510 Disc Brake Upgrade Problem

[brodster]

This weekend I am going to troubleshoot the brake system on my 510. I ripped out almost all of the brake system, except for some of the original lines that are tucked in to the rear suspension because those were very difficult to get to.

 

In the front I am running 280zx brakes: New rotors, new/rebuilt calipers, new brake lines.

 

In the rear I am running 1986/1987 Maxima calipers and 1982/1983 200sx rotors. All new/rebuilt parts.

 

I installed a rebuilt 1979 280zx Master cylinder. Looks like this: http://www.rockauto.com/catalog/moreinfo.php?pk=309611

 

To dial in the rear brakes, I decided to install an adjustable proportioning valve:

http://www.wilwood.com/MasterCylinders/MasterCylinderProd.aspx?itemno=260-11179

 

Problem: Rear brakes are weak. The front locks up well before the rear with the proportioning valve fully open. When we bled the rears, pressure seemed noticeably weak.

Because the 280zx came with front and rear disc, is it not advisable to use a proportioning valve to dial in the front/back brake balance?

 

Possibly I used the wrong proportioning valve?

 

Possibly the rear line got kinked during the install.

[Icehouse]

I had a similar problem, turned out to be a bad master. It was obvious though. It had a leak on the big fitting, the one the brake line screws into.

 

Did you hook the brake lines up correctly. The front resistor is the rear brakes and the back resistor is the front brakes.

[Eagle_Adam]

The front resistor is the rear brakes and the back resistor is the front brakes.

 

That shit has fucked with me so many times you'd think i would know by now, but i still seem to forget :rofl:

[I'm BLUE]

invited yourself to bench bleed master before install ? ( I assume you have/tried many times ) If not crack that baby open and carefully bleed the sucker !

 

Have you had the pleasure of dialing the proportioning valve back and forth ( a number of times ... like quite a bit lol ) to tell if it is indeed working ?

 

Did you have a chance yet of installing a disc brake residual pressure valve in your brake plumbing ? = http://www.jegs.com/...948183/10002/-1 I have only plumbed 1 in my lifetime. I do know that all my 240z's had them ,,, so I assume most cars have one or something similiar (semantics).

 

Residual pressure valve quote from Jegs.com = "JEGS residual brake pressure valves retains minimal fluid pressure by preventing drain back in the brake lines in applications where the master cylinder is located below the calipers. This eliminates excessive travel and that dreadful spongy pedal feel. The 2 pound residual brake pressure valve is designed for disc brakes while the 10 pound valve is used for drum brakes."

 

I would also look for a kinked hardline or a pinched softline since install as you suggested ( it happens to all of us or karma haha )

 

I too would look at the brake master cylinder carefully ,,,just keep an eye on it mostly :)

 

Hate to throw money at stuff ,,, as a last resort ,,, but JEGS.com sells inline pressure gauges for your brake systems.

 

I honestly have always pondered if the cheap proportioning brake valves ( like my cheapo wilwood ) really work well over periods of time or have a failure rate of some kind lol. Just keep adjusting carefully for that sweet spot !

 

Installing a proportioning valve will only help your situation ;)

 

occasionally some re-manufactured stuff = poop ,,, I doubt in this case but just a thought in your troubleshooting woes !

 

 

:)

[brodster]

I didn't put in a residual pressure valve. I didn't think I needed one for my application, but it may solve the problem.

 

I didn't bench bleed on the bench per say before installation, but I bled the crap out of my system after install. I will re-bleed the rear system again.

 

As far as the rear, when I was bleeding I got plenty of bubbles at first (as expected) but the fluid went solid eventually. I ran a ton of brake fluid through the system too. However it just bled really slow like the line was restricted somewhere. Both calipers bled the same way, so the problem should be upstream of the tee in the rear brake line.

[Guest Rick-rat]

Did you clean out the lines you didn't replace? I did my 620 all the way around, isuzu calipers rear, D 21 on front, 280 ZX master, no proportioning valve, no residual pressure valve. brakes work great

[brodster]

Not yet. I will give that I try once I get a chance to start troubleshooting the brakes.

 

I am still sorting the vibration problem on the drivetrain.

 

Thanks

 

 

Did you clean out the lines you didn't replace? I did my 620 all the way around, isuzu calipers rear, D 21 on front, 280 ZX master, no proportioning valve, no residual pressure valve. brakes work great

[q-tip]

The vibration is either your lack of alignment or a bad u joint some where, drive line or half shafts.

[datzenmike]

The zx master has residual valves right at the output lines. They all do, you don't need more. The residual valve would prevent drain back IF the master was below the calipers, but name oen Datsun that is built that way. The residual valve maintains a few pounds of pressure on the pads to keep them gently against the rotors to keep them clean.

 

 

 

Proportioning valve? Most Datsuns don't have one. Front and rear bias is engineered at the factory by using smaller wheel cylinders at the back than the front or smaller calipers at the back than the front. The master cylinder is also designed to apply pressure to the fronts first ... this is why the fronts are at the back of the master. Because you have mixed and matched calipers the bias is totally out the door anyway.

[Jesse C.]

_{You don't need a proportioning valve. Most see the block on the shock tower and think that is proportioning valve, but it is not, it is just for the brake warning light. Also, you might want to get yourself a B210 brake booster, in case you don't have one, to make the brake pedal easier to push.}

 

_{Almost all disc setusp around here are running what you have and have never used a proportioning valve. Just factory stuff!}

 

_{Good luck!}

[brodster]

The vibration is either your lack of alignment or a bad u joint some where, drive line or half shafts.

 

Last weekend I worked on the car and had the dougger drive it. You could here some clunking when you popped the pedal. He thought the vibration was driveline related or something in the diffy, half shafts. When I get a chance I will start looking into that. Wouldn't surprise me if it was just a bad U-joint. The thing sat idle for about 6 years.

 

Proportioning valve? Most Datsuns don't have one. Front and rear bias is engineered at the factory by using smaller wheel cylinders at the back than the front or smaller calipers at the back than the front. The master cylinder is also designed to apply pressure to the fronts first ... this is why the fronts are at the back of the master. Because you have mixed and matched calipers the bias is totally out the door anyway.

_{You don't need a proportioning valve. Most see the block on the shock tower and think that is proportioning valve, but it is not, it is just for the brake warning light. Also, you might want to get yourself a B210 brake booster, in case you don't have one, to make the brake pedal easier to push.}

 

_{Almost all disc setusp around here are running what you have and have never used a proportioning valve. Just factory stuff!}

 

_{Good luck!}

 

This kind of begs the question to whether a proportioning valve will even help anything. I figured I could probably get away with not having one but I figured it would help me dial in the brake F/R bias. Normally and practically speaking, if the prop valve is operating correctly, it shouldn't be restricting the rear brakes when fully open? So besides the extra expense, complexity, etc. adding a proportioning valve shouldn't really hurt the system performance. But I am curious as to whether other 510 owners who have upgraded to rear discs without a prop valve have a problem with the rears ever locking before the front? If it doesn't even occur, it seems worthless to put a prop valve in the system.

[Uber Deaf One]

This kind of begs the question to whether a proportioning valve will even help anything. I figured I could probably get away with not having one but I figured it would help me dial in the brake F/R bias. Normally and practically speaking, if the prop valve is operating correctly, it shouldn't be restricting the rear brakes when fully open? So besides the extra expense, complexity, etc. adding a proportioning valve shouldn't really hurt the system performance. But I am curious as to whether other 510 owners who have upgraded to rear discs without a prop valve have a problem with the rears ever locking before the front? If it doesn't even occur, it seems worthless to put a prop valve in the system.

 

I've never heard of this happening. I would imagine it is possible the proportioning valve IS restricting the rear brakes when fully open maybe slightly? If you're confident everything else is ok and working as intended, remove the proportioning valve and see what happens.

[Marsh510]

Bringing this back to life. i am also having the same problem. running zx fronts and maxima calipers in the rear. Currently using the stock 510 m/c, just ordered the zx m/c. anybody ever find a solution?

[Tech-guy]

I also recently upgraded my rear brakes to the same configuration: Maxima calipers and 200sx rotors but I did not install a manual proportioning valve.  After an initial 2 mile drive using the brakes hard I was disappointed in the weak rears.

I inspected the rear brakes and saw that on both the left and right the pads were not making contact across the entire surface of the rotors.  On the outer side of the rotors the pads made contact on the outer one third of the disk.  On the inner side of the rotors the pads made contact on the inner one third of the disk.  Bottom line is that the pads are not totally parallel to the rotor, they are skewed slightly!  This could be due to the mounting surfaces on the adapter plate not being totally parallel. With pressure on the brake I could observe good contact between brake pad and rotor out near the edge of the rotor. But there was an observable gap between the pad and the rotor near the axis of the rotor. I tested the gap with an 0.008 inch feeler gage and it would not go in.

 

I have removed the adapter plates and plan to have the two surfaces milled parallel.

 

The other possibility is that the backing plate mounting surface where the adapters mount is not totally perpendicular to the axis of the rotor (rear axle).  On a drum brake system there is no reason for that backing plate surface to be highly controlled.

 

This may all be a mute point because after some miles the pads will wear in and make contact across the entire rotor surface.

 

[datzenmike]

The stock MC is set up for disc fronts and drum rears. This is not optimal for disc rears. The residual valve in the stock master should be removed and a disc residual valve swapped in for the rears. 

 

The front rear bias is designed into most Datsuns by varying the rear wheel cylinder sizes. This eliminates the need for, and the complexities of, a proportioning valve.  Lowering the car, larger tires (more grip) stiffer springs all contribute to changing the need for more or less bias. Take the car out on a deserted paved road generally what you normally drive on. Speed up to 40 MPH and apply the brakes harder and harder until lock up occurs.  (please use you head doing this!!!) Take a look at the rubber marks. In an ideal world the backs will start to lock just as or just after the fronts do.

 

If no rear lock up you need a larger rear caliper as there is no easy way to increase the line pressure. If the rears lock before the fronts, get smaller rear calipers, trim the pads so less surface on the rotor or reduce the line pressure to the rears with a manual proportioning valve.

[Tech-guy]

After milling the mounting surfaces to be truly parallel, the slight misalignment of the brake pads relative to the rotors has disappeared.

They now make contact across the full face of the rotor.