (street)
    Federal 595 rs-rr 245/40r17 and 255/40r17 on OE cobra r wheels (race)
    AOD rebuilt with a 6 clutch direct drum, Koline steels stacked with 8 clutches, Kevlar band, superior shift kit, new torque converter. --Everything else stock and fully functional.

  9. #9

    Default

    Quote Originally Posted by qikgts View Post
    How much throttle are you giving it in the above example or is this at idle with no throttle input?


    If it comes down to needing the prop valve rebuilt, that can be done too.

    https://www.musclecarresearch.com/va...-E0ZC-2B328-AA
    Thanks for this lead... I ordered one of these kits for my parts stash....

  10. #10
    FEP Power Member fgross2006's Avatar
    Join Date
    Sep 2014
    Location
    Freeport NY
    Posts
    2,024

    Default

    Quote Originally Posted by qikgts View Post
    How much throttle are you giving it in the above example or is this at idle with no throttle input?


    If it comes down to needing the prop valve rebuilt, that can be done too.

    https://www.musclecarresearch.com/va...-E0ZC-2B328-AA
    I'm not giving it any throttle. With the tires off the ground and the car in drive, the tires spin on their own. Engine idle speed is the answer to your question. And at minimum RPM, the rear brake at maximum pressure on the brake pedal will not stop the rear wheels from spinning.

    The adjustment is tight enough to feel maximum drag on the drum when trying to spin the rear wheel with the trans in neutral. Adjusting them tighter is not the answer. And we replaced both wheel cylinders and verified movement when the brake is applied with the drums off.
    Last edited by fgross2006; 07-17-2023 at 09:47 PM.

  11. #11
    FEP Supporter
    qikgts's Avatar
    Join Date
    Jan 2010
    Location
    Rockledge, FL
    Posts
    1,461

    Default

    Quote Originally Posted by fgross2006 View Post
    I'm not giving it any throttle. With the tires off the ground and the car in drive, the tires spin on their own. Engine idle speed is the answer to your question. And at minimum RPM, the rear brake at maximum pressure on the brake pedal will not stop the rear wheels from spinning.
    You'll have to have someone check the system with a pressure gauge at the rears to confirm if this is some kind of issue with fluid. The correct PSI specs should be in the factory service manual if not, I'd bet Jack Hidley will know.

    Maybe the wheel cylinders aren't actually correct for the application and can't move the shoes far enough? Presuming that you have the primary and secondary shoes in the correct positions on both sides?
    '85 GT

  12. #12
    FEP Supporter
    qikgts's Avatar
    Join Date
    Jan 2010
    Location
    Rockledge, FL
    Posts
    1,461

    Default

    Quote Originally Posted by Bentley View Post
    Thanks for this lead... I ordered one of these kits for my parts stash....
    No sweat!
    '85 GT

  13. #13
    FEP Super Member gr79's Avatar
    Join Date
    Jun 2009
    Location
    SE Michigan
    Posts
    5,147

    Default

    Locked the rears up driving in the rain Friday.
    Car rear slides to the right a couple feet at 40 mph.
    Was unintentional. A quick firm stab did it.
    Another car made a jerky turn into a median turnaround cut.

    Wonder what these rear brakes would do during an off the ground brake check?

    474 and 569 shoes are similar enough to interchange most year vehicles using them.
    Motorcraft Br75B do 9" Mustang 83-93, Capri 79-86, T-Bird 81-88, LTD/Marquis 83-86.

    474 number adds Fairmont/Zepher 78-83. Mustang II, Pinto back to 1975.
    474 year span is 1975-1988.
    569 number year span is 1986-1994.
    BR-75B year span is 1983-1994.

    Wheel cyl got changed over in 1980. Difference or change unknown.
    Last edited by gr79; 07-18-2023 at 02:02 PM.

  14. #14
    FEP Power Member fgross2006's Avatar
    Join Date
    Sep 2014
    Location
    Freeport NY
    Posts
    2,024

    Default

    Quote Originally Posted by qikgts View Post
    How much throttle are you giving it in the above example or is this at idle with no throttle input?


    If it comes down to needing the prop valve rebuilt, that can be done too.

    https://www.musclecarresearch.com/va...-E0ZC-2B328-AA
    I ordered one. I'd feel better if it came with a new spring but the seller says its not needed and he doesn't have one to furnish.

    Honestly though, if I rebuild this and it doesn't solve the issue I'm gonna be pissed. My mechanic prefers trying the rebuild before moviing on to an adjustable proportion valve.

    What sucks is he has a junked 87 in his yard that i have picked for parts before but it has a plastic single chamber master cylinder and totally different proportion valve.

  15. #15
    FEP Power Member
    Join Date
    Nov 2007
    Location
    San Mateo, CA
    Posts
    2,273

    Default

    Quote Originally Posted by fgross2006 View Post
    I ordered one. I'd feel better if it came with a new spring but the seller says its not needed and he doesn't have one to furnish.

    Honestly though, if I rebuild this and it doesn't solve the issue I'm gonna be pissed. My mechanic prefers trying the rebuild before moviing on to an adjustable proportion valve.

    What sucks is he has a junked 87 in his yard that i have picked for parts before but it has a plastic single chamber master cylinder and totally different proportion valve.
    You do know the rear brakes are all the same drum brakes. The 87 4 cyl disc brakes are the same as the 84-86 brakes. That means the 87 4 cyl. master cyl should work on the 84-86.
    Fox Body/3rd Gen MCA Gold Card Judge
    84 SVO 24K miles, 85 Mclaren Capri Vert. 84 GT Turbo Vert.
    88 Mclaren Mustang Vert 20K miles, 89 Mustang LX Sport Vert,
    03 Mach 1 7900 miles, 74 Mustang II, 69 Mustang, 67 Mustang, 07 GT500,
    14 Mustang CS/GT, 15 F150 FTX Tuscany, 16 F250 Crewcab, 67 Tbird 47K miles

  16. #16

    Default

    Quote Originally Posted by KevinK View Post
    You do know the rear brakes are all the same drum brakes. The 87 4 cyl disc brakes are the same as the 84-86 brakes. That means the 87 4 cyl. master cyl should work on the 84-86.
    Just be aware there may be thread differences (size, and SAE vs metric) between the different years.
    1985 Mustang GT (Mothballed...Desired restomod parts acquired...Top of my project list for my 2024 retirement!)

  17. #17
    FEP Supporter
    qikgts's Avatar
    Join Date
    Jan 2010
    Location
    Rockledge, FL
    Posts
    1,461

    Default

    Quote Originally Posted by fgross2006 View Post
    Honestly though, if I rebuild this and it doesn't solve the issue I'm gonna be pissed.
    Did you buy a $10.00 bouns tool for your mechanic when you ordered the kit?
    https://www.musclecarresearch.com/brake-valve-tool
    '85 GT

  18. #18

    Default

    Quote Originally Posted by 85GTGuy View Post
    Just be aware there may be thread differences (size, and SAE vs metric) between the different years.
    Big change seems to be the 87 up MC connections went to metric......

  19. #19

    Default

    I forgot, the first time I rebuilt my brakes I screwed up the shoes, that does make a difference.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    K&N filter in a stock dual snorkel, GT40 heads, Edelbrock 3721 intake, MSD 8456 Dist., MSD 8227 coil
    Comp cams XE254H, hypereutectic pistons
    Hooker Super Comp Shorty Equal Length Headers, catted BBK H-pipe, full custom duals
    Maximum Motorsports caster/camber plates and strut tower brace, 3.73 rear, dura grip (both Yukon)
    Ford Performance Springs, Firehawk A/S 225/55r16 on LMR TRX r390 wheels (street)
    Federal 595 rs-rr 245/40r17 and 255/40r17 on OE cobra r wheels (race)
    AOD rebuilt with a 6 clutch direct drum, Koline steels stacked with 8 clutches, Kevlar band, superior shift kit, new torque converter. --Everything else stock and fully functional.

  20. #20
    FEP Power Member fgross2006's Avatar
    Join Date
    Sep 2014
    Location
    Freeport NY
    Posts
    2,024

    Default

    Quote Originally Posted by qikgts View Post
    Did you buy a $10.00 bouns tool for your mechanic when you ordered the kit?
    https://www.musclecarresearch.com/brake-valve-tool
    I didnt know I needed that. I just ordered one.

    The more I think about, the more I think refurbishing the original proportion valve is the best option. I have good braking power. my fronts and rears are new within the past 2 weeks. New master cylinder, new rear brake cylinders, adjusted tight as a drum and yesterday i'm driving around with the brake light flickering. Not solid on, but flickering. Today it wasn't on at all.

    Has to be the proportion valve.

  21. #21
    FEP Supporter
    qikgts's Avatar
    Join Date
    Jan 2010
    Location
    Rockledge, FL
    Posts
    1,461

    Default

    Good deal! Guess we'll all find out soon!

    Just to complete a thought... I mentioned above that maybe the new wheel cylinders are somehow incorrect and I bring it up again because I noticed that MM has wheel cylinders listed for sale that provide more rear bias. They recommend them for specific drag car combinations with big's and little's. I'm not advising they will fix your issue but instead mention it to make the point below.

    https://www.maximummotorsports.com/B...air-P1620.aspx

    Obviously, there are parts out there that are real similar to one another and most people wouldn't ever know the difference by looking at them, but would wind up getting bad performance once they were installed. Call it Chicom, spec drift, application consolidation, whatever. Over the years we've all seen the parts listings for our cars become inaccurate and it blows. Maybe you can do some measuring/comparison with known correct parts/the ones that were on there before?
    '85 GT

  22. #22

    Default

    Did you do an excellent job bleeding your MC? Brake light is troublesome. The valve shouldn't cause that.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    K&N filter in a stock dual snorkel, GT40 heads, Edelbrock 3721 intake, MSD 8456 Dist., MSD 8227 coil
    Comp cams XE254H, hypereutectic pistons
    Hooker Super Comp Shorty Equal Length Headers, catted BBK H-pipe, full custom duals
    Maximum Motorsports caster/camber plates and strut tower brace, 3.73 rear, dura grip (both Yukon)
    Ford Performance Springs, Firehawk A/S 225/55r16 on LMR TRX r390 wheels (street)
    Federal 595 rs-rr 245/40r17 and 255/40r17 on OE cobra r wheels (race)
    AOD rebuilt with a 6 clutch direct drum, Koline steels stacked with 8 clutches, Kevlar band, superior shift kit, new torque converter. --Everything else stock and fully functional.

  23. #23

    Default

    If you reseal your valve, use only brake fluid on the orings for installation lube.... Do not use grease, oil or wd40....

  24. #24
    FEP Power Member fgross2006's Avatar
    Join Date
    Sep 2014
    Location
    Freeport NY
    Posts
    2,024

    Default

    Quote Originally Posted by qikgts View Post
    How much throttle are you giving it in the above example or is this at idle with no throttle input?


    If it comes down to needing the prop valve rebuilt, that can be done too.

    https://www.musclecarresearch.com/va...-E0ZC-2B328-AA
    So I got the o-ring kit and the break bleeding set-screw. I'm hopefully going to start this project this upcoming week depending on my mechanics availability. I read through the instructions on cleaning the hard parts in ammonia. I was thinking white vinegar. Anybody have experience with cleaning the brass parts on a proportion valve?

    Also, It says the clean the bores so I will need round wire brushes. Does anyone know offhand what diameter the bores are on a proportion valve and what size wire brushes I'll need to clean them out?

    Also, brush by hand or on a power drill rotating at medium speed better?

    Last thing, what holds the proportion valve bracket to the frame? is it welded, riveted? I don't see screws or bolts to remove.

  25. #25
    FEP Supporter
    qikgts's Avatar
    Join Date
    Jan 2010
    Location
    Rockledge, FL
    Posts
    1,461

    Default

    I cleaned mine out when I gutted it. I just used clean brake fluid and brake cleaner.

    Any nylon or brass bristle brush that fits will work. Small tooth brushes included. Do enough to get it clean but don't go so far that you're removing material as brass is pretty soft. Hand power should be fine for this.

    If I remember right there's a stud on the bracket that goes through the sheet metal and it's retained with a nut on the wheel side.

    Circling back to the original concern, were the drums ever measured and confirmed to be in-spec? Also, was the master cylinder push rod length checked and verified to be correct?
    '85 GT

Page 1 of 3 123 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •