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emripires

620 brake issue

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I've recently installed the Mike Klotz hardbody conversion to my 76 620.

 

Here's my setup:

 

v6 Hardbody callipers, rotors, pads, lines etc.

15/16" master cylinder

Oem booster

rear Oem drums, no proportioning valve or residual valve.

 

The issue I'm having, is the front brakes always have a bit of pressure, rears have none like normal. The brakes work fine when I want to use them, but when I'm off the brakes, the fronts are always a bit on.

 

I have tried adjusting the brake pedal bolt in and out, made no difference. Brakes still drag...

 

Does anyone have experience with this problem who can maybe point me in the right direction?

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I think it's the master cylinder push rod that may needs adjusting. It's connected to the back of the brake pedal. Take out the pin to separate, Loosen the lock nut and turn the adjustment in to shorten the travel. 

 

This will allow the master to return fully to it's rest position and allow any pressure to vent fluid back into the reservoir.

 

Don't forget to tighten the lock nut and be sure to replace the clip in the clevis pin that holds it in place.

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I think it's the master cylinder push rod that may needs adjusting. It's connected to the back of the brake pedal. Take out the pin to separate, Loosen the lock nut and turn the adjustment in to shorten the travel. 

 

This will allow the master to return fully to it's rest position and allow any pressure to vent fluid back into the reservoir.

 

Don't forget to tighten the lock nut and be sure to replace the clip in the clevis pin that holds it in place.

I did adjust it, a few times now, but I did not see a difference in pressure. Would I have to bleed the brakes again after adjusting it? Or drive it around after?

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When the push rod is adjusted properly, you should have a few mm of looseness when you push down on the pedal with your thumb.

 

If the fronts are dragging they will get hot.  Do they get too hot to tough the rotor?

 

OK, next time this happens, loosen the brake line fitting to the front brakes at the master. That would be under the rearmost reservoir. If fluid spurts out then yes there is trapped pressure. If not, it's either something else, like a stuck caliper piston, possibly the inner lining of one of the flex hoses has de-laminated and is acting as a one way valve... or imagination.

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When the push rod is adjusted properly, you should have a few mm of looseness when you push down on the pedal with your thumb.

 

If the fronts are dragging they will get hot.  Do they get too hot to tough the rotor?

 

OK, next time this happens, loosen the brake line fitting to the front brakes at the master. That would be under the rearmost reservoir. If fluid spurts out then yes there is trapped pressure. If not, it's either something else, like a stuck caliper piston, possibly the inner lining of one of the flex hoses has de-laminated and is acting as a one way valve... or imagination.

Yes, the rotors are super hot, they're definitely dragging. I'll play around with it some more, see where it gets me. Thanks Mike,

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If both are hot then unlikely both have a stuck caliper.

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The front and rear circuits changed between various m/c's.  The rear circuit is setup for drums and will have a residual valve in it.  If you happened to connect them in reverse, that would cause your fronts to hang up.  

 

When you put the caliper on the rotor with the pads....were they nice and loose to start with?  You're running the v6 rotor with the v6 calipers....right?  

 

On the pushrod.....the pedal has to have a return spring on it so that it comes all the way up on it's own.  The push rod needs to be able to wiggle just a bit.  Verify that the piston in the m/c is coming all the way back when the pedal is released.  You should be able to see it come up against the e-clip....unless you have a rubber boot in the way.  

 

You might also try the stock m/c.  We've seen quite a few brand new m/c's be bad out of the box.  

 

If you remove the debris filter in the m/c reservoir, you should be able to see a small hole in the bottom.  With a bright light, you can typically see into the hole just enough to tell if the piston is blocking it or not.

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Nissan masters have the reverse circuit at the front and the front circuit at the rear . Usually there is an R and an F cast into the casting.

 

 

 

 

 

If you remove the debris filter in the m/c reservoir, you should be able to see a small hole in the bottom.  With a bright light, you can typically see into the hole just enough to tell if the piston is blocking it or not.

 

Never thought of this, but good idea.

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So, I pulled the master cyl out of the brake booster.. brakes still held, opened bleed screw on front channel, brakes still held. Opened the bleed screw on the caliper, still held...

 

These are "new" remanufactured Raybestos calipers from RockAuto.. Could they really be faulty?

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Raybestos is not the sign of quality they used to be.

 

 

I like to use CENTRIC brake parts. Never an issue.

If I'm not using factory parts on my customer's cars we use CENTRIC only.

 

 

When you installed all of this stuff we're they free moving?

 

Brake pads too thick? I've seen that plenty of times.

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Disc brakes, like all brakes, change motion into heat... they can and will get hot. How hot is hot?

 

Disc brake pads are always in contact with the rotor.

 

 

 

Well every thing sounds normal, so lets examine your claim they are dragging.

 

So, will the truck roll on a flat surface? Can you easily give it a shove and move it????

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It'll move, but when I'm rolling into a stop sign 1 or 2 km/h, it'll stop on it's own. They're too hot to touch, and when I take off from the light, there is a bit of a harsh sound, I'm not sure if it's from the dragging pass side brake or not, but it wasn't there with the drum brakes. I had a feeling it was from the new wheel bearings being too tight, but I took off the caliper all together, and the hub spins great.

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Are you using cheap pads too?

 

Is this sticking only happening on one side?

Compare pad thickness of all 4 pads.

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Are you using cheap pads too?

 

Is this sticking only happening on one side?

Compare pad thickness of all 4 pads.

Raybestos, it's sticking on both drivers/pass. The sound seems to be coming from pass side though.

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Do you have a micrometer? Can you measure pad thickness?

 

I'm wondering if you got 4x4 pads instead of 2wd pads.

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Take calipers off. Slowly step on pedal, see if the pistons will extend.

 

 

Don't go too far though. You'll have a big mess/bigger problem on your hands.

 

 

 

Maybe throw some pics up. Maybe we can see if there is something obvious you could be missing.

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Is that what you bought?

 

 

Toss those pads and buy a new set from a local shop.

 

You have zero clue what pads those are. Loaded calipers just get whatever scrap is laying around to fill them.

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Is that what you bought?

 

 

Toss those pads and buy a new set from a local shop.

 

You have zero clue what pads those are. Loaded calipers just get whatever scrap is laying around to fill them.

xD, I've never had this issue on Rockauto. Usually everything I get is awesome, but I'll try that.

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Never trust loaded calipers.

 

 

 

I learned that long ago.

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Never trust loaded calipers.

 

 

 

I learned that long ago.

I will try that out, and reply back, thanks mate.

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Shot in the dark, really.

 

Without the car in my stall I'm just reaching here.

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How tight were the pads when you put the caliper/pads over the rotor.  Did they slide on easily?  I'm wondering if the caliper is not centered over the rotor and one side is pressed against the rotor.

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