Spongy Brake Problems....AARG

[AndrewKing]

HI All,



I recently bought a 1993 W250... Great condition, 168K, AC, and auto... . Only thing I noted when test driving was that the brakes felt spongy when first applied but if you let off for a split second and got back on the brake pedal the pedal not only felt firmer but also didn't sink as far down..... I questioned the previous owner and he said it was a problem with the brake adjusters..... I didn't really buy that but he also mentioned that he had replaced the master cylinder 2 years ago..... Anyways I bought the truck and took it to my regular repair shop where they again replaced the master cylinder... Got truck back... . same problem... . Back to shop... . they powerflushed the brake system..... got truck back... . same problem!..... Took back... . then they replaced that RAF (??) valve... got it back and the problem is still there!!! AARG... . $400+ into the brakes and the problem is still there... . Is this a diesel thing or is there something the shop is missing?

Any help would be Greatly appreciated...

Thanks

Andrew

 

[TKingsbury]

I think I'd check out the booster. Will it hold vaccuum with the brakes applied and unapplied.

Travis. .

 

[JLuechauer]

I would check the drag on the rear brakes. I set my when the axles are removed so there is no resistance from the other wheel and diff. I tighten the adjuster untill the brakes are touching the drum (you can hear it grind against it). The rear brakes set the petal height, and this may solve your problem. Also check and see how far down your can depress the E-brake( should only go about half the way down or less) that should also tell you how tight the rear brakes are.

Let know if this helps good luck

 

[ARedetzke]

Check your brake booster. If it is bad, the pedal gets that no power assist feel as the vacuum leaks out (pedal sinks a little and gets hard). Then the "brake" light by the "wait to start" light will come on. At least that is what mine did.

AJ

 

[JZellers]

I had the same problem with my '92 W250 when I bought it. I replaced the master cylinder, which didn't help. Then I replaced the rear ABS valve. After bleeding the valve and both rear wheel cylinders, it was a little better. After I got more agressive with the bleeding (pumping several times to agitate the air as opposed to depressing the pedal once with the bleeder cracked), the pedal is where it should be.

 

[Lock93]

I agree with JLuechauer's comments. I had the same prob; fixed the same stuff and no change. then I thought I had a rear axle seal prob on a long vacation we took. Dropped the truck a local BigO for inspection (we were on vacation and had better things to do). No prob with the axle seals, and when they put it back together: no spongy brakes. Didnt charge me anything, so I'm guessing no new parts when in while it was apart. Just better adjustments and bleeding.

 

[RSchwarzli]

When you figgure it out, let us know, as I have the same problem, and I am sure others do to.

 

[AndrewKing]

Hi all,

Thanks for the input... . I talked w/ the shop today and told them I'd bring the truck back for them to work on yet again... . I did tell them that I really didn't appreciate spending $400+ and that they needed to get whatever is wrong fixed for free (lest I ask for my $$ back on what they already charged for the "fix")... . I'll keep you posted since this appears to be a fairly common problem?... . I hope there is a fix and that this is not simply something us first genners just have to live with... .

Andrew

 

[TKingsbury]

Andrew

Just wanted to let you know that we all don't live with this problem. I am happy with my pedal feel, the proportioning is another story all together.

Travis. .

 

[tugboatphil]

Andrew,



I swent through the same thing last winter. It finally turned out to be the adjustment on the rears. I turned them out several clicks and have had good brakes since then.

 

[desertrat1]

I agree with checking your adjusters, adj. of rear shoes, and bleeding the system. If still no better try this.

Sometimes a sticking caliper piston will have the effect you describe. It takes a couple of pumps to extend the piston out until you quit braking. The piston gets sucked back in the caliper too far when you let off the pedal. Try pinching off each brake hose one at a time and push your brake pedal to see if you can find the source of your problem. BTW my brake pedal is rock solid, goes down very little when applied, and stops reasonably well for a truck this size. There is no reason your brakes should be that way.