| starting replacement of power brake booster [message #359849] |
Wed, 28 October 2020 11:44  |
rgogan
Messages: 82
Registered: February 2004
Location: Milwaukee, WI
Karma: 0
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Decided to replace the master cylinder(MC) and the power brake booster after 46 years of service. I was concerned that critical studs would break off in my Wisconsin coach that already required a frame replacement because of rust. Miraculously, the MC mounting stud nuts, the bracket to the power booster and the power booster mounting stud nuts all came off with minimum trouble. The real challenge was the removal of the 4 nuts on the power booster mounting studs that were barely accessible through the dash power level control panel that was removed. 3 of the four nuts were removable with a shortened deep socket and swivel adaptors. The left lower nut was totally inaccessible. It was finally removed by cutting the plastic dashboard just to the left of it and removing it after a solitary pop rivet was removed. The rubber boot on the power booster has deteriorated badly. The insulation on the firewall also needs replacing.
Now I am toying with the idea of installing a sensitized brake booster to get a lighter brake pedal pressure. Some vendors are selling a completely new unit with a new rubber boot but they are coming through with metric studs. Also some GMCers have reported problems in the eye that attaches to the brake pedal extension has not been the right length and either too high a pedal or too low a pedal results. Also the new units are expensive. Rock Auto offers to rebuild the original unit sent to them for $89 plus shipping. The new units are in the $250 to $350 price range.
Any recommendations based on anyone's experience?
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| Re: [GMCnet] starting replacement of power brake booster [message #359853 is a reply to message #359849] |
Wed, 28 October 2020 13:50  |
powwerjon
Messages: 849
Registered: March 2013
Karma: -2
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Senior Member |
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What year coach do you have? Where are you located at?
This is not a first time dance for GMC coach owners. To get at the 4th nut you need to cut the lower dash to gain access. Just put a aluminum plate to cover the hole when your done.
http://www.gmcmhphotos.com/photos/bob-dunahugh/p60045-brake-booster-nuts-in-2777-and-2778-gmcs.html
As for Master cylinder and power brake booster the absolute be kit come from Dave Lenzi which include a proper correct MS, correct length push rod between the MS and PB, and a sensitized booster. It is reasonably price and is bolt it.
You can contact Dave with the information at the top of his website.
http://www.gmcmotorhomemarketplace.com/lenzi/index.html
You also need to consider adding an aux vacuum pump to the braking system, remember when the motor is NOT running you have about 2 or 3 pumps before the brake do not work very well.
Regards,
J.R. Wright
GMC Great Laker MHC
GMCGL Tech Editor
GMC Eastern States Charter Member
GMCMI
78 GMC Buskirk 29.5’ Stretch
75 GMC Avion (Under Reconstruction)
Michigan
> On Oct 28, 2020, at 12:44 PM, Robert J. Gogan via Gmclist wrote:
>
> Decided to replace the master cylinder(MC) and the power brake booster after 46 years of service. I was concerned that critical studs would break off
> in my Wisconsin coach that already required a frame replacement because of rust. Miraculously, the MC mounting stud nuts, the bracket to the power
> booster and the power booster mounting stud nuts all came off with minimum trouble. The real challenge was the removal of the 4 nuts on the power
> booster mounting studs that were barely accessible through the dash power level control panel that was removed. 3 of the four nuts were removable
> with a shortened deep socket and swivel adaptors. The left lower nut was totally inaccessible. It was finally removed by cutting the plastic
> dashboard just to the left of it and removing it after a solitary pop rivet was removed. The rubber boot on the power booster has deteriorated badly.
> The insulation on the firewall also needs replacing.
>
> Now I am toying with the idea of installing a sensitized brake booster to get a lighter brake pedal pressure. Some vendors are selling a completely
> new unit with a new rubber boot but they are coming through with metric studs. Also some GMCers have reported problems in the eye that attaches to
> the brake pedal extension has not been the right length and either too high a pedal or too low a pedal results. Also the new units are expensive.
> Rock Auto offers to rebuild the original unit sent to them for $89 plus shipping. The new units are in the $250 to $350 price range.
>
> Any recommendations based on anyone's experience?
>
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> GMCnet mailing list
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| Re: starting replacement of power brake booster [message #359854 is a reply to message #359849] |
Wed, 28 October 2020 14:08 |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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Senior Member |
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I bought a sensatized booster like 9-10 years ago from Jim bounds. it makes a significant difference in how the brakes feel. I can drive my coach barefooted if needed, it does not take much force to stop. My friend eleganza that has stock booster yet, his stops, but I need to be wearing shoes when I drive his coach. there has been changes over the years on some peoples boosters they supply.
Dave Lenzi has a sensitized booster he sells. I was going to install one while I was upgrading to the 80mm calipers, but circumstances changed, and I did not get one from him when I did my 80mm brakes.
I would highly recommend if you do go with a sensitized booster that Dave would be the one to supply it.
as for access, I have been able to use a door shim to separate the dash from floor and sneak my craftsman ratchet wrench onto that lower nut. I would guess a 77-78 coach with the air switches to the left of driver, it might take some cutting for access.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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