Ironhead71

Hey guys, so i've had this rather strange brake problem that I can't quite figure out.

1990 GTU with four piston calipers, non-abs.

So I tore apart the whole front of my car putting coilovers on it, I ended up replacing alot of stuff, but one thing i didn't touch was the brakes. I took the calipers off the knuckles and hung them in the wheel well with some wire.

They sat for about a week like this. I picked up some new-ish rotos off of a friend and put them on. After I get everything buttoned up, I find I have almost no brakes. I lose a bunch of pedal, and it feels like the rears are only working. I'm not losing any fluid.

All the lines are staneless so its not like rubber lines that are expanding too much. However, if I do pump them while driving I can get a little more pressure where the fronts feel like they're doing something...but its not much.

I recently put in a new brake master, and everything was fine with that (about a month?) until i put the coilovers on.

I never took any brake lines off, i simply pulled them off and hung them, and put them back on.

The only things I can think of is that maybe a piston or two is getting stuck however I have never expierenced that before, so I don't know what the symptoms of it are. The proportioning valve perhaps could be going bad....I don't think it has anything to do with the booster, because I would still retain my brake pressure..I tried bleeding them, and did get a bunch of air out, but it didnt make that much difference. I'm going to bleed them again, for kicks and to make sure thats not the issue.

Kinda stumped here, just looking to get some sort of an opinion.

Any advice is appreciated. Thanks!

cone_crushr

iTrader: (18)

Sounds like you've still got air in the lines. Not sure how air got in if you previously installed the new master cyl and didn't open the lines since then. Did you bench bleed the master before installing it?

turboIIrotary

iTrader: (9)

By moving around the calipers it probably knocked some air bubbles loose try rebleeding all the lines.

gerald m

When you bleed your brakes start with the one closest to the master,( Front driver side first) (front passenger next ) when you work on the rear the same thing applies that way you don't suck the air from the closest wheel back into the system and cause more air to enter the lines .. When you bleed your brakes pump them up slowly and bleed them off slowly and don't put to much pressure in the system with the brake pedal Excessive pressure brakes the air bubbles up smaller and makes it harder to do a good job .. Same as the calipers if there are two bleeders always bleed the one closest to the brake line first then the other.. That is the only way you can get all the air out .. If the calipers were sticking they usually stick on .. You should have a buddy help you bleed them I think the self bleed hoses are just B.S. Remember pump them up hold down on pedal open bleeder, bleed every thing out tighten bleeder pump up and repeat .. I am sure you know how to go about pumping them up and so on but you would be surprised how many don.t .. If the master is by passing you will see a flow of fluid in the fluid pot but don't stick your face over top just have your buddy push the pedal very slowly and watch if it is by passing you will see fluid movement but I think you just have air problems Hope this helps ..

BomberMan

iTrader: (4)

Personally, I don't ever bleed brakes. I think it is a waste of time when you could just flush the whole system. Basically get a bottle or 2 of break fluid and bleed it in the proper order until it all comes out clear. Nothing like a fully fresh hydraulic system.

If you suspect a caliper or piston may be sticking, I would attempt to go for a "hot drive" if it is safe to do so and check the temperature of your wheels after. Or if you have a friend handy have him carefully apply the brakes while the car is on the lift while you check the operation of the pistons.

turboIIrotary

iTrader: (9)

Thats wrong the manual says bleed the lines that are farthest from the MC so, RR, LR, RF, LF.

gerald m

Well I won't argue with you turbo that is the way I was taught and it works all the time so I guess it must not make a lot of difference.. but I think you will find that is for abs brakes ..

scathcart

Possible that when you hung the calipers, you hung them above the matser cylinder, and the brake fluid in the front calipers drained back into the MC, and when you remounted the calipers, the lines then had an air bubble in them. This air in the lines compresses when you step on the brakes, giving a lack of clamping pressure. This is easily remedied simply by bleeding the brakes.

Wilwood sells a residual pressure vlave that maintains 20-10 psi in the lines at all times to prevent this exact problem for situations where the master cylinder is permanently mounted below the brake calipers.

Ironhead71

So upon further screwing around with it. I've come to the slightly confusing conclusion that my brake booster is to blame. However, I can't fully understand why.

Realizing that i get full brake pressure when the car is not running (booster not getting vacuum) and having the pedal go to the floor when it starts, I pulled off the vacuum line going to the booster and pumped the brakes, which resulted in plenty of pedal. Had my pops re attach the line with my foot on the brake and car running, and sure enough....to the floor and beyond.

This is what I don't understand. From my very limited knowledge of how boosters work (just a diaphram with vacuum pulled on one side to aid in braking no?) if you lose your diaphram or lose vacuum, your brakes turn into manual brakes and it becomes very hard to stop...however this doesn't result in pedal loss...am i right or wrong with this? Got a new (used) booster and will be installing it this weekend hopefully...but can anybody shed some light on this?

j9fd3s

iTrader: (3)

this is kind of normal, if you have air in the lines. when its properly bled it won't do that.

you're overthinking this, try the basics, bleed the system, and go from there

Ironhead71

Bled it a few times. Still feels like a pile of ****.

misterstyx69

iTrader: (142)

Bleed it thoroughly..not just Crack the wrench,spit and close.
Start at the rear passenger...pump,pump,pump,pump,pump...HOLD PEDAL!!!!crack bleeder.Spit...close bleeder.DO THIS at Least 3 times( I like 5 myself to assure no air)..make sure that you do NOT run out of Brake fluid IN the master or else you start back at step One!
Rear driver's..same
front passenger..ditto
front driver's...what he said/\/\!!
If that doesn't work,.post up again..

Rx7Ridah

iTrader: (8)

Bleed the p-valve first then rr, lr, rf, lf in that order as per the brake servicing and flushing guide at the dealership I used to work at specifically for our cars. There is a 23 mm bolt on the side of the valve (if I'm remembering the size correctly). I too had spongy brake feel at one time for no apparent reason after some minor other servicing. That was the only order I was able to get proper feel back. Also if you are/want to test the calipers it can be done easily with a piece of wood (2x4 or hammer handle) placed in the middle of the pistons with the caliper removed from the bracket. Have an assistant slowly press the pedal (I mean SLOW!) and observe the piston movement. Do one caliper at a time and NEVER press the pedal without something replacing the rotor and pads or you will blow the pistons out of the caliper forcing a rebuild. Also verify that the rear caliper slides are moving freely or else your loosing 50% of the rears.