Topic: HELP disc brake swap-mushy brake petal

[theslayer85]

I followed this link http://board.marlincrawler.com/index.php?topic=75186.0
 and the one given for pirate to do my rear disk swap.  I used 85 rotars and calipers in the rear with Dave's brackets.  The swap went pretty good and I was super excited for it, but now I have a mushy brake petal.  I bought a proportioning valve from summit racing http://www.summitracing.com/parts/SUM-G3905/ hoping that would help. I installed it, which required buying more tools which isn't always a bad thing.  I reblead my brakes just by gravity and still have a mushy petal.  I blead it again with someone pushing the petal and yet again still a mushy petal.  Then bought a one man brake bleeder that is also gravity fed.  As I was bleeding the brakes the petal got more ferm but once I finished and tested it it was mushy again.  I have read that a dual diaphram master cylinder helpes with the flow to the disc brakes.  However, I went into a parts store today and they had no idea what I was talking about with a dual diaphram master cylinder.  I also kind of figured that a mushy petal ment that there was air in the line and the proportioning valve  and new master cylinder only helps engage the rears better.   Did I do anything wrong?  Does the location of the proportioning valve matter?  I put mine up right next to the master cylinder, would it make a difference if it was in the back right before it droppes to the axle?  With the dual diaphram master cylinder what are they talking about?  How does it help and will it fix my problem? 

I wanted to do this swap on the cheap but it is looking like it wont be. 

[OOPS]

I have read that a dual diaphram master cylinder

You are looking for a dual diaphram brake booster not MC


Does the location of the proportioning valve matter?

No, it is fine there.

I reblead my brakes just by gravity and still have a mushy petal.  I blead it again with someone pushing the petal and yet again still a mushy petal.  Then bought a one man brake bleeder that is also gravity fed.  As I was bleeding the brakes the petal got more ferm but once I finished and tested it it was mushy again.

Is this how you are bleeding your brakes?

"...This is from the FSM and it works great..."
1. Drivers side rear
2. Passenger side rear
3. Passenger side front
4. Drivers side front

[Cheesemaker]

First of all its a dual diaphragm brake booster, not a dual diaphragm brake master cylinder.  
Did you get the Toyota 1" master cylinder?
And you will need these on the rear calipers.
http://www.summitracing.com/search/Department/Brake-Systems/Part-Type/Residual-Pressure-Valves/?Ns=Rank|Asc
It will help hold pressure in the calipers, when you let off the brake, the pressure goes back to the master cylinder, and when you pump the brakes, you have to recharge the line.  The residual pressure valves, will keep pressure in the caliper and the line.  So, you should have better brakes.  But I can't remember what psi to use, they have 2 and 10 psi.  

[OOPS]

Or you could have bought this set-up from Dave. It is all set-up and ready to install, including the residual pressure valve.

http://www.davezoffroadperformance.com/store/adjustable-brake-proportion-valve.html

[theslayer85 [OP]]

Or you could have bought this set-up from Dave. It is all set-up and ready to install, including the residual pressure valve.

http://www.davezoffroadperformance.com/store/adjustable-brake-proportion-valve.html

I was wondering why Dave's wanted over a hundred dolars for his valve.  I saw on summits web site that the same proportioning valve was 38 to 40 dollars so somehow his price was three times more.  It is because it has more than just the proporting valve. 

[theslayer85 [OP]]

I have read that a dual diaphram master cylinder

You are looking for a dual diaphram brake booster not MC


Does the location of the proportioning valve matter?

No, it is fine there.

I reblead my brakes just by gravity and still have a mushy petal.  I blead it again with someone pushing the petal and yet again still a mushy petal.  Then bought a one man brake bleeder that is also gravity fed.  As I was bleeding the brakes the petal got more ferm but once I finished and tested it it was mushy again.

Is this how you are bleeding your brakes?

"...This is from the FSM and it works great..."
1. Drivers side rear
2. Passenger side rear
3. Passenger side front
4. Drivers side front

that would explain why the parts store had a hard time figuring out what I was talking about.  This helps knowing that I asked for the wrong part. 

Yes that is how I did the brakes.  I always blead them from the farthest from the master cylinder working to the closest.

Now the question is does the location of a residual valve matter?  It looks like on daves picture of the set up that it is right next to the proportioning valve. 

[OOPS]

Now the question is does the location of a residual valve matter?  It looks like on daves picture of the set up that it is right next to the proportioning valve. 

No it does not matter.

[theslayer85 [OP]]

No it does not matter.

do I need one per rotar so two of them or will one to the main line going to the rear. 

[theslayer85 [OP]]

I found this on some summits web site under the product description for the residual valves.  the master cylinderis mounted above the horizontal plane so do I need a 2 lb or 10 lb?

Ideal for drag racing, Street Rods, and many off-road applications, these inline residual pressure valves from Wilwood retain a minimum brake line pressure to help eliminate excessive pedal travel. These 2 lb. valves are used in disc brake applications where the master cylinder is mounted below the horizontal plane of the calipers, and fluid drainback occurs, causing excessive brake drag. With drum brakes, 10 lb. valves are used to compensate for return spring tension in the drums. They're made from billet aluminum and are color-coded for easy identification.

[OOPS]

do I need one per rotar so two of them or will one to the main line going to the rear. 

One before the "T" on the rear end.

[OOPS]

I found this on some summits web site under the product description for the residual valves.  the master cylinderis mounted above the horizontal plane so do I need a 2 lb or 10 lb?

The one that came with the set-up from Dave'z is a 10 pound.

[theslayer85 [OP]]

The one that came with the set-up from Dave'z is a 10 pound.

hey thanks i saw they were color coaded so in the picture it was a 10 lb.

[theslayer85 [OP]]

Ok so I got the residual valve in BUT my petal is still not right.  I can lock up the fronts now but the rears will not lock up unless I pump the petal.  I know I asked before but does the order of the proportioning valve to the residual valve matter?  Right now I have it master cylinder, proporting valve, then residual valve.  My thought are that the proportioning valve sets the amount going to the rear then the residual valve may screw up that pressure or setting.  Should I change the order so I am proportioning the fluid after it goes through the residual valve.  Also I know the other upgrade is the dual diaphram brake booster. Is it an absolute requirement to do the new brake booster, I was trying not to spend a ton of money on this and every time I have to pull things apart it takes the truck out of service for a while. 

[Cheesemaker]

Do you have the 1" master cylinder?  Or the stock 13/16" cylinder? 
How much have you played with the prop valve?  Wide open should allow the rears to lock up. 



Edit: Another thought.  How does the inlet and bleeder valve on the rears look?  Cause I've heard that there is a chance of getting trapped air in the calipers.  Which could be causing the pedal feel. 

[theslayer85 [OP]]

I have never changed the master cylinder so it is stock. I doubt the previous owner changed it.  I have played with the proportioning valve.  I would drive it, mash on the brakes, get out adjust it, and do it again.  The adjuster is maxed out and still will not lock up.  I need to go look and make sure I am turning it the right way.  I know I looked before but now that it is not working I question everything I did in the swap. 

the inlet and bleeder valves look good.  I have bleed the rears several times and should have all the air out.  I did use the rotots and calipers from a parts truck so I wonder if because they have sat for a while if they are no good. 

[OOPS]

Can you post up a picture of the rear brakes?

Wilwood instructions.

"Rotating the adjuster knob clockwise until it is all the way in will provide full pressure delivery to the
calipers. Rotating the knob counterclockwise will incrementally reduce line pressure up to 57%
when the valve is fully out. If this range of adjustment is not sufficient to properly balance the
vehicle's bias, changes to other components within the system may be necessary."

[Cheesemaker]

Another idea, what condition is the brake hoses in?  Age can make them swell under pressure too.  Just like my gut after a good dinner.  

I do know a common issue with converting to rear disc brakes, is generally due to the smaller master cylinder.  

[scoutrunner]

get a master cylinder from a 90-95v6 runner or or pickup it has the 1"MC with the dual diaphram booster, I used to have to pump mine not they are great, I found the complete booster with MC on Ebay for 50$

[theslayer85 [OP]]

As a truibute to dumb-ass-ery The Slayer is dead. I was driving the truck even with the rear breaks a little off.  I also found out that whenever I did brake it would pull to the drivers side.  As I was coming down a dirt road I tried slowing down, which pulled to the left and sent the truck hard drivers side into the ditch.  I hit the ditch so hard it broke the u bolts off my axle and fliped me over.  I think I endoed and turned all at the same time i wouldhave loved to watch the video of it after.  the truck ended up facing 180 degrees the other direction and on the drivers side.  So now that I know what else I need to fix my brakes maybe it will be on the next rig. 

[jimbo74]

wow! sorry to hear that.... at least you are ok though

[Cheesemaker]

That sucks.  Time to start pulling and salvaging parts.