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Old 04-21-2017, 09:41 PM   #1
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Brakes Soft

When I bought my 1983 300 the brakes were kind of spongy. I had to pump them a couple of time to get a decent brake. Not great.

I had the front brakes done but still spongy even though they bled them. Eventually I had no brakes (not fun) due to the master cylinder leaking.

I replaced the MC and redid the back brakes myself. See the .

So now I still have a spongy brake. I can bleed the brakes and get decent pressure but then by the end of the day it will be soft again. Seems like a leak right? Thing is I am not losing fluid. When doing a multi day trip last summer I would bleed the brakes every morning and top off the MC. Then by the end of the day it would be spongy and I would have to pump it 2-3 to firm up the pedal. I would stop at the end of the day and check the MC and it would still be topped off? Could I still have a leak? Doesn't seem like it.

Any ideas? I also have a new Hydro Boost that I am thinking about installing. I am not sure how that works but It would be something to try.

John
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Old 04-22-2017, 12:04 AM   #2
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You are losing fluid somewhere and it sounds like a fair amount. Did you have all four brakes tested for effectiveness on a roller? If it's not leaking at the MC or hydroboost, then it's probably at one of the wheels. Is it only one chamber which is being refilled and which one.

If you replace the hydroboost, have a look at Chris Craw's recent post on the topic. Do not dispose of all the pieces e.g. Rod, retainer spring as you will need them again.


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Old 04-22-2017, 04:44 PM   #3
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Boom Sounds;

No that's just it. I am not losing any fluid. The only time I have to add fluid is when I bleed the brakes.

Thanks for the tip on the hydroboost post. I will check it out.

John
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Old 04-22-2017, 04:50 PM   #4
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Brakes soft but not loosing fluid?

Master cylinder bypassing internally? Hoses are kaput and swell up under pressure. But I don't think that problem would get better with pumping.

Any chance to figure out the line size, type and nut that attaches to the MC. Remove lines, insert plugs. Bleed by cracking plugs. Then push on brake pedal. Hard as a rock or mushy gushy.
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Old 04-22-2017, 05:03 PM   #5
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I'm assuming you're keeping an eye on your power steering fluid also. (Hydroboost). We had a heck of a time getting sufficient medal on my 310. We just kept bleeding and bleeding. New pads, new master cylinder, new flex lines. Tried different methods of bleeding. Finally got all the air out of the system, I think. These P30s are pretty notorious for air getting trapped in the brake lines. Ive read and read and seems like most folks have the same problem. We ended up using the two person method of bleeding and did get them feeling good. I also adjusted the connecting rod in the brake pedal linkage and that helped in reducing the amount of travel in the pedal before it got firm. You may want to look at that. Vertical rod with threaded adjustment on bottom. Just follow the linkage and you'll see it tucked away between the firewall and the grill.

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Old 04-22-2017, 05:25 PM   #6
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Many of the (cheap) rebuilt Master cylinders are crap. The way to test them is to press the pedal down and keep the pressure on the pedal. If the pedal continues to bleed down the Master Cylinder is bad. I once went through 3 before I got one that held the pressure. I would also replace all the rubber brake lines (3), if you haven't already.
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Old 04-23-2017, 06:36 AM   #7
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Many of the (cheap) rebuilt Master cylinders are crap. The way to test them is to press the pedal down and keep the pressure on the pedal. If the pedal continues to bleed down the Master Cylinder is bad. I once went through 3 before I got one that held the pressure. I would also replace all the rubber brake lines (3), if you haven't already.
What Peter said. The replacements are pretty much a crap shoot as to whether you get a good one or not. Ten years ago the shop that replaced the MC on my old 310 went through 9 of them before they got a good one.

Brad
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Old 04-23-2017, 06:37 AM   #8
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Oh man! I like these suggestions. I have a new hydroboost and the power steering pump sounds like it is going. Makes noise when I crank the wheel. Maybe I will replace the hole shebang. However first I'll see if I can get these brakes good and hard. The brakes are a closed system so the hydroboost shouldn't have an impact on the pedal getting soft right? If there was a problem like air between the hydroboost and the power steering pump I would have a firm pedal but not a lot of pressure right? I would be pushing on firm brakes but not stopping. Right? If I can get a firm pedal and decent braking in the morning but by dinner time it's soft and I have to pump to stop I should be focusing on MC, bleeding right? Seems like I must still have air in there.

I like the tests for the MC, using plugs and applying firm pressure to see if the pedal holds. I will start there.
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Old 04-23-2017, 06:49 AM   #9
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I don't think the hydroboost can be removed without removing the brake MC as well. So even if you get the brakes working right you'll still have to remove the MC to replace the hydroboost. I would replace the hydroboost, brake MC and power steering pump all at the same time and get it over with.

Your soft pedal sounds like a bad MC. I replaced the MC on my Argosy but haven't been able to drive it yet. If the pedal is soft I'm pulling the MC and sending it to a company that specializes in rebuilding them.

Brad
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Old 04-25-2017, 12:17 PM   #10
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Hi - one other potential lead. I think there was a Chevy service bulletin referring to an air lock and collapsed fuel line which might cause similar symptoms. They fixed the issue with stronger hoses on the later models. Have a look at the motorhome chassis guide. It's in there somewhere.


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Old 04-25-2017, 03:12 PM   #11
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Brain freeze, I responded to the wrong post! Soz.


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Old 05-15-2017, 06:09 AM   #12
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Anybody have a reliable source for these parts? I probably need a master cylinder and a power steering pump. Seems like there would be someone out there who has established themselves as a reputable supplier.

Thanks

John
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Old 05-15-2017, 06:18 AM   #13
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Quote:
Originally Posted by jkaftan View Post
Anybody have a reliable source for these parts? I probably need a master cylinder and a power steering pump. Seems like there would be someone out there who has established themselves as a reputable supplier.

Thanks

John
Rock Auto, Autozone, O'Reilly's etc.....they are very standard parts for a Chevy motorhome chassis of the model year. The first couple of years of MH were made from parts bins but after 1977 things become very standardized.
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Old 05-15-2017, 06:49 AM   #14
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John,

I've used Rockauto for a lot of parts but when it comes to something that has a core charge the return shipping can get expensive.

So for parts like a Hydroboost, Master Cylinder, etc I just go to O'Reilly or Napa and purchase them locally.

Brad
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