1G Intermittent spongy brakes

[dwb]

What can cause brakes to go from firm pedal, then suddenly spongy for a pump, and then back to firm?

I recently upgraded my 1ga (non-ABS) single piston front calipers to 2-piston 3kgt base model front calipers (reman units). I also have new 1g SS brake lines on all four wheels along with a fresh brake booster vacuum line (cut to size EVO line with check valve).

I bled the front calipers like I've done many times before (single-man bleeding) - jug of old brake fluid with a tube submerged attached to the bleeder. A stick propped between the seat and brake pedal. Open/close bleeder, reposition stick, open/close bleeder, repeat half a dozen times. No more air bubbles. Refill brake fluid reservoir. Move to next wheel.

Everything looked good, no leaks, and never sucked air from the reservoir. Fresh fluid.

While bedding the new pads I noticed what I thought was just brake fade. Firm pedal after firm pedal and then suddenly the pedal is spongy and then goes back to firm the next pump.
So I decided to bleed all four wheels. Same bleeding process as above. No change, still random spongy brakes.
OK, so the master cylinder must be the culprit. I bought a new Dorman MC and installed it. Bench bled it first. This time when I bled the lines, I kept the bleeder open and pushed enough brake fluid through to bring the reservoir from over the max line to the min line. Then did 4 or 5 stick-bleeding like above. Refilled reservoir and made sure it never went much below the min line. I did this on all four wheels in this order: right rear, left rear, right front, left front. I pushed plenty of fresh fluid and there should not be any air in the lines. 100% fresh fluid.

It's still randomly spongy. For the most part the pedal is firm but when I do some spirited driving and brake right away, even sometimes when driving normal, I get a spongy pedal and then back to normal. Is it possible the proportioning valve or brake booster is causing this?

TLDR: installed reman front calipers and got intermittent spongy brakes. Installed new master cylinder. Bled the lines 3 separate times. Still intermittent spongy brakes.

 

[DSMPT]

Did you check if the wheels freely spin when the brake gets spongy? When like this happened to my 1g, the cause was stuck/non-smooth brake caliper pistons. I cleaned the brake caliper pistons and replace the piston seals, then the issue never come back.

 

[dwb]

Did you check if the wheels freely spin when the brake gets spongy When like this happened to my 1g, the cause was stuck/non-smooth brake caliper pistons. I cleaned the brake caliper pistons and replace the piston seals, then the issue never come back.

Now that you mention a stuck piston, I had a little difficulty getting one of these reman calipers over the rotor. I figured a piston needed to retract a bit and would loosen once it got some fluid. Definitely worth a second look.

 

[TerminalTalon]

I’d only trust a two man bleed operation.
Three pumps, hold, and open bleeder. Repeat until no air.
You could have a bad booster but a lot of these reman’d parts are sketchy and I’ve been doing this so long now that we see continual failure from a lot of parts suppliers. Have them warranty the calipers out in general or just the one you are talking about and see.

I should probably do a write up but here’s an example.
Autolite-the official sparkplug of NASCAR
What plugs do NASCAR’s run? NGK
In no universe will I ever leave Autolites in any vehicle. They are usually junk. I’m not talking about a direct misfire but you can feel the combustion isn’t clean.
Another one is German cars & Bosch plugs. There’s a TSB for VW/Audi misfires. Fix-remove Bosch plugs. Install NGK. I’m not saying Bosch plugs are bad. I’m pointing out that the standards of excellence to produce a brand that competes globally is held by few.

 

[mikellinos]

If it was air in the system it should be always spongy.. First I would confirm if the master cylinder is coming all the way back when the brake pedal is not pressed.
Assumed all the parts on the brake system they work as they should, a randomly soft brake pedal for a pump or two it means randomly your pads are pushed a bit away from the disc, usually is wheel bearing play which can cause movement to the brake disc, or loose bolts on the brake calipers but that could also cause some kind of knocking noise during braking and i also saw this happening at least 1 time from flexion of the steering knuckle/wheel bearing spindle at small light weight cars that they were never intended for racing/wheel spacers/big wide wheels.

 

[dwb]

I took some time over the weekend and removed, disassembled, and inspected the caliper that I thought was possibly sticking. I used compressed air to push the pistons out and one piston came out a little easier than the other, but no smoking gun. So I swapped the piston cups for a set that looked to be in better condition. Reassembled, bled, but the issue remains. I also verified that all caliper bolts and lug nuts are tight.

I’d only trust a two man bleed operation.
Three pumps, hold, and open bleeder. Repeat until no air.
You could have a bad booster but a lot of these reman’d parts are sketchy and I’ve been doing this so long now that we see continual failure from a lot of parts suppliers. Have them warranty the calipers out in general or just the one you are talking about and see.

It's not air in the system. I've done one-man bleeding for the better part of 20 years and never had a problem.
I've already had one reman caliper replaced due to cross threaded slider pins. They let me keep the core. That allowed me to piece together two "good" calipers. Both calipers now have parts from the "bad" one.

If it was air in the system it should be always spongy.. First I would confirm if the master cylinder is coming all the way back when the brake pedal is not pressed.
Assumed all the parts on the brake system they work as they should, a randomly soft brake pedal for a pump or two it means randomly your pads are pushed a bit away from the disc, usually is wheel bearing play which can cause movement to the brake disc, or loose bolts on the brake calipers but that could also cause some kind of knocking noise during braking and i also saw this happening at least 1 time from flexion of the steering knuckle/wheel bearing spindle at small light weight cars that they were never intended for racing/wheel spacers/big wide wheels.

This is a very interesting perspective and maybe exactly what's going on here. I've done some tests and isolated the issue to being only after I've made a hard turn without braking. The next brake is soft. So my rotors are flexing in relation to the caliper bracket. Wheel bearing(s) seem to be the next possibility.

 

[dwb]

I've definitely confirmed that cornering left or right without braking is what's contributing to my issue. It's not as intermittent as originally observed. The harder I turn, the spongier my pedal. Wheels up in the air, turning left/right, does not cause the issue. I've also recently noticed a bit of a pull to the right when trying to maintain a straight line.

I've replaced front wheel bearings in the past but probably 50-75k miles ago. I've never done rear wheel bearings. What do you think the possibility is the rear is the problem? I personally feel the front is more likely based on symptoms but rear based on last maintenance.

 

[mikellinos]

To eliminate any possibilities about the bearings you have to lift the car and while the wheels are on the air check them for any play, try to rock the wheel by catching it top and bottom, should be minimal movement.

 

[TerminalTalon]

How are the hoses?

 

[dwb]

I got a chance to check for wheel bearing play and I didn't find any noticeable movement at any wheel. Pretty much what I expected. I did, however, find the front right caliper was dragging. That's the same caliper I removed, disassembled, and swapped piston cups last weekend. So weird because I couldn't find anything visually wrong with the caliper. The pins move freely.

I never had this issue until I swapped to the 3kgt calipers, so it would make sense one of these reman calipers are to blame. Also explains why it wants to pull to the right when trying to maintain straight. I just can't understand why it "frees up" after cornering.

I'll see if I can get a warranty replacement on that caliper. Finger crossed since it's been over 30 days since purchase.

 

[mikellinos]

I got a chance to check for wheel bearing play and I didn't find any noticeable movement at any wheel. Pretty much what I expected. I did, however, find the front right caliper was dragging. That's the same caliper I removed, disassembled, and swapped piston cups last weekend. So weird because I couldn't find anything visually wrong with the caliper. The pins move freely.

I never had this issue until I swapped to the 3kgt calipers, so it would make sense one of these reman calipers are to blame. Also explains why it wants to pull to the right when trying to maintain straight. I just can't understand why it "frees up" after cornering.

I'll see if I can get a warranty replacement on that caliper. Finger crossed since it's been over 30 days since purchase.

I had same issue with my left OEM caliper, randomly was dragging and had also vibration on the brake pedal during braking, my pins also were moving freely, the problem always was going away after fresh grease was added on the pins, but also always was coming back after few hundred miles of driving.
I found out the problem was that was a lot of play between the pins and the caliper bracket and that was causing the caliper to not be always parallel with the disc, it was stacking in a bit tilted position so it wouldn't move freely. New bracket and pins solved the problem.
But i never had spongy pedal with that problem.

 

[dwb]

Whelp, I have another reman caliper en-route. Good on Summit Racing for sending replacements no questions asked. Fingers crossed this one is actually "good"

 

[TerminalTalon]

It could also be the hose.

 

[RamenPride]

My experience with a stuck/seized caliper piston is a hard pedal, not spongy. I know you've bled the brakes multiple times already, but maybe try gravity bleeding or pressurized?

 

[dwb]

My experience with a stuck/seized caliper piston is a hard pedal, not spongy. I know you've bled the brakes multiple times already, but maybe try gravity bleeding or pressurized?

I've tried gravity bleeding too.
I think it gets spongy whenever it un-binds or whatever is happening when it stops dragging. Even if a different caliper doesn't fix the pedal feel, I need to fix the drag.

 

[FIBA M - EC17PSE]

With the engine off pump it till its hard and come back in a few hours. Is it still stiff or soft?

 

[dwb]

With the engine off pump it till its hard and come back in a few hours. Is it still stiff or soft?

Overnight and then some, still stiff.

 

[FIBA M - EC17PSE]

Overnight and then some, still stiff.

have you changed your booster hose at any point? this seems more VAC related since it does hold full pressure so that's bled off once you start the car, I want to guess the 1 way check valve in the booster to manifold line is gone or not there or you got a hole in that line

basically if the valve is NOT in place you will get a stiff pedal when you build boost/pressure and then it will go and have a softer feel but only because your fighting a pressure difference.

its where i would start next

 

[dwb]

have you changed your booster hose at any point? this seems more VAC related since it does hold full pressure so that's bled off once you start the car, I want to guess the 1 way check valve in the booster to manifold line is gone or not there or you got a hole in that line

basically if the valve is NOT in place you will get a stiff pedal when you build boost/pressure and then it will go and have a softer feel but only because your fighting a pressure difference.

its where i would start next

I replaced the vacuum line/check valve last year with an oem evo (cut to length). I could test the check valve but it doesn't feel like a booster issue.

This issue started after replacing the front calipers & rotors a month ago.

 

[FIBA M - EC17PSE]

I replaced the vacuum line/check valve last year with an oem evo (cut to length). I could test the check valve but it doesn't feel like a booster issue.

This issue started after replacing the front calipers & rotors a month ago.

hmmmm and you confirled no leaks in the bleed screws and as we know it hold full pressure over night so this is an odd one

 

[dwb]

A bit of an update. My spongy pedal is better, but not completely fixed. Here's what I have done and discovered since my last post.
I received another reman caliper/mount and swapped it for the right side that was dragging. After inspection of the old caliper and bracket on my workbench, it was binding up on the guide pin (pin without the rubber boot). If I messed with the mount/caliper by hand, I could get it to un-bind and move freely until I compressed the mount fully back down then it would bind up again. For giggles, I swapped the guide pin for another lock pin (with the boot) and lo and behold, I couldn't get it to bind at all. Smooth as butter.

I got the replacement caliper installed and determined it really wasn't much better. It didn't drag quite as much, but still more than the left side. Same issue as the bad caliper, binding up on the guide pin. Since swapping to the slightly less-binding caliper/bracket helped my pedal feel, I think this has been my problem all along. I may replace the guide pin for another lock pin and see how that works. I've tried researching what exactly the guide pin does vs. the lock pin and I can't really find much. Anyone here have any info on what role each slide pin does? Or what happens if you mix them up?

Anyway, I lied about no leaks. I was looking at my left front wheel and and noticed little oil drips all over inside the rim. I poked my head under and found this:

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Looks like a small leak from the bleeder (it's tight) and a bigger leak from at least one of the pistons. I went back to Summit Racing and requested yet another replacement. It's probably going to be after Christmas before I see it (back ordered). This will be the FIFTH (!!!) caliper so far. Two from the original purchase and now three replacements. I'll be lucky to piece together two good calipers. That being said, these "Centric Semi-Loaded Calipers" remans ARE ABSOLUTE GARBAGE. "All calipers are treated with an anti-corrosion finish" is a straight up lie. They rust immediately and now I have to paint them so they don't look like a rust bucket as seen above. The mounts are already worn out, I'm lucky if the boots don't have holes in them, and the ugga duggas they like to use on the slide pins and bleeders are causing more harm than good.

This has been quite the experience for a couple $40 calipers. Like the saying goes, you get what you pay for.

 

[dwb]

Final follow up on this thread. I got the front calipers sorted out, and thought it was fixed, but still had an occasional very slight sponge after a hard corner.

I replaced the front wheel bearings. Even though I replaced them less than 50k miles ago. They did sit outside without an axle for a few months. New bearings helped some other symptoms, but still some sponge.

The Solution...
I discovered the front left wheel had some ever-so-slight bearing play. Brand new bearing, everything torqued to spec. Going against my better judgment, I put a cheater on that axle nut. Torqued it until I could slip the pin through again and no more spongy brakes.

PS I received the 5th replacement caliper 6 months later in June, not December like I mentioned above.