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Soft/Low Pedal? Weird

1985xjlaredo

1985xjlaredo

NAXJA Forum User
Location
Kansas City
So my brakes have lost about 50% at least of the stopping power that they had. When I press the pedal at first it drops about 2 inches before it even seems to grab, Then it feels normal for about a half inch. It starts to feel like it has "hangups" where it gets stiff for about a millisecond then goes soft. It also feels like it is getting weaker the more I press it. When I finally do get stopped it it has maybe 1/4" till it hits the floor. I searched and found nothing like what I was going through with this. Thanks In Advance!
oh yea 88 Laredo No ABS 4.0L
Zan
 
Look for external leaks. Check all fittings for "sweating". Be sure to pull the rear drums and check the wheel cylinders. If you don't have external leaks, then it's probably a bad MC. Sounds like an internal leak (fluid bypassing the piston seals as you press on the pedal).
 
OK checked all the fittings and the calipers and wheel cylinders, everything looks dry. Should I just replace the MC to see if that fixes my problem? What do I need to replace it? I have the FSM but it's kinda vague on how to bench bleed it.
 
One way to check out the MC without replacing it, is to plug the two output ports. You should then have a hard pedal that does not sink. If it's soft, or slowly sinks to the floor, with moderate foot pressure, then it's bad, and needs replaced.
 
should I just get some bolts to go into it? What about clamping off the soft lines that run to the wheel cylinders and calipers?
 
1985xjlaredo said:
should I just get some bolts to go into it? What about clamping off the soft lines that run to the wheel cylinders and calipers?
Click to expand...

First do not clamp off the soft lines, that will ruin them, plug the lines with the proper line plug, do not use a bolt.
 
Clamping soft lines with the correct tool is OK, if done properly; don't use vise grips!
Plug the MC with correct tubing plugs, not bolts. You could use old lines with flare nuts, and cut the lines; of course, you have to seal the cut line.
 
I've seen pictures of them in brake articles discussing there use.
I looked through my "favorites", but can't readily find the the most resent I've read. I did find reference to their use in a Volvo article: "--Brake Job Tips: Hose Clamp; ABS Sensors

Forcing Dirty Fluid Back into the ABS:

[From Motor Service Magazine]-- Just opening the bleeder as you may have done in the past isn't good enough anymore. You've got to choke off that hose. [Editor's note: you can buy inexpensive plastic pliers with rounded jaws designed to clamp rubber brake hoses without damage, just enough to keep most of the fluid from passing through. Check your auto parts store. And don't squash the hose, just clamp it ] And note there is some controversy about this: Ford and GM do not recommend clamping because of the potential for damage to the hose.
 
I've got a set of the clamps, but am not brave enough to try 'em on brake hoses! They work great on closing off fuel hoses for quick repairs and such, but I think damage to the soft inner liner on brake hoses would result from pinching the hose enough to stop fluid pressure from the MC.

All signs point to MC piston bypassing fluid instead of building pressure, so I'd look into rebuilding or replacing it before "yo no stoppo"

--Shorty
 
The brake hose clamps I've seen are more sophisticated than those described in the article I copied, above. I don't think I'd use the pliers-looking ones. For me, it's mute anyway, sence I've got SS flex lines all arround.
 
Well ill just replace the master cylinder I guess. does anyone know what size the couplers are on the master cylinder? Anything I should know other the obvious?
 
While you have the master off, check the rear seal to make sure it wasn't leaking fluid back into the vacuum booster. I've seen this many times, the fluid will eat the seals/diaphram in no time flat. If theres a bunch of fluid in the booster, you might want to replace it also.
 
Ok cool anything else.
 
Ok I found the probem to be a vaccum line was split. Sometimes it would stop great and then the next it didn't have any power brakes at all. New hose and walla better than ever since I did all the other shit we talked about on here before I thought to look at the hose.
 
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