Rear brakes locking

[adam]

Hi all,

 

I was just after a few ideas of what could be causing my rear brakes to be locking up before my fronts.

 

But before I go any further, some background information..

 

It's a 1973 240z, I'm currently running the standard brakes all round, disk fronts and drum rears, and I have recently changed to a standard 260z brake booster, fresh 'standard replacement' master cylinder, and fresh seals in both wheel cylinders.

 

What could be causing the rear drums to lock up before the fronts?

 

I am in the process of ordering/buying a new pair of drum shoes, but I have a feeling this won't stop it for some reason? Could it be the brake proportioning valve/NP valve?

 

Any ideas would be greatly appreciated.

 

 

Cheers,

Adam

[C.A.R.]

Haven't got the 2 brake lines around the wrong way in the MC have you?

[adam]

That sounds like such a silly mistake but I was under the dash doing the bolts while a mate did the lines so I will have to double check that!

[44014]

Did you change your rear wheel cyl because they were leaking ?

If your shoes are contaminated they will bind when applied .

 

[adam]

Had a look at the brake lines at the master cylinder and it doesn't appear to be installed the wrong way. All looks normal there..

 

One wheel cylinder was leaking before the reseal, yes! That may be the reason why it's locking up.

 

I am in the middle of purchasing new brake shoes so hopefully that sorts it out.

[Enzo]

Hi Adam , As Lurch says. On the 240z master cylinder the front brakes attach to the front of the master cylinder and on the 260z the front brakes attach to the rear of the master cylinder. (closer to the booster). If they are the wrong way around the rears will lock up first.

David

[adam]

Very interesting, David.

 

The line that's currently connected to the front reservoir on my master cylinder is definitely controlling my rear brakes (so the 260z setup). The lines don't appear to be able to be accidentally mixed around with the way the hard lines are bent though? I can't say for sure whether they can be mixed around because I didn't connect them up at the time..

 

Could it possibly be the replacement brake master cylinder that I've purchased? The one I have in it at the moment has part number JB-1130, can anyone confirm whether this is the correct master cylinder for me?

 

If it matters at all, the front reservoir on the master cylinder is smaller than the rear.

[Enzo]

OK.

    From what I understand 240z to August 1971 had the front brakes attached to the front of the master cylinder (to the shorter, fatter reservoir).

    From September 1971 onwards 240z, 260z and 280z had the master cylinder with the front brakes connected to the rear of the master cylinder (shorter, fatter reservoir). The lines will have to be bent to line up. Have a look at the service manual.

Regards David.

[adam]

Thanks for your help, David.

 

My car's brake lines and brake master cylinder setup look identical to the service manual, front reservoir controls rear brakes while the rear reservoir controls the front.

 

I think at this stage, we'll have to assume it's the rear brake shoes causing them to lock up first. I have ordered a new pair and I'll have to install them and see how everything pans out.

 

I'll be sure to update this thread either way with a result. Let's just hope it stops the rear brakes locking.