"soft" brakes

[TShikoski]

Ok gang, I'm back!



After suggesting that the lawn had a lower priority than stoping quickly, I have a reprieve to complete my brake job.



I have bled the system several times and there are no air bubbles coming from the bleeders, but the brakes are still soft going to the floor with constant pressure on the pedel. I did not experience this prior to the change out of the calipers on the front and new pads around.



Suggestions please.



Tom

 

[paccool]

No warning light coming on?? Could be a leak in the booster but the dash warning light should come on if it there is.



Did you bleed the anti lock/proportioning valve area by the master cylinder? I have not had to do this but I believe there is a procedure for this in the manual.



Is the master cylinder leaking by?



Stan

 

[TShikoski]

Hi Stan thanks for the quick response... .



No warning light... I have by-passed the ABS valve when I made the conversion to disc brakes on the rear... . Just discovered that the brake pedal is "firm" with engine off, but with engine running, the pedal falls away. I think this means possible booster or related components problem. More later after I check things further.



Tom

 

[TShikoski]

Ok gang, here is the scoop..... When I disconnect the vacuum hose to the booster check valve, I have "Good" vacuum. (no gauge, but when I put my thumb over the hose end, the vacuum pump continues to draw with no discernable reduction in vacuum). Removed the booster check valve, and using a visual and vacuum test, all checks out. No leaks. With the engine running but with the booster check valve out of the power booster, I have a firm pedal. I think this means a possible bad booster. Any thoughts?



Tom

 

[paccool]

The way the book said to check the booster is to let it build a vacumn and then turn the key off, apply the brake taking it to a firm pedel - there should be enough vacumn assist for three applications like this. If your hearing is good (read- better than mine! ), turn the truck off and listen for a leak under the hood and under the dash. When mine started leaking, I didn't get a light warning for awile but stopping coming off the freeway was a real trip! I could get stopped but if I had to sit at a light with the brake on, the pedel would fade. as the engine came back up to a higher RPM, the vacume would build back up and I was OK.



I replaced the booster and master cylinder after the warning light started coming on and alll was well for a while. The next problem was about 6 months later when the light came on again. Turned out the rebuilt cylinder was leaking at the area where the rod went to the booster. had some fade if the peddle was held down very long. Put on a NEW master cylinder this time and jhave not had any trouble since then.



Stan

 

[1stgen4evr]

brakes

"still soft going to the floor with constant pressure on the pedel"



Do I read this to be; with constant pressure on the pedal, the pedal slowly creeps to the floor. If yes, you have a master cylinder problem (if there is no leak anywhere). Why didn't it show up before? Just lucky you. But a possible explanation is that in the course of doing all you have, something (trash) got into the master cylinder such that it now leaks by the washers. Pushing fluid from the calipers and then pumping them (the old ones and the new ones) out simply ingested the trash from the reservoir or the caliper. You might purge the master cylinder enough to eliminate the problem, but I doubt it. Most likely, you will need a new or rebuilt master cylinder. I usually replace the booster with the master cylinder. NAPA price for the set isn't much more than the master cylinder alone.



James

 

[TShikoski]

Thanks James and Stan. I have just returned from the NAPA store with both a booster and master cylinder. What the heck, as long as everythig is apart, do 'em both. I'll report tomorrow on my success.



Tom

 

[TKingsbury]

If you let your master cyl reservior go empty while you did the front brakes, you have air in your master cyl and it needs to be "bench bled". This can be accomplished on the truck. Just disconnect the lines at the master, put in some master cyl bleeder fittings and route hoses to the reservior (these are available at parts store). Make sure the master is full of fluid and have someone slowly stoke the master while you keep the ends of the hoses in the fluid and stoke until no more bubbles come out. When the fluid is bubble-free, re-connect the lines and bleed the system again. Hopefully you can try this before you tear everything off. Might be able to return the other stuff.

Travis. .

 

[TShikoski]

No luck yet!

Well , I am up against the wall and in need of some serious help!



What started as a "simple" brake job has turned into a horror story!



1. Replaced all calipers with rebuilt NAPA store products.

2. Installed new semi-metalic pads around.

3. Had a "soft" brake pedal after two bleeds (see above).

4. Replaced booster.

5. Replaced master cylinder with a rebuilt from NAPA.

6 Bled through 1. 5 qts of fluid (just to make sure).



Now I still have the following problem.....



Using a vacuum gauge on the hose coming from the vacuum pump, i show 28 in Hg. This reading is steady and does not diminish with the engine off.



At the valve on the booster, I connect the vacuum line from the pump; block one of the other lines and connect the vacuum gauge to the other connection point, I show 28 in Hg at engine idle with no pressure on the brake pedal. Pressing the brake pedal, the vacuum drops to 13-15 in Hg and slowly recovers when pedal is released.



With the engine off, (and hence no vacuum and assist on the brake system, pedal is "firm" with no appreciable fall to the floor and no increase in pedal height with a "pump" on the pedal. With the engine running, pedal goes slowly to the floor and even with a "pump" on the pedal, there is no appreciable increase in pedal pressure or height. I have checked the whole system, and no indication of leaks were found. In fact, you can repeat the engine "on" soft pedal routine several times with no loss of fluid level in the master cylinder... ... .



I was wondering if under the influence of the vacuum boost, the master cylinder is leaking and should revisit that component. The NAPA guy sez that they have very few failures of rebuilt master cylinders, but I guess there is always a first time.



All thoughts appreciated as we hope to leave on vacation soon and the wife has started to look at the used truck ads in the newspaper!



Tom

 

[dodgenstein]

Sounds like the MC is bypassing internally. Try plugging off the ports. The pedal shouldn't move very much and should stay at that position until you release it. If it falls any it is bleeding past the internal seals.

 

[1stgen4evr]

rebuilt master cyl

Sometimes they are bad but I would try the procedure that Dodgenstien mentioned. Also I would really stab the brakes a couple of times (maybe just for the personal satisfaction). Mastercylinders can make you prematurely grey sometimes.



Sorry you aren't closer.



James

 

[TShikoski]

Too much vacuum?

Well, I purchased another rebuilt master cylinder (no new ones available until Monday!), bench bled it with plugs in the holes and by the time I finished the bench bleed, I was not able to push the plunger in, and no bubbles were coming out, so I believe that I got a "good" bleed. carefully mounted it in the truck and connected the lines. Bled all calipers by pumping the pedal hard two or three times before opening the bleeder valve. Upon completion, pedal was up more than before and hard as a rock. Upon starting the engine, with all vacuum hoses connected to the booster, the pedal again became "spongy" and went to the floor.



Checked the vacuum at the booster end of the vacuum pump hose and at idle, have 28 in Hg. increasing the RPM did not produce an appreciable increase in the amount of vacuum. Service manual sez 8. 5 in Hg at idle to 25 at higher RPM's so I am wondering if there is such a thing as too much vacuum which causes the MC to have fluid bypass internally?



This one has truely given me the run around and I am running out of things to change not to mention $$$! I'd take it to the local brake shop, but I dont know what they would do different from what I have already done.



All help and WAG's appreciated



Tom

 

[CLiberty]

I went thru this on my 86 gas truck (same brakes system, only no ABS). First, make sure the reat brakes are adjusted, any "slack" in the rear shoes can show up big time in the pedal. If that does`nt help try reverse injection bleeding using a Phoenix Injector . I have one because thats my trade but either way , if you work on your own stuff it`s a super handy (and effective) tool to have. On my 86 I wound up flushing alomst a gaalon of fluid thru it before i was satisfied I had all the air out (YES I can be very"finicky about my ride#ad
). Bottom line is, that truck has awesome brakes (also has stainless flex hoses). Air can be a real pain to get out... no matter how much fluid you pump thru the system, it likes to hide in the nooks an crannies, and reverse flushing is the best way to get it out (IMO of course#ad
).

 

[RCapehart]

Well, I purchased another rebuilt master cylinder (no new ones available until Monday!), bench bled it with plugs in the holes and by the time I finished the bench bleed, I was not able to push the plunger in, and no bubbles were coming out, so I believe that I got a "good" bleed. carefully mounted it in the truck and connected the lines. Bled all calipers by pumping the pedal hard two or three times before opening the bleeder valve. Upon completion, pedal was up more than before and hard as a rock. Upon starting the engine, with all vacuum hoses connected to the booster, the pedal again became "spongy" and went to the floor.



Checked the vacuum at the booster end of the vacuum pump hose and at idle, have 28 in Hg. increasing the RPM did not produce an appreciable increase in the amount of vacuum. Service manual sez 8. 5 in Hg at idle to 25 at higher RPM's so I am wondering if there is such a thing as too much vacuum which causes the MC to have fluid bypass internally?



This one has truely given me the run around and I am running out of things to change not to mention $$$! I'd take it to the local brake shop, but I dont know what they would do different from what I have already done.



All help and WAG's appreciated



Tom

I went through 2 master cylinders and a combination valve trying to fix mine only to find I had air in the lines. I feel I had one bad MC but I am not sure about the 2nd one or the conbination valve. I replaced one MC because it was recirculating. I replaced the calipers to get rid of a right pull and updated to the stainless lines because my truck is getting older and I wanted them. So I had a lot of new parts to pull the fluid through.



I could not get the air out of it. I bench bled the MC. I tried a mighty vac, speed bleeders with a bag and buddy bleeding with a tube and a bottle and someone on the peddal.



This morning I took it to a shop and had them power bleed it. Thats all it took! They said sometimes you get one stubborn like mine.



My peddle would go down some when you pushed on it. If you would pump it a couple times and then hold it would fall to the floor. Not now its fixed!



Just my $. 02 worth of what fixed mine!



Ron

 

[dpuckett]

I'm having a similar problem with mine. I have put 1 new MC and 2-3 remans in it, and the pedal still feels spongy. THough I can pump it up and it will hold for a few seconds, then fade to the halfway point. Against my better judgement, (and a lack of place to do it on my own), I let my g/f's boss do the hydraulic work, and HE says there aint nothing wrong with my brakes. See if I recommend Advanced Automotive of Cape Gir. again... ... . He has replaced the proportioning valve ($100), MC ($25+$20 core), booster ($120), and bypassed the ABS valve- to no avail. He's sure of one thing, then when that fails to fix it, he blames it on the old Dodge brakes, slack in the pedal, I'm too nit-picky. (No, I just like a firm pedal when I have a whole new system) He has renewed my faith in my low opinion of shops overall Oo. Anyway, his latest theory is, bad rear brakes (which, by coincidence, and 100Kmi, DO need replaced), so I am trying that, then seeing about going to court over the labor and parts he has thrown at it, trying to "fix" my probelm.



Daniel



PS- believe it or not, I had to go through 3 NEW MCs before I found one that held up. From now on, it's Bendix (OEM, stock) only, and NEW. It IS possible to get 3-4 bad ones in a row- BTDT. ANd of course, the parts guys tell you they NEVER have any come back defective

 

[TShikoski]

More of the same

Well, I have bench bled the MC for the second time. Used the plastic plugs on the ports; pushed about 1 inch and waited for 15 seconds repeat about 25 times. The pressure on the piston finally became stiff enough that I could no longer push on it with the broom handle, so carefully mounted the top, caried it in a flat horizontal position to the truck and installed very carefully. I left the plugs in place and carefully pushed on the brake pedal which produced a firm and non faltering stroke. After hooking up the two brake lines, I bled at the top of the porpotioning valve where I had some air, then at the junction block mounted on the frame below the prop valve and then started at the passanger side wheel. After going around the horn and using approximately another quart of fluid, I had a "stiff pedal (no engine - no vacuum) I thought I had it solved, however when I started the engine, the pedal again sunk to the floor..... #@$%!

I guess I'll need to wait until Monday and pick-up an OEM MC and see if that makes any difference.

I am learning far too much about this brake stuff!







I checked out the bleeder recommended in a previous post and thought about building something like it, but am not sure if it would produce any better results in the hands of this amateur.



Tom

 

[TKingsbury]

One thing concerns me, pushing the plunger 1 inch doesn't sound like enough. You need to bottom out the plunger on each stroke, or you will not get all of the air out. I like to do it on the vehicle so you have the pedal to make it easy. It's best to have someone pump while you watch and give instruction.

Travis. .

 

[DValentine]

I too have heard stories like this one. I changed the fluid in the truck last summer, with a vacume pump that I found in a pawn shop..... electric, cool little unit. I think that you might try the Mighty vac hand pump brake bleeder that you can get at any parts house. Make sure you have the calipers on the right way... ... I have put them on wrong... so the bleeder is in the wrong place..... (swapped left and right) Just a thought.



Dave