[PontGuy]

Mike,

I flipped back through the posts and yes, yours do seem to match up exactly with the ones that gave me so much trouble. They were not leaking externally, but seem to allow air back into the system when the pedal is released. They probably work fine for drum systems and if you have a residual valve on a disc setup. But not with the stock 69 disc setup which I am sure did not come with a residual valve.

The Napa ones do not seem to let air in so they are a big improvement. But, after a couple of weeks, or months, or years of use I wonder if this will still be true. There is no way to tell that they are a problem other than air getting into the rear lines. So the residual valve still seems like a good idea.

Also I am not sure if the Napa parts are the best out there, but they are definitely better than the ones we started with.

Walt

[Shiny]

Sounds good Walt, but if I were you I wouldn't think too hard about about adding a residual pressure valve unless you start having trouble. I have been thinking I was crazy for all these months as there seems to be no-one else with the same grief. This tells me it is not a common issue.

I am still wondering, though, why my 70 repair guide shows residual pressure valves in the M/C on drum/drum cars but does not mention it being anywhere in the rear system of a disc/drum car. I still want to believe the residual pressure function was somewhere else in the system, regardless of how it was implemented.

Or maybe the M/C on a drum/drum car was more likely to "suck" back on the rear system and it just wasn't needed on a disc/drum car because the M/C was different?

Were the rear cylinders (and in general, the whole rear brake design) the same on a drum/drum as on a disc/drum car? I would think they were, so this whole topic is still a point of curiosity for me.

I am now also curious about the difference between your new cylinders and the leaky ones. I wonder if your new ones are a newer design with the "expanders" on the piston cups? hmmmm

Regardless, I plan to follow your lead when I am next re-united with my car.

Mike

[PontGuy]

I think that this problem may be more common than everyone realizes, at least on the early cars. I am not convinced that the rear brakes on my 69 ever really worked as intended. The brake system stopped the car OK, certainly better than the old 4 drum systems, but there is absolutely no sign of wear on the rear drums which tells me the front discs have always done most the work. Throw in wheel cylinders that are not up to original factory standards and so allow a bunch of air in, and it could take it over the edge.

Also remember that factory discs were not all that common back then. I've owned several Lemans, a GTO, and a Firebird from that era and this is the only one with factory discs.

Hard to believe that I started with a brake system that was completely shot, replaced everything, and then had problems with all the new stuff too. I don't know what I would have done without this forum.

Walt

[Blk 76]

Glad to hear that you have your brakes working. I was getting alot of air at the rear cylinders also and replaced the master/rear cylinders and now my brakes work good. I had thought more of my problem might have been the master but now you have my wondering if it was the cylinders all the time. I really do not care now because it was worth the cost of the master and wheel cylinders to have good brakes. The wheel cylinders were from Auto Zone and the new ones came from O'reillys auto parts. I need to replace the rear cylinders on my Tran Am and I will get them at Napa or O'reillys

[Shiny]

Blk 76 - yes, the rears were the last thing I suspected since I had replaced those, the rear hard line, and the rear flex line when I first started converting to front disc. Pretty humiliating to think how I replaced every other component, including two master cylinders, if the rear cylinders were the problem all along.

Walt - I have to believe the issue was my unknowing purchase of "leak-prone" cylinders and not the original design. The cars of this vintage that I owned in my younger days never had disc brakes, but they all stopped good enough. My whole problem started when me and my son drove the car home after we bought it and the manual drum/drum brakes were so bad we were scared. The first thing we did to the car was re-do the brakes. After we did this, the car still didn't stop worth beans, so we decided to upgrade to discs on the front. I think I assumed they were never going to work any better. Now I think the design wasn't the problem, it was because they weren't working right after I replaced them and I was too ignorant to recognize it! Oh well, I know the discs will stop the car better (eventually), so I'll console myself.

As for this forum, I have to admit I am a little disappointed I didn't just post a cry for help and get told the solution. This has been my experience with every other issue I have had. This has been a challenge, to say the least. I would not have stuck with it, however, without the support, and most importantly, other people like you that had similar problems and could problem-solve together. That part is huge.

[My442]

How are you bleeding the brakes?

I always use a MityVac that applies a vacuum to the wheel you are bleeding.

Start at the passenger side rear, then the drivers side rear, then to the passenger side front, and finally to the dirvers side front.

I would look closely at the front brake hoses - sometimes the copper washers don't seal.

If you pull the master cylinder off, check the inside of the vacuum booster for fluid.

That is the only other place it could go if you do not have any leaks in the lines or hoses.

[Shiny]

My442 - thank you for the suggestions.

This is a long long boring story, but there are a couple of us here that think the problem is air being sucked into the rear cylinders when the pedal is released fast, without any fluid leaking back out. Sounds far-fetched, but is the only thing that explains what has been experienced and is apparently more than just folklore.

I do appreciate the suggestion on bleeding, and wish my problem had been caused by that.

[PontGuy]

I finally got my car out of the garage this afternoon!!!

First the brake update- they work perfectly! The pedal is good and hard and the car stops fine. The wheel cylinders did the trick. My brake light is still lit but now I am sure that the switch is just stuck. I need to figure out how to free it up and get it centered, but it is just one item in a long to do list and it won't stop me from driving.

Pulling the car out of the garage the first time was a bit scary. I just replaced/rebuilt everything- engine, trans, fuel system, wiring harnesses, brake system, suspension bushings, exhaust system, and the list goes on. So I wasn't really sure what was going to happen. I have a long list of things to work on, but the car drove fine and the combo I put together will be exactly what I wanted once I get all the bugs out. I got no lack of attention during the maiden run, of course having the hood off probably didn't hurt...

Walt

That's me in the pic with the big grin on my face. I just pulled it out of the drive for the first time and gave it a little gas, and the big engine broke the rear tires. Yeah, that's what its all about!!!

[Old Goat 67]

Hooray for you guy!

[Shiny]

Yoohoo!!! that's gotta feel great! probably explains that big grin !

I'm happy for you and glad to hear it went well. You must have covered a lot of details to have it go so well. Nicely done!

And, yes, I'm really glad to hear you have brakes.. way to go !!

[PontGuy]

Thanks guys. After all the trouble with the brakes I was actually more worried about them than anything else, but they turned out to be a non-issue. I still have plenty of debugging and tuning to do before putting the hood back on and declaring the car fully functional though.

If I ever figure out how to re-center the switch I will post on it. I have some ideas...

Walt

[Shiny]

Walt - After all I have been through on my brakes, it seems as if replacing the rear cylinders is the first thing I should have tried. Who knew? I'll be home for Christmas and will try to squeeze in some car time. When I left, the car was stopping pretty well with the residual pressure valve, but I am definitely swapping the rears now too.

I don't know if the switch interacts with the metering or proportioning function in the valve, but you may want to fix it before you find out the wrong way. The techs at Inline Tube told me it can interfere with the bleeding, so who knows? Let us know when you get that figured out.

[Brad_bb]

Shiney, did you ever get more done? I'm waiting for that Hooray post, where you tell us problems solved. Don't give up man. "Knaw on it, son" -from Cool Hand Luke

Gosh, reading this post makes me think twice about changing over my 64 gto to disc/disc! I've been trying to learn about what parts are available for my changeover, and it's not easy with varying info from a number of sources. I like the fact that these retro fit kits use off the shelf parts from later vehicles, but unfortunately many companies show a pic of their kit and don't tell what caliper, or rotor they are using(the application like a 99-02 Astro Van AWD caliper). I'm all confused about what combo valve, MC and booster, and possible adjustable prop valve, to use. Oh well, I'll do my research, see if I can get a successful install, and then write about all my findings on these forums.

[PontGuy]

Brad, I wouldn't get discouraged- having good brakes is well worth it. And I really don't think that most people have near the problems that Mike and I did. But sorting out brake issues can be a real pain and hopefully this thread has helped others out.

By the way my brakes are still working great, though I am still waiting for the switch to magically center itself. It is on my to-do list but I am concentrating on other areas right now.

Walt

[Shiny]

Brad,

Thanks for the encouragement. I won't give up... I might not eat 50 eggs, but I will fix my brakes !

You should not hesitate to do the swap on yours. The odds of it being as painful as my experience are about 2 (Walt and I) out of 1000 (other people on this forum that never suffered this problem). You have a lot of satisfaction to gain, and it really is straightforward.

I posted Walt's photo again to summarize the knowledge we gained - rear cylinder style on the left is good, the style on the right is pure evil.

As far as my hooray, I am close, as I do have brakes now, but I did it by adding a residual pressure valve bandaid and will whoop louder when I finally exorcise the rear cylinder demons. It was too cold when I was back home at Christmas, but I will get it done some day.

[Shiny]

I am opening this up again (like an old wound) because I am finally motivated to replace the rear cylinders in my car that were letting air suck back in.

I had cobbled up mine by installing a residual pressure valve, which worked, but I never trusted it so was on a do-over. Now I'm not so sure.

If you read the saga below, PontGuy had solved the same problem with a simple cylinder exchange.

I went out and bought a pair of the 37024 cylinders from NAPA about a year ago, same as PontGuy.

I was convinced they would have cup expanders behind the rubber cups, but before I put them on, I opened them and found they do not.

^#&*! I said.

So then I looked closely at PontGuy's pics, and his say "Assembled in ???", mine say "Made in China". His casting has a number 29452-S and "USA". Mine have nothing in the casting.

Before I think these are better than mine, can anyone tell me:

1. Should these rear cylinders have metal cup expanders or spring expanders like in a seal?

2. If so, where do I get them?

I looked at Inline Tube's catalog and they had a picture of inner springs with cup expanders on each end, so I thought "eureka" and ordered them. They showed up today and the picture is still there, but the expanders are not...

^#&*! I said.

3. Should I expect these NAPA cylinders to be less prone to sucking air than the ones I have? How can I tell? Is there a way to find out? Pull a vacuum on them?

Thanks for any info

[PontGuy]

Wow, this is like opening up a very old wound!

My "made in USA" Napa cylinders have worked great, and its been 3+ years now.

I swapped the original rear end out with a 12 bolt about 1-1/2 years ago and re-installed the same cylinders. A few minutes of bleeding and back to perfect brakes again. Other than that I have not done anything to the system. I even have enough faith in the brakes to run the car down the 1/4 mile now.

I never did get the distribution block switch centered though...

[Shiny]

Hi PontGuy

Good to hear from you, and really glad to hear your brakes kept working.

Sorry to revisit this but as you can tell, I am understandably reluctant to assume these newer parts will be any better than the ones I have since they are not the same casting nor origin as yours.

Any chance you had them open and can confirm or deny presence of a metal expander behind the cups?

I attached a diagram of what I was expecting to find in the NAPA cylinders but did not.

I have no idea if they are supposed to be there, but I would expect the purpose was to reduce the chance for sucking air back in.

[PontGuy]

Good to hear from you too. Been a long while since we worked through this problem. Since then my car has got a new interior, the dash and console restored, exterior bodywork and paint, and various engine upgrades in addition to the new rear, wheels and tires. But I have not touched the brakes.

No I never opened up my NAPA wheel cylinders so do not know what is in them. They could have cup expanders or maybe just tight tolerances on the pistons. Either way they work perfectly and I hope they will last as long as I have the car- which should be many years.

My first thought is just to try the new cylinders. The difference when bleeding was very obvious compared to the cylinders that didn't work. The fluid I got was perfectly clear (not milky) after getting the big air bubbles out. But since you have the residual valve installed you should get clear fluid even if the cylinders are not really right. How hard would it be to remove/bypass your residual valve in such a way that you can re-install it without difficulty? Bleeding and testing without the residual valve would be the true test.

[Shiny]

My goal was to get rid of the residual pressure valve while I was replacing my booster and relocating the combo valve... basically trying to reduce the extra connections and cleaning up some of my "creative" installation.

So just replacing the cylinders without knowing they will work sounds like a chance to start all over.

I went back to my 70 shop manual and pulled the attached.

Says the original master had check valves, the original rear cylinders had cup expanders. Now, my replacement Disc/Drum master has no check valve, the supplier could never confirm the repro combo valve had a rear check valve, and the NAPA cylinders I have do not have the expanders.

So I'm not eager to find out I need them again...

Anyone know where to get rear cylinders or rebuild kits that actually have cup expanders like shown in the picture from the manual?