Spongy pedal after axle swap

[j20brett]

Trying to diagnose my spongy pedal issues. Stock m/c and vacuum booster in good shape. Went from disc/drum to disc/disc (79 ford dana 60/14 bolt with chevy calipers). From what i have read, i think the master cylinder is plenty big. I am 99% sure i have bled all the air out. Could the proportioning valve be the issue since it is the factory disc/drum valve? The pedal will firm up and lock up the brakes but only just before the pedal hits the floor.

[AwesomeJ10]

I feel that should be considered 'normal' when using the stock master cylinder.

I have two rigs in which I performed a similar axle swap:

'78 J10 with a GM d60 up front with stock 1 ton single piston discs and 14 bolt with GM 3/4ton single piston discs out back. Been running this for years. Stock master cylinder/booster. The brakes are good, but a tad spoongy.

'92 YJ with a D44 HP from a '78 ford with stock 1 ton dual piston discs (same brakes as your D60). 14 bolt with GM 3/4ton single piston discs out back. Stock master cylinder/booster. The brakes are pretty spoongy and require more 'travel' than I think they should. very spoongy. They work GREAT after you depress the pedal a little more than you should...

I know that both of these rigs are 100% bled out.

I think the resolution to this problem is to install a 'matching' 1 ton master cylinder designed for a disc/disc configuration.

[j20brett]

After more reading, seems that i have whats called low pedal, not spongy. Mine will come to a stop, just before it hits the floor.

I agree about the bigger master, and i did buy one with a 1.25" bore but i was just going to make sure that would fix the issue before i installed it. Also, did you have to depress the little button on the prop valve while you were bleeding the system?

[AwesomeJ10]

did you have to depress the little button on the prop valve while you were bleeding the system?

The only rig that I've ever messed with that button was my '88 GW that I did a rear D60 w/drum brakes. I never was able to get those bled out/adusted like I wanted and I was messing with that button. Ended up swapping to a 14 bolt with discs and it was fine.

I'm not even sure my J10 has that button or not. Never messed with it.

How are you bleeding your brakes? I use a $15 dollar vacuum bleeder and feel that works great!

[j20brett]

I have a vacuum bleeder but for it to work right i need to wrap the bleeder threads with teflon tape. I keep pulling air past the threads. Ive gravity bled and manually bled them also.

[AwesomeJ10]

I don't think you are supposed to use that teflon tape. It can get loose and end up in the brake system, causing problems down the road.

I've used my vacuum bleeder on many different types of cars/trucks and have NEVER had it pull air through the bleeder threads. You are only supposed to crack it open, just a little bit. If it's still pulling air through the threads, then maybe it's pulling too much vacuum? Or maybe the bleeders are messed up? Or maybe the threads on the calipers themselves aren't right?

[j20brett]

Its probably that i was impatient and opened the bleeder up too much. Ill get the master changed out and rebleed the system and see what happens. I did read something interesting the the service manual; it says to start at the closest wheel to the master and bleed to the farthest away.

[AwesomeJ10]

that's opposite of what I've always done.

I bleed the right rear first and start working closer to the M/C from there.

Don't forget to bleed that new M/C pretty good.

[j20brett]

M/C can be bled mounted to the truck right? Doesnt have to be on the bench?

[AwesomeJ10]

no

you bleed a master cylinder on a bench vise to securely hold it.

it should come with some little inserts that screw into the ports. and then some little hoses that go from the ports into the reservoir.

the idea is that you screw them in and route them back to in the reservoir so they are in the brake fluid. then you slowly depress the plunger to get all the bubbles/air out. takes a little time.

it should come with instructions

[j20brett]

I get that, but why does it have to be in a vice?

[Stuka]

You can bleed it in the truck. Just run the tubes up into the reservoir and pump the peddle, as opposed to using a screw driver when its mounted in a vice.

Only possible issue is the master is canted back slightly when mounted. So you may want to jack the back of the truck up a tiny bit to level it out.

[Tatsadasayago]

I used to bench bleed MCs rather than do it in the vehicle most of the time because it allowed me to 'feel' the valves move through the bore(s) and verify the piston seal was intact and not leaking. A rough bore would kill the inner seals in a hurry and sometimes I would have to finish hone a reman MC. A bit anal on my part but it kept comebacks down.
There is no real problem with doing it on the vehicle besides risking a fluid spill that will eat painted surfaces--something I never cared about on my rigs, but was careful about when working on other peoples vehicles.

Bench bleeding without a vise would be messy and holding the MC still and upright while bleeding while possible, would be like herding cats.

[serehill]

Matter of preference there is not bad way. I've never done one on a bench & never will. I put mine (Perfect Vice) in the truck bleed it there & be done with it. Bench bleeding you have to be careful don't spill anything. On the truck you only do it all once. If you can't do it on the truck it's not the M/C's fault. To each his own & what ever turns you on but on the vehicle bleeding is far simpler to me. Bench bleeding does not add anything. It doesn't change what has to be done. I only intend to bleed it once. It does make 1 procedure into 2. I've read a bunch of articles about bench bleeding & never seen one tangible reason for it. Lots of folks say it easier but I've never seen any fact based reason why. BUT that is ONLY my opinion. Nothing is easier than vacuum bleeding to me. If I replace a MC & vacuum bleed it to the furthest wheel I'm done. I do bleed the other wheels but it's usually a waste. I put it on & short pump it. I like short pump for 30 or 40 pumps then bench bleed it the rest of the way. That burps a lot of air out of it so it doesn't have to go through the whole system. There no way you can totally bleed in one shot bench bleeding it. I'm not saying bench bleeding doesn't work even though it's way overcomplicated it does work. It's certainly your call. there was a comment that made me LOL about doing it in the vehicle causes spills. how do you move it from the bench to the vehicle without spilling on paint which could be exterior.

I haven't figured out yet with a vacuum tool how you got the tubing on the threads something is wrong with that picture.

[Tatsadasayago]

there was a comment that made me LOL about doing it in the vehicle causes spills. how do you move it from the bench to the vehicle without spilling on paint which could be exterior.

Easy: set the lid on it, which will keep the bleeder hoses from flopping around, wrap in a shop rag and take it to the vehicle to install.

I made that comment based on experience.
Probably every one of us has had our foot slip off the pedal during the bleeding process and had the fluid shoot out of the MC and onto things under the hood, and even on the fenders. It only took me once to learn that a mistake can ruin things. Some reading this thread may have never bled brakes before and my intent was to help them avoid mistakes if possible.
Placing the lid on the MC is good unless the recirc hoses are being used but the gap allows fluid to leak or even spray out should the foot slip or the pump action is too aggressive. Most of us know not to get crazy with the pedal, but some haven't learned that yet. Not everyone has a vacuum bleeder or knows how to use one properly so the pump and bleed method might be the only choice.

I'm not sure why you felt the need to insult me over something so minor as a different method, but if it made you feel superior then it's all good Mr Vendor.

[serehill]

There was no intent to insult anyone over a difference in process/opinion. Nor did I take your difference in process as an insult either. A difference of opinion is not that. Yours differentiated from mine remember? The statement wasn't intended as a call out. I didn't single anyone out or use a name. In my opinion it isn't more spill proof. MAYBE I'm just clumsy.
If you feel insulted then I apologize to you. As previously stated they are only my opinions.

Sole intent here is to assist J20 Brett. He was asking for assistance & thoughts.


Totally agree there's more than one way to do this process. I put the cover on & snap it shut. Yeah it's a pain but mostly spill proof. That's while bleeding on the vehicle. I for one haven't had the squirting experience. Just the way I was taught. My uncle owned a custom garage & he would have killed you if you were bleeding with the cover off. I assure you I agree what ever works the best for anyone is the way to go. Bench bleeding is a very popular way to do it for reasons others like.

I paint mine also. So zero leaks are the goal.

I've seen the bench bleed process also. It's far from spill proof. Bolting a half covered M/C on & removing the bleeder lines & installing the brake lines are a mess to me. It also reintroduces air into the system. To me everything bolted together in a stable spot, lines already bolted to it & stable so I can see it all work is just my way.
Since after you bench bleed it & you put it on the vehicle you have to re-bleed the entire system pour fluid in the M/C. So all of that spill issue is still there.

Excellent point though about finding faulty parts. I agree that can happen most of the time bleeding under pressure is when I've seen it. Just because it doesn't leak on the bench doesn't mean it won't though.

Simply discussing the different strokes for different folks. Again no wrong way simply different techniques. Dealers choice.

I have digressed. The method could be the cause of the spongy pedal but air I would bet is the root cause. Make sure you open & close the PP valve & re bleed. There's air in there.

This link will take you to multiple videos about the subject. There's even video on the bench process. It directly addresses spongy brakes.
http://www.youtube.com/watch?v=KTY2iBkFeV0


Good luck to you brettj20!
Also Brett the PP valve will be a little whacky & will cause not enough pressure to the rear disk. It's barely notable but a disk/ disc PPV would be better on the street. The master cylinder certainly has enough volume.

[Tatsadasayago]

My bad serehill. Bad day, bad news and pain meds sometimes cause me to over-react.
Apology accepted and offered.

Carry on!

[serehill]

Thanks Tatsadasayago

NO WORRIES what so ever. Difference of opinions always do that. Been there. This is all water under the bridge. I fear one day I might accidentily run out in from of Brett

[j20brett]

Ha! Hey the brakes work and i can lock them up no problem, it just takes full pedal travel to get there. Im pretty sure a larger master will solve the issue. I locked up the 42's while being pulled by my wife in my other truck. So i wont run over you...more than once anyways

[serehill]

LOL sounds like you might want to check shoes for wear & make sure the back shoes are properly adjusted. if the4 back shoes are not adjusted properly you have lots of travel.