Brake Drag Please Help

[xtahoex]

Hi all I am new to the community but not new to Datsuns.

 

I currently have a 1971 1200 with an SR20DET.  Everything is going well except I have some nasty brake drag occurring and I don't know why.  I have searched online and tried different remedies.  The setup I have is Wilwood dual master cylinders routed to a Wilwood proportioning valve.  Then there is individual lines to the front brakes.  Then braided lines to 280zx calipers.  When the car is off and has set for awhile the car will roll easily when in neutral.  After driving and using the brakes the car will not roll easily in neutral and sometimes will only roll under power.

 

I have rebuilt both master cylinders.

I have made new hard lines from the proportioning valve

I have adjusted freeplay in the brake pedal.

I have bought and installed fresh braided hoses.

Greased the guide pins.

I just bought 280zx caliper rebuild kits and will rebuild the calipers next.

 

I just got back from a drive and the front wheels were sticking.  I jacked the car up and relieved the pressure on the front passenger caliper and it seemed to free up the wheel.  Which if I understand it correctly, indicates an issue upstream (like a kinked hose, but there is none).  

 

It's difficult to tell if the rear brakes are experiencing the same issue due to the drag created by the differential.

 

Anyone have any input?  

 

 

[datzenmike]

If you are absolutely sure you have some pedal play...

 

Raise the car and try to turn the front and rear wheels by hand. Transmission in neutral. This will tell if the rears are also dragging. The differential should almost be frictionless to turn. This will indicate if only the fronts are affected or it's common to both.

 

If loosening the brake line relieves pressure then obviously pressure is trapped. I'm not familiar with after market stuff but I assume there are front and rear residual valves in the masters? Drum brakes usually have a residual pressure of 8-12 PSI while disc brakes are only 2 or 3 PSI. If you have the masters switched and are using a drum brake master OR the drum brake residual valve the caliper will be rubbing the rotor with 2-5 times the pressure needed.

[mklotz70]

I was going to, pretty much, say the same thing as Mike.  The pedal rod needs to have a small amount of play.  Does your brake pedal have a return spring or is in resting it's weight on the push rod?  The residual valves would be my next thing to look at.

[xtahoex]

Thanks for the responses. 

 

The brake system was installed originally by the previous owner and does not have residual valves.  I have installed other brake systems on other cars and from my understanding they are only important if your master cylinders are mounted below the level of the slave cylinders?  The masters in this car are mounted as high as they can be (almost can not get fluid in them because the are pushed up against the cowl).  

 

Brake pedal has a return spring.

[mklotz70]

Just fyi.....the datsun m/c's have the residual valves built into the m/c.  Maybe wilwood doesn't.  

 

Not great vids, but the second vid shows the valves.....or at least what datsun uses.

 

http://www.bluehandsinc.com/brake-master-cylinder-anatomy.html

[datzenmike]

Even Nissan used them and the masters are all above the calipers and wheel cylinders. The master would have to be several stories high to produce the required weight of fluid in the lines on the calipers. Having the pads just against the rotors keeps them clean and instantly ready. Drum shoes have farther to move and need more pressure to take up all the slack.

 

Well if no residual valves then the master is not allowing all the fluid to return to the reservoir. This is almost always the push rod adjustment. Can you wiggle the push rod???

 

Is the rear circuit doing the same?

 

Is the rear master preventing the front master from returning fully?

[xtahoex]

Here is a video of the free play.  It has about 3/8" of pedal free play before the master cylinders actually engage.

 

[datzenmike]

I would have expected the brake pedal to be between the two masters to center the load on that rod. The right side is unsupported and way out on the end. You can see it flexing from the load and it looks like it was welded?

 

It appears that there is enough play. Which one is for the fronts?

[xtahoex]

Good eye... You are absolutley correct.  I can't take credit for that deisgn (previous owner).  The front master would be on the left in the video.  There is not any room to fix the "balance bar" at this point so I just have to make do with it. 

 

It also appears that there is enough free play to me too.

[thisismatt]

wtf. That video is not very conclusive to me, and wtf is that hack job. You shouldn't be driving in public with that sh!7 show. Wow.

[xtahoex]

The bolt is not welded.  You are seeing a sleeve over the bolt that keeps the two masters from pinching together.  Again, I don't like it either.

[thisismatt]

Looks like a beebani product ?

[xtahoex]

Alright you got me motivated to rip out the pedal assembly... I will get to it soon.  In the mean time...

 

 

[datzenmike]

Well it has to be in the master or pedal linkage or a mystery residual valve. Maybe the rear master is not letting the front master return all the back. On a dual master there is only one pedal play.

[xtahoex]

On 12/22/2018 at 4:49 PM, thisismatt said:

wtf. That video is not very conclusive to me, and wtf is that hack job. You shouldn't be driving in public with that sh!7 show. Wow.

 

 

So I spent about 7 hours unf*cking the pedal assembly.  That is the most cramped area that I have had to work on in a while.  I added a Tilton balance bar and fixed the pedal arms.  Seems like a smoother operation.  I need to take it out for a drive and test it out for drag.  

 

Thanks for the motivation thisismatt...  

 

 

[datzenmike]

Biggest most important safety device is still your brakes.