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Brake failure

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  • Brake failure

    Well , happy 2008. I start the new year with two seemingly insurmountable problems. firstly , I have a Chev 400 in my Silverhawk , coupled to a Jag XJ steering rack.When I turn full lock on the steering , I loose my brakes , which recover after a quick pump or two of the pedal.I know that there should not be any connection between brakes and steering. The brakes and steering work perfectly at all other times.I have no brake fluid leaks . Could this have siomething to do with the engine revs slowing at full lock and thus not providing enough power to keep the vacuum level in the brake booster ?. Secondly , will the size (diameter ) of the steering pump pulley have an effect on the amount of assist given to the power steering , ie larger pulley , more assist and vice versa ?

  • #2
    WOW, Never heard of this. Just a guess, check your rubber brake hoses to see if they are long enough and getting pinched/streched when the wheel is turned to the full postion. When you pump the brakes the pressure is enough to refill the line. Good luck and let us know.

    Comment


    • #3
      Thanks KG , I have checked and re checked the hoses , even repositioned them without any change.I have a BMW 5 series front discs and booster working off the original MC. I am in the process of ordering a dual MC but I cant see how this would change things .

      Comment


      • #4
        Mike,
        When you loose your brakes in a full lock, are you by chance backing out of a drivway with a slight "dip"? You did not state if you have drum or discs up front.
        On my "original" kits, we mounted the caliper in front of the king pin as did Studebaker. With that set up, "we" found that in baking out of a driveway, with the steering wheel turned all the way to left or right, the caliper would hit the frame rail lip, and push the piston back into the housing. Same EXACT symptons you are having! first step on the brake, no brakes, next time full pedal. Check the back of the calipers to see if they are scraped.
        If that is it, very easy to fix.

        Jim
        "We can't all be Heroes, Some us just need to stand on the curb and clap as they go by" Will Rogers

        We will provide the curb for you to stand on and clap!


        Indy Honor Flight www.IndyHonorFlight.org

        As of Veterans Day 2017, IHF has flown 2,450 WWII, Korean, and Vietnam Veterans to Washington DC at NO charge! to see
        their Memorials!

        Comment


        • #5
          Jim can handle the brake part...
          But on your power steering...
          Are you running the Chevy p/s pump into the Jag rack?
          If the Jag rack is anything like the Fomoco rack, the psi from the Chevy p/s pump may be more than the rack needs, making the rack quick and jittery. It also 'could' dead end the p/s pressure hose and that backs up and causes the pump to groan and lug down the engine, sometimes even causing it to stall at idle (full lock turn at idle RPM). There is a replacement p/s pressure relief piston that can go into the back of the p/s pump ('if' it is the older style p/s pump) that reduces the psi to slow the rack down and ease off on the pump a bit. There are also 'adjustable' versions of this valve (Heidt's) that allows you to dial it in to where you want it to be (which might be a good thing because the Jag spec might be different than a Fomoco spec.) Changing the pulley size will only affect the rate of flow, and not the psi, as that is set by the pressure valve. But the recovery time after input might change. Putting a smaller pulley on might help a low rpm low pressure problem. A larger pulley might aggravate a low rpm pressure problem.
          Hope the info helps.
          Jeff[8D]
          HTIH (Hope The Info Helps)

          Jeff


          Get your facts first, and then you can distort them as much as you please. Mark Twain



          Note: SDC# 070190 (and earlier...)

          Comment


          • #6
            Those ford systems just have a weaker pressure regulator spring, don't they? Can't you just take the pressure hose off, unscrew the fitting, take out the spring and get a different one or grind it shorter?

            Comment


            • #7
              Hi Jim/Jeff , I do have discs upfront and they are mounted in front of the king pins , I will check for marks on the back of the caliper , but sounds promising. As for the steering , I think Jeff is right , the steering is a bit jittery and I did burst the pump feed pipe into the rack but thought it was just a bad hose.I am running the Chevvy pump and it seems to be generating too much pressure , can you advise where I could find the adjustable pressure relief piston (website)and how would I install it.

              Comment


              • #8
                quote:Originally posted by mike gaines

                Hi Jim/Jeff , I do have discs upfront and they are mounted in front of the king pins , I will check for marks on the back of the caliper , but sounds promising. As for the steering , I think Jeff is right , the steering is a bit jittery and I did burst the pump feed pipe into the rack but thought it was just a bad hose.I am running the Chevvy pump and it seems to be generating too much pressure , can you advise where I could find the adjustable pressure relief piston (website)and how would I install it.
                You need one of these. Both high and low pressure lines have to run through the valve and it gives you infinate adjustability. The lines going to the pump are not installed at the time of the pic.


                Jerry Forrester
                Douglasville, Georgia
                Be sure to check out my eBay store
                http://stores.ebay.com/CHROME-CHROME-CHROME_
                for your shiny Stude stuff

                More pix of Leo the '55 Pres HT here...http://tinyurl.com/2gj6cu
                Jerry Forrester
                Forrester's Chrome
                Douglasville, Georgia

                See all of Buttercup's pictures at https://imgur.com/a/tBjGzTk

                Comment


                • #9
                  ISTR reading in a hot rod mag a while back that you could somehow modify the GM pump by snipping a spring or something to mate it to a Mustang II/Pinto rack. perhaps that would also be advisable for a Jag rack. hopefully a web search will turn up what I'm talking about.

                  nate

                  --
                  55 Commander Starlight
                  http://members.cox.net/njnagel
                  --
                  55 Commander Starlight
                  http://members.cox.net/njnagel

                  Comment


                  • #10
                    quote:Originally posted by N8N

                    ISTR reading in a hot rod mag a while back that you could somehow modify the GM pump by snipping a spring or something to mate it to a Mustang II/Pinto rack. perhaps that would also be advisable for a Jag rack. hopefully a web search will turn up what I'm talking about.

                    nate

                    --
                    55 Commander Starlight
                    http://members.cox.net/njnagel
                    Tried that Nate, it doesn't work. Even bought the modified valve (the one in the pump)from one of the StreetRod product vendors, that didn't work either. The only thing I have found that works is the Heidt's PS pressure control valve. First hand, personal, hands on experience.

                    Jerry Forrester
                    Douglasville, Georgia
                    Be sure to check out my eBay store
                    http://stores.ebay.com/CHROME-CHROME-CHROME_
                    for your shiny Stude stuff

                    More pix of Leo the '55 Pres HT here...http://tinyurl.com/2gj6cu
                    Jerry Forrester
                    Forrester's Chrome
                    Douglasville, Georgia

                    See all of Buttercup's pictures at https://imgur.com/a/tBjGzTk

                    Comment


                    • #11
                      Just a thought, might the inner lining of the brake hose be collapsing when put in a bind? I have seen this happen before. The pressure goes behind the lining, and collapses it.

                      Comment


                      • #12
                        Yup... And it is adjustable, for those of us that are metric insensitive)
                        (Ya done good Jerry... Way better than I tried to 'splain it)
                        Jeff[8D]
                        PS: I have Jerry's shiny chrome crap on my yellow POS, and I like it just fine


                        quote:Originally posted by Jerry Forrester

                        quote:Originally posted by mike gaines

                        Hi Jim/Jeff , I do have discs upfront and they are mounted in front of the king pins , I will check for marks on the back of the caliper , but sounds promising. As for the steering , I think Jeff is right , the steering is a bit jittery and I did burst the pump feed pipe into the rack but thought it was just a bad hose.I am running the Chevvy pump and it seems to be generating too much pressure , can you advise where I could find the adjustable pressure relief piston (website)and how would I install it.
                        You need one of these. Both high and low pressure lines have to run through the valve and it gives you infinate adjustability. The lines going to the pump are not installed at the time of the pic.


                        Jerry Forrester
                        Douglasville, Georgia
                        Be sure to check out my eBay store
                        http://stores.ebay.com/CHROME-CHROME-CHROME_
                        for your shiny Stude stuff

                        More pix of Leo the '55 Pres HT here...http://tinyurl.com/2gj6cu



                        Deep-N-Hock Acres
                        Brooklet, Georgia
                        DEEPNHOCK at Gmail.com
                        '37 Coupe Express
                        '37 Coupe Express Trailer (project)
                        '61 Hawk (project: Ist Gen Owner - project)
                        Mysterious Project Z
                        http://community.webshots.com/user/deepnhock

                        HTIH (Hope The Info Helps)

                        Jeff


                        Get your facts first, and then you can distort them as much as you please. Mark Twain



                        Note: SDC# 070190 (and earlier...)

                        Comment


                        • #13
                          BTDT....
                          After experimenting, I feel that the grinding, shimming, guessing, and various rote methods are far inferior to the Heidt's adjustable method....
                          (Ask the cheap CASO that I am... I have NOT installed the Heidt's setup yet....)
                          (Even though I say out loud that "I will" every time my setup growl's at me in a less than ideal brake application..)
                          This is a learning curve that should be shared....
                          (But, I will stack my amateur setup up against anyone...anytime...geography respective[])
                          Jeff[8D]


                          quote:Originally posted by N8N

                          ISTR reading in a hot rod mag a while back that you could somehow modify the GM pump by snipping a spring or something to mate it to a Mustang II/Pinto rack. perhaps that would also be advisable for a Jag rack. hopefully a web search will turn up what I'm talking about.

                          nate

                          --
                          55 Commander Starlight
                          http://members.cox.net/njnagel



                          Deep-N-Hock Acres
                          Brooklet, Georgia
                          DEEPNHOCK at Gmail.com
                          '37 Coupe Express
                          '37 Coupe Express Trailer (project)
                          '61 Hawk (project: Ist Gen Owner - project)
                          Mysterious Project Z
                          http://community.webshots.com/user/deepnhock

                          HTIH (Hope The Info Helps)

                          Jeff


                          Get your facts first, and then you can distort them as much as you please. Mark Twain



                          Note: SDC# 070190 (and earlier...)

                          Comment


                          • #14
                            Jeff, IIRC you're using a hydroboost as well, aren't you? In your app. probably using the GM pump with the stock PRV is the way to go, then use the Heidt's adjustable thingy *only* on the PS part of the circuit. (I assume that you have the HB tee'd off of the PS lines...)

                            nate

                            --
                            55 Commander Starlight
                            http://members.cox.net/njnagel
                            --
                            55 Commander Starlight
                            http://members.cox.net/njnagel

                            Comment


                            • #15
                              Thanks for all the advice and here is the result of my efforts.
                              1. Thanks to Jim Turner the brake problem is sorted , the brake caliper was fouling against the chassis on full lock and forcing the plunger against the disc. I had looked for this problem in the past but always with the car on jack stands which allowed the suspension to drop and the fouling wasnt visible.Also installed a non return valve on the booster. just looking at the brakes made me decide to order Jim's dual MC but cant seem to raise him on the net this week.
                              2. I have had the rack refurbished and the shop technicians found that the filter was blocked, the mounting bushes worn and I also decided to replace the tie rod ends. Steering is fine and tight now. I also replaced the inner and lower outer A arm bushings , being sure to spread the lower outer arm on re assemly with an appropriate bolt. It all worked great and didnt need any special tools.I do have a query though , the manual says to tighten the lower inner cap screws to 65ft/lbs and the upper to 50 ft/lbs once the weight of the car is on the suspension. I asked the technician at the alignment shop to do this for me but he was insistent that all the cap screws should be fully tightened to lock the bushings in place. He has a lot of experience on old cars but is his advice correct , it seems logical to me ? 50 to 65 ft/lbs is not very tight considering that it is tightening up against the rubber bush.What would the effect be of over tightening the cap screws ?

                              Comment

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