Grrrr brakes again

flstf09

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I posted awhile back about my brake issues.Thought it was a vacuum issue due to a large cam.Finally got the vacuum pump on and things didn't change.I have 2 man bled,vacuum bled,gravity bled and pressure bled,no improvement .Pedal feel is good just don't seem to make enough  pressure.

 

Mister 4x4

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Refresh our memory: Is your booster holding vacuum? 

I replaced my entire braking system as a result of building the car, and I was having issues of no power-assisted brakes despite the original brake booster.  After chasing my tail with a new hose, coupler, and everything else, I broke down and bought a new booster from GPS Automotive: http://gpsbrakes.com/ and all was good... great pedal and the brakes work awesome.

Anybody else will sell a 'suitable substitute,' which won't be a good fit, as well as the local parts stores that say they can get you a rebuilt unit will require you to ship to Cardone for a rebuild - which who knows how long that'll take.

Anyway - just a thought regarding the integrity of the booster might be the problem with your vacuum.  Disregard if that's not the issue.

 

flstf09

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Booster seems to be holding.Brakes worked fine before I changed engine,new flex lines front and rear.Didnt change calipers because they looked good but they are unknown.Changed master cylinder all rotors and drums were turned.New pads and shoes.Rear wheel cylinders appeared to be new.Rear brakes adjusted properly.Ive been chasing this problem for nearly 2 years now.Dont seem like they are making enough pressure to " clamp".Brakes wont pump up.I haven't just started throwing parts at it yet because I thought it was an engine vacuum problem.Maybe I just need to replace and upgrade everything,should've done that to begin with but there was no issue before.

 

Mister 4x4

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OK - I might have something for you to check.  When I put mine back together, I went with all-new factory-style everything (OEM replacement), to include new brake lines, calipers, master cylinder, distribution block, etc. - literally "everything" except the booster, since I ran into issues trying to get an OEM-style new one or mine rebuilt.  I got it all back together, bled, and I could not get my pedal to firm up - couldn't figure it out... chased my tail for about a year after I got the car running - after several pumps, it would hold, but not good enough for driving.

After I received the booster and installed it, the problems still persisted - so 'that' wasn't it.

I did some more research, bugged the guys here, and thought about trying a bunch of different things... and then the light bulb went on for me when I was under the car - I'd installed the calipers on the wrong sides (passenger on driver, drive on passenger).  Crap!  Once I swapped them back to their correct sides and bled the system again, it was all golden... finally.  The way I determined it was noticing that the bleeder valve was lower than the brake line inlet.  Duh... felt like an idiot afterward.

I don't know if that might be your issue, but it wouldn't hurt to check just in case.  (although, you did say the brakes worked fine before the engine swap and you didn't change the calipers)

Have you checked your power brake distribution block?  I understand that if the proportioning valve gets 'tripped,' it won't work right until it's 'reset,' which I ain't gonna lie - I'm not entirely sure what that means.

Do you have your brake booster vacuum line system hooked up to the base of the carb, or straight to the intake manifold inlet toward the rear of the engine?  I put an elbow on mine and went straight off the intake manifold.  My 351C-2V has a pretty healthy cam in it (CompCams Magnum 270HR - 270/270, .566" lift, 110 degree lobes - 215/215 @ .050") - haven't experienced any vacuum issues.

Sorry if I've thrown out things that you've already checked - these are the things I've run into with mine.

Hope it helps.

 

flstf09

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It's on manifold vacuum. Calipers are on correctly.I haven't gotten into proportioning valve or distribution block issues yet.I talked to gps brakes and got some advice on some things to check.My cam is 590/620 247/[email protected] .050 110lsa I'm making about 8-10" of vacuum at idle.Pump is supposed to put out 20".

 

flstf09

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I've adjusted mc pushrod at least 5 times too.I bet I'm getting close to 5 gallons of brake fluid used over the last couple years.

 

Mister 4x4

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Oh Geez - that's a monster cam!  :bravo:

Is it possible you just don't have enough brakes for that fire-breather?   :cool:

Wow - definitely more than just a mild head scratcher on this one.  I wish I had more ideas on this.  I'll be keeping an eye on it though, 'cuz now I'm curious as well.

I wonder if there's some kind of a pressure gauge you could put on the end of each brake line to find out what kind of line pressure you're working with... as well as if there are some specs you can bounce against to rule out the calipers and wheel cylinders without having to just simply throw new parts at the problem (because going the route of simply upgrading will only be throwing more expensive parts at the issue).

Good luck, Brutha!

 

flstf09

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The cam isn't in a 351c so it's not really a monster.Its in a 521.I really want to think it's the booster but it holds vacuum.

 

flstf09

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If something was wrong with the proportioning valve could that cause a lack of pressure at the calipers/cylinders?What can go wrong with the distribution block?

 
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Did you use stock pads up front of something more aggressive like ceramics? Our cars don't generate sufficient pressure for ceramic pads.

If you want to, you can PM me your mailing address, I'll pack up and send you a brake line pressure gauge and you can check and see what you are getting and if you are in the right range pressure wise. I won't need it til late this summer, just send it back when you are done.

 

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Read this thread to answer your most recent question. https://www.7173mustangs.com/thread-disc-brake-proportioning-valve-blocked?highlight=distribution+block

The booster is not going to work right with 8 in./hg. Assuming  the booster and check valve are good, you could try advancing the initial timing to see if it picks up the vacuum enough to operate the booster, what is initial timing now? Again assuming the booster and check valve are good, if the increased initial timing doesn't work, a vacuum pump and an additional reservoir may be used to provide the needed vacuum.

Chuck

 

flstf09

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Thanks for the offer on the pressure gauges Jeff but I may have found the issue,at least a major part of it.I checked my booster last fall and it was ok.Ran a check on it again last night,it won't hold a thing,0".Tried pumping it up with my hand vacuum pump couldn't get squat.Hooked up the electric pump which is putting out 20" Tee's a vacuum gauge in between the pump and the booster.Didnt build anything at all 0".Pump just ran and never shut off.Pump is functioning correctly shuts off at 20" kicks on at 15".Took the old booster out,which is a pita with a big block.It was in very rough looking shape,very crusty on the back side.I sure hope I can get the new one in without hosing it up.

 

Mister 4x4

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Wow - I'm wondering if maybe with a new booster, you might not need the vac pump.  :chin:

Are your clearance issues due to the thickness of the booster, or the diameter of the booster?  I ask because the 'replacement' booster I ordered from NPD is thicker, but smaller in diameter (not to mention the bolt pattern for the firewall was different).  The GPS Automotive booster I have on mine now was a direct replacement and fit perfectly (had it changed out in about a half hour).

Glad to hear you're getting closer to resolution. ::thumb::

 

flstf09

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I'm ordering one from GPS.Yes it's due to the thickness.The studs will come out of the holes but not alot.Had to tweak the brake pedal rod down pretty good and remove valve cover to get it out and it was still very tight.I hope I don't have to pull engine to get the new one in.

 

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