345 Motorhome with weak brakes - Replaced Master Cylinder

[Paul and Tam]

I'm in need of a little advice. I've replaced my master cylinder and cannot get any pedal height/resistance. I think I have some air in the rear lines.

The front brake system was bled tonight using a one man bleeder and that seemed to go well.

Rear bleeding is going slow, pushing much less fluid than the old master cylinder did when I flushed the system last week. Since I using a one man bleeder I'm not sure if it is a lack of fluid being pushed down the line, or if it is drawing fluid back when I release the pedal. There is literally no resistance at the pedal.

My plan for tomorrow is to try a vacuum pump bleeder on the right rear caliper and see if I can draw out a bubble. After doing a little more reading tonight I think I should have replaced the rubber brake hose between the chassis and the rear axle. If I can find one local in the morning I still may.


Details:
The new master cylinder is a Wagner, ordered from Amazon Prime for quick shipping. Bench bleeding was minimal. Fluid pretty much ran straight through it, and I think a gravity bleed would go pretty quick.

History:
The old master cylinder had a failed lid seal, and I found the interior full of jelled and chrystalized brake fluid. Pedal effort has been high since we bought the motorhome 10 years ago. I had turned the front rotors 5 years ago to fix the pulsing and the lid seal looked good then. I tried flushing the system last week, but even after pushing new fluid to all four calipers pedal effort was still very high when stopping the motorhome. I tried the hydroboost test and it seems to be providing plenty of brake assistance.

Should I be looking at anything other than replacing the rear chassis to rear axle hose and using the vacuum pump to draw the air bubble out of the rear circuit?

Thanks. All feedback and advice is appreciated.

- Paul

[mayco]

I dont know why these brakes are so hard to bleed but it seems to be a common problem. I had no luck with a hand held bleeder. Went back to the two person method and finally got a good pedal, but it took several attempts. I bled the brakes, drove the rig, bled again, drove the rig.....finally got them feeling good and strong. No problems since.

Mike

[mayco]

Definitely replace your flex lines!!

[bkahler]

Paul, on the P30 chassis there is a brake proportioning valve that if the plunger gets pushed off center you won't be able to properly bleed the brakes.

I bought one of these Combination Proportioning Valve Bleed Tool to bleed my Argosy brakes and it should be the same one for your 345. I haven't actually bleed the brakes as I'm not quite to that point so needless to say I've been reading these brake bleeding threads with interest!

Do some research on bleeding brakes with proportioning valves. Lots of info out there.

Brad

[Paul and Tam]

Brad, Thanks! Any idea where this proportioning valve may be located on a 345? I'll probably find it following the brake lines...

- Paul

[bkahler]

Paul, it's the shiny brass block in the lower center of the attached picture.


If you look at the curved frame member under the radiator you'll find it on the drivers end. There is a wire going into the top center of the proportioning valve and that's where the switch is located. You unscrew he switch, screw in the service tool and bleed the brakes. When you're done put the switch back in.

Brad

[Paul and Tam]

Pictures, or it didn't happen.

Before photo of the master cylinder.


And this is why I decided to replace it.

New rear flex hose (chassis to axle) in hand, going out to replace the hose, gravity bleed the hose before reattaching, then bleed to the rear wheels.

No proportioning valve tool available locally, I may need to expand the search.

Wish me luck.

Feedback, advice, and comments welcome.

- Paul

[tevake]

I'm with Mike on your bleeding issues, try having someone press the pedal while bleeding at each wheel to get a strong volume thru those lines. Make sure to keep the master topped off.

That pic is scary, some of that gunk could still be in the lines. That's why pushing a lot of fresh fluid thru could help. The lack of volume that you are getting at the rears is a concern.

Keep at it till you get a solid peddle. They all seem to have a lot of peddle travel even when adjusted well.

Cheers Richard

[Paul and Tam]

Noon update. The new rear flex hose looks like it will fit, but the lines are rusted in place. I don't have a line wrench the correct English sizes, and metric is not quite close enough. Decided to abandon the flex hose replacement for today so the penetrating oil has time to work.

The vacuum pump seems to have drawn out a lot of air. Then I got about 6 oz. of fluid from each rear caliper. I did this with the lid off the master to allow a free flow of fluid. It seems to gravity bleed.

Next up is the one man bleeder. Taking a little break first.

Thanks again for the advice and feedback. We have a camping reservation for tomorrow through Sunday at a near-by bluegrass fest, so I hope to have The brakes working by tomorrow morning. I may need to call the son-in-law over to pump the brakes while I work the bleeders. My wife's knees won't allow her to do the pumping.

- Paul

[3wd67rg]

Can you find anyone else to help you do a two person brake bleed? It's so much more efficient.

We used walkie talkies to keep in touch in order not to be yelling out the windows at each other and I played scrabble on my iphone at the same time. I also have bad knees and hips, (chondromalcia patella, torn meniscus, bursitis and arthritis), but I just kept switching off which leg I used to help my boyfriend accomplish the job. I took a four ibuprofen, (military candy), before we began, and an extra Tramadol later. I survived! lolz

[3wd67rg]

Ahhhhh... upon rereading your last post I see you have a SiL to call on, great! Good luck and let us know how it goes.

[TomKirk]

Bleeding brakes is a two man job.

Bleed brakes in proper sequence. Bleed rear brakes first. Then bleed front. Start with right rear. Finish with left front.

Flush the system. Keep bleeding 'til fluid runs clear.

Look for prop valve under front X-member.

Tom

[Paul and Tam]

Success.

I deviated a little form the norm. Recapping the events of the day: I had tried to bleed the rears first using a one man bleeder, then the fronts. The fronts were pushing fluid about as well as the old MC, the rears were not. That brought us up to this morning.

Most everything regarding the left rear is in a previous comment. Between the vacuum pump and the one man bleeder I took another 9oz + more fluid. The last 3 oz. was flowing about the same as the old MC.

Then to the right rear. No luck with the wheels on, so off they came. The vacuum pump was used to draw about 12 more oz. of bubbly fluid. In between I had my wife pumping the brake pedal until her knees gave out. Then back to the vacuum pump, then the one man bleeder. And ... then I suddenly had some pedal resistance.

Around this point I finally had about the same volume of fluid flowing per pump as the old MC using the one man bleeder, but with the back bleeder open the old MC had more resistance than this new MC.

Thinking that the last of the bubbles were out I fired up the engine. Brake light is on. Pump and the light goes out. Pump again and it comes on at the bottom of the stroke. Pump 3 and it is out again, and out for good. Pedal is getting more firm.

Total of 3 quarts of brake fluid was used for the MC swap. This on top of the two quarts used to flush the system last week. The fluid coming out is very clean.

I took it for a test drive. No more pulling, brakes are about 20% better than with the old MC. Not as much improvement as I'd hoped, not enough for my wife to drive the AS, but better than it was and that's good enough for today.

Lessons learned - when swapping out the flex hose to the rear axle I will drive up onto some 2x10's to give me a little more room to move around under there. The flex hose ends are soaked in penetrating oil, and hopefully the weekend drive will help work the rust out. The flex host definitely needs to be replaced - it's very stiff and the outside cover is pretty cracked.

Thanks again to all who commented.

- Paul

[tevake]

It's a little late to bring this up, Paul. But it does sound like you will be revisiting your brakes shortly

using Dot 4 brake fluid is not a bad idea. I've had my fluid boil in my 345
When driving down from Lake Tahoe. Not a comfortable experence.

I have since flushed the brake fluid and replaced with dot 4, replaces the brakes in the tag axel, rebuilt the brakes in the drive axel.
And learned to use the gears and engine braking to avoid such drama.

I think using the higher temp dot 4 fluid is a step on the right direction.

Cheers Richard

[Paul and Tam]

Thanks Richard. Yes, revisiting soon. I used Valvoline Synthetic DOT 3/DOT 4 for the first 4 quarts. The last 3/4 quart was Penzoil Synthetic DOT 3. Walmart was out of the Valvoline when I went back for the last quart. The DOT 3 is in the rear circuit only... which probably gets hotter than the front when everything is working properly. Hopefully they will have more Valvoline next time I visit.

Everything worked well enough getting here today. Only 90 miles. I noticed that the brakes work better as they warm up during a stop from 60 mph.

- Paul

[tevake]

Glad you are out enjoying your coach.
Your discription of the brakes coming on more strongly with a bit of time on the peddle could be caused by restriction in the old flex lines. Might want to keep your nose pealed for the smell of dragging brakes after a stop. Could be slow to retract also.

Pardon me, just how my mind works when partway thru a system rebuild. Envisioning the issues that could come from the yet to be replaced parts.
It's a sickness, but motivating.

Have a fun trip.

Cheers Richard

[Boom Sounds]

My old brake hoses collapsed on the inside and caused lots of issues. It's a straightforward job to bleed and replace them, also well worth it. Don't mess with brakes and batteries; that's served me well.


Sent from my iPhone using Airstream Forums

[Paul and Tam]

Today's adventure... after weeks of soaking in penetrating oil I finally got the old flex hose off. The differential end came apart well enough, but the frame end was truly stuck. As I replaced he hose I realized that the drivers side of the connector block is the high side, which is where the bubbles go. And this is why bleeding the drivers rear first seems to be more effective. After a gravity bleed of the hose hanging from the frame I connected the brake lines on top of the differential. Gravity bleed continued. Once connected, and the master cylinder refilled, I did a one man bleed using the left rear only and all the air seems to be out of the system.

A couple of quick photos for posterity.

A test drive showed slightly lower brake pedal effort, but not the improvement I expected. I think the rest of the brake hoses will be replaced soon.

And here is the old flex hose. The date code is June 1987. What I thought was deteriorating rubber was in fact undercoating. Really. Probably should have had a little more light under there.