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Question about brakes...new mc and booster

7

77crewcab

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Lubbock, Texas
Okay here is the story. I just put on a new mc and booster but the pedal still travels allmost to the floor before feeling firm. I bench bled the mc but see very little fluid movement when the pedal is pressed. There is no barely any fluid coming from the rear when trying to bleed. the front driver side has a lot of fluid and bubbles and the front pass. has the bleeder broken off. (I'm trying to get it out to replace tomorrow) Any way I am thinking that the pushrod isn't long enough to push the mc all the way in. Am I correct in thinking the adjustment is the two piece rod to the brake pedal? Can I just unscrew it some to lengthen the stroke? Currently I have it tightened all the way. Also where can I get a new pushrod boot. I currently don't have one and don't want the booster to get damaged by not having the boot. Not to mention the exhaust fumes coming through the firewall in that location. Any help folks?
 
Somethin' ain't right, and adjusting around it is bad.

Why the boosters don't come with the boot is beyond me. I had to steal the boot off my old one when I got the refurb last week.

Yes, you can screw the rod in and out to change travel -- though I think it's the opposite direction, as it's a pull affair, not push, I think -- but I don't like it. It's just gonna mask whatever else is wrong with the system.

And brakes are not something you want monkeyed with like that /forums/images/graemlins/smile.gif

I'm wondering if you have a serious hydraulic problems (like, collapsed or bulging hoses or lots and lots of air). When you're bleeding, did you clamp the proportioning valve so it was bypassed?

-- A
 
There is no proportioning valve on mine. It is a 77 3/4 crewcab if that matters. It just seems like the piston in the mc isn't moving enough to get all the air out. but mainly with the rear brakes.
 
Huh. Is the p-valve a 4WD thing, I wonder ... I haven't looked at my /forums/images/graemlins/crewcab.gif to see if it has one.

Umm, the rear (wheel cylinders) take less pressure/fluid to activate than the front (calipers), which is why the reservoir for the back is so much smaller than the front.

Leastaways, I seem to recall it's that way. /forums/images/graemlins/dunno.gif

Presuming that's the case, this would 'splain why you get less fluid at the rears.

I'd still fix the leaky bleeder(s), and look for the recent posts about DIY power bleeders. I gotta do that here in a bit when I replace the master on my six pack.

-- A
 
all dual circuit brake systems (seperate lines for front and rear) should have a p-valve sumwhere. this is the first time i've heard of one without it. sounds liek a hack job to me.
 
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all dual circuit brake systems (seperate lines for front and rear) should have a p-valve sumwhere. this is the first time i've heard of one without it. sounds liek a hack job to me.

[/ QUOTE ]

Jah. Just looked it up in the service manual: "Combination valve, used on all models with disc brakes." Combines a metering valve, a failure warning switch, and the proportioner.

For the original poster, are you SURE your booster is good, has good vacuum, etc?

-- A
 
Seems to have good vaccuum for the booster though with the engine running in park if I press the break the engine revs momentarially. Where should the proportioning valve be? Maybe I am just missing it. I was under the impression that it would be right next to the mc. As in the brake lines go into the p-valve whick connects to the mc if the truck had one. As far as the rears I get a little fluid come out the drivers side (1oz maybe) and hardly any out of pass side. I tested the booster before I put on the mc to make sure the rod pushed out and it didn't seem to come out very far (1/4 inch or so. But the sticker on the booster said it may need some adjustment which is why I am wondering.
 
[ QUOTE ]
Seems to have good vaccuum for the booster though with the engine running in park if I press the break the engine revs momentarially. Where should the proportioning valve be? Maybe I am just missing it. I was under the impression that it would be right next to the mc. As in the brake lines go into the p-valve whick connects to the mc if the truck had one. As far as the rears I get a little fluid come out the drivers side (1oz maybe) and hardly any out of pass side. I tested the booster before I put on the mc to make sure the rod pushed out and it didn't seem to come out very far (1/4 inch or so. But the sticker on the booster said it may need some adjustment which is why I am wondering.

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The combo valve is up on the front crossmember for 4WD's; I think it's elsewhere for 2WD's, but no, it's not right by the master. That'd make sense /forums/images/graemlins/rotfl.gif

I'm wondering if you have goo in the hardlines or something -- that power bleed is sounding better and better.

And did yours really come with a TH350 as a C/20, or did somebody borrow the TH400?

-- A
 
It came from the factory as a 350/350 crewcab and from what I can tell a camper special as well. The PO put in a 454 out of a 74 Chevelle. I plan on putting in a Caddy 500/400 combo hopefully soon. Goo in the lines would make a lot of sense. The olde mc had so much crud in it I could scrape it out with my finger like mud. What should th combo valve look like. What is a power bleed and how would I get it done? Thanks for the help.
 
Ooh. Caddy/TH400 combo would be sweeeeeeeeeet!

Umm, combo valve on 4WD's is a metal junction fitting maybe 6" long, with brake lines going into it. I assume the 2WD version is much like that. I'd go look, except my truck is two miles away, grr. Trace the brake lines, you'll find it.

Search for power bleed or look for my posts, there was a thread about this last week. In short, you put pressure (~10psi) into the master, forcing brake fluid in (and hopefully air and goo out on the far end!)

-- A
 
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It came from the factory as a 350/350 crewcab and from what I can tell a camper special as well. The PO put in a 454 out of a 74 Chevelle. I plan on putting in a Caddy 500/400 combo hopefully soon. Goo in the lines would make a lot of sense. The olde mc had so much crud in it I could scrape it out with my finger like mud. What should th combo valve look like. What is a power bleed and how would I get it done? Thanks for the help.

[/ QUOTE ]


I can take a stab,

go look at your master cyl, there are two hard lines with spirals in them that lead down towards your frame. Follow these lines down..

right at the frame, you will run in to your power steering box and pump lines, they are held to the frame with a 2 inch wide bracket to keep them from moving around..

right by this bracket you should see a wire 12 guage wire, this wire has a plug on it that plugs on to a wire leading to the combo valve. this should be located on the front most crossmember, it is a rectangle shape, 5-7 inches long with two lines coing in through the top and 1 on each side.

also..


have some one push the pedal for you with the motor off, do you hear a hissing or swoosh noise? If so it may be possable you got a bad booster or somehow damged it.

if that is not the case, did you swap you calipers or have them off any time lately? If so you could have mounted them on the wrong side, thus causing the bleeders to be flipped and not work.

I would also say to check everything before you start adjusting things, if you put the right booster in and it is working, I would consider getting it power bled.

Power bleeding is done in a shop and can really help out sometimes, I would think 50.00-60.00 is the price for that.

Also take a look at your front rotors, are they there and alive or in ok shape? If they go out, or come apart you can destroy a caliper, look for fresh fluid, a unloaded caliper is just 15 to 18 bucks at auto zone too. While you are on the hunt, look at the rear drums and look to fresh fluds or leaks. Also make shure you get a bleeder screw, if it is leaking or not sealing you will have a hell of a hard time, dont just ask for one when at the parts store, take one in, alot of the times you will be buying a few before you get a good counterman, buy a line wrench while you are at it to prevent stripping them.

If you are young or just ambitious, head down to auto zone and start replacing hard lines 3.00 to 7.00 each, break lines, porportioning valve ect..but this is just throwing money at the problem, if you are young that is not the best idea. Just take your time, check everything twice and look at everything as the possable problem, and dont be afraid to ask questions you think are stupid, the only stupid question are one's not asked "unless it comes from me" /forums/images/graemlins/smirk.gif


Brakes can really suck sometimes, after you rebuild your brake system and figure out how they work it aint that bad. Also please fill out your profile and location, someone on here may be just up the street..

Some pizza Or beer will get you most peoples help for at least a hour ot two /forums/images/graemlins/thumb.gif

good luck, also if you need any pics or have questions or want someone to peg questions over the phone, just reply back and ask! /forums/images/graemlins/waytogo.gif
 
Thanks that helps a lot and I think I know what you are talking about for the combo valve now. The only thing I have done so far is replace the booster and mc and the calipers are in the correct position. The one bleeder screw that is broken doesn't seem to be leaking at all no fluid around it, didn't even know it was broken until I tried to get a wrench on it. The post on power bleeding seems like a good tip and I may wind up trying that. I thought I had filled out my profile but will check again. I am in Lubbock, Texas if there is anyone around I would appreciate help or just someone to "talk shop" with. I'll go back out tomorrow to work on it some more and try to get things in order. Truth is I am on workmans comp for a herniated disc in my back an so I have to go pretty slow when working. I worked about 5 hours strait on it in the heat and gave up for some heavy meds. But tomorrow is another day! Thanks for all the helpful replys.
 
I used to be a brake mechanic so here's my 2 cents. 1st you'll need a lot of new brake fluid so make sure you have it before you start. You mentioned that you bench bled the mc. Did you bleed it on the truck also? If not I would start there. When you loosen the line you can wiggle the hardline and tap on the mc with your wrench to jar any air bubbles free. Do each side a couple of times and keep in mind you may do this again once you've gone over the whole system. Once you've finished the mc you can bleed the proportioning valve for good measure, same process as above. Next go to the rear and bleed the farthest one out, then the other side. Fix the bleeder on the front and bleed them passenger side first then driver. Once you're done jack up the rear and adjust the rear brakes (reach through the backing plate w/screwdriver) until you can hear the shoes lightly dragging when you rotate the wheel. The brake pedal adjusting rod should have a very small about of play between the rod and and booster and the same for the booster to mc. While you're at the wheels bleeding the brakes you should listen and look for movement of the caliper and wheel cylinders to insure they are working, if not you need to rebuild/replace as necessary. Once this is done you should have a good firm pedal, if not you may have the incorrect mc/booster combo. Power or pressure bleeding is good if you're alone but not really necessary for your vehicle so I'd use the money for new calipers/wheel cylinders/hoses. Good luck! /forums/images/graemlins/thumb.gif
 
As stated above start with replacing the broken beeder. You may have to just buy a new caliper. The new mc/booster will do nothing until the system is properly bled. Bleed the brakes with the truck off, not running.
 
o, forgot to mention it before, the p-valve is a bitch. i had to bleed my brakes for like 4 hrs to get it to do its job. /forums/images/graemlins/yikes.gifcucs once it feels a circuit has no pressure, it cuts it off. course, maybe mine was just a pita cus its so old. i dunno. just my 2cents.
 
Well I went out and got a rebuilt caliper today and I think that solves the problem. I didn't get to try it until after dark so just to test it and see if the caliper and broken bleeder was the problem I zip tied it to the tierod and hooked up the brake line to it and did a quick bleed of that one wheel and the difference is amazing. Even with a very quick bleed and just hanging there with nothing to squeeze against the pedal pressure is almost normal now. Now in the next couple days I'll have to go out and swap the calipers all the way and rebleed the system. Thank you very much to all who replied and the helpfull tips.
 
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