Screen Removal Bargman L-300 Door Handle brakes Satellite Fuel Tank Fire Extinguishers Roof Antenna Tech Talk Forum Shortcut Motor Oil Window Generators headlights batteries Radiator AC Unit Grab Handle Wiper Blades Wiper Blades Door Locks Door Locks Door Locks Door Locks Rims Front Shocks Rear Shocks Front Tires Oil Filter Steps Roof Vent Awning Propane Tank Mirror Info Clearance Lights Clearance Lights Clearance Lights Clearance Lights Clearance Lights Spartan Chassis Gillig Chassis Freightliner Chassis P-32 Chassis MCC Chassis
    Forums    Tech Talk    Hydra boost brakes.
Go to...
Start A New Topic
Reply To This Topic
Hydra boost brakes.
 Login now/Join our community
Glassnose Aficionado
Supporting Member of 2/09
Picture of Danny Z
On our recent trip I noticed the pedal was going down a little too far, so I checked the fluid and the front reservoir was about empty. I filled it up and the pedal came right back up. After a day of driving it was a little soft again and again it was low. It got progressively worse but we made it home safe and sound, but the area of the master and boost is soaked with fluid. It appears to be coming from the plunger where it goes into the boost, but there's so much fluid it's hard to tell. I tried cleaning it with purple power but I can't get it clean enough to see where the leak is originating. I think I'm going to take it in to my service place, where they work on fleet trucks, but I'm wondering if anybody has any insight as to what kind of job this could turn into. BTW, the boot had pulled back from where the piston enters the front of the booster.

79 Barth Classic
Posts: 3770 | Location: Venice Fl. | Member Since: 07-12-2004Reply With QuoteReport This Post
Supporting Member of 6/19
posted Hide Post
It I remember correctly , changing the master cylinder on a hydro-boost system is the same as changing a master cylinder on a vacuum booster setup .

Sam Miniature Schnauzer
3.8.2009 - 9.24.2021

93 30ft Breakaway

Posts: 397 | Location: Mooringsport,LA | Member Since: 05-30-2019Reply With QuoteReport This Post
Supporting Member of 1/21
Picture of Duane88
posted Hide Post
Changed the master cylinder on both 88 and Nose, both are hydro boost. it is a fairly easy job.

Jack up the drivers side front, remove the wheel, pretty much exposes the cylinder, mounting bolts and for access to the lines might have to go through the dog hose or if you have one the access door just in front of the accelerator pedal. Sounds like the loss of brake fluid has shown you where it is leaking. the booster is probably ok, if the fluid loss is in the master reservoir, do not know if a new boot is available.

My guess is a mechanic would take a bit over an hour and the cylinder is about $80.

Rock auto has replacement master cylinders, but mine on 88 was not the one listed so needed to take it to the Auto store to make sure it was the right unit. They want the core anyway. the cost after shipping was not that much more.

25 Ft Glassnose, 2792, 1982
454 Engine
Plain Jane Interior
Original Paint
Posts: 1730 | Location: Clinton Iowa | Member Since: 04-02-2017Reply With QuoteReport This Post
posted Hide Post
before you take this anywhere i suggest you do this

fill the master cylinder with brake fluid

buy a digital temperature gun . they cost maybe $20.00 and i do not think a expensive one is better than a cheap one

learn to use it . take your street car out for a drive get under it and measure and record the temperature of each the calipers and each brake disc /drum . you can point it( the gun) at the item from 6 inches to 10 feet away but learn to be consistent in what you point at and what you measure and the apx distance .. the gun will have a red dot which will appear on on the thing you are trying to measure as .

try using the gun in the house and measure the temperature of the stove or the toaster inside and out until you get consistent readings .. if you cannot repeat your test in the house you are doing it wrong . . keep learning .

take your car not your rv , out for a spin use the brakes as usual or maybe a little heavy .. get underneath measure again ..
c make cross on a clipboard and record each wheel you will see the reading go up

do it again after using the brakes on your car very very hard for 5 minutes . you will see the temperature of the calipers and disc are now higher . the disc could be as high as 500-700 degrees
F . THEY ARE HEATING UP DUE TO FRICTION this is normal and ordinary physics

the temperature of the left and right rear calipers ...should be the same ( not exactly but within 10% thus the left rear disc is 500F the right rear disc should be between 450 and 550 F )

if one is more different than 10% the higher one is working harder that the other ie sticking
open or closed .

the caliper may be lower than the disc , and the front may be different than the rear , but the left and the right should be the same .

after you learn to do this try it with your barth . ( take a book and plan on some time ) use the brakes HARD hard until l they get soft


this is what i think you will find .

ONE OF YOUR DISC /DRUMS is 300 degrees hotter than the other side on the same axle , it may be 600-700 degrees F and the same thing on the same axle . this means that caliper /brake is sticking on and dragging and not releasing . the friction is causing the heat (normal) ..

the heat over 400degrees F HEAT will boil the brake fluid dot 3 and dot 4 are about the same . the boiled fluid is a gas not a solid and thus it compresses when you step on the pedal hard

the fluid is now a gas and it expands and as it is bigger and it takes up more room so it pushes fluid out the vent hole in your in the cam of your master cylinder . your brakes are now mushie .

retake the heat readsing in 15 minutes . write everything down as you do it on the shets with the crosses
Posts: 59 | Location: Royal Oak, Michigan | Member Since: 06-14-2020Reply With QuoteReport This Post
posted Hide Post
ran out of room

if last week , it was the rear section of your master cylinder that was low then the problem is the rear .. or visa versa

you have now boiled your brakes .. stay parked for an hour , your brakes will now feel normal . the gas has now cooled down and become fluid and thus will be solid .

you can add fluid and drive home normally or you can get underneath with a 24 inch screw driver and try to drive back the pad 1/8 or 1/4 inch.
. you have now " freed up the caliper ( do this ten times with someone else pumping the brakes up each time and you have removed the rust which is sticking your calipers and do this each time you are going to use your rv after disuse for 6 or more months ) or take it to a shop and they will rebuild your brakes for $1500 which most likely is unnecessary .

or lub your caliper puck with brake fluid and push it in and out ten times.
do not do this unless you have done brakes on your car at least ten times over the last 20 years .

this is getting too long ... call me 248xxxxxx789 vvv 38o3vvvvvvv i will be glad to talk to you

if you do not get this maybe you should disregard it

if someone tells you to change to a more expensive brake fluid type 4
rather than type 3 or high temp racing fluid , disregard that answer
type 4 is ok but even it is overkill

you Barth is very old tech , fix what is wrong do not paint it with high teck paint
Posts: 59 | Location: Royal Oak, Michigan | Member Since: 06-14-2020Reply With QuoteReport This Post
posted Hide Post
just read it was front 1/2 of your master cylinder thus the problem in in the front
Posts: 59 | Location: Royal Oak, Michigan | Member Since: 06-14-2020Reply With QuoteReport This Post
Glassnose Aficionado
Supporting Member of 2/09
Picture of Danny Z
posted Hide Post
Thanks Jack, I have a digital therm and use it regularly at gas stops, and everything is fine. Pretty sure the problem is a leak, still have to diagnose it but we'll get it fixed before the next big trip. [This coach never sits more than 2 to 3 weeks.]

79 Barth Classic
Posts: 3770 | Location: Venice Fl. | Member Since: 07-12-2004Reply With QuoteReport This Post
  Powered by Social Strata  

    Forums    Tech Talk    Hydra boost brakes.

This website is dedicated to the Barth Custom Coach, their owners and those who admire this American made, quality crafted, motor coach.
We are committed to the history, preservation and restoration of the Barth Custom Coach.