Advice on Swap to Dot 5 - New MC

Brakes for your Classic Mopar

  1. Mattax

    Mattax Just the facts, ma'am FABO Gold Member

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    True!
    The problem with the OP's setup is that's it's no longer a matched system.
    I'm pretty sure I found replacement parts for mine.
    Best bleeding IMO is the old fashioned way. The disks should be gravity bled if your patient (and lucky).
    For the rear lock up, go over the drum system to make sure everything is up to snuff. Nothing should be grabby. Make sure the front linings have the same or higher friction ratings (marked on the edges or back as a two letter code). Smaller rear wheel cylinders may be in order to reduce the force. Then when you go to front disks, you can reavaluate that decision if need be.

    Look at the newest Brake tips here:
    Master Technician Service Conference - Chrysler's Training for Mechanics
    Drum hardware was changed '68 to '69 so those details from anybooklet '68 and older prob won't apply to what's on your 8 1/4
    mymopar may have the same and some of the newer MTSC booklets the Imperial Club doesn't have.
     
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    • AJ/FormS

      AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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      It would be fine if the gunk stayed in the reservoir cuz it's just taking up space,lol.
      But if Dot4 is heavier and gravitates downward,into the Silicon, IDK.
      In a motorcycle, front brakes at that, I wasn't taking any chances, it had to come out.
      I was a pretty good mechanic; servicing all makes of motorcycles/ATVs/Sno-mobiles/ and various small-engine equipment; and got paid top wages in my field, more than some, maybe many,papered automotive dealer technicians. Brakes were particularly important to me, cuz people trust their mechanic to not let them get killed.In over 20 years, I rebuilt, reconditioned/restored/repaired/etc, a lot of brake systems, and had exactly one incident, caught before the bike left the shop. Getting the Dot4 out immediately, is too easy to take a chance.
      When I say gunk; I actually don't recall what I saw, except to say it was immediately apparent that those two fluids were not friends. That was about 25 years ago, or when Dot5 first came on scene.
       
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      • 70DusterBob

        70DusterBob Well-Known Member

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        I appreciate the information Mattax. I also appreciate everyone's input. Seems like every time I go to work on a different system with my Mopar, a whole universe appears on how to deal with it. The ignition system for example. Tons of systems, tons of ways to do different things. Brakes by far are the most important system in the automotive assembly of systems. Don't matter how fast your car is if you can't stop it. I agree, the system has been altered. I'm not sure how to remedy the system other than to upgrade to Discs soon. I just put 450 horses under the hood and won't be stepping on it anywhere near a place I will need to stop. But still, I have to be careful. I will do the wet road test to see if they are locking appropriately. I suppose the front should lock at the same point that the rear do??? Just to be sure, I'm not clear on that.

        Other than that, I got a good lesson in Silicone Brake Fluid. My buddy swears by it. Do you or does anyone know if it prevents the WC's from deteriorating as rapidly as they do with normal fluid?? It seems to me if the normal fluid absorbs moisture, it will rust the lines, that will generate debris which cuts the cups and makes them bleed. Is that right? Since the silicone doesn't absorb at least "as much" water, it seems like it would cause the cups in the WC's and the O-Rings in the MC to last a lot longer.

        Whenever I do a conversion to Discs, I will be sure to research hard on finding the right Proportioning valve and make sure the system locks up correctly. But for now, I will use the same Dot 3 that is in it to completely flush the system, since it has been a long time since it has been. I will most likely get new lines for the rear and front, and put new rear WC's, and a new MC all at the same time I install the Discs. I think that is what I read somewhere in these posts was that it is a good time to switch to Dot 5 when you are doing a resto.

        Thanks again!!
         
      • 70DusterBob

        70DusterBob Well-Known Member

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        Cool!
         
      • 4spdragtop

        4spdragtop FABO Gold Member FABO Gold Member

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        I didnt read all the replies. We did the same brake fluid swap. Dot 3, peeled our paint, so we said screw it(heard all the benefits) and swapped to DOT 5.
        Our 67 cuda has factory discs front and drums rear.
        We did not flush, what we did was simply add DOT 5(purple) to the reservoir and manually flushed(dad on the brakes and me on bleeder). Flushed till we saw purple and then did a little more.
        That was done in 2012. Zero issues 7 years and 15k later.
        Oh forgot, replaced steel jumper lines on front discs last year, so obviously had to bleed brakes. ZERO issues.

         
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        • AJ/FormS

          AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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          Blessed
           
        • famous bob

          famous bob mopar misfit

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          My whole system was new about 9-10 yrs ago, I dodnt remember if I put 3 -4-5 in it . It is al4 wheel dics, 87 diplomat alum, master cyl.
          That being said, I don't think I put dot 5 in it --------------------
           
        • Mattax

          Mattax Just the facts, ma'am FABO Gold Member

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          Correct. If either end is to lock up it should be the front first.
          Practical testing is difficult to cover all scenarios. At low speeds - nailing the brake pedal will almost certainly cause the fronts to lock, especially on slick surface.
          Why? There's not much tire traction, weight is distributed front and rear, and the brake force available can easy hold the drum or disk. Drums are self-energizing so slamming of the pedal is worse than with a disk.
          At high speed or using a more modulated braking force, nothing should lock up. The application of the brakes at speed causes the weight to shift forward - you can see and feel this on more softly sprung/damped vehicle but it happens to every vehicle. With less downward force on the rear wheels, there is less traction and it becomes easier to lock the rears. Tires and condritions that allow maximum grip, higher initial speeds, are all going to be factors in shifting weight forward. Really hard to test this thoroughly. Obviously driver's braking technique is also an important factor.

          That seems to be a big reason people switch to DOT5. Off hand I don't know a study that proves it but might look into the reason the military and US Post Office use SBBF for most of their fleets. Also the service internals and procedures they use.
          There's a bunch of references cited in this paper - see if there's one on that aspect. http://www.niagarabritishcarclub.org/index_htm_files/Brake Fluid.pdf

          Not really. The Glycol based fluids aborb the moisture and have corrosion inhibitors. Somewhat similar to propylene and ethythene glycol anti-freeze. By absorbing moisture glycol based brake fluids insure there are no free water droplets in the system. But the more moisture the brake fluid absorbs, the lower its boiling point, and also the corrossion inhibitors get used up, etc.
          That's when corrosion starts. I usually see it in the master and front disks first, but that may simply be the quirk of my experiences.

          Suppose it depends on what the cups are made of but the important thing is the brake fluid is compatible with the materials. Once corrosion starts the real issue IMO is the damage to the cylinder walls and pistons.

          That will work. No doubts there!

          Everyone has a different opinion on this! The only times I would really discourage a switch to DOT5 would be: racing - particularly road racing or road course events, if a manufacture says not use it (eg Wilwood) with their products, and with any anti-lock system that doesn't work with it due to the viscosity etc.

           
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          • jos51700

            jos51700 Well-Known Member

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            I think we're agreeing and not realizing it.

            What happens when you add DOT 5 to a DOT 3 system? Nothing abnormal! Don't believe me? Ask Harley Davidson! They switched from DOT 5 to DOT 3 in the late 2000's. The only part numbers in their system that changed were the master cylinder lids, because they indicated the change in spec fluid. All the seals and other parts were unchanged.
            Plenty of mouthbreathing HD guys dumped in DOT5 without realizing that there had been a change. No problems! (Note, these are the same guys that think the fluid is being used, like engine oil, so they top it off, not realizing why they can't get the pistons to retract when it's time for new pads)

            Rick E-berg has always advised that it's ok to mix DOT 3 and DOT 5. The characteristics that are different have no effect on the functionality of the fluid.

            Ask Penrite why they're wrong!

            It wasn't from mixing DOT 3/4 and 5. In 2004 I mixed all three in a baby food jar, and even punched a hole in the lid so it could absorb some moisture. I finally threw it away a couple years go. No gunk.

            This person gets it.



            My personal opinion about why they say not to mix is twofold.
            #1, it's difficult to define what you can put in the system, and saying what can mix makes that more unclear. Mineral oil brake fluid, which is a thing, should never be run in a 3/4/5/5.1 system. The materials in the cups and seals is totally different.

            #2, Manufacturers have to dodge any liability arising from unclear instructions.
             
          • AJ/FormS

            AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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            IMO a good way of brake testing is to do a series of stop tests at say 50mph. Get the car up to speed and then roll into the brakes, progressively harder with each application.
            What you will notice when the rear brakes are not working at all, is a goodly amount of front-end dive as the weight transfers from the rear to the front, even with 1.03T-bars. As you increase the rear pressure,and the rear does more and more braking, the dive lessens. Too much rear pressure and it begins to skid. Just right is when the whole car just hunkers down,still with a modest amount of dive, just before rear-end skid. Leave it like that for a few weeks, then adjust as may be necessary to prevent swapping ends.
            Then enjoy one of the best darn braking street-Mopars ever built.
            I remember in 73/74, a highschool buddy of mine took me for a ride in his newly purchased Corvette (year unknown but looked modern for that year). It was a heck uva ride for sure, BB and all; but the thing I remember most about that car was it's braking. Up to that point, I had never experienced brakes like that.
            My 70 Swinger 340,4-speed had pretty good brakes, but it was easy to get into trouble with that car, with its skinny E70-14 Polyglass belted tires, so you had to learn to actually drive that little monster. Come in too hot, and I had to ride it out hoping for the best while steering around obstacles as best as possible. Sometimes winning and sometimes not.
            With the Corvette, it had the brakes for back-up when you screwed up.
            When I built my car, I remembered that Corvette. And on the budget I had,I still wanted that kind of brake back-up; after all I was 25years older now.The KH 4-piston set-up with 10x2s out back, and big N littles hit the mark pretty close, for this streeter.
            That Corvette cornered pretty good too, compared to my Swinger anyway.
            I was glad when those factory tires wore out, and I put fat radials on bigger wheels, whoa, different world.
             
          • Mattax

            Mattax Just the facts, ma'am FABO Gold Member

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            Actually we disagree on the logic and therefore the conclusions.
            1. Key difference is that I conclude that it is inadvisable to mix SBBF DOT5 into a system with DOT3, 4, or 5.1 type fluids or vics versa.
            2. Our logic is different because our understanding of the performance requirements of FMVSS is different. These are the minimum requirements for each of the fluids - fluids defined by industry standards (SAE) - and not design guidelines or advice for use in a system.
            3. Additionally the weight we each place on manufacturer recomendations differ. I do not dismiss them as simply legal stratagem. For a change to be acceptible to an automobile manufacturer the component would have to pass both design and production validation testing. Those tests usual involve both component and full system testing, in typical and extreme environments, and in sufficient quantity to pass those tests 100% of the time statistically at 6 sigma (or more!). (sigma = standard deviation)

            If Harley davidson has a tech bulletin stating the SBBF may be added to the systems already containing non-SBBF without a complete fluid change over, then its probably fine to do on those systems.
             
          • 70DusterBob

            70DusterBob Well-Known Member

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            Thanks for the tip on the test braking. From 50, there are plenty of places to go 50 around the hill country where there are no close trees, people, pets, poles or cars! So 50 sounds about right. I can let off the brake if it goes squirrely or something and know I need to fix something at what is still a safe speed. Then gradually braking harder and harder each pass would be a safe way to test the reliability and function of them without too much risk.

            Overall a great way to test how they do. My reasoning is with the larger in diameter and width of the rear tires is what I think someone said in a reply here; it would take more psi of brake fluid to do the same job as the front because of the tire diameter and width. The proportioning valve was built for a 72 Dart with factory 4 Drum brakes. But yeah, the difference is 1/2" wider shoes in the back, which maybe offset by the larger and wider rear tires... So it "Should" be close I would think. If it isn't I will have to upgrade to the discs sooner than later. I know a shop that is professional about their work. Only took me 54 years to find them, lol. But they do quality work, Mopar is their specialty, hell, the guy has a 69 Charger for God's sake! He is good at this stuff, tons of factory and after market manuals, and he does his research. Cheap???? No way, but when you are asking someone to do a perfect job on a 49 yr old car, modified, mixing and matching parts, cheap just don't cut it!

            Oh, and yeah, I will try the wet road slam on the brakes test from 30mph, after a few roll into the brakes tests also at 30 which isn't fool proof, but should tell me if one of them is wayyyyy off. Right?
             
          • Mattax

            Mattax Just the facts, ma'am FABO Gold Member

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            There is no proportioning valve in your car.
            It had drum brakes.
            Read through this one 1970 Chrysler Imperial Hydraulic Brake Service Guide from the Master Technicians Service Conference Session 274 or watch the filmstrip.
            When you change to disks, then either add a proportioning valve or switch to a combination valve.

            Hydraulic pressure does not act in direct relationship with drum braking system. The relative size of the cylinder does effect the force for a given amount of pressure but it leverages the shoes - and then on a servo drums (which is what we've got) the primary acts on the secondary increasing the force. Many original brake shoes had a different material for the primary and secondary shoes to fine tune the braking. And yes the relative size of the lining contact surface also plays a role because a given force will be spread out over a larger or smaller area. Lots going on in drum brake design.

            Rear lock up. Be careful and there are no guarentees when the back gets loose. Fishtailing turns into tank slappers pretty fast. Catch a change in surface sideways and all bets are off.
             
          • jos51700

            jos51700 Well-Known Member

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            Reading the federal motor vehicle safety standard in its entirety kind of IS the design guideline, isn't it?

            Or did I miss what standards were for?

            And the SAE standards that underline the fmvss covers the component and system testing, to a T.

            But the lawyers still gotta do what they gotta do, regardless of engineering.
             
          • 70DusterBob

            70DusterBob Well-Known Member

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            What was the little bronze colored box that the MC went to then? I don't have time to look over the info you provided, but everyone else told me that was the proportioning valve. It is mounted on the frame, and if I remember right, it divides the front one line into two front lines, and the rear one line into two rear lines. Does that not proportion front to rear or just side to side?

            I will look over the info you provided tonight. When I have more time. But thanks for the data, all information is needed and appreciated.
             
          • Mattax

            Mattax Just the facts, ma'am FABO Gold Member

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            Distripution block or safety switch block
            rear is single line out/

            Nope. just tees the front and feeds through for the rear.

            Well you can look over the material from Cheysler and make your own decisions about everyone's knowledge. ;)
             
          • 70DusterBob

            70DusterBob Well-Known Member

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            You've got a point there. Most of what you hear in circles comes from the circle and not the source.

            Goin' to check out the source materials now.
             
          • 70DusterBob

            70DusterBob Well-Known Member

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            Thanks Mattax,

            I read it and it seems to me to be a metering block. There is also a switch block that looks just like the one in the pictures. I don't remember exactly what the metering block looks like, will have to take a pic of it.

            Won't be soon. But I will try to make sure the box is a metering block and not a proportioning valve. Your right though, only one line comes out to the rear, where it divides on the differential.

            Appreciate the manual!
            Bob
             
          • Mattax

            Mattax Just the facts, ma'am FABO Gold Member

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            Distribution block or they call it a safety switch since the block carries the brake warning switch.

            Metering valve was only used on some disk brake systems to reduce front lock up on icey surfaces at low speed.
             
          • 70DusterBob

            70DusterBob Well-Known Member

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            Oh, Learn something new everyday around here! lol

            It does look like a distribution block in the pictures, terminology makes all the difference between looking stupid or smart.
             
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