Captain Obvious

I am probably going to be in the market as well and was hoping you would get some good responses here. Not sure why nobody wants to help... :paranoid: Maybe because it won't make the car go faster? How about trying that new turbo carpet. I've heard it can add a few hp.

Round tops or flat tops? On the round top carbs, the body casting used for the front carb is different externally than the rear one. The float bowl castings are different as well, front to back. Mirror image kinda thing. It would not be easy to swap round tops to the "incorrect" positions. On the flat top carbs, they used the same basic body casting for front and rear and just dressed them up differently depending on what position they were intended to be used on. It would be relatively easy to swap the positions of the carbs by moving the linkage and the idle air control fittings.

Anyone notice that the holes in that billet bar are located farther away from the cam than the original bar? I know, I know... If the tubes fall off of your original bar, then it won't matter how close to the cam they used to be, but has there been any discussion about that distance? The reason I'm asking is because I just started a project of recreating my spray bar with a better design, and I was going to make the geometry similar to stock because I wanted the holes close to the lobes.

I've messed with a grand total of two spray bars so far, and one had gaskets while the other did not. No idea if someone had been in there messing around before me though. Here's madkaw's thread you're looking for: http://www.classiczcars.com/forums/showthread.php?23392-cam-oiling-investigation I think the original spray bar implementation is very poorly done. The idea is great, but the implementation was a misapplication of materials.

Steve, It's definitely treasure. Thanks for helping the cause. I haven't measured needle profiles yet, but I will post results as soon as I get the chance.

Yeah, Sometimes Ol' Bessie just won't leave the barn until I give her a quick milking :laugh:

Wow. That's karma. You must've pissed somebody off recently. :paranoid: Hey, out of curiosity, did your new brake cylinder come with new mounting slider clips, or did you have to reuse your old ones? I ask because awolfe over in this thread: http://www.classiczcars.com/forums/showthread.php?44115-Brake-Cylinder-Retaining-Shim is looking for mounting clips and a dust boot. It's been so long since I bought new cylinders that I can't remember if they came with clips or not. PS - If your new cylinder comes with new clips, I betcha he'd love to have your old ones if you were just going to toss them. I offered him mine, but you'll probably have your brake work done before I do.

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.