Brakes not working, need help.

[xterraminator]

So I have a problem with my brakes. Just to give you a bit of history the truck is getting a sas done to it and so the truck sat parked for about 10 months. The flexible brake lines were removed about 2 months ago. So today installed the new calipers on the front axle and new flex lines front and back. We filled up the reservoir and bled the brakes in the proper order as per the manual. Did it twice just to make sure all the air was out. When the truck is turned off the brake pedal goes about half way, will build up pressure and stay there nicely. All seems fine. The problem starts when the engine is started. As soon as the engine is started the pedal goes all the way to the floor and when pumped I can never get it to feel right, seems to slowly go to the floor. When the engine is running we saw some air bubbles coming up to the fill port where you add brake fluid. We checked there were no leaks, the oil does not drop, the check valve between the air intake to the booster is fine(allows air to flow one way). When we turn off the engine and then pump the brakes it seems to go half way with good pressure and holds in one place when depressed. When the pedal is depressed and the engine is started it gets sucked to the floor. At this point not sure what the problem is. Any suggestions would be nice. The funny thing is that the brakes worked great before I took it off the road.

 

[TheFauxFox]

Look into getting a bigger brake master cylinder.

 

[metzican]

^ that, or maybe you need to bleed the master distribution circuit, I don't know if gen 1's have one or not.

 

[Prime]

Seals in the master cylinder sound shot. Time for a new one methinks.

 

[TheFauxFox]

Seals in the master cylinder sound shot. Time for a new one methinks.

Save yourself some trouble later and get a bigger one.

 

[Prime]

True.

 

[xterraminator]

Casper,

I did bleed the brakes in that order, did it 3 times or more. When depressing the brake pedal and bleeding the brakes it was done when the truck was off. With the truck off the pedal does half way and stays there, does not go down any further. All is fine. Its when the engine is started the vacuum pulls the cylinder in so that the pedal goes to the floor much easier. Can't pump it up and have it hold like when the engine if off. I never did bleed the master cylinder as the manual says and you could be right there could be air in there or the abs block. The strange thing is when we bleed the brakes no air comes out, its all liquid which is good. The air bubbles developing and coming to the fill port once in awhile don't look good.

 

[xterraminator]

either tonight or tomorrow I will take the master cylinder off. I think it needs to be cleaned and inspected and then I will bleed the master and re-install. One the brakes are bled and still worky then I guess I need a new master. Its just puzzling how the brakes work with the engine off and when the engine is on(vacuum on the brake booster) brakes go all squishy.

 

[Prime]

When the vac is on the booster it gives the pedal a LOT more force than you can administer on your own. That's why they're called power brakes.

So it exaggerates any imperfections in the braking system.

 

[metzican]

Thats the way my brakes where when I changed out the lines. Then I re bleed them really wheel. Used one of those giant bottles. and they firmed up they are stilll not rock solid but 10x better then they were.

 

[xterraminator]

Thanks for all the great feedback! I will take the master off and see how it looks and bleed it which was never done from beginning. Worse case scenario might have to replace it. Should anyways its 14 years old.

 

[xterraminator]

So here is an update:
1. Removed the 2 brake lines out of the master cylinder and performed a master cylinder bleed. Master bleed went well.
2. Bled all brakes lines, no air in lines. Looks good.
3. When I depressed the brake noticed air bubbling to the top of the reservoir with engine off. I decided that the master cylinder was defective.
4, Installed and bench bled the new master cylinder.
5. Bled all the lines in the proper order twice until no air bubbles were visible.
6. With engine off the brakes seemed to go down half way and it held its position after a few pumps.
7. Turned on engine, depressed brake, guess what. NOT working, soft all the way to the floor. Its only when vacuum is applied to the brake booster is when it fails.
8. Gave up, not sure what is next, will consult a mechanic. I have no idea why this is not working.

 

[xterraminator]

I went to Nissan dealer today, they were useless, they said bring it in most likely its a bad brake booster. I went to another shop they said that when the truck is off the brakes should pump up hard and hold halfway, when the truck is on it should go down more and feel a little bit softer. I ended up calling a mechanic who will come tomorrow morning. He thinks that there is still air in the system somewhere. Also because I have larger calipers on the front much more fluid to move. More updates later. Talk about frustrating.

 

[Prime]

At this point, I'm leaning towards the booster as well.

 

[xterraminator]

I went to Nissan dealer today, they were useless, they said bring it in most likely its a bad brake booster. I went to another shop they said that when the truck is off the brakes should pump up hard and hold halfway, when the truck is on it should go down more and feel a little bit softer. I ended up calling a mechanic who will come tomorrow morning. He thinks that there is still air in the system somewhere. Also because I have larger calipers on the front much more fluid to move. More updates later. Talk about frustrating.

I think the booster is good because when I turn the truck off and pull out the vacuum hose out of the brake booster you can here the relief a air going inside because there was vacuum in there. Because of the check valve on that line, any vacuum can't get out until the one hose on the booster is pulled off. I think it is fine. Lets see when the mechanic comes tomorrow. I have also been seeing on the internet that the stock master cylinder might not be big enough for the newer dana calipers on the front. Its the only thing different in the brakes from stock.

 

[xterraminator]

Mechanic came today we replaced the rear shoes bleed everything no go. Vacuum booster is fine. Have concluded the master cylinder is not big enough to push the fluid in the front calipers. Will be sourcing out a bigger alternative. Does anyone know where to find the link where someone swapped out the xterra one for a Chevy one?

 

[xterraminator]

Other guys on here what did you do when you did a sas? Any brake mods?

 

[xterraminator]

So guy what would be the best master cylinder to use? From the internet search I see guys are using the 78 chevy c30 pickup 4x2 MC or dodge 1500? I am trying to find a posting on how the swap went.

 

[xterraminator]

The whole brake thing is frustrating. Before I parked the truck the brakes did work. The only difference is the front single piston calipers. They must use a lot of fluid than the stock ones. My last resort is to pull the master off and just see if the booster is working ok. I still agree with you casper the stock one should work. Trust me I will get to the bottom of this. Can the plunger that comes brake booster be adjusted to come out a little further? There are no leaks, bled well and when the engine is turned off the brakes can be pumped up to 50% pedal stroke and it holds. When the engine is started the truck put in drive and brakes applied to the floor the axles actually turn very slow. Truck is up on supports btw. Here is one question can the abs unit be bypassed 100%?

 

[xterraminator]

So last night I worked on it and had a feeling the new front calipers had an air pocket trapped inside because the bleeder screw is on the bottom side of the caliper. I suspected I had them in the wrong place so I swapped them. Now the bleeder screw is now on top. Once I bled them a lot of air came out and right away the brakes were hard, pedal could not even go 1/4" down. To make sure I bled the front and back for about on hour. All looked good. When I start the truck with the vacuum assist its better, the pedal goes down half way, then slowly sinks to the floor. I now suspect that there is air in my abs unit and that I will need the dealership to pulse it. For now I will make due how it is and continue working on it. In the end it can go to Nissan for final brake testing and purging. At least its way better than it used to be. I am still tempted to bypass the who abs unit as a last resort.

 

[TheFauxFox]

Is this thing still road legal? Do you plan to keep it road legal? I never liked trailer queens :

 

[xterraminator]

Is this thing still road legal? Do you plan to keep it road legal? I never liked trailer queens :

As soon as I can get the brakes going, and finish the back body work it will be street legal. The only thing that will not be legal for the time being is that it does not have side passenger seat belts for the back. Their gone and I have to re-invent how to mount those. Middle lap seatbelt is stock.

 

[TheFauxFox]

As soon as I can get the brakes going, and finish the back body work it will be street legal. The only thing that will not be legal for the time being is that it does not have side passenger seat belts for the back. Their gone and I have to re-invent how to mount those. Middle lap seatbelt is stock.

You could replace them with 5-point harnesses. I have some that I can part with for pretty cheap.

 

[xterraminator]

You could replace them with 5-point harnesses. I have some that I can part with for pretty cheap.

The point where the shoulder strap/ seatbelt pulley mounts to is gone. nothing in the frame pillar to mount to. I will use the outside lower mounting points, possibly just lap belts but I am thinking this might not be legal because its going away from stock setup. 5 point would not work, nothing to mount to.

 

[TheFauxFox]

The point where the shoulder strap/ seatbelt pulley mounts to is gone. nothing in the frame pillar to mount to. I will use the outside lower mounting points, possibly just lap belts but I am thinking this might not be legal because its going away from stock setup. 5 point would not work, nothing to mount to.

Interior cage, man!

 

[xterraminator]

So yesterday I removed the abs unit and was able to gain 10% more braking power. All the brakes are free of air and when the truck is running pedal goes about half way then slowly sinks. Looks like I need a bigger master cylinder.

 

[Jack Stilts]

‎
Hey y'all. Having a similar issue.

The X has been sitting in the driveway for over a month. Started a few times. Just got the steering gear replaced today; went to drive it, and I've barely got any pressure in the pedal. Fluid was low, so I topped it off. Still nothing.

Never done anything with brakes other than changing pads & rotors, so I'm not sure where to start. I read about the master cylinder replacement, but I have no aftermarket parts under there other than the tie rods and centerlink and such.

‎

 

[BEEFY]

Check your wheel cylinders in the rear drums to see if they are leaking. As I had that happen to mine a couple years ago.

 

[Jack Stilts]

No leaks, bone dry. Fluid is still full in the reservoir. It's strange.

 

[Prime]

That does sound like the seals in the master cylinder are shot.

 

[xterraminator]

Sorry I forgot to give you an update. Few weeks ago just bled the brakes good and in the end the stock MC works great. Its been fine ever since.

 

[Jack Stilts]

Well I'll plan to do both - replace the master cylinder and bleed the brakes.

Anyone want to give a quick how-to for either of those?

 

[Prime]

The master cylinder is strictly a bolt on affair. The important thing is to bench bleed it. There should be instructions on that with the cylinder. After you replace it, you'll have to bleed all 4 corners anyway. Unless you have speed bleeders or a pump, it's a two man job.

 

[Jack Stilts]

How...messy is that. I'm wondering if I can pick one up and recruit / convince (bribe) one of our helpful WENT fellows to assist while I'm there.

 

[Prime]

Brake fluid. It's messy. It gets everywhere.

 

[Jack Stilts]

Copy that. Bad for Tread Lightly. I'll plan for it when I get back.

As always, thank you sir.