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Thread: Brake Booster?

  1. #1
    Join Date
    Aug 2009
    Location
    Bow Valley, NE
    Posts
    77

    Default Brake Booster?

    I've got a '79 Scout II with a 345 and 4 speed manual, which has been sitting for about 12 years and I just got it running great and its hell of a fun ride. It's time to examine the brakes they work but go all the way to the floor and if I want to get the pedle back to it original location I have to pull it back with my foot and I know it needs all new brake hardware but was wondering if thats is just air in the lines or if the booster is shot?

  2. #2
    Join Date
    Feb 2009
    Location
    Aiken, SC
    Posts
    2,423

    Default

    Flush the system before you do anything else. The lines are undoubtedly full of water, and the master cylinder is probably rotted.

    You can do this with the engine off, so the booster won't affect things. It will be harder to push the pedal, but it's a better way to flush the system. You need to replace all of the fluid before you start messing with adjustments.

    The next step will be to fire it up and re-evaluate. At that point, you may start to find leaks. You really need to pull the drums on the rear and look after you flush. You also need to make sure the shoes are properly adjusted. Only then can you properly evaluate the condition of the system.
    Allan E.
    Curmudgeon Extraordinaire
    Charter Member, Old Hippie IH Club
    Old fashioned binder freak

  3. #3

    Default

    ---There's also only one way to check a brake booster (on the vehicle) that I know of, and all repair manuals describe it the same way. LOL, for fear of being wrong I will tell you to check a manual, but IIRC:

    1. (Engine off) Purge vacuum by pumping brake pedal a couple times.
    2. Start engine & allow chamber to fill (about 2 seconds), press and hold brake pedal
    3. Shut engine down and release brake pedal
    4. Press brake pedal down, note height from floor and release pedal
    5. Press brake pedal down, note height from floor and release pedal
    6. Press brake pedal down, note height from floor
    7. Brake pedal height should have grown each time the pedal was pressed down, verifying that chamber is holding vacuum until brake is applied
    8. Keeping foot on brake pedal, start the engine and pedal should fall 1.5"-3" verifying that vacuum assist/booster is operational

    ---Walking outside 24 hours after you last drove it and pulling the check valve will show if either the grommet or check valve is faulty, leading you to think it is the booster. Making sure air only passes one way through the check valve will save you a few bucks, but I prefer to replace them together. Purchasing a new grommet & check valve (if you don't hear the vacuum released when pulling the check valve) and performing the test again will probably tell you that is where the problem was and only cost you roughly $6. If not the grommet/check valve and the booster is still considered faulty, rebuilt as an assembly (master and booster) is the cheaper way and you don't have to worry whether or not the actuating rod is adjusted correctly (needs to be done with a home-made [described in the manuals] depth gauge).

    ---Again, check any service manual, don't just take my description as law because I might have forgotten something and like I said there is only one way to perform the test. That's not to say no one has used their mighty-vac vacuum pump to test a brake booster after finding out what max pressure would be. Sort of perform a leak-down test. That I am sure would tell you if the seal(s?) was/were leaking and not holding vacuum or the diaphragm was nonoperational for a similar reason, but on the vehicle the test is performed similarly to as I described above and as I was instructed decades ago, only one way.
    Last edited by Thomas; 10-27-2009 at 11:09 PM.
    ---Thank you,
    -T.R.E.Jr. (Fortiter Et Recte & Soyez Sage)

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  4. #4

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    Quote Originally Posted by BLACKATTACK76 View Post
    I've got a '79 Scout II with a 345 and 4 speed manual, which has been sitting for about 12 years...
    ---Wow, don't know how I missed that and glad I looked back over it before I left the thread.

    ---As said, flushing the system is necessary after that length of time. I would suggest draining the system and using alcohol (even rubbing alcohol) to bleed the system. Then drain and disconnect both ends of the lines, blowing them out with compressed air. Bleed again with alcohol, maybe a few times and blow out with compressed air. Flush with brake fluid by bleeding and then replace all rubber and seal-like stuffs, including Calipers and wheel cylinders. Replace Master Cylinder and booster, if booster fails the test or unless you want to purchase both as a package.

    ---When bleeding I use speed bleeders and then replace them with solid bleeder fittings once all air is purged. I then bleed the wheels once more to get rid of the air bubble(s) created when swapping fittings. Speeds up the process and minimizes fluid needed IME.

    ---To bleed the fronts properly you will need a helper or a tool to hold the bypass button on the Proportioning Valve so the calipers will fill completely before fluid supply is cut off.

    ---I just purchased this tool...
    (Click for larger image)


    . . . ... which is for ABS. I am sure with very little alterations I could make it work for both ABS and for the maximum 14# of holding pressure my* Scout's proportioning valve requires (there's two [major] types used on IHs that I know of from my manuals and trucks/past trucks). FWIW, anything more than the specified pressure and damage will be inflicted upon the bypass valve.

    ---Gotta run. HTH.
    Last edited by Thomas; 10-27-2009 at 11:42 PM.
    ---Thank you,
    -T.R.E.Jr. (Fortiter Et Recte & Soyez Sage)

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  5. #5
    Join Date
    Oct 2009
    Location
    Colorado Springs
    Posts
    69

    Default

    I had a similar problem on mine when I got it. The previous owner said he did a whole brake job and seeing as he was a mechanic I took his word (learned not to do that again).

    Anyways, similar problem, pedal would go all the way to the floor and would take some going to pop back up. Wasn't till my brakes seized on the highway that I checked them. Turned out my brake fluid looked more like 10W-30 then brake fluid. So I sucked all the fluid out and ran basically an entire bottle of new fluid through it. Haven't had a problem since.

  6. #6
    Join Date
    Apr 2009
    Location
    San Luis Obispo, California
    Posts
    283

    Default

    I know how u feel Rascus, been there. Ive decided im past the point of taking peoples words for things hehe, I'm just overhauling the whole beast, im just gonna rip everything out and replace 100% of my brake system, I don't wanna deal with bleeding.. and i want to know exactly what i have, and that what i have is done correct lol (because i did it)

    Braided steel 8" extended lines
    stainless steel complete hard line set
    Got a brake booster to add to my axle out of a 75 which has disc
    Adapter bracket kit for drum to disc in the front
    New master cylinder
    New 2-1 valve

    Only think that will remain original is the proportioning valve and the pedal ha ha and i might replace the valve someday if i go to disc in the back as well.
    -72 Scout2 - SBC350 with RV camshaft, 4 speed manual Trans, D20 xfer case with CV drive shafts.
    -Dana 44 Detroit locker rear.
    -Dana 44 (out of a 75) Rebuilt /w trutrac limited slip frnt



    ~Conquest is not in our principles. It is inconsistent with our government.

    ~T.J.

  7. #7
    Join Date
    Oct 2009
    Location
    Colorado Springs
    Posts
    69

    Default

    That's going to be a summer project for me. Rip all the brake system out, probably convert the rear to disc as well. You'll have to let me know how the braided steel lines work out for you.

    Another thing he told me was new master cylinder, he just replaced the cover, that doesn't count!

  8. #8
    Join Date
    Apr 2009
    Location
    San Luis Obispo, California
    Posts
    283

    Default

    If you are gona get a new Master Cylinder, i would suggest This
    http://www.summitracing.com/parts/DHB-M80568/

    Summit sells brand new Master Cylinders for 50$ which i was pretty surprised about. The boosters are pricey tho.. I got a remand for around 150$ i think from my friends John and Joe over at BCB

    www.Backcountrybinders.com

    Hes really helpful and can get almost anything for equal or slightly less than the big sites.
    -72 Scout2 - SBC350 with RV camshaft, 4 speed manual Trans, D20 xfer case with CV drive shafts.
    -Dana 44 Detroit locker rear.
    -Dana 44 (out of a 75) Rebuilt /w trutrac limited slip frnt



    ~Conquest is not in our principles. It is inconsistent with our government.

    ~T.J.

  9. #9
    Join Date
    Apr 2009
    Location
    San Luis Obispo, California
    Posts
    283

    Default

    They are really nice, im in the process of installing them.. But they are very pricey i will warn you haha
    -72 Scout2 - SBC350 with RV camshaft, 4 speed manual Trans, D20 xfer case with CV drive shafts.
    -Dana 44 Detroit locker rear.
    -Dana 44 (out of a 75) Rebuilt /w trutrac limited slip frnt



    ~Conquest is not in our principles. It is inconsistent with our government.

    ~T.J.

  10. #10
    Join Date
    Aug 2009
    Location
    Bow Valley, NE
    Posts
    77

    Default

    Hey thanks for the replies and sorry I haven't replied back I've been out in the middle of South Dakota so that means no computer. Yes I agree with dealing with the brake system before diagnosing the brake booster. Also took off the master cylinder it looked just like 10w30 oil and one of the resevoirs were empty. So I bet the i need new wheel Cylinders and how do I get all the fluid out of the system with out any special tools?
    Last edited by BLACKATTACK76; 10-29-2009 at 04:36 AM.

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