power brake assist issue
Have an account? Register

Forgot your password?

Forgot your username?

 
Likes Likes:  6
+ Reply to Thread
Page 1 of 5 1 2 3 ... LastLast
Results 1 to 10 of 48
  1. #1
    24v
    Official RnS Addict 24v's Avatar
    Join Date
    Mar 2011
    Location
    Cork,Ireland
    Posts
    627
    Images
    111
    Post Thanks / Like
    24v is offline

    power brake assist issue

    hopefully someone can help

    i have isuzu npr running gear including brake system and steering box
    i have changed the rear axle to a larger model nqr as there is a better ratio.
    this has bigger diameter drums also.
    the isuzu master cylinder is mated to its own hydro boost valve to assist instead of vacuum from the factory.
    i have a 6bt 12v fitted and am taking the feed for the hydro boost from the ps pump as is standard.
    i have a high pressure line from the pump and after about 12 inches i have a tee to the isuzu ps box.
    low pressure from the hydro boost is teed back in to the hose just below the reservoir
    the ps pump on the cummins puts out about 2100 psi which i think is too much for the hydro boost

    my issue is that i have to stand on the pedal as hard as i can just to get it too stop
    it will lock one rear wheel in gravel

    should i adjust the output pressure on the ps pump to reduce to about 1650 psi
    is that the issue?
    hydro boost bad?
    plumbing wrong?
    brake fluid is bled and seems good at each wheel

    chassis originally had 16 wheels but because of the larger rear drums are now 17.5

    any advice would be welcome
    Work to live don't live to work....
    V8 BMW powered 55 chevy pick up bagged
    Cummins powered ford f8 Big Job

  2. Remove Advertisements
    RodsnSods.co.uk
    Advertisements
     

  3. #2
    Off the Xmas card list kapri's Avatar
    Join Date
    Apr 2009
    Location
    Portsmouth
    Posts
    23,745
    Images
    12
    Post Thanks / Like
    kapri is online now
    Not a clue as never been involved with anything like that !

    However working on the same principles as normal brakes I would have suggested chceking the pedal ratio and going down an m/c size as it sounds like either not enough line pressure or too much volume from too larger a m/c which would reduce line pressure .

  4. #3
    24v
    Official RnS Addict 24v's Avatar
    Join Date
    Mar 2011
    Location
    Cork,Ireland
    Posts
    627
    Images
    111
    Post Thanks / Like
    24v is offline
    Thanks. Just to clarify it’s the running gear of my 51 ford. I thought as the master cylinder is right for the front that it would lock them. So I’m unsure wether it’s master cylinder or hydraulic plumbing that’s causing my hard pedal
    Work to live don't live to work....
    V8 BMW powered 55 chevy pick up bagged
    Cummins powered ford f8 Big Job

  5. Remove Advertisements
    RodsnSods.co.uk
    Advertisements
     

  6. #4
    Off the Xmas card list kapri's Avatar
    Join Date
    Apr 2009
    Location
    Portsmouth
    Posts
    23,745
    Images
    12
    Post Thanks / Like
    kapri is online now
    It then goes back to is it original pedal ( and so ratio ) ? Guess one way would be to disable the hydraulic assist and see how it all feels ? Is it possible to get the hydroboost back to front so it's pushing the wrong way ?

  7. #5
    24v
    Official RnS Addict 24v's Avatar
    Join Date
    Mar 2011
    Location
    Cork,Ireland
    Posts
    627
    Images
    111
    Post Thanks / Like
    24v is offline
    I could plumb the hydro boost the opposite way if that’s what you mean?
    It’s a system I don’t like but am stuck with as it’s expensive to convert to vacuum.
    I think from research I’ve too much pressure from the cummins pump
    I don’t know the hydroboost pressure for an npr
    Thanks for your help so far Kapri
    Work to live don't live to work....
    V8 BMW powered 55 chevy pick up bagged
    Cummins powered ford f8 Big Job

  8. #6
    Official RnS Addict mygasser's Avatar
    Join Date
    Dec 2009
    Location
    faversham, kent
    Posts
    13,687
    Images
    514
    Post Thanks / Like
    mygasser is offline
    lots of 70's to 90's and on diesels had belt driven vacuum pumps for the servo so not hard to swap to servo assist. even if you bolt the master cylinder to the bulkhead and use a remote servo it'll work. as kev said what's the pedal ratio? that can make the pedal feel very 'wooden' with low effort in the same way as too big a bore master cylinder.
    neil.
    need a job done on your project? i may be able to help.

  9. Likeskapri liked this post
  10. #7
    24v
    Official RnS Addict 24v's Avatar
    Join Date
    Mar 2011
    Location
    Cork,Ireland
    Posts
    627
    Images
    111
    Post Thanks / Like
    24v is offline
    Ok thanks.
    I’ll check the pedal ratio and let you know.
    I’ll search on remote servos also
    Thanks for the tip
    Work to live don't live to work....
    V8 BMW powered 55 chevy pick up bagged
    Cummins powered ford f8 Big Job

  11. #8
    24v
    Official RnS Addict 24v's Avatar
    Join Date
    Mar 2011
    Location
    Cork,Ireland
    Posts
    627
    Images
    111
    Post Thanks / Like
    24v is offline
    What’s the opinion on electric vacuum pump kit?
    Work to live don't live to work....
    V8 BMW powered 55 chevy pick up bagged
    Cummins powered ford f8 Big Job

  12. #9
    Off the Xmas card list kapri's Avatar
    Join Date
    Apr 2009
    Location
    Portsmouth
    Posts
    23,745
    Images
    12
    Post Thanks / Like
    kapri is online now
    They work fine but are expensive new.I used on eon a mates car to provide his vacuum wipers with consant vacuum via a homemade holding tank ( Large bore drainage pipe with glued on caps).They are available on old Volvo 'brick' turbos and the s and v ranges though most breakers have no idea they are even fitted or what they are for. foun dunder the front sing on S and V Volvo versions, don't know where on Bricks.

  13. #10
    24v
    Official RnS Addict 24v's Avatar
    Join Date
    Mar 2011
    Location
    Cork,Ireland
    Posts
    627
    Images
    111
    Post Thanks / Like
    24v is offline
    Thanks. What do you think of these?

    https://www.ebay.co.uk/itm/303169465080

    https://www.ebay.co.uk/itm/164211901466

    https://www.ebay.co.uk/itm/392799173095

    Would I need 2 remote servos?
    One front and one rear?
    Work to live don't live to work....
    V8 BMW powered 55 chevy pick up bagged
    Cummins powered ford f8 Big Job

+ Reply to Thread
Page 1 of 5 1 2 3 ... LastLast

Quick Reply Quick Reply

Register Now

Please enter the name by which you would like to log-in and be known on this site.

Please enter a password for your user account. Note that passwords are case-sensitive.

Please enter a valid email address for yourself.

Where you live, Town\City\County etc.

Please enter your full name
This field cannot be edited once it has been completed other than via contacting the site admin. Please make sure the information is correct first time.

Log-in

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

    Bookmarks

    Posting Permissions

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