Rear Brakes stick because of my master cylinder

[SledZ]

My Rear Brakes stick because of my master cylinder, I think. I drove around the neighborhood (testing) and after hitting the brakes several times my rears eventually lock up!

If I relieve the pressure at the rear master cylinder valve it frees the brakes up.

So I bought a rebuilt master cylinder but no matter how I bled it it would not give me any pressure, plus I had to swap the lines around for the front and rears. I took the rebuilt back and put my original back and am thinking of getting a brand new master cyl.

Has anyone had this problem?

I saw a couple other posts on rear brake drums that are locked up,,this could be your problem. Thanks for any help

[2adz]

Sounds like you have debris in your brake system. It is letting fluid pass towards your rear cylinders but is not letting it flow back. Do you have new flexible hoses? What happens sometimes is that the flexible hose will break down on the inside causing an obstruction. When you bleed the brakes in the rear is the fluid dark? Start with the easiest part and work your way to the more difficult. You may need to pressure bleed the rear brake lines.

[Bambikiller240]

Usually when rear brakes are locked, it is because the Rear Wheel cylinder is buggered up (gummed up, or rusted up).

My experience with rebuilt Master cylinders has been very poor. I quit buying them 20 years ago, now I only buy NEW when the need arises.

I'd flush out the lines to the brakes with clean, fresh fluid, then bleed the system. Start by bleeding the master itself, the right rear, left rear, right front and left front.

[SledZ]

I do have one new wheel cylinder on one wheel but the other I cleaned up. I have new stainless braided line and new brakes all around. I have a Mity Vac that I use to bleed that works great.

I think I'll take out the other wheel cyl and replace it with a new one, which I cheaped out and didnt do in the begining and see what happens.

Thanks

PS I have heard that it is best to buy new master cylinders also...

[SledZ]

New rear cylinders did not help, the rears still build pressure and eventually lock up after 10 or so pumps, then have to release pressure from the master cylinder to get going again. Looks like I'll be ordering a master cylinder shortly...

[Bambikiller240]

Originally posted by SledZ

Looks like I'll be ordering a master cylinder shortly...

Strange circumstance. If I remember correct, there is only one Piston in the m/c, with two seals, each at different locations on the piston (one for each circuit (F & R). Odd that pressure builds to apply the brake in both circuits, but is not released durring normal operation in only one circuit. I don't understand how this can occur.

Check with Chloe at www.midwestz.com (she's an supporting advetizer on the club site). I think you'll find she can give you a great deal.

[Ed]

This might not help but, I thought I'd pass it on just in case. On my motorcycle. 1974 CB750. I had the same problem with the front brakes. After about 10 pumps the brakes would stay locked and get extremely hot. I finally found that the brake pad was sticking in the caliper. Maybe your shoes are sticking?

[SledZ]

It is a doozie of a problem. It's really weird that it builds pressure like that. Last night I test drove it over to my brothers (2 miles) and by the time I got there I was close to locking up. Forgot to put the emergency brake on before I opened the valve and my car took off rolling, aagghh!!!

The pedal has very little give maybe an inch and it firms up tight even with vacuum so I am wondering if it could be that pressure valve in the back since there is no give in the pedal. If that valve is not "valveing" then it could be my problem.

After hearing Bambi's comment about the MC valves it just might be that. I'll have to do some more troubleshooting....

I bought some items recently from Midwest Z and really liked her service.

Thanks

[billcapp]

I have experienced the same problem. I had rebuilt my master cylinder and replaced my vacuum booster at the same time. After driving for a short distance (using brakes 3-4 times) they would lock up. Had to tow it home 3 times. I found that the master cylinders are different as are the boosters. (check my gallery for one of the differences) (master courtesy of Carl Beck) Don't worry Carl, I'll return it soon. I had to jury rig the booster to work properly (wrong size threaded shaft out of the booster connecting to the pedal) which I shall return and the plunger end going from booster to MC can be different (length and/or diameter). I corrected this problem by adjusting the plunger end about 3 times (trial and error) until it didn't lock up anmore. Try adjusting the booster rod (between MC and booster) if the other suggestions don't work.

PS the 71 MC is different from 72-75 and costs 3 times more. I must like "three" today. Sorry about that.

Bill:geek:

[SledZ]

Saw your picture of the master cylinders. I have the one on the left because the ® is toward the rearend and the (F) is toward the front end. Funny I have a 71 MC on a 72 and now I know why the rebuilt MC did not work at all.

So I can't swap out my HIGH Dollar MC for a less expensive one without the rod?

I'll fiddle with it tonite and see what happens..

Thanks

[Tiburon]

Well, I may just have the answer here.....

because your old brakes in the rear are drums....they needed a RESIDUAL pressure valve in order to help keep the rear wheel cylinders on the verge of being engaged....(because the reservoir is so small and he run to the rear so long)

If switching to rear disks, it is recommended to switch to a master cylinder with the provision with for both front and rear discs....it is also recommended to install an adjustable pressure valve like theunit wilwood uses...

How do I know this? Well the Mustang crowd also like going 4 wheels discs...this is something often talked about and a whole bunch of them blue oval lovers have run into this problem....did I? nope....I saw the tough time they were having and researched it.

It could be as easy as removing the pressure residual valve and adding the adjustable regulator for the rear.

call Nissan Motorsports tech line...they may have a kit for this.

hope this helps

R

[SledZ]

That sounds like a good place to look. I'll have to post an ad to see if anyone has a used rear regulator, not sure I want to mess with these brakes anymore!!!

I did check the rod in the MC and made sure everything was "plunging" ok which it is. I havent had time to work on it in the last couple weeks but want to get that regulator off in the back and check it out.

Thanks for that info about the adj regulator!