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Hydroboost test

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by mouse, Jul 18, 2005.

  1. mouse

    mouse 1/2 ton status

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    As an earlier post indicated I finished installation of the hydroboost brake system 1 day before heading to 3 solid days of offroading at Divide Ride '05. The brakes remained (incredibly) strong the entire time, through mud, rocks, and very long downhill sections.

    I did have one burp. After the first long steep uphill, we stopped (for a jeep overheating...), so I checked things out uder hood. The master cylinder cover had leaked some fluid out from the cover, down onto the lines. I had it close to topped off, so I figured it would spill a little and then I would be good for the rest of the time.

    When the day was done (and some 1-2 mile down hill sections where brakes were used a lot) I checked things out again. The rear half (much smaller than half, but you know what I'm talking about) of the reservoir had spilled more out and the level was about half full. The front was about 1/8th of an inch from the top.

    This got me thinking that the leak is probably more than just spillage. My theory is that without the Willwood porportioning valve (will order soon) and a bit too much rear brake bias, that I am probably getting some boiling of the brake fluid in this rear circuit (smaller reservoir - less cooling too). Hopefully rebalancing the front/rear bias will eliminate this problem - it ruined my nice paint job on the brackets for the boost lines...

    Any thoughts or similar experiences? What porportioning valve do you recommend (the Summit valve description only modulates between 100 - 1000 psi.....http://store.summitracing.com/partd...UM-G3905&N=4294922533+4294918719&autoview=sku)

    By the way - this setup kicks @ss. I can modulate the brake strength over big rocks and on the down hills. It inspires a whole new level of confidence in my blazer off road. (Now if I only had a locker - I'll save that for another post)
     
  2. Eric M.

    Eric M. 1/2 ton status

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    I doubt brake fluid boiling is your problem and I'm not sure a prop. valve would even help with that. If you redid your rear brakes as well, the self adjusters in the back may have "adjusted" tighter. I've noticed the same thing after a few brake jobs. You might just fill it up and watch it after your next trip.

    If it's still low, I'd look for a small leak somewhere. If you notice the rear res. is low and the front is overflowing, you've got a problem with the seals in the master. Is everything new in your brake system? How are the rear cylinders? Are all the connections tight?

    If boiling is your issue, your best bet would be to upgrade to DOT 4 or 5 fluid (remember to flush the system of ALL the old fluid first). But I'd exhast every other option before doing that. I've never heard of boiling fluid on our rigs, especially on a slow moving trail run. Brakes get a work out when tring to repeatedly slow down a disc or drum from 100MPH, not from keeping a truck from slipping on a steep descent.

    Good Luck,

    Eric M.
     
  3. mouse

    mouse 1/2 ton status

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    Thanks for the reply. I'm hoping the leakage on the master cylinder lid is from extreme angles, not boiling. Only the rear has lost any fluid, and after the trip, it has not lost any more. Everything in the brake system is new (minus the stock hard line). The rear uses large GM calipers from TSM, and is the reason I need an adjustable porportioning valve. All connections are tight and there are no leaks, except where it is visible coming from the master cylinder lid. I guess I have bad luck finding lids that seal well.

    Thanks again for the reply.
     

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