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| Re: [GMCnet] Vacuum brake boost [message #241932 is a reply to message #241925] |
Sat, 01 March 2014 18:03   |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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Senior Member |
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Turn the engine off and see if it made any difference in the braking effort and feel. You'll have to use up residual vacuum (if there is any) with a few pedal pumps and see if the pedal is harder. Do this on a deserted highway if you can find one(or late at night). Then (when you have come to a stop)with your foot on the brake, start the engine and see if the pedal goes down any farther when the engine runs. If the engine vacuum is making a difference you can feel, you have answered your question. Vacuum boosters are not prone to be faulty, usually very reliable and long lasting. Most of the time corrupted by leaking master cylinder or long periods of non-use.
Harder pedal/higher effort braking can also be caused by glazed brake shoes and pads and burnished rotors and drums.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: [GMCnet] Vacuum brake boost [message #241933 is a reply to message #241925] |
Sat, 01 March 2014 18:05 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Ron,
I agree with Ken vis-à-vis the booster and would like to add that Dave Lenzi is building sensitized boosters as well; here's a link
to his contact information:
http://www.bdub.net/lenzi/index.html
I copied the following out of Maintenance Manual X-7525 for you:
POWER CYLINDER TROUBLE DIAGNOSIS CHART
Before checking the power brake system for the source of trouble, refer to the trouble diagnosis of drum and disc brakes. After
these possible causes have been eliminated, check for the cause as outlined in the following chart:
CAUSE - REMEDY
Broken or damaged hydraulic brake lines - Inspect and replace as necessary
Vacuum Failure - Check for:
Faulty vacuum check valve or grommet - Replace.
Collapsed or damaged vacuum hose - Replace.
Plugged or loose vacuum fitting - Repair
Faulty air valve seal or support plate seal - Replace
Damaged control valve - Replace
Bad stud welds on front or rear housing or head - Replace, unless easily repaired
Defective diaphragm - Replace
Restricted air filter element - Replace
Worn or badly-distorted reaction disc - Replace reaction disc
Incorrect reaction disc - Replace with correct disc
MASTER CYLINDER, WHEEL CYLINDER AND DRUM BRAKES TROUBLE DIAGNOSIS CHART
EXCESSIVE PEDAL PRESSURE REQUIRED TO STOP VEHICLE
CAUSE - REMEDY
Brake adjustment not correct - Adjust brakes.
Improper lining - Install factory specified shoes
Improper shoes -Install factory specified shoes.
Grease or fluid soaked linings - Correct cause and replace linings, if necessary. Replace.
Rusted wheel cylinder - Check wheel cylinder piston and boot for damage.
Wheel cylinder link incorrectly aligned - Install link
Compensating port not cleared - Check pedal linkage, stop light switch adjustment
Brake pedal binding on shaft - Lubricate with Delco Brake Lube #5450032 (or equivalent)
Glazed linings - Sand surface of linings
Bellmouthed, barrel-shaped or scored drums - Replace or resurface drums in left and right hand pairs.
SINGLE PISTON DISC BRAKES TROUBLE DIAGNOSIS CHART
EXCESSIVE PEDAL EFFORT - DISK BRAKES
CAUSE - REMEDY
Malfunctioning power brake - Check power brake and repair if necessary
Partial system failure - Check front and rear brake system and repair if necessary. Also check brake warning light,
if a failed system is found and light did not function, repair as necessary.
Excessively worn shoe and lining - Check and replace in axle sets
Piston in caliper stuck or sluggish - Remove caliper and rebuild or replace
Fading brakes due to incorrect lining - Remove and replace with original equipment lining
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
-----Original Message-----
From: Ron & Carol Barkley
My 1976 Eleganza II requires a heavy foot on the brake. I am a third owner
of the coach and don't know if the vacuum brake booster has every been
replaced. Could this be the reason for the hard brakes?
Ron Barkley
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Vacuum brake boost [message #242080 is a reply to message #241925] |
Sun, 02 March 2014 19:37 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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| rvandcabarkley wrote on Sat, 01 March 2014 16:13 |
My 1976 Eleganza II requires a heavy foot on the brake. I am a third owner
of the coach and don't know if the vacuum brake booster has every been
replaced. Could this be the reason for the hard brakes?
Ron Barkley
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GMCnet mailing list
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It can be but there may be basic problems with the system overall. I would make sure everything else is in shape before resorting to just covering it up with a sensitized booster.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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