Customs dual master power booster upgrade not working

After a brake failure with my rebuilt single master power booster I decided to upgrade to a dual master with 8" power booster kit. We took the rear line off the junction box and ran it up to the rear port on the master and plugged off where it used to go and ran the front lines to the front port, no proportioning valves. The brake light switch was installed in-line as the master cylinder didn't have an outlet like the original did. We verified there is vacuum, and the pedal is rock hard, but when the car is turned on and put into gear at idle, you have to apply a ton of pressure onto a hard brake just to keep it from rolling. It seems as if the power booster is not engaging, and at the very least I would expect the manual brakes to work.

The shop that did the installation e-mailed me and let me know that they think both the original vacuum check valve on the intake and the one on the new booster are both installed, so effectively there might be two check valves, but they said they verified there was vacuum in the booster (not sure how) so they didn't think that would matter. They also mentioned that it took a lot of force to crack and move the pedal the first time, but it is still remaining pretty stiff and barely moves.

Any thoughts and suggestions on troubleshooting this or figuring out whether we have a bad new booster? Need help. Want to drive this before winter.

Thanks,

Joe G

 

Sounds like it's not hooked to a good place on the vacuum.

Put up a pic of where the hose is on the motor.


If vacuum is present at the booster, you should be able to hear a whoosh if you pull the booster check valve out (after the motor was just shut off, and not touching the brake)

Also, if you hold the brake down, then start the motor, your pedal should drop towards the floor. If not, probably no vacuum

 

Check the pressure at the master cylinder with the vacuum unplugged and then with it plugged in and the engine running to verify that the booster is providing ***istance. Is the bore size of the new master larger than the one you replaced? I would ***ume that the master was matched to the booster to provide the proper pressure but stranger things have happened.

 

Please don't drive it until you get it figured out! (but you knew that) I don't understand what you did with the rear line. There should be one line coming forward from the rear axle, that goes to one port on the master cylinder. the 2 front lines have to go to a tee then a single line from the tee to the other master cylinder port. Brake light switch must be teed into either front or rear line.
If the "shop" that did the conversion, left 2 check valves in the system, (or doesn't know if they did) don't trust anything they did!

 

Rear port is usually primary, and should be used on your front brake circuit. There are some exceptions to this rule, but I dont know what they are.

 

Instant T has this correct. If you had a shop do the conversion, and they did not know this, take it to a shop who does know brakes.
Further, we need to know: 4 disc? 4 drum?, or a combination?? All have their unique requirements as to plumbing.
Lastly, 8 inch boosters are notoriously weak, better to go full manual than use one of these.

Cosmo

 

Sorry, it is four drums. Wolfcreek-Steve, it is hooked up exactly as you described. They blocked off the one port on the 'T' just below the master because the rear used to come into the back of it. I'll make sure we try these things in the morning and then go from there. To me, it sounds like they aren't even creating pressure in the master to generate the manual brakes, let alone the power booster, so perhaps a problem with the rod/clevice? Also, two check valves could cause a problem even if there's vacuum at the booster? Just asking. I'm not an expert by any means. The shop did all the work. I've been spending all the money :/

 

Running the line to the rear directly off the MC and blocking that port at the junction block is fine. The acid test for a booster not working is: Engine off, pump all the vacuum out of the booster. Foot on the brake, start the car. The pedal should drop (not to the floor) noticeably.

 

If the booster isn't working you don't just have manual brakes. As Cosmo said 8" boosters are ****. I went through the 8" booster h***el years ago. Finally I s****ped a brand new MPB booster and replaced it with a $10 junkyard booster that 70K+ mi later is still working fine

 

I have to

I will definitely have to check this. So, if I understand correctly - the port closest to the booster is the primary one and feeds the front brake lines? Also, I had consulted with several shops who had told me that they use 7" boosters for 57 Chevys and that an 8" should be more than enough for mine, but again I'm not an expert. Is there a better size booster? The new booster and master were bought as a kit and pre-***embled. It has a 1" bore.

 

The original stock boosters for this car wouldn't let you seperate the single master to replace with a dual. If I want to upgrade to dual I have to swap out the booster, as well. Any ideas?

 

As far as I am concerned, the BEST booster for any system is the one that came from the car that matches the front brakes. Yeah, I know they're large. Do you know WHY they are large?? Because they HAVE to be. If you do not have the room, try a properly sized manual system, especially on drum brakes, as they self-energize and really do not need a booster. Alternatively, you could use a remote booster, though you'll need to go back to the single reservoir master, unless there are dual remotes of which I am unaware (always a possibility).
I nearly forgot (CRS syndrome), Hydro-Boost. Small, powerful, and powered by the hydraulic pump, like the one powering the steering.
Cosmo

 

Yes. The first piston the pedal contacts is the first to activate, so it is the first circuit to apply. These should be the Front brakes. The second piston is actually activated by pressure created by the first piston. If drive a car with rear brakes as the primary and come to a hard stop, you're going to fishtail all the over the place and probably poop your pants. (I learned this the hard way in high school auto-shop. Mr. Lingenfelter was not happy that I road tested without his inspection first.) The only vehicles I know of with rear primaries are Big Rigs, but that is because trailer weight is focused on the rear wheels.


[/QUOTE]I will definitely have to check this. So, if I understand correctly - the port closest to the booster is the primary one and feeds the front brake lines? Also, I had consulted with several shops who had told me that they use 7" boosters for 57 Chevys and that an 8" should be more than enough for mine, but again I'm not an expert. Is there a better size booster? The new booster and master were bought as a kit and pre-***embled. It has a 1" bore.[/QUOTE]

 

Sounds like one of the check valves is hooked up backwards and not allowing vacuum to the booster. You should only have one check valve (at the booster that will allow vacuum to p*** and to hold vacuum when the engine is off. easy to check. With the engine running pull off the hose (and fitting) from the booster. Huge vacuum leak or the engine will stall. If not one of the two valves is backwards.

 

The master cylinder port closest to the booster is the primary, but does not always feed the front brakes! You need to know for sure how to plumb the master cylinder you are using, if not obvious by the larger front brake fluid reservoir on older masters, or on modern two-piece masters with single fill plenum reservoirs.

The 7" single diaphragm boosters are useless, imo. Much better to use a dual 7", 8" or larger single diaphragm booster.

 

I think there's enough room...The one that came with the car was long, whereas these new boosters are wider in diameter. The original was 4" in diameter and about 8" long. Just not sure how to determine what would be the right size. A few of the techs I spoke with at various 'hot rod stores' online said 8 inches.

 

I am having the same problem on a disc/disc brake system, mustang II front and Ford 8.8 rear end, very poor braking and hard pedal. I have upgraded from a 7in dual to a 8in dual booster with a Corvette 1- 1/8 in master cylinder and adjustable purporting valve. On my master cylinder the large chamber is in the front not next to the booster and that is where I have my front brakes connected. I have 15 to 18 inches of vac at idle and a7.5 to one pedal ratio. I have removed the proportioning valve from the circuit and still have the same problems. Could it be that the smaller chamber in the master cylinder, closest to booster should be for the front brakes and not the back? Everything has been bleed and all components are new and I still can't lockem up on gravel, maybe I should try it on wet gr***, LOL.

 

It's real hard to do this third hand. We have not the opportunity to speak with the folks actually DOING the job, just the owner, who may have their ear, or whom they may think is just interfering.

Brakes are important, almost as important as they are misunderstood. Upgrades are not always upgrades. Information is not always correct. Many may not believe me. The aftermarket is not always your friend. The aftermarket can be full of ****.

My opinion is that you cannot go far wrong by adhering close to what the factory did. In your case, match the bore of the master. What size booster is best?? From a car that is at LEAST as big as yours (duh, ya know), so use a full size car booster (***uming the brakes are for your avatar vehicle), NOT an aftermarket booster intended for a car less than half the size (duh, again, ya know). Plumb the master as Instant T stated, and for the reasons he stated, for they are valid.

For D Dan's case, as hijacked as the case is, the master you SHOULD use is the M II master and pull the residual valve out of the rear line. 1 1/8inch bore is exactly opposite of where you need to go for more stopping power.

Cosmo

 

if the pedal is hard and won't budge , look for a crimped or flattened line , sometimes when brake lines are bent too tight the insides collapse preventing fluid flow . check the lines near the master where there is any tight bends . as for the booster if its a twin 8" there is enough surface area to pull the brakes its equivelent to a single 10" as thats what they used on the 4th gen f bodys due to space and they have good brakes . if its a single you have to have a real high vacuum producing motor to make them work and some apps they have to use a electric pump to make them work , as for hydroboost , thats th eway to go , look at the astrovan units as they are the most compact .

 

All of the lines are stainless steel, so no crimping. They said they think the booster may be bad so they are swapping it out for another 8" dual. Just waiting for the replacement from the manufacturer. Tell me if THIS sounds right: The company that had rebuilt the original Delco single master/booster told me that it probably leaked because we didn't break the seal in soon enough after installing the unit on the car and putting the brake fluid in. They said that after being rebuilt, within 6 months, if we installed it but didn't use the car, the seal could be compromised. Does that make any sense??? We had put it on the car within a month or two of getting it back and only used it a few times to get it on and off the flatbed doing bodywork. I replaced the brake light switch and apparently had let air into the system and after that is when I lost brakes. Lines were bled and had a good pedal then during a test drive they failed and the leak under the master/booster was discovered. Here's some pics of the new, non-functioning upgraded setup. You can see where the brake light switch is inline with the rear brake line in the 2nd photo and vacuum line coming off the intake to the booster in the 3rd:

:

 

I see the problem , the Vac*** hard line from the manifold is collapsed or looks like its collapsed near the t fitting by the carb and linkage . bet you unscrew it put a nippple in ther and rubber hosed it to the check valve on the booster it might work .

 

My experience plus a friends with those aftermarket dual 8" boosters are that they aren't worth the powder to blow em to hell. If you look at 90's Chevy/GMC vans they have a booster that's about 8-9". That's what a friend and I both used to replace the MPB **** boosters. Also if I'm remembering correctly after 12 years MPB specifies 18"+ on vacuum in order for their booster to work. Anything less and they attribute non working brakes to low vacuum

 

I see what you're looking at but that is a steel line. The shadow is falling on the curve so it looks collapsed, but they were reading perfect vacuum out of the end of that line.

 

That may be the next step. This booster is made by The Right Stuff Detailing. They do specify between 16-18" of vacuum at warm idle which we verified we have. Any particular model that you recommend? Would you buy new boosters for the GMCs or a rebuilt one off of one?

 

Maybe I am too ****, but if a SHOP did THAT job, "You are SOOOO fired!!!"

Adaptors on lines, instead of getting the right fitting and flaring the line to fit?? The ONLY time you should use adaptors is if: A) you have no idea what 'flaring' means. B) It's a Geo. C) you are NOT getting paid to do this. If you're getting paid, you DO A BETTER JOB!!

Words fail me on the brake switch abomination. It's asking for a spongy pedal.

That steel vacuum line, hanging out in the breeze with nary a clamp to hold it, will vibrate and fail, soon.

Yeah, this is being critical, BUT YOU PAID FOR THIS!!! It should be A++++, not C grade work.

Cosmo

 

Will the adaptor on that front port cause any 'problems'? Really curious because I'm not sure why that is there. They have all of the equipment at the shop to flare lines. As for the brake switch thing...what could they do to make that better because there are no other ports to plug the switch into? Thanks for the input. I will p*** it along!

 

The switch is Teed in pointing upwards. That way air can get in there, and not bleed out, that's what cosmo meant by improper installation! Air in there will always give you a spongy pedal.

 

So, should I ask them to T it upside-down or sideways and somehow clamp it down, maybe to the inner fender? Will that help?

 

they need to replace the T with all those adapters and short line with a NAPA Weatherhead T part # 652X3 and then the switch will thread in directly to the T middle port