On my '91.5 W250 I'm having some little problems with the brakes on the truck. It has a brand new brake booster(put it on last night),new master cylinder,rotors,pads,brake lines and shoes on the rear. I've bleed out the whole system really well but I still don't have much of a pedel. I can drive the truck just fine down the road but when I hit the brake pedel it goes down almost 1/2 way before it ever seems to engage to start slowing down. After the 1/2 way mark it'll come to a holt in a HURRY if I'm not real sensitive on the pedel. It feels like a old 60-70s truck with no power brakes is the best way I can describe it. Seeing how most all the braking system is fairly new only thing that I can think would be causing it to have a real spongy pedel would be the vacumn pump I believe it's called. Bolted to the front cover and the power steering pump is bolted to it. I'm not as in the "know" about the old CTD as I am gassers so this would be my best bet. Could the pump go bad and cause it to feel this way? It'll still run,drive and stop fine I just have to get a feel for the pedel a little better. All the other CTDs I've owned stopped really well and felt like the brakes where engaging just after touching them. Any helpful hints on this,is it the vacumn pump or something else? Any idea what sorta $$ the pump would run in price? Thanks yall

 

One of the simplest gauges to install is a mechanical vacuum gauge.

Before condemning your vacuum pump, get yourself a dash-mount vacuum gauge (it need not be pricey), and monitor the vacuum.

29 inches Mercury is a perfect vacuum; anything over 20 on the gauge should be sufficient.

Also, get a hand-held vacuum gauge--about seven bucks at Harbor Freight--and disconnect the big line at the pump to compare readings against the dash gauge, thereby diagnosing whether there is a leak somewhere in the system.

Usually, low, or no, vacuum will result in a very hard to push pedal.

 

Ok where would I need to hook the mechanical gauge into? Just into the main vacumn line running from the booster to vacumn pump? If the pump is actually GOOD what else would possibly be a problem on this thing? The master cylinder is fairly new(few months at the most) but for some odd reason could it be bad causing a bad pedel? I'm running out of ideas on what to check if it's not the pump. Going to call a fellow tomorrow that has a vacumn pump. If it isn't much I'm going to buy it and toss it on just to see. I need to be driving the truck two weeks ago but having to bum a truck for the time being...which ain't a good feeling

 

A bad vacuum pump will give you a hard pedal. If everything is bled properly (you bench bled the master, right?) and the rear brakes are properly adjusted, I'd suspect the RWAL dump valve.

 

Alright if it is the dump valve is it the one bolted onto the frame? This is a picture I shot of what looks to me to be a proportioning valve but is if the dump valve? If not then where is the thing lol I don't know for certain if the M/C was bench bled because it was put on the truck BEFORE I bought it. If the picture is of the valve could unplugging the electrical connection help the spongy braking? I've bled all the brakes and the front bleed out REALLY well the rears bled out fine but didn't seem to squirt as well as the fronts. Sorry for having so many posts but just trying to get this figured out. Thanks

 

RWAL valve is in frame over rear axle.

 

Well I put a used RWAL valve we had on the truck and went to bleed them and the valve had a squishing sound coming from it while bleeding the rear brakes. So I bled the rest of the system then fired it up to check. The pedal seemed a good bit stiffer at first then on the third pump it almost went to the floor just like it done before Now I've ordered a reman valve from Advance Auto Parts thats supposed to be here tomorrow morning. I'm going to stick it on and bleed everything out really well and see how that goes. If this doesn't fix it I think I'm going to pull my hair out LOL Any helpful hints if this doesn't cure the problem?

I don't know if the m/c was bench bled before put on because like I said it was on it before I bought it. Could I possibly just take the line loose at the m/c and let it drain out for a little while. Then hook it back up and bleed from the RWAL valve and so on? Thanks

 

If you have been driving the truck and bleeding the lines, then, most likely, the master has by now bled itself.

If the master was a rebuild, it could very well be no good.

I have went back and swapped the third time, before I got a good one; quite common for new-rebuilts to be bad, or go bad real soon.

 

Another thing to check is.. when you replaced the brake booster was it adjustable or not..
I had to replace mine and it was adjustable. 1st time I put it on I had no pedal took off master cylinder and adjust brake booster and had very touching brakes, then took it apart for a third time and got it correct..

the third time I was smart and used my old brake booster to measure how much distance it had going into master cylinder.

 

good call bruiser , i would look at that to if the rod isn't adjusted right it will give you fits. if you push on your pedal hard and fast and the pedal stays at that height . then push slowly and the pedal goes close to the floor , blame your mc. i bought one of those rebuilt junkers this fall will replace with new shortly. instead of buying a new rwal valve why don't you bypass it with a couple of couplers and a short chunk of line. if that is it then replace it.

 

The rubber hose between the vacuum pump and brake booster often deteriorates right after the pump, it gets soft and porous and leaks. I had a hard pedal on one of my trucks, replaced that line, now its fine.

 

Simple question, are your rear brakes adjusted up tight?

If they are loose the MC has to push them out to engage the shoes before you will start developing any pressure.

When my pedal starts getting low I automatically know it is time to tighten up the rear brakes.

 

Also a good call.

 

Alright I bought a new RWAL valve and got it put on today. Also bought all new bleeder screws because one of them was trying to strip out while bleeding. Starting trying to take all the other screws out that I've had out before and EVERY SINGLE ONE OF THEM rounded off even with the correct size tubing wrench...talk about doing some cussing!! Then to beat it all the bleeders in the calipers are different thread then in the wheel cylinders. So everything is on hold yet again until tomorrow. I'll post back for certain to tell you if it cures my problem and so forth*everybody cross your fingers for me* haha