Gale Banks 80'

Before replacing the Master Cylinder again I would do my homework on the Bore size, who made it and who rebuilt it. I would also check the above thread on the leverage that the Brake Peddle has for a Non Power Brake car. If You think You are headed for Wilwood You may start with one of there's. I have never herd of Lonestar, but I see they are a major wholesale supplier for some of the Corvette Vendors. If Trackdogg is a dealer they must be good. If You still have there sleeved one why not re seal it or have them re do it. I'd like to see the Seals and to why they failed so soon. Its just something that needs to be done on a Corvette, measuring the run out of the Rotors when ever doing Brake work. The only time I wouldn't was if I still had an original Rotor with the Rivets still in. Those are getting far and few between.

Gale Banks 80'

I would do a quick test of the Master Cylinder. Mark how far down the Brake Peddle is from the firewall when depressed as far as it will go. Then I would open all 4 bleeder screws at the Calipers. Will the Brake Peddle now move further, closer to the firewall ? If not You have something mechanically wrong between the Brake peddle and or the Master itself.

ajrothm

When the brake pedal is pushed down pretty hard (way more so then you would normally to stop the car), I'd say there is about 2-2.5" between the pedal and the floor... Enough room that I can put my left foot under it when pushing it down with my right foot.... Crack a bleeder at the same time and the pedal will drop all the way to the floor.

***NOTE***
When I push the pedal beyond the stopping point I mentioned, if I FORCE the pedal down, I can get it pretty close to the floor... But I mean this is like leg press type pressure. Not sure if its the MC bleeding down or the calipers all swelling seals or something but... In driving situations, it would have locked the rear brakes up way before hitting the pedal this hard.

I'll pick up the new MC tomorrow and take measurements and post pics of it. These are NEW MCs I am using, not rebuilds.

ajrothm

So after looking into this a bit, it seems my front rotors are either originals, or they are original to the hubs they are mated too as the rivets are still there. I have no idea if they are MY original rotors...I kind of doubt it with 157k miles and the rotors in this nice of condition.

I'm going to buy a dial caliper setup and measure the run out as now I am curious.

When I picked up my trailing arms from Tracdogg, he already had the rotors on the hubs.... well, a couple months ago when I changed that first rear caliper, I pulled the rotor off to clean it up...I didn't pay any attention to the orientation, I just slapped it on. So maybe there is a chance I put it on in the wrong spot and has excessive run out...if its acting up, it IS the side I believe causing the pulling problem.. Only its the rear. The pulling problem began not too long after replacing the left rear caliper so... Maybe I'm on to something.

I definitely need to measure run outs...

OMF

I was sitting on the can flipping thorugh the service manual ( don't you guys laugh....I know you do it too ) and came across the troubleshooting section..... so, remembering your problem, I looked what it said for pulling brakes. One of the things said to check for loose calipers.....another thing for you to check.

BLUE1972

Just a thought
how close are the brake lines to the headers... a heat issue?

wcsinx

A blown MC piston can imbalance pressure front to back not left to right.

ajrothm

Yeah I'm just changing the MC because its never really had that firm of a pedal since this MC went on 5 years ago. Its a lifetime warranty deal so I figure while I have the proportioning valve off for cleaning, I'd change the MC too. I know it won't help the pulling problem.

mds3013

On the rear rotor, the parking brake adjustment access holes should indicate the orientation. My '77 started having this similar braking imbalance recently also. If I find the answer I will report. Good luck with it mike...

Kacyc3

if this started after replacing the left rear caliper, have you tried replacing it again?

ajrothm

No I haven't but the thought crossed my mind. I did inspect it closely last week and it's not leaking and everything seems normal with it.
Got a good bleed on it.

ajrothm

Round 6

The Saga continues..

*Action item 1

Today I pulled off the MC, while it was off, I disconnected the brake lines at all 4 calipers and blew brake cleaner from the front MC out line thru the proportioning valve and out of both brake lines, plugging them one at a time to force more pressure thru the opposite line.. I did this on both lines, verified good flow of brake cleaner thru both sides, then blew it all dry with compressed air. I performed this act on the rears as well, verified good flow from both rear lines, blew em dry with air. Reconnected lines to the calipers.

*Action item 2
Install new MC, I bench bled it until there was no air bubbles and nearly rock hard on the plunger. After installing it, I decided to try a trick I saw on youtube... The vid recommended jacking the rear of the car up to get a certain level on the MC.... After doing this, SURE ENOUGH, I got more air out of the rear MC section... I was shocked at how much additional air came out when doing this. At this point, the pedal is rock hard...



Get the middle bubble to the rear of the tube on the level...

This works, no doubt about it.... Learn something new every day.

*Action item 3
Replaced left rear caliper, mainly because it seemed my pulling problem started after I changed this caliper...Also it had a bleeder that was a little sloppy in the threads when cracking it up.. So I replaced it.

*Action item 4
Pressure bleed the whole system to perfection....tap on the calipers with a hammer while bleeding, did the whole rotation 3 times. Could not get even the smallest bubbles out of any of the bleeders.

Rock hard pedal,, about 3/4" of free play then the pedal gets VERY firm... Never had this firm of a pedal feel... So I am making progress...

*Action item 5
Measure rotor run out.... I go out and buy a $250 Starrett dial caliper setup so I can accurately measure run out... To the best of my ability, here it what I had..

LF

RF


LR


RR


All are within the .005" spec for GM... Although the left rear is RIGHT on the borderline.. Hard to get an accurate reading on the rear since its so hard to spin the hub smoothing with the half shafts connected... Definitely close enough in my book.

Head out on the test drive and yep....still pulling to the right under soft to medium braking.... Moderate braking from 50-60 mph definitely has a pull.. The system feels like the right rear activates first, then it pulls right, then it seems the left brakes come in and straight it up some... Definitely has improved braking power though and pedal is FIRM...

On HARD braking, the right rear wheel locks up first, then the car pulls LEFT.... (WTF!).... Under EXTREME braking from high speed down (75-80), once you get down to 30 mph or so, the right rear locks up, car goes left, get in the brakes harder then the left front locks up (ironically) and the car skids crossed up as the steering wheel yanks either direction.... The whole panic braking thing is just a mess.... The whole system just seems way unbalanced under hard braking.

This is leading me to believe the proportioning valve is malfunctioning, eventhough it had good flow through it, maybe its doing something weird when under pressure...besides that, its literally the only thing I haven't changed besides the hard lines themselves.

Other then the Proportioning valve, I have no idea what else it could be...

I guess my next trick would be to buy the caliper pressure measuring tools and start testing pressures... Whats weird is the car pulls right under medium braking (so left brakes not working right???) yet under heavy braking the left front brake locks up...(so maybe it is working??)

SO I'm still stumped.... After about 7 days of labor on this and more gallons of brake fluid then I care to discuss...

thecorvette

I will throw my 2 cents in...

1) Could any of the brake pads have been contaminated by a leaking caliper?

2) It might be worthwhile to unbolt each caliper during the bleeding process and point the nipple straight up. It is a long shot I know but possibly, for whatever reason, one side is not able to expel all the air while bolted to vehicle.

3) Did you bleed the entire system with the vehicle tilted forward or just the master cylinder? I seem to remember something about that on a C2. This was a few years back so maybe someone else could chime in on this. Long shot I know, but just brain storming here.

Dan

ajrothm

As I mentioned, it just seems that the flow control to each caliper is not consistent, and varies more and more as additional pedal pressure is added. This is the weirdest $hit I have ever seen...

I'm so close to pulling the trigger on a Wilwood kit its not funny...but my luck, it would still pull. I HAVE to figure this out...

Tomorrow, hopefully I can find a new proportioning valve and get it installed and bleed the whole system again. If that doesn't fix it, I don't know what to do then.

gungatim

super nice job on the problem solving approach you posted. only thing is I would have saved $240 and went to HF for a dial guage, but to each his own...

now, read what I posted about that distribution block and proportioning valve. No you don't have a proportioning valve, but I posted that because it kind of helps explain how the valve you do have moves, and you can see the cutaway. it could have a clog or missing chunk of o-ring on that valve and it is moving around in there.

you can do a couple things, one, for $8 on ebay, there is a screw in tool that locks the valve in the centered location. helps to bleed. you pull the brake light switch, screw it in its place, and it holds the valve. that would keep it from moving around, but wouldn't be a definite prognosis, as the valve may still have some clogging in ther.

second thing: get a new valve. my guess is leaning toward something stuck in there that is partially clogging, under hard brakeing the valve moves and the gunk shifts around...

keep working methodically and you'll get there. Super nice looking car by the way!!

ajrothm

Well my lesson in futility MAY be paying off... making progress...

I started out by going to a local vette shop to get a new proportioning valve and all new hard lines, pretty much the LAST of anything that could be replaced in the brake system. While there, I was speaking with the owner and telling him the problem of pulling right.... as soon as I mentioned that, he said to check/replace the RIGHT rear caliper... I was like "Huh?".. The right rear works best, its the only one that I can get to lock up..Its my "Good" Lonestar Calipers stainless one... He said exactly....He sad replace it. He said its likely that one of the pistons is not retracting 100% and therefore the cylinder its in is already loaded with brake fluid and that piston is closer to pressing on the pad then any of the other pistons in the system.. I thought well hell, at this point, that's the only caliper that I haven't replaced this week...

I picked up my new proportioning valve and lines, then headed to O Reilys to get a right rear caliper, I figured if anything, now I would have a matching set of calipers again and all less then 3 wks old. I get home and decide to put the caliper on first, then bleed the system again before installing the new proportioning valve and lines, JUST so I can keep track of what does what in this process. I install the caliper, bleed the whole system twice. At this point I have put about 2 gallons of brake fluid thru this system...(no lie). Pedal feel is good... Maybe not as rock hard as I had it yesterday but better then its been previously.

I go drive the car, seems to be stopping slightly straighter, maybe a slight pull to the right here and there at slow speeds....I head to my test road to do some brake tests... First try, right rear locks up first, then left front locks up...Same crap... But after a few more tries, the left front started locking up first and the right rear right after. About 10 more stops had the car stopping pretty damn straight....Just the slightlest input on the steering wheel easily kept the car straight, I think that's just correcting the alignment/tire wear etc etc and the car's natural tendency to pull right while driving normal. I was doing some panic stop tests from 70-80 mph and was able to get it stopped pretty fast, pretty straight with my hands on the wheel.. I did this until I started experiencing some fatigue and sponginess in the pedal...also had smoke coming off the front brakes...LOL

I'd say now the car stops 95% straight about 95% of the time...That's with no hands on the wheel. I wouldn't say its "fixed" but much much better. There still seems to be the slightest slightest balance problem between the corners... Still feels like the right rear activates first, immediately followed by the fronts. It balances itself out during the stop but not on the initial hit.

This is probably liveable, but still not 100%... so next week sometime, I'm going to install the new proportioning valve and all new hard lines... That basically means EVERY brake component is new besides the rotors. I'll bleed the system again and see what it does, that's about all I can do with it. If it ends up at least as good as it is now, and stays consistent, I'll probably try and live with it.

The fight goes on tho...

doorgunner

aj.............................you seem to be more hardheaded than the brake system........

Thant's a GOOD thing!

BLUE1972

just a thought .. have you checked the front of the rear trailing arm mounts to see if there is play front to back ?

best of luck..

Gale Banks 80'

One thing You mentioned was when a Wheel Locked the car pulled in the opposite direction. That's what is supposed to happen. A skidding Tire has no where near the braking ability of a rolling tire. That's the whole reason anti lock brakes were invented for the C4 Corvettes.
You also mentioned that with repeated stops the pulling to one side gets better. If one side is doing more work than the other it will develop more heat. Heat creates fade, and once faded its got less braking ability which might equalize the weak side with the strong side. Letting the system cool should produce the original symptoms.

Kacyc3

Good to hear you made the car safer, unfortunately not completely fixed.