Please help me troubleshoot brake issues :)

Hi Everyone, like the goose I am I stuffed up my rear drums somehow  Seeking some assistance with my braking issues as follows:

I have stock brakes so rear drums & 2 piston fronts.

1) The stock brake booster that came with my car wasn't working, so I bought a larger booster & 15/16 master cylinder from a 280zx. I installed the new booster but have kept the 7/8 MC for now so I don't have to bleed brakes etc. at this stage.

The booster is working fine but now my brakes lock up very easily, after adjusting with the pushrod at different lengths all it did was change the pedal stiffness. Even loosening the pedal very loose the brakes still lock up at the end of the pedal travel.

I've come to the conclusion that the booster is a bit too powerful for the stock brakes? If so that means I will either need to source an exact replacement for my stock booster or get that one repaired/reconditioned. I'll keep the 280zx booster for when I do larger brake conversion.

- Is there anything else I have missed when checking why the brakes lock up easily?

- Is there anywhere in sydney/west suburbs that can recondition brake boosters or would it be cheaper to source a replacement for eg. online ebay/zstore etc.

2) I took off my rear drum covers to have a look at the condition of the brakes, the pads still have plenty of meat on them but now I've stuffed up my brakes somehow, I feel so silly.

I had my handbrake off the whole time, I pumped the brakes with the covers off to have a look if I could see anything wrong, I think pressing the brakes with the drum covers off is a bad thing?

On the Driver side drum, the little metal bar that engages the teeth for the handbrake is now stuck in place & my handbrake has no resistance at all, I can pull it all the way up to a 90 degree angle. :-\

I've tried pushing the bar back in place but it won't budge, the cable connector seems fine I disconnected the cable from the bracket & had a bit of a play with it. I'm stumped on how to fix it.

3) I took the drum cover off the passenger side drum, no issues with the handbrake, the teeth are engaging properly with the small metal bar.

The issue is I can't get the cover back on over the pads I was able to pull it off without too much force, just a bit of wiggling back & forth but now it won't fit back on, the pads are getting in the way. The handbrake lever is off as well when I try to put it back on.

Is there a particular trick to getting the covers back on?

Sorry for the long post, any info is much appreciated as always

I can't believe I stuffed up my brakes so badly hahaha, all I can do is laugh, call it a day, relax for the rest of the night & tackle it tomorrow

Cheers!

Pushing the pedal down with the drum off will allow the piston in the rear cylinder to push out further than it should. Either or both pistons could be out to far and jammed. Take the tops off the brake reservoir and try and push the rear cylinders in to push the fluid back up to the reservoir.

You need to make sure the pistons are all the way back plus as I said in the other reply adjust the bottom adjusting screw in to minimum. (you rotate that gear like part to screw the thread in or out to adjust the shoe) Normally if you look at the backing plate you can see where the shoes used to sit to give you an idea.

I would say the hand brake may be not working properly because it has popped out of where it should sit. You need to check that is all back in the correct place on both sides.

Do you have a lip on the outer edge of the drum braking face? This sometimes makes it hard to get the drum on and then you have a big gap between the shoe and drum once on.

I would be surprised that a booster that is too big would cause the brakes to lock. Are the fronts and the rears both locking or just the rears?

hard to see from the photo but it looks like you have popped the cylinder and it has twisted in the bore, that lining should not be touching the edge like that. lucky it is not pissing out fluid, you need to relieve the pressure at the piston (screw driver lever the pad away from the piston ) and push it back in, I am guessing you pumped the brake pedal with the drum off??

Edit ah you beat me oldmate !!, also check your front pistons are not siezed they will cause rear lock up as well

Bigger booster will provide more force I guess - did you also change the master cylinder because if this is bigger than stock you can end up over braked.  Bigger booster should mean less pedal pressure required on the brakes so if it is much bigger it could be part of the problem ?

very helpful information,

makes sense now it's explained to me, never had to work on drums before

I used the 280zx booster but kept the stock 7/8 MC for the time being.

I'm confident now all I have to do is push the piston back in & bleed out any air, I'm more concerned about what I did to the handbrake, the metal rod on the underside of the piston that engages the teeth doesn't want to budge at all. The passenger side handbrake gear is working properly though.

Thanks again everyone!

Edit: Another noob question, So just to clarify I can push the piston back in either by rotating the gear or levering it back in with a screwdriver levered against the shoe/brake pad lining?. Just don't want to make things any worse for myself than I already have

Hi Yo Yo

If I were you, I would have a good read of the brakes section in the factory service manual or Haynes manual until you understand how they work. That way, when you get them back together you can be confident you have got it right. (Not that they are difficult, just a bit different to most as they are a single piston, sliding wheel cylinder)

Then, pull the shoes off, remove the wheel cylinder from the backing plate so that you can push the wheel cylinder piston back in (if it has popped out) but only after confirming the seal is soft and looks ok. Otherwise,replace the wheel cylinder, it's only going to leak in a couple of weeks otherwise and then you'll be replacing your shoes too.

When you reinstall the wheel cylinder, clean and lubricate at the backing plate where the wheel cylinder slides and where the hand brake lever sits, as well as the self adjuster thread. This is just general maintenance stuff but may as well be done while you are working in that area, and will allow you to confirm it is all working as it should.

BTW, do you think it possible that your front brakes are seized (not working) which is causing the rears to lock up?

Also, the FSM is available at www.xenons30.com if you didn't already know 

Hope that makes a bit of sense.

Good luck

Mick

Thanks Mick!

I have  copy of the FSM on my laptop so I'll definitely have a read, the picture posted up by oldmates260z in my other thread pretty much clarified it for me but I'll definitely look at the handbrake section as well.

It was just my impatience & general "she'll be right"attitude that got me into the bind I was in.

My next order of business once this is sorted will be to get the front discs machined & replace the pads anyway because who knows when the last owner changed them (if ever )

Makes sense that there could be something wrong up front to cause brakes to lock. Do the fronts lock?

If I were you I would do all the seals in the master and all other brake cylinders. You cannot afford to be without brakes  This car may have sat around for a long time and the seals and bores in the cylinders could be in poor condition.

Cheers

Tim

fronts don't lock, I only hear the back tyres screech & at high speed it has a tendency to fish tail.

That being said the front pads could be glazed over or the discs might be slightly warped (although I didn't feel any wheel shudder on braking) or both so I'll definitely look at the fronts as soon as I clean up my mess on the drums.

after reading the fsm the "metal bar" on the drum I was referring to is actually called the "wheel cylinder lever" I'm confident the handbrake not working is due to the piston pushed out too far, causing the lever to remain stuck. hopefully this fixes two problems in one.

Just to confirm my earlier post. When I suggested the front brakes may be seized, I was meaning the caliper pistons may be seized, preventing the pads pressing against the rotors. I was not suggesting the front brakes may be locking up.

I know I'm digressing but, when I rebuilt my front calipers a year or so ago, I found the brake fluid galleries between the inside and outside caliper halves were blocked with gunk and took a fair bit of effort to clear.

This would likely cause an imbalance between inner and outer pad pressure.

What I'm suggesting is, if you don't know the condition of your brakes, it is probably wise to pull them down to be confident about their condition.

Mick

Were the brakes working perfectly fine before you fitted a second hand ( condition unknown) booster?

Said booster came from a four wheel disc braked car, that runs a different specfication fxed rear line pressure reducing valve.

Send your original vac booster unit off for reconditioning, refit.

You may find problem goes away.

If all things were same prior.

Has car been left sitting for some time?

With open brake hoses/lines to atmosphere? Moisture will get in, and can work its way via thefluid, especially if old, into pistons in rear slaves and front calipers.

As above, pull the fronts off, no need to seperate the two halves to get pistons out.

A fresh set of piston bore seals is probably a good idea.

Then pull rear slaves off, a jammed or cocked piston can cause lock up.

Replace the slave seals.

Clean the bores up, if not pitted with some very fine wet and dry of 2400 grit, in kero.

Thanks Everyone, got my rear drums sorted out. I pressed on the brakes with the engine running so it had full power to the brakes while the drum cover was off, I won't be doing that stupid mistake again! Haha

disassembled the shoes, the piston got stuck at an awkward angle so had to jiggle it a bit to get it free, luckily no damage so just popped it back in & greased up the the other adjustment wheels, the piston came out with so much force that the "wheel cylinder lever" came out of place, no damage which is good but I will still need to adjust the handbrake lever as i still need to pull it up to almost 90 degrees to get the brakes to engage properly.

For the record I have kept the stock 7/8 MC on with the 280zx booster until I get a disc conversion & 4 pot fronts.

I adjusted the shoe settings as suggested by Tim aka oldmates260z. I think the adjustment was the culprit, now that I have adjusted the rear drums properly I no longer have touchy brakes that want to lock in the rear. Huzzah!

I ordered a set of front pads & will get a mechanic to machine the front discs, they might as well put the new pads in for me & a full fluid flush while it's there.

Just wanted to thank everyone here for their input and advice, it's really helped me out and I've learnt a bit more about these awesome machines in the process

The 15/16 master is for a four wheel disk brake equiped car BTW and won't work with rear drums. Better off rebuilding original 7/8 and booster or grab another good booster of another 260Z.

Would not the 15/16th master, when compared to the 14/16th master, just give a slightly stiffer pedal, as it is trying to push more volume through?

The 16/16th master ( 1inch) is certainly a mch harder pedal.

Or,,, s there particular internal valving within the 15/16 ZX master specific for the disc rear end?

The ZX's come with a anti knock off type of valve in the line at the rear.

I've had trouble with the rear drum brakes lockng, solved that by removing the rear line pressure reduction unit, and fitting a adjustable line pressure reducing valve ( Willwood screw knob thing)

Some have used the five position lever type valve.

Both work well.

Would not the 15/16th master, when compared to the 14/16th master, just give a slightly stiffer pedal, as it is trying to push more volume through?

Problem is that because of the bigger bore it creates more hydraulic pressure in the system (more brake fluid being pumped through)

Driving race cars with 1", sure much stiffer pedal, leg muscles get a workout, but, far less pedal travel, ie NOT to the floor, this gives much confidence in the brakes, and with no booster, you get better " feel" through ball f your foot.

Can it be confirmed, does the ZX 15/16 master have different internals to the stock 14/16 Z master?

If they're same, then it is a improvement, in some respects, but not as "hard" a pedal as a 1"

I'm soon to convert a single master single system, into a twin master split system, on a 1966 Datsun.

Have a few ZX masters that could work.

Problem is that because of the bigger bore it creates more hydraulic pressure in the system (more brake fluid being pumped through)

Negative ghost rider!

more fluid yes, more pressure no.

You can not have one and the other.

If you have a smaller master cylinder you push less fluid but can apply more force.

larger master cylinder you push more fluid but with less pressure.

All this is based on keeping the same brake calipers of course.

G'day mate, you say your out west,take your brake booster to Mark at Penrith Brake & clutch, they rebuilt my 280ZX unit for $200

They will also machine your discs for you as well at a reasonable price. If you go to them tell mark that alan recommended them & that you know Carlos from Z car Classics. If you are going to fit bigger brakes up front I'd suggest Hilux units, got mine on E'Bay from a guy up at Central coast way pretty cheap. Also if you fit bigger units up front best you fit new discs as well , got a new pair on E'Bay for $74 recently. If you need any more advice with this give me a call on Mob #0405291467.

                            Regards: Alan.

Thanks for the info & generous offer mate, It's good to know there's a local shop that's familiar with early zeds. I'm only 20 minute drive away from Penrith

Will just see how my last inspection goes tomorrow. It's my last chance for rego before I would need to pay for another inspection.

So far I have flushed the whole brake system & made sure no air was left

Replaced front pads & had a local shop machine my discs

adjusted rear shoes as best as possible

adjusted the booster rod so the pedal wasn't too soft or too touchy.

The brakes feel a LOT better. Less twitchy and more progressive but I still feel that the 280zx booster is overpowered for the stock brakes even with the 7/8 MC which is why I've been having issues balancing it all out.

Unfortunately my stock booster wasn't working since I got the car from Japan so I don't really have a point of reference either.

Plan of attack if I fail to pass rego inspection tomorrow is to get my stock booster reconditioned & have a brake shop iron out the kinks for me

If only I could take time off work & uni this whole process would go a lot quicker

If you fit the 280ZX which is a 9Inch unit as opposed to the 260Z which is a 7inch type you are naturally going to exert more pressure on the standard system you have in place ,If you are going to leave your motor standard your existing brakes will be adequate enough. If your running a L28 ,etc then start increasing your brake system to cope with the added power. Give Mark at Penrith Brake & clutch a ring & he'l help you I'm sure.

                                                        Regards: Alan.

Yeah I bought the 280zx booster & 15/16 MC as I plan on doing bigger brake & rear disc conversion.

This is because I want to do an engine swap & want the extra braking power.

It was just co-incidence that the stock booster wasn't working since I got the car imported so I tried the 280zx booster

I took my stock booster to Penrith Brake & clutch, should be able to pick it up tomorrow & put it back in after work. If this fixes the brake problem then we know for sure that the 280zx booster is too big for stock drums & 2 piston fronts.

All the lads in Group S racing Z's run standard brakes allround, some run next size up master, and std booster.

They work just fine.

No need to upgrade, even with 290 fwhp engines.

Pretty decent power upgrade, and, we run up to 1 hour/25 lap races.

They do get regular maintenace.

Hmmm good to know, I suppose that means I could put more money into the engine/diff/suspension if the standard brakes are ok

This is only ever going to be a road car...just have to get it on the road first haha!

Got the booster tonight so fitted it back in.

I can conclusively say for sure that a 280zx booster is too powerful for stock 240/260z 2 piston front & rear drums.

With the 280zx booster the rears would want to lock up even with moderate pedal pressure.

Now that the stock reconditioned booster is back in it's braking perfectly.

I'll take it for another inspection first thing on sat morning. fingers crossed!

  Out of curiosity how far did you adjust the back brakes up. Also having read your opening address you state that your stock boster was shot. Did you get that one repaired too.             

                          Regards: Alan.