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Old 12-30-2016, 08:19 PM   #1
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1976 Dodge Sportsman Class C, Brake Issues-won't hold pressure

I have a 1976 Dodge Sportsman Class C Motor home. I have replaced the master cylinder, power booster, front calipers, rear wheel cylinders, pads and shoes. I have bench bleed the master cylinder, bleed the brake lines and also reversed bleed. It took all the fluid it needed to fill up the master cylinder from the wheels but still can't keep pressure on the break. It pumps up but won't hold the pressure. Was wondering if anyone has some input. Thanks in advance!
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Old 12-31-2016, 09:47 AM   #2
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Welcome to iRV2.

If your brake pedal slowly drops and you have no external leaks, the master cylinder is suspect.
Was the replacement you've installed a new or re-manufactured unit ?
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Old 12-31-2016, 10:04 AM   #3
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Welcome to iRV2.

If your brake pedal slowly drops and you have no external leaks, the master cylinder is suspect.
Was the replacement you've installed a new or re-manufactured unit ?
Thanks! It is brand new and the second one I have tried.
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Old 12-31-2016, 03:26 PM   #4
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I started working at Chrysler /Dodge dealer in 75, put in 33 years there. I'll scratch my head and post anything else I can think of on Monday.

Does the pedal go down any time you pump it up ?
Or only when the engine is running ?
Will the condition exist when the coach is stationary ; or does it happen when driving only ?

I'll throw this in only because I saw another mechanic in the shop do it once ; and spend hours trying to bleed the brakes.
The single piston calipers used on these vehicles are virtually the same side to side, the mechanic had mounted the calipers on the wrong side , and was trying to bleed the system with the bleed screw below the flex hose attachment , instead of above; where it should be; to be the high point to get all the air out of the caliper.
Also, if you haven't already , have a helper hold pressure on the pedal while you check the front and rear flex hoses for bulges , under pressure.
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Old 12-31-2016, 03:31 PM   #5
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I started working at Chrysler /Dodge dealer in 75, put in 33 years there. I'll scratch my head and post anything else I can think of on Monday.

Does the pedal go down any time you pump it up ?
Or only when the engine is running ?
Will the condition exist when the coach is stationary ; or does it happen when driving only ?

I'll throw this in only because I saw another mechanic in the shop do it once ; and spend hours trying to bleed the brakes.
The single piston calipers used on these vehicles are virtually the same side to side, the mechanic had mounted the calipers on the wrong side , and was trying to bleed the system with the bleed screw below the flex hose attachment , instead of above; where it should be; to be the high point to get all the air out of the caliper.
Also, if you haven't already , have a helper hold pressure on the pedal while you check the front and rear flex hoses for bulges , under pressure.
I pump the breaks, holds pressure, let go for 5seconds and petal goes Back down to the floor. It is even worse when it is running. Calipers are correct cause the bleeder is at the top of the caliper. I have reversed bled the brakes system 2 times with no air apparent. This is the second MC I've put on this week and the only thing I can think of is that. I am going to try a new MC. It's a mystery...thanks for your input, I will check back.
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Old 12-31-2016, 04:26 PM   #6
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First point; Did you adjust up the drum brakes nice and tight and back off a bit. If not, a lot of pedal travel will be wasted there. I've known people who stop adjusting at the first sound of shoe to drum contact.

Second point; Master cylinders for drum brakes have check valves to prevent all of the pressure from draining from the wheel cylinders. Make sure yours has one. It should be in the MC, in the hole, where the line to the rear brakes go.

Third point; Are your bleaders on top on the rear wheel cylinders ?
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Old 04-11-2017, 09:01 AM   #7
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Originally Posted by krystofdavid View Post
I have a 1976 Dodge Sportsman Class C Motor home. I have replaced the master cylinder, power booster, front calipers, rear wheel cylinders, pads and shoes. I have bench bleed the master cylinder, bleed the brake lines and also reversed bleed. It took all the fluid it needed to fill up the master cylinder from the wheels but still can't keep pressure on the break. It pumps up but won't hold the pressure. Was wondering if anyone has some input. Thanks in advance!
I am having this same exact issue . if you have solved this can you please let me know how. Mine is the exact same motor home. Thanks.
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Old 04-14-2017, 07:43 PM   #8
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Fixed!

Hey all sorry for the late response, it has been a long past couple of weeks with my grandmother passing away. I talked dad into changing all the hoses even though they appeared to be "ok", we cleaned the proportion valve and also readjusted the shaft to the Master Cylinder and WAHH LAHHH breaks!

I am still convinced it was the rear hoses cause that was my thought since we did everything else.

Thank you alll for your help, We both really appreciate it!

Lori and Dave Krystof
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