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View Full Version : Peddle fade on the tow rig...!



MoonWorks
05-23-2008, 09:41 AM
I've only had my tow rig since sept of last year. It stops ok for the most part but at times when you are sitting at a light etc, the peddle starts to fade. Let it up and press it bad down and it will usually hold.

I've noticed here lately that I only have about half the breaking power unless I pump the brakes. Which really bothered me when I towed to icebreakers as it seemed really bad that trip. I don't like have 10k behind me and I'm constantly pumping the brakes to slow down. Not safe at all.

I haven't found any air in the lines yet but am going to bleed it out again really good this weekend. Someone else told me the mc was bad but it doesn't leak at all and in my experience...they leak when they're bad. True?

Last possibility I can think of is if it's vacum controlled somehow and I have a leak in one of the vac lines. Anyone know this on a 92 f250 w/ a 7.3 international.

Thanks!

OverkillZJ
05-23-2008, 10:36 AM
I'd check for vac leaks like you said, that truck shouldn't have that much trouble stopping assuming your trailer brakes are setup right!

cLAYH
05-23-2008, 12:40 PM
Check the rear drum brake adjustment. Had a '92 Dodge Diesel that had a similar problem. Brakes would NEVER self adjust and after 3-4 months I would notice weak braking on the first application and good breaking on the second. Adjusting the brakes in the rear manually would take care of it for another 3-4 months.

MoonWorks
05-30-2008, 12:05 AM
I'm going to bleed everything out this weekend and adjust the drums in the rear like clayh suggested.

Matt...you've seen the trailer I tow before. It weights 4200 lbs by itself so with the zj on it I'm pulling about 10k total so it does take a little more to stop it than usual.

I've adjusted the brake box so its a little more sensitive than usal but it still cuts in and out quite often. Matter of fact, I can look at my brake lights at night and once I press the pedal...if I let off of it at all the lights go out. They shouldn't until my foot is off the pedal completely. So I have to be pressing good on the pedal to activate not only the brake lights but the brake box as well. Anyone seeing any connection in my problem at all.

1fox2go
05-31-2008, 12:30 AM
Check the rear drum brake adjustment. Had a '92 Dodge Diesel that had a similar problem. Brakes would NEVER self adjust and after 3-4 months I would notice weak braking on the first application and good breaking on the second. Adjusting the brakes in the rear manually would take care of it for another 3-4 months.

my zj wont self adjust the drums anymore, I would check that if you dont have any luck with the vac

MoonWorks
05-31-2008, 09:35 AM
Other than visual inspection which can't be the most efficient way...whats the best way to search for a vac leak?

elmer_fud
05-31-2008, 01:02 PM
sounds sort of like what was happening when the master cylinder in our truck went bad. We would be sitting at a light, and the pedel would loose pressure and to to the floor. If you pumped it once it was fine again. The master cylinder was probally 20 years old though

MoonWorks
05-31-2008, 01:29 PM
sounds sort of like what was happening when the master cylinder in our truck went bad. We would be sitting at a light, and the pedel would loose pressure and to to the floor. If you pumped it once it was fine again. The master cylinder was probally 20 years old though


Mine isn't far from that actually. Its a 92. But like I mentioned before...from my experiences when the mc went bad it would leak. I've never replaced one that wasn't leaking anyway.

1fox2go
05-31-2008, 04:19 PM
Check the vacuum canister, It only takes a hole the size of a needle make it not work properly

Easiest way I can think to check that would be to remove the canister and plug up all the lines, if the problem is still there chances are the vacuum canister is good, then it could be the lines themselves....tedious process


or you could get a new MC and get an upgrade, but then if that doesnt fix it, thats money spent towards fixing the problem

MoonWorks
05-31-2008, 06:56 PM
Starter fluid is the best for checking vacuum leaks. I had a temporary brain fart and completely forgot about it. Shadow is coming over tomorrow to help me bleed everything out. I'll check the vac lines then.

sah81
06-01-2008, 12:12 AM
Sounds like it could be the mc. They can leak internally as well, which causes insufficient brake pressure, but no external leaks. A booster problem or vacuum leak would cause a stiff pedal, not a spongy pedal.

MoonWorks
06-01-2008, 08:26 AM
They can leak internally as well, which causes insufficient brake pressure, but no external leaks.


Thats what a buddy of mine told me last night.

cLAYH
06-01-2008, 12:12 PM
Get the truck working properly without the trailer and then look into the trailer problems

Your trailer weighs #4200 empty?!??! What the heck kind of trailer do you have? A 30ft 20K equipment trailer?

When you say you press on the brakes and the lights come on and the you let off the brake slightly and the lights go out, what lights are you reffering to? The taillights on the trailer or the leds on the face of the brake controller?

MoonWorks
06-01-2008, 02:41 PM
Its a 12k construction trailer. Its a buddy's trailer...I would never buy the thing. But it gets me through until I can get my own trailer.

The lights I'm talking about are my brake lights on the back of the truck and on the brake controller. Both the tail lights and the brake controller light come on and off at the same time. What activates the brake lights on these btw? Not that that would be the problem...just curious. I'm headed outside now to work on it.

MoonWorks
06-03-2008, 11:39 PM
So, I've checked for vac leaks...nothing.

Adjusted the rear drums...

Swapped the mc...

...Same results. The pedal still fades.

Now what about the booster? When the truck is off you can pump the brakes and the pedal will get hard as a rock but once you start it...it will fade out. Haven't driven it yet but just by sitting still and moving it all of 10 feet backing it out of the garage...I know it's not right. So how can I "test" the booster.

Mtn WJ
06-04-2008, 01:07 AM
Did you swap the master cylinder with a new or rebuilt one. Classic case of a bad master cylinder.

You may also have bad wheel cylinders at the calipers and drums.

Otherwise another instance of pedals creeping down would be you need pads and shoes. However with bad pads and shoes you typically only need to double, tripple pump the brakes and you can stop. The pedal does not always creep down after you pump enough for a hard brake pedal feel.

MoonWorks
06-04-2008, 10:36 AM
I'm pulling the shoes today. I adjusted them the other day and I think one of them is now adjusted all the way out. The LR shoe is the one I'm talking about and I also had to bleed that one from the line vs the bleeder b/c it was stripped and frozen. Hopefully the cylinders are good but we'll see. I don't have any signs in the rear of them leaking though.

MoonWorks
06-04-2008, 06:25 PM
Pulled the new reman mc I got and got a brand new (not reman) mc. Benched it and tossed it in. Blead the hell out of everything.

Pulled the drums and cleaned and adjusted the shoes...

I've got vacum from the pump and the booster is fine...

The pedal still falls. POS...I'm not touching it anymore tonight. :(

cLAYH
08-14-2008, 12:58 AM
Does it have ABS? Some vehicles with ABS(like my ZJ) need to have the ABS pump cycled while bleeding the brakes. This is done with a scan tool.

CurtP
08-15-2008, 12:30 AM
Starter fluid is the best for checking vacuum leaks.
Only if your engine is cold. Nothing like having starter fluid light off on you when it hits a hot intake manifold. I'm still growing my arm hair back out from a using starter fluid about a month ago on the Porsche. Propane/MAPP gas works better, IMO and doesn't light off nearly as easily.


As for bleeding brakes, a Motive brake bleeder is an absolute must (or other, similar pressure bleeder). You can build your own using a pressure sprayer - there's instructions all over the internet showing how to do it, but a basic Motive bleeder kit is <$50.

MoonWorks
08-15-2008, 10:28 AM
2 month old but...I finally got it together.

I said f the whole thing and replaced the master, booster, rear cylinders, front calipers, adjusted the drums, and bleed the piss out of it. Peddle would still hold fine until I started the truck then it would fade a bit. I slammed on the breaks a few times and now its fine.

I guess I had a little air stuck in the abs system that's on the rear axle only. Thats the only think I can think of. I've driven it quite a bit and towed with it a couple times now w/out issue.

And all the shit i replaced needed it anyway so it wasn't a waist of money.

markr
08-28-2008, 12:42 AM
It could have been the valve just after the MC . The hard lines from the MC run to this valve, some people call it the proportioning valve. it has a safety plunger in it so if one side looses all preesure the other side still works, it is ussually on the frame just under the MC. slamming the petal would possible return it to the normal postion!!

MoonWorks
08-28-2008, 10:23 AM
it is ussually on the frame just under the MC.

That's exactly where it is...and I blead the crap out of it. Don't think it was the issue but either way, this was resolved 2 months ago anyway.