Problem Solved

MR 69ER · October 04, 2003, 09:33:23 PM

G'day people I've got a 69 big block roadster & i've got a problem with my braking system. After bleeding the complete system rear first then the front I get a good peddle for about 500k's then loose it. When I say loose it I mean all the way to the firewall the brake warning light comes on then eventually they pull me up. I have replaced all four calipers with complete new ones & also replaced my master cylinder with a new one but some how air is getting into the system. If I bleed the brakes they come good again and so on. No I am not cooking the brakes and I am using the right brake fluid, I have also replaced all the fluid in the brake lines when I had the new calipers & master cylinder put on. If anyone can shed any light on my situation I would appreciate it as I am getting sick of contiually having to bleed the system every couple of months.
Thanks
Steve:20:20:20:20

George80ONE · October 04, 2003, 10:05:06 PM

Hi Steve,
A question. When you have to re bleed the brakes, do you get any air out of the lines? If so, you are not fully bleeding them. My mechanic bled the rear first, then the front and then the rears again. If there is still air in the lines then you can jack the rear of the car up and this will force the air when bleeding the brakes, to the highest point which will be at the rear. So the last bleed should be at the rear.
Also, check that the discs are running true. One of my problems with my brakes was that the discs needed machining. Over a long distance, the uneven movement against the rear calipers was causing problems.
Hope you can fix the problem.
George.;35

MR 69ER · October 05, 2003, 08:47:20 AM

G'day George
Yes we do get air out of the lines and we do the back again after we have done the full cycle and the peddle comes back really good but like I said after a good hundred k"s I can feel it getting worse & worse and then eventually nothing at all. I have also had all four discs machined (which I forgot to mention in my earlier thred) so I dont think it could be the discs. I have heard though that if your rear wheel bearings were not the best that this could be creating a problem simular to what you mentioned, this is known as piston slap but one would think that with brand new calipers and no evidence of leaking brake fluid that the rubber seals around the piston would be doing their job and not letting air in, I am at a loss.
Steve:20:20:20

Brutus · October 05, 2003, 10:44:10 AM

Steve...I'd suggest you may have far too much runout in your discs which is causing your brakes to pump the pistons.
Check out this thread from another forum which should shed some light on your problem.
http://www.digitalcorvettes.com/forums/showthread.php?s=&threadid=3490

MR 69ER · October 05, 2003, 10:58:22 AM

Brutus all that makes sence but wouldn't the piston seals prevent air fron getting in and also would there not be traces of fluid leeking?
Steve:20:20:20

Brutus · October 05, 2003, 11:20:19 AM

That would seem the obvious thought, but sometimes physics like tp play nasty mind games with normal thinking people. All I can suggest is that you check your runout and see where that leads you. Saying all this tho, I must admit to not having done my own yet, but I'll be checking them out as soon as I lay my hands on a dial indicator.

Bob

MR 69ER · October 05, 2003, 04:37:27 PM

Thanks for that Bob I'll be checking them next chance I get. Once I too get hold of a dial guage.
Steve:20:20:20

Twin_Turbo · October 05, 2003, 10:02:12 PM

The V lip seal is designed to keep fluid from leaking out under pressure, unfortunately it's great at letting air in (when the piston moves yet there's no pressure on the fluid side of the piston to keep the air grom getting in)

This seal acts like a piston pump and it SUCKS! IT's a the source of about all caliper related problems, not only does the trapped air make your pedal feel soft, it also means moisture gets in, the fluid deteriorates and the water wills tart to boil when you're on the brakes, also it will corrode all the inside of the caliper causing sticking pistons and even more leaks.
To fix it check rotor runout AND bearing play on the wheels involved. If it's the rotor, shim it as good as you can and if you can't get it spot on have the rotor trued. Replacing the seals in the calipers w/ o ring design stuff is a very good idea.

77CVT · October 06, 2003, 09:15:14 AM

Steve - I feel your pain! I went through this for years and there is only one thing to check and that's the runout with the disc bolted up on the car. Were the disc's machined on the car? If you can get it around 4 thou that's good but shoot for under 8 thou. I ended up shimming (which is not recommended by others) the fronts on my old '77 prior to the Canberra Convention. By the time I got down there my pedal was to the floor! ;eek It was the rears that were the problem then.

I took the springs out from behind the brake pistons on the fronts and after the convention I took the rears out and my pedal was fine from then on. Don't let people fool you into thinking taking the springs out is a no-no! :b4

C3 brakes work great but are a real PITA at times! O ring seals are the way to go but you MUST fix any runout problem first or you are wasting your time.

George80one had a problem with his rear hub not running true so it is not always the disc. That is why I shimmed my fronts.

Good luck!

PS. - Are you going to Bathurst again this year?

MR 69ER · October 06, 2003, 10:07:27 AM

Thanks for that everyone & I will be checking the run out on the discs very soon. Yes Chris I am heading up to Bathurst again this year but this time for a different cause. We (Corvette Owners) will be doing the driver parade lap before the big race on Sunday morning. YEAH HA. As it is our 50th Anniversary they wanted Corvettes to do the lap this year instead of the traditional Mustangs. There are about 15 cars from Sydney heading up early on Sunday morning with the rest of the group (About 40) comming from the Canberra club. Hence trying to sort out my braking problem before streaching the RED ROCKETS legs down Conrod should be a great day. Are you making the trip again?:20:20:20

77CVT · October 06, 2003, 03:47:32 PM

Yep - I'll be there. I will definitely be looking for you guys on Sunday as you will no doubt have the chicky babes to take around as well! :22

Brutus · October 06, 2003, 05:06:09 PM

Typically I have to work over the whole Bathurst weekend this year.....hell, I even have to work Xmas day this year too!
Oh well maybe next time.:b2

Bob

MR 69ER · August 14, 2004, 08:01:14 PM

Wow I had to pull this one out of the archives. At long last it looks like my braking problem has been solved. What was it I know is the question on everyones tongoue. Well I can't narrow it down exactly as I did 2 things at the same time and now the problem is gone. Firstly i renewed the rear wheel bearings and had the discs machined again but the problem was still there. So although the calipers where re-cores I questioned the quality of the job done on them so I put new seal kits through both of the rears and re-assembled & put them back on the car. Whilst trying to bleed the system I could not get the outer nipple on the left rear to seal off. Although it was not leaking fluid I could hear air in the bleed hose when the pedal was released. After examining the bleed nipple I saw that the air hole at the bottom of it was squashed & obviously not sealing up properly. I got another bleed nipple, it sealed, got a good peddle & have done about 1000k's & the peddle is the best it has ever been.
Like I said I don't know what did it either the seals or the nipple but I have bled the brakes before myself & i'm sure I would not have missed the dud nipple. Anyway it is nice to put this to bed & hope that all my explorations & the end result will help someone else.
Again thanks for all your input.

Cheers
Steve:20:20:20:20:20:20:20:20:20:20:20

77CVT · August 16, 2004, 09:20:34 AM

Happy days!

Great to hear things are better. Sounds like you had as many troubles as me and my '77! The rear hub is a cause for excess runout - George in our club had his rear hub machined and it fixed his problem. I had trouble with a bleeder nipple as well.

I had 10 thou runout on the rear (4 thou in front) before the Canberra convention and by the time I arrived I had hardly any brakes! It doesn't take much.

I'd say both things contributed to your problem.

MR 69ER · August 16, 2004, 08:22:42 PM

Yeah it was a bit of a tricky one but in the end got the bugger. My last option if all this didn't work was the proportioning valve as there was no other may for air to be getting in, but i didn't have to go there. Again thanks for all your advice.

Chris are you comming down for Fox? it would be great to see you on our turf, Gary mentioned something about you might be so anyway I will leave it up to you. Also don't forget to mark you spot on the hill at Bathurst this year. I want to see a massive sign that says IF YOU WANT TO REV IT CHEV IT and I promise you i will bag them up just for you, but only if i see that sign. So get you wife & kids working on it out in the garage NOW.
The 5 girls, 2 men, 3 dogs, 1 horse & 4 cats that they put in the car might not all still be with me at the end of the lap but heck, isn't that what they call SCRUTINERING.

Cheers
:20:20:20:20:20:20:20:20:20:20:20