1978 620 brakes, late engagement

[Speedymaru]

I have a 78 620 and the brake pedal goes far down before actually engaging. I'm not sure how to fix them. The brakes leave a lot to be desired too. I was thinking of replacing the front pads. Would this change anything for the pedal? Is there a place to adjust it? I'm not worried about the rear shoes because when I had the wheels off, I was able to turn them, but also felt the resistance so I know they're working. Any advice?

[wayno]

You could have air in the lines, or if someone has been messing with the master it may have the rod adjusted wrong.

You might need a new master brake cylinder also, or the rear drums might be to loose, has it sat a long time?

[Speedymaru]

Okay. Is there any way to check if there's air or do I just have to bleed the system? The PO installed a new master cylinder right before I bought it. I don't believe the rear brakes are too loose, because there was a decent amount of resistance on them. I may be wrong however. The truck sat for about 7 years before I bought it.

[datzenmike]

 Check the master cylinder reservoirs for fluid. If low top up. If empty there may be air now trapped in the lines.

 

Adjust the rear wheel cylinders. But first loosen the E brakes. Spin the wheel by hand while adjusting them till they rub. Pump the brakes several times to center the shoes and continue tightening them while turning. When they rub slightly after pumping the pedal it's good. Now do the other side. Adjust the E brakes back.

 

Pads have no effect on the pedal.

[Speedymaru]

I just checked the fluid levels, both reservoirs are full to the max line.

 

I'm kind of thinking it's the MC rod. Of course I could be wrong, I don't know a lot about brakes.

[datzenmike]

If you don't know leave it alone. Check the rear shoe adjustments and be sure..

[wayno]

I would just try bleeding the brakes and get the air out of the lines, do the rear first.

Sometimes people that don't know how to bleed brakes do the front first, or they don't get the rear brakes completely bled, then they go and bleed the fronts and that makes it very hard to get the back brakes completely bled, you need to bleed the back brakes till you are getting a lot of fluid out of them every time you open the bleed screw, if it barely comes out every time then you have problems, that is when you will have to open the front circuit and let it pump out onto the ground while you bleed the back brakes.

Of course if the rod is not adjusted correctly this will make things difficult, basically you have to feel the play in the pedal, but the booster messes with you, you should only have a 1/4 inch max play before it starts pushing on the back of the master brake cylinder.

[Speedymaru]

Okay will do. Does the wheel need to be off to check the rear brakes? And what do you mean by disconnect the e brake? Do you mean just make sure it's unengaged, or do I actually need to disconnect something?

 

And okay sounds good. I made a one-person bleeder, and now I just need to buy some fresh brake fluid then I can bleed them.

[datzenmike]

Loosen the adjustment so it not interfere with the adjuster on the shoes. They may be fine but it must be eliminated as a cause. The rear shoes out of adjustment will eat up a lot of pedal travel.

[2wheel-lee]

I think one of the clues here was that the PO replaced the master cylinder before you got it. Likely, the problem has existed since that point. It's possible - and probable - that he didn't bench bleed it, so it's likely that there is air in the system. 

[wayno]

You should actually disconnect the e-brake, what happens is it gets adjusted as time goes by and the shoes get worn and it gets adjusted again, by the time the shoes need replaced guys try to get the drum on and it will not fit, everything is loose yet the drum will not go on, that is because the e-brake is still slightly engaged even though the handle is in the released position, so when adjusting the brakes after say something was replaced, you need to start over and adjust everything, the e-brake is the very last thing to be adjusted.

Release or at least loosen the e-brake cable under the truck so that the cables are sagging loose, adjust the rear brake shoes, bleed the brakes completely, adjust the rear drums again, then connect the e-brake cable and do the e-brake adjustment.

[mklotz70]

Nothing wrong with all the other suggestions, but I'll throw in a couple of other things you should check.

 

Pump the pedal.  If it pumps up and gets firm on the 2nd or 3rd pump, you have an adjustment issue with the rear brakes.  If it's spongy after it pumps up, you have air. 

 

As for the m/c, check underneath the dash....the pedal should be pulled up by a spring.  While it's at the top, you should be able to just wiggle the push rod.  The wiggle should go away when you push the pedal down about a 1/4".  Now check the m/c under the hood.  Datsun swapped the front and rear circuits over the years and rebuilders rarely pay any attention to making sure they're actually rebuilding the correct parts.  There should be an "F" and an "R" on the vertical round area just above where the lines connect. Make sure that the lines are connected correctly.  You can just physically follow the lines to figure out which one is front and which one is rear.  There's a chance that the new m/c has them backwards of the original and the PO simply hooked them up to the same position.

 

If you absolutely can not get any help to bleed the brakes, you can gravity bleed them.  There are one or two other ways to do it by yourself, but that's probably the most reliable way.  Google it....I'm sure there's plenty of info on it.

[Speedymaru]

The pedal gets a little bit firmer, but is still spongy. I bought brake fluid and I'm going to bleed the brakes. I checked the pedal and rod, and there is about 1/4 in of play.

 

I'm going to bleed the brakes and make sure the rear drums are adjusted correctly.

 

One question, where on the truck do I disconnect the e-brake?

[Speedymaru]

Forgot to add one thing. Would this be an okay way to bleed them? https://m.youtube.com/watch?v=n1NvtUwfRJc

[Speedymaru]

The drums are supposed to rub a little bit correct? Is that properly adjusted? Is there anything else I need to check?

[mklotz70]

http://community.ratsun.net/topic/65468-adjusting-521-drum-brakes/

 

no time to watch that whole vid, but what I did see looked good

[Speedymaru]

That's a great write up, I'll definitely do that soon.

 

I went ahead and bled the rear brake circuit. There's already a huge difference in the pedal. Much harder and engages much earlier. I'll be doing the front soon, then will adjust the rear drums and do that test that the article mentions.

 

Thanks again for everyone's help!

[Speedymaru]

Finally got a chance to test the brakes on the road after bleeding front and rears. Brakes are good to go now. Drove to the top of a fairly steep hill and let the brakes do all the work on the way down. They worked great and had no issues. Thanks for everyone's help!

[Gery]

So, I was just at the brake shop due to seeping rear drum brake cylinders.  They sent for the listed parts for my 1978 620 pickup.  The cylinders they sent — though listed as fitting— were not correct.  The Ones I need are configured in a diagonal.  I’ll try to load pictures later, but does anyone know of some difference specific to the ‘78s?

[datzenmike]

The '78 had a front and rear facing shoes with the wheel cylinder at the top and the adjuster at the bottom. Diagonal? did you mean bolt pattern?

 

It's 40 years old, maybe someone swapped older brakes on or the whole axle. Pictures I guess.

[Gery]

I’m photo sharing challenged....sorry.  ?

Looking at the exposed brake hub from the outside, the cylinder oriented is parallel to the ground....but, then viewing from the the other side of the hub (from under the car) the axis of the connections are at roughly 11 and 5 o’clock.  I did find (fingers crossed) the correct cylinders (#w51303) on eBay.  Apparently they are specific to the ‘78 and ‘79 pickups.

[Gery]

I got the correct cylinders.  They did have a different orientation than the common ones listed online.  They also were listed as proper for the car...so just case of multiple parts.  Thanks