Captain Obvious

So, back to the original question about the sources of changes to base timing in the 260-280... Belief so far is that the mechanical and vacuum advance functions are the only two sources of changes to base timing. There are no electronic modifications to timing other than the auto-trans cars switching to the retarded pickup once the engine has warmed up. Anyone want to bring up any divergent ideas, or do we stick a fork in it?

To be honest, I haven't actually looked for that wire with my own two beady eyes. It's in the FSM, but I don't know if it actually exists in reality. As for that relay, yeah, the same relay controls EGR and spark timing (on the auto). In fig EE-60 and in the text above that figure on page EE-27 (Engine Electrical) they refer to the same relay as the "Advance Control Relay". Same thing goes for fig EE-79 on page EE-34. They call it the "Advance Control Relay". The physical location of the relay is shown in fig ET-51 on page ET-26 (Engine Tuneup) and it also mentions that the same relay controls EGR and spark timing functions. So, why am I calling it the "EGR Relay"? Because if you look at the wiring diagram (the whole car wiring diagram - both manual and auto), you'll see the same relay down in the lower left hand corner (just like it is in the car) and it's referred to as the EGR Relay. As shown on page EC-16, that relay has two sets of contacts in it, one normally open, and one normally closed while the coil is controlled by the water temp switch. The normally closed set controls the signal going to the EGR solenoid valve, and the normally open contacts control spark timing. It works like this... When the water is cold, the water temp switch is open, and the relay coil is not energized. The NC contacts are closed (EGR disabled), and the NO contacts are open (use advanced timing pickup). When the water is hot, the water temp switch is closed, and the relay coil is energized. The NC contacts open (which enables EGR), while the NO contacts close (which tells the ign. module to use the retarded pickup). I know how it's supposed to work, and I still find that chart on EC-16 confusing! One thing that helps is to know that the picture shows the configuration of everything when the coolant is hot.

Man... That's cold. You know what's funny? I've gathered all the parts to convert my 74 to the 77-78 style rear brakes because I think its a better design. Next time I go into mine, it's going to be to pull off all the 74 stuff and replace it with 77 stuff! I don't know when that's going to be, but if you're still looking for pre-77 clips by then, you're welcome to mine. Once I change over, I'm not going back! I can hear it now... "Yeah, the stupid P.O. pulled off all the original brakes and replaced them with parts from 77. What an idiot!"

Excellent! I love it when a plan comes together! I haven't looked, but I'm positive there must be a "gross cable slack" adjustment in the e-brake mechanism somewhere. Either at a yoke somewhere, or right at the handle you grab. If it holds the car now, it sounds low priority, but I'm sure it's adjustable for starting slack. Has to be...

Yes, the dwell function is controlled by the ignition module. Got it. Someone has to make sure you don't burn up the primary side of the coil while still allowing it to build up enough field to get a good spark when you break the primary. Points do that mechanically in the 240, but in the 260-280, that function is part of the ignition module. Now when you're talking about the GM HEI module and say that it works as long as you don't need the pickup coil switching function, you're talking about the dual pickup distributors and the ability to switch timing between those two different pickups, right? I don't know how temperature comes into it for the 280's, but I can tell you how the 260 works: Manual-trans 260's have a single pickup distributor while the auto-trans 260's have the dual pickup distributors. In the auto-trans 260's with the dual pickups, the ignition module uses the signal from the advanced pickup when the coolant is cold but then switches over to the retarded pickup signal once the engine has warmed up. There is a temperature control signal derived from the coolant temperature switch that comes through the EGR relay and tells the ignition module that the engine has warmed up. On the manual trans 260's, they have just one pickup although the same temperature control signal derived through the EGR relay still goes to the ignition module, I don't know what (if anything) the manual trans ignition module does with that signal. That, in fact, is one of the things that got me started thinking about this stuff in the first place... I've got a manual trans car with a single pickup distributor and I'm wondering what, if anything, does the ignition module do with that temperature signal. If they aren't making any changes to the timing advance based on engine temperature, then why does that signal go to the module at all? They're already using a different wiring harness for the auto trans cars, so why did they bother to include that wire to the module if they aren't doing anything with the information? In other words, if the timing on the manual trans 260s doesn't change with temp, then why do they bother to tell the module that the engine has warmed up? Does that wire even connect to anything inside the module? Anyone ever opened one up?

Wait a minute... Do you mean "firmer" or "higher" pedal when you pump it? "Higher" after you pump it would be too much travel in your rear brakes. "Firmer" after you pump it would be air bubbles still hiding in the system somewhere. Here's what I think you're talking about: You hit the brakes and the pedal goes closer to the floor than what would be considered "normal" before it reaches end of travel. But once it does reach end of travel, the brakes work fine and the pedal feels firm and won't travel much more than that point. In other words, the pedal stops abruptly at end of travel... It's just that the end of travel is too close to the floor. Then if you let the pedal up and then hit it again quickly, the pedal still stops abruptly and feels firm, but now stops higher off the floor than it did the first time you hit it. Is that what's going on? Also, are you were having the adjuster sticking issues on the new side, the old side, or both? I apologize for asking so many questions. I just want to make sure we're chasing the right demon.

Actually... Now that I think about it, I'm not so sure the retaining slider clips come with a new cylinder. I've done complete new cylinders in the past, but I don't remember if I had to re-use my old rusty clips. I know the dust boot should come with the new cylinder, but I'm not sure about the clips. I've got some pics of new cylinders downloaded and I don't see clips in the photos. Would suck to buy whole new cylinders for those parts and then STILL not have usable slider clips. :disappoin

Thanks guys. Yeah, I don't know anything at all about the ZX's, so I probably should have excluded them. Although, since you can pretty much drop-in some of the ZX distributors and modules into earlier cars, I suspect that not all of the ZX's have computer controlled timing. Not sure if I've asked the question correctly, so at the risk of beating a dead horse, I'll do it again. On the 260 and 280, there's a pickup in the distributor that sends a signal to an ignition module near the passenger's feet. When the ignition module near the passenger's feet sees the pulse from the distributor it cuts the current to the primary side of the ignition coil which causes a spark. That's all the ignition module does, right? There's no timing modification done in that module adding any additional advance or delay to that spark, right? It sees a pickup pulse - It breaks the primary circuit. That's all it does. Some propagation delay is inevitable, but that prop delay is fixed and does not change on purpose based on any RPM, vacuum, or temperature conditions. And just for curiosity, since we're talking about it... In the automatic trans modules, it switches which pickup pulse it pays attention to once the engine has warmed up, but other than that, the manual and auto are identical.

I'm not an ignition guy and I'm having a hard time even figuring out how to ask this question, but here goes... What are the sources of changes to base timing in the 260-280? Is there any spark timing control done in the ignition module near the passenger's feet, or is all the timing control done in the distributer with mechanical and vacuum advance? By that, I mean... I know they use the typical weights-n-springs mechanical advance in the distributer, and I also know they use a typical vacuum advance with an actuator on the side of the distributer, but is that it? Are those the only two sources of advance or is there additional RPM derived electronic controlled advance done inside the electronic ignition module? And no, I'm not talking about temperature switching between the two different pickups in the auto transmission cars. That's not RPM related.

Haha! Don't quote me on that one inch. It's been years since I've messed with the adjuster in detail. Let's say "around" an inch, OK? But... Now that I'm thinking about it... Is this on the brand new wheel cylinder, or on the old one? Seems very odd that a brand new, clean one would have any issues spinning the adjuster gear. If it's the old one, then I suspect you've got grunge in the threads on the hidden side of the adjuster wheel. If it's the brand new one... Hey... At least now you have a strong bubble-free stream to the rears now!

I don't think Rock Auto has either of those unless you buy an entire wheel cylinder. I don't think they offer the dust boots or mounting slider clips separately. I have seen them recently though somewhere... Probably ebay. Pretty sure about the dust boots. Less sure about the mounting sliders. Stupid design. :stupid:

I agree. Sounds like more than one issue at play here. Let me recap to make sure we know where you are at now... Originally you had brakes that went to the floor and took 2-3 pumps to get any pedal at all, and even after you got some pedal, it seems the braking was happening only on the front axle. In addition, you couldn't get fluid out of the rear cylinders when bleeding. Then... You bled right at the master, and again at the corners. After that bleeding, there is now a strong bubble-free stream of fluid out of both front and rear corners when bleeding, but you still have brakes that go to the floor on the first hit and require pumping once to get firm pedal. Is that where you are now? As for the rear adjusters, I really don't think there are any stops on that adjuster wheel. You're doing the adjusting with the drum off? If you keep turning it and watching the shoes spread, you will eventually reach the point where the adjuster stalk completely unthreads from the cylinder. From memory, I believe the threaded stalk is about an inch long, so you should be able to screw that adjuster wheel out about that much, and there is NO WAY you should be able to get the drum back on with the shoes adjusted out that far. If you can, then there is something seriously wrong somewhere.

You should be able to lock up the rear drums with the adjuster, and the adjuster wheel should not be difficult to turn until that happens. It's been a while since I've been in that deep into the pre-77 brakes, but I believe if you keep turning, and turning, and turning... And if by some weird set of improper circumstances occurs the shoes don't contact the drums... You'll eventually wind the adjuster stalk completely out of the cylinder. I don't remember any stops on that thing anywhere. You know that the two sides adjusters rotate opposite directions, right? "Bottom to top" should tighten the shoes. Can you hear the adjuster lever clicking over the teeth in the wheel as you turn it?

No. I'm with AxtellZ. Sounds like a master cylinder issue. Sounds like it needs to be primed. That, or it coincidently failed at the same time as your rear cylinder.

As long as the aluminum of the cylinder itself isn't pitted. The pistons came with a corrosion resistant coating of some type, and yours is obviously gone. I believe you can get new pistons, but once you pay for that, you might as well just have replaced the whole thing. So you're going in after this AND spindle pins? Now there's a thankless job!

Yummmmmmmmy! You're not thinking you're going to rebuild those puppies, are you?

I'm not much for the body kits, but I gotta say that I like the front profile of that.

The small one.

I'm sure you already know this, but just because the fluid level in your master cylinder is low, doesn't necessarily mean that you have a leak. At least not with simple disks like in the front. The volume behind the caliper pistons increases as the pads wear, and that extra volume is taken up by brake fluid from the master cyl reservoir. With rear drums, I guess it's not that clear... The rear wheel cylinders should always relax to the same position, so there shouldn't really be any change in the reservoir level at rest, but if your rear adjusters weren't working properly, that may not have been the case. The rear pistons may not have been pushed all the way "home" and you may have used some of the fluid from the tank to take up the extra volume. I know, I'm reaching here, but that's all I got. (On edit): Actually, thinking about it some more, the rear cylinders push directly on the shoes, not on the adjuster mechanism. So the pistons should not be pushed home as the shoes wear. The adjuster mechanism should hold the shoes apart, so I guess the same situation exists in the rear as the front. The brake fluid in the master cyl will drop as the shoes wear. What you could end up with if the adjusters aren't working correctly is excessive pedal travel. Only other info I've got would be that I've seen the same white crumbly corrosion on aluminum brake parts in the past. My theory is that it is a slow leak, and the brake fluid (being hygroscopic) is attracting moisture from the atmosphere and that combination of brake fluid and water is causing the aluminum to corrode. In any event, with all the issues you did find, it sure wasn't a wasted effort!!

I agree. Must just be a mistake in the docs. Sure is a good thing that I don't read directions, or I may have followed them!

You're talking about the pre-77 rear cylinders, right? They're very different than the 77-78's. I'm sure that spring you're talking about is supposed to fit narrow end snugly around the locating boss on the back of the piston and the wide end pushing against the inside of the cylinder. You're saying that all the pictures show that spring installed wide end against the piston???

Actually the rear disks with the parking brake that would stick on was not the "mini-drums inside the rotor" style. They had the parking brake function built directly into the caliper. The concept was sound, but they used some stupid roller bearing on the parking brake pivot shaft that would rust in place to the shaft. Hope it turns out that your flare isn't leaking. Out of curiosity, you originally started this because you were chasing a low fluid level in your master cylinder. Did you ever find the smoking gun for that?

Wow. Three test parts and you're getting good doubles. I know who I'm callin' next time I need a hardline replaced! Glad you got the adjusters figured out. Lube em up and, keep them dry (backing plate boots in good shape) and use the parking brake frequently enough to keep everything mobile. Doesn't have to be every time, but more than once a month. I've been inside lots of drums over the years, and I gotta say that the late 280's are one of the better ones. It's the simplicity, and the room to work. Don't hate the drums... As a matter of fact, I've had other cars with rear disks that I was actually afraid to use the parking brake because it would intermittently get stuck engaged. It was a bad combination... Steep driveway, manual transmission, parking brake that would stick ON, and a very worn engine with barely any compression left. Do the math.:paranoid: It was like Christine.

Phew... Right before I hit the post button, I realized how long that post was. I was worried that I was off track. When did I become so wordy...? :tapemouth I've had a bunch of flaring experience also, and it's a pain. Thankfully, I've never done enough of it to warrant buying my own flaring tool set, so I borrowed a double flaring set from a buddy and found that the mandrel that came with the cheap double flaring sets is crap. It didn't fit well into the tubing and was almost impossible to get decent results. I finally gave up and turned my own mandrel that was tight fitting into the hardline tubing. Results turned out much better. I would hope that the more expensive flaring sets have better accessories. Even so, I bet there's significant finesse that must be learned before getting good results. Make a complete single flare first? Make a partial single flare first? Make half the bubble flare and then rotate the tubing 90 degrees before finishing it? Now that you've been through it, you know the drill.