47-55.1 Master Cylinder/Booster HELP!!

[NeoJuice]

Originally Posted by dsraven

on the "which line goes where" I would connect the front brakes to the larger threaded port. smaller threaded port would be the rear. also check how the prop valve you have works as some have metering valves that restrict flow/pressure to the rear brakes on hard brake applications. this is to stop rear wheel lock up and keep the rear of the car where it is supposed to be, behind the front. if the master had 2 different sized reservoirs the larger res would normally be the front brakes. masters with 2 hugely different sized reservoirs are usually for disc/drum brakes because the rear wheel cylinders don't vary as much, fluid wise, as the front calipers do as the brakes wear out. caliper pistons are usually much bigger diameter than the wheel cylinders so they displace more fluid and as the brake linings wear they require more to top up. hopefully this didn't confuse you more.

Taking a closer look at the corvette master this weekend the front port (larger bowl) is the 1/2-20 port and the smaller bowl (close to booster) is the 9/16-18 port. So should I still plum it the same way? Larger bowl to the front brakes and smaller bowl to the rear brakes?

I had a little garage time this weekend so I started to bend up the new lines. I got all new fittings as well as female tube joiners.

[NeoJuice]

Update- I got the corvette master cylinder bench bled and re-installed in the truck. I flared up some new lines and used the joiners to connect them to the existing lines. I pumped the pedal a couple times to check for leaks and none found at this time.

I haven't had the chance to bleed the lines yet because I was waiting for my vacuum pump to arrive. It arrived yesterday from Jegs. Before I proceed with bleeding the lines I want to verify that I have all the lines plumed correctly. See attached image. This is how I have it plumbed in the truck.

I'll get a plug for the back of the carb and plum the hose directly from the vacuum pump to the booster.

[NeoJuice]

One thought that just occurred to me. Should the 2lb residual valves be closer to the proportioning valve or like in the image further away.

My rear 2lb valve is near the back of the truck currently. I put it up near the rear b/c the rear calipers could possibly be higher or at the same elevation as the master cylinder and I didn't want a possibility of loosing some pressure on the brake pedal.

Thoughts?

[paintman]

Alot of people say the res. valves are supposed to be as close to the MC as possible. Although, the same people that say this can't give any good explanation as to how the location makes any difference. If you do a google image search you will see that they are place all over. I placed my front res. valve about 3 inches away from the MC. My rear Res. valve is about 24" away, and after the prop valve.

[paintman]

Curious to know why you think you need a vacuum pump. Not trying to be a smart ass. Just going through some brake issues myself.

I have also been told I need a vacuum pump. However, It seems to me that if after you bleed the brakes and have a rock hard pedal, you should still have a rock hard pedal once engine is running if you have low vacuum. No? After all the booster is there to help pull the pedal down for you. Thus making the pedal easier to depress.

[NeoJuice]

After I got the truck tuned by a buddy it's running 10-12" vacuum and 32 degrees total timing and 10 degrees base timing. The low vacuum is because of the cam the previous owner put in the truck. When the truck was running I had little to no brakes at all. You need at least 18 inches of vacuum to properly operate the booster as far as I'm aware. The Leed pump does 25"hg

Between swapping out the master cylinder for the corvette MC and adjusting the booster push rod and adding the vacuum pump I hope to resolve all my brake issues.

I went with the LEED pump b/c it's quiet. I could have got another style and paid less but I didn't want a noisy a$$ pump and I also wanted a simple two wire hookup in a self contained unit. I didnt want to deal with something like this https://www.performance-world.com/El...p-p/841001.htm

I hope this weekend to get the pump installed and all the brakes bled. Then I can test from there.

Thinking about it after the fact I should have spent that money on a OEM style CAM, I had it all ripped apart earlier when I did the timing chain & I would probably be ahead in the $$ dept lol.

As you can see in the video it's got a pretty good lump in the idle.

https://photos.app.goo.gl/BCa9hN5qPyCJ6zU37

[NeoJuice]

Originally Posted by paintman

Curious to know why you think you need a vacuum pump. Not trying to be a smart ass. Just going through some brake issues myself.

I have also been told I need a vacuum pump. However, It seems to me that if after you bleed the brakes and have a rock hard pedal, you should still have a rock hard pedal once engine is running if you have low vacuum. No? After all the booster is there to help pull the pedal down for you. Thus making the pedal easier to depress.

From Wiki:

A brake booster is an enhanced master cylinder setup used to reduce the amount of pedal pressure needed for braking. It employs a booster set up to act with the master cylinder to give higher hydraulic pressure to the brakes and/or lower force applied on the brake pedal through a brake booster push-rod. The brake booster usually uses vacuum from the engine intake to boost the force applied by the pedal onto the master cylinder or may employ an extra vacuum pump to enable it. Without the engine running the brake pedal feels very hard and ineffective on the braking capability. An "active" booster is a non "conventional" booster where a solenoid is used to open the booster air valve to automatically push the master cylinder forward to perform some forms of dynamic stability control.

[paintman]

Thanks Neo! I guess I need to invest in a vacuum guage and see whats going on. I also have a lumpy cam in my 292 six banger. Although, even with the wiki explanation of how a booster works, I just can't get my head wrapped around...........How can it be when the engine is off, and you have a hard pedal, logic would say if when the engine is running and there is not enough vacuum, you should still have a hard pedal. Not a soft pedal.

[NeoJuice]

Best thing to do would be to get a vacuum gauge hooked up and see what your pulling.

My buddy who set the timing & carb adjustments on my truck came to my house with a timing light and vacuum gauge. I know there are lots of videos on you tube about troubleshooting engine issues with just a vacuum gauge.

[NeoJuice]

Originally Posted by paintman

Thanks Neo! I guess I need to invest in a vacuum guage and see whats going on. I also have a lumpy cam in my 292 six banger. Although, even with the wiki explanation of how a booster works, I just can't get my head wrapped around...........How can it be when the engine is off, and you have a hard pedal, logic would say if when the engine is running and there is not enough vacuum, you should still have a hard pedal. Not a soft pedal.

DsRaven? he might be able to chime in on this. I'm no expert or claim to be one and my advice should not be used to operate a motor vehicle in any way lol.

[1project2many]

It seems to me that if after you bleed the brakes and have a rock hard pedal, you should still have a rock hard pedal once engine is running if you have low vacuum. No? After all the booster is there to help pull the pedal down for you. Thus making the pedal easier to depress.

Sort of. You can probably imagine drinking soda through a straw. You create a vacuum at one end of the straw and air pressure at the other end forces your drink up the straw and into your mouth. Now pinch the straw in the middle. Create the vacuum on one side but nothing goes through the straw. Release the pinch and what happens? Well it depends on how much vacuum you're creating. If you create a little vacuum then the drink will flow slowly. If you create a bunch of vacuum the drink flows quickly.

In a booster there is a valve which seals the booster off from air pressure like like your hand pinching the straw. The engine creates vacuum on the master cylinder side of the valve and air pressure applies the brakes when the valve is opened. If the engine is only producing a small amount of vacuum then you will get assist, but it will be very little and the brakes will feel like they apply slowly. Things can get a little more complicated because the brake booster has a check valve on the vacuum side which "stores" vacuum. If you were to rev the engine and snap the throttle closed you would create high vacuum for a very short time. This increased vacuum will get "trapped" in the booster and when you apply the brakes they will apply just fine. But if you release and apply the brakes again the "trapped" vacuum will be depleted and the brakes will again apply slowly. So the pedal may not be rock hard after startup, but pressing the pedal two or three times in a row would cause it to apply slowly and with very little assist.

How can it be when the engine is off, and you have a hard pedal, logic would say if when the engine is running and there is not enough vacuum, you should still have a hard pedal. Not a soft pedal.

Both logic and experience tell me the same thing. If I started the engine and the pedal was substantially easier to apply after two or three applications I would not say there is insufficient vacuum for the brakes. I would look elsewhere for the cause of a too-soft pedal.

[mick53]

I bought my vacuum pump from Master Power Brake. They say it doesn't need a reservoir but I will probably put one in. It came with a gauge for testing or you can leave it on there. It's not a very nice gauge.I plan on taking the engine out of the loop. I'm running a 4-71 blower on my 292 so vacuum is a problem. I think it was about $600.

[NeoJuice]

Originally Posted by mick53

I bought my vacuum pump from Master Power Brake. They say it doesn't need a reservoir but I will probably put one in. It came with a gauge for testing or you can leave it on there. It's not a very nice gauge.I plan on taking the engine out of the loop. I'm running a 4-71 blower on my 292 so vacuum is a problem. I think it was about $600.

I looked at the master power kit but decided to go with the Leed brake vacuum pump instead.

I plan on taking the engine out of the loop as well. Just going to plug the back of the carb.

[dsraven]

also, like one project says, check the one way check valve in the booster to ensure proper operation. it should allow vacuum to enter the booster but not allow it get out through the hose. use the check valve with the new pump as well. stuff fails, it's life. the check valve is there to allow at least one normal brake application with boost. after that there will be a progressively harder pedal with each application until there is no boost at all. the issue is that power brake vehicles also have a larger bore master cylinder usually so the effort is increased to get the same amount of braking when there is no boost. thus the rock hard pedal.

[NeoJuice]

I know I havent posted an update in a while. I got the leed brakes vacuum pump back in June and finally got it mounted and installed. After the install and test the brakes still felt a little spungy with vacuum.

So I had my mechanic buddy come over to help with a two man brake bleed since the one man bleed wasn't doing the trick. We bled it good and found some more air in the lines. Once we were confident all the air was out we now focussed on the booster & master cylinder and did a big adjustment on the booster pin. I thought when I put on the corvette master that I adjusted it out enough but apparently I didnt.

We took the bolts out of the master cynlinder and moved it slightly out of the way. I pressed on the pedal to push the pin out and he adjusted it out quite far. Then put the master back in place and it wouldnt sit flush. Push the pedal down again and screw it in a little. Still wouldnt sit flush. Push pedal again and adjust in. We did this a couple times until it was just sitting flush. Moved the master out of the way one last time and locked the pin in place.

We now had good firm pedal and did an adjustment to the prop valve for the rear tires and everything was looking to be working good. At the time this was all going on I had the truck up on crib blocks and we decided to do a brake stand test. So I fired up the truck and put it in gear, held the brake pedal down and gave it some gas. The rear brakes didnt start to let go until about 2800-3000rpm. My buddy said that was pretty good depending on what type of torque converter is in the truck and gearing etc etc.

So now I was on cloud 10 thinking that everything was working correctly.

Part 2 of this story to follow.

[NeoJuice]

My buddy left and over the next couple days I got the tires on and down off the crib blocks to do some further testing. I have a tandem garage (two cars on one side) so there was plenty of room to do some brake checks.

Fired up the truck and let it idle for a bit to warm up. Popped it into drive and gave it some gas and tested the brakes. They felt real good. Went in/out of the garage down onto the drive way multiple times doing everything from soft to hard braking and everything felt pretty good. The pedal didn't feel spungy and the vacuum pump appeared to be doing it's job.

So......I decided to be a little adventurous (even though the wife was home) and figured I would take it up the block and road test the brakes and bit and come back. Its a quiet street, so I started doing some break tests at 10-20km/hr and the brakes felt good. Did some hard/soft braking and I was happy. As I was puttering up the block about 1.5 blocks from home now I was getting ready turn around soon. So I gave it a little gas and "BANG,CRASH" I slammed on the brakes and shut off the truck. I got out and looked under the truck and my drive shaft was on the ground & still attached to the rear end.

My first thought was WTF just happened? I look at the rear diff and its pointed to the ground basically. I continue to utter many many cuss words that this just happened. I'm 1.5 blocks from home as well remember. So I put my four way blinkers on and proceed to try and figure out what to do next. I figure I'm going to need some sockets to get the c-clamps off the u-joint and a jack to try move the diff back into place. When the diff dropped it also wrecked all four bolts but luckly the u-joints appear to be ok and the drive shaft doesn't appear to have any damage. Also lucky my brake lines didn't rip off or wreck my e-brake. You can see the brake lines twisted in the pictures. I'll have to check the e-brake as well after resetting the pinion angle.

Upon initial inspection looking at the rear diff I thought the rear diff had spun. It did indeed spin so I thought that the U bolts weren't tightened down enough. My neighbor came along in his 65 mustang and got out and took a look and even he couldn't believe his eyes. He said the perch's weren't welded to the rear end. It even had me stumped why this wasn't done and even something that I should have even needed to check.

The PO had the entire frame sand blasted and powder coating so it didn't make sense to me why they weren't welded. The diff is out of a 1980 transAM and the old perches were probably removed for the difference in width and the TCI rear leaf kit. The truck didn't have a drive shaft it in when I bought it so the PO probably thought he would do it later on. But why sand blast and powder coat everything then have to sand it off and weld it later. Doesn't make much sense to me.

So with the help of my neighbor and my father we pushed the truck back home and into the garage. My wife was not impressed to say the least when she found out I took the truck out. Since this happened last Sunday or the previous Sunday the truck hasn't moved and I'm not sure how I'm going to reset the pinion angle. I thought I was going to get on the road this summer but I'm not sure now. Might just have to pack it up and wait until next year.

Thoughts?

[NeoJuice]

One more.

[mick53]

You should be able to reset your pinion angle with a phone app. Be careful not to warp your tubes when welding the perches. Looks like you got lucky. Should be an easy fix.

[jweb]

You’re really lucky this happened at a low speed and close to home, could have been much worse at highway speed.

My driveline folded in half at 100mph on the dyno. Ruined my brand new exhaust and dented my floor. Can’t imagine what could have happened on the freeway.

[NeoJuice]

Originally Posted by mick53

You should be able to reset your pinion angle with a phone app. Be careful not to warp your tubes when welding the perches. Looks like you got lucky. Should be an easy fix.

I talked with my buddy and he has a TIG welder and can weld the perches back onto the rear for me so that's not a big deal. I have a small MIG but it would probably take multiple passes to get it done.

[NeoJuice]

Originally Posted by jweb

You’re really lucky this happened at a low speed and close to home, could have been much worse at highway speed.

My driveline folded in half at 100mph on the dyno. Ruined my brand new exhaust and dented my floor. Can’t imagine what could have happened on the freeway.

Ya for sure I'm definitely lucky. Now I just have to figure out how to reset my angles.

I found one article online that said "Vehicle Set-Up: Make sure your vehicle is at ride height - suspension loaded. You can not have your rear end "hanging". The vehicle does not have to be level, no matter the angle of the car you're still measuring the difference between the two angles."

Since the truck is so low I think my option would be to disassemble my wood crib blocks into to shorter maybe 8" cribs. Get all four tires up on the cribs so the truck sits higher off the ground.

Once the tires are up on the cribs use some jack stands to support the frame near the rear and carefully loosen the u-bolts enough to spin the rear back into place and set my angles.

That should give me enough room to slide under and get the tranny and diff pinion angles. Snug up the u-bolts and get the drive shaft back in. Then I can remove the rear tires and have my buddy TIG weld the perches back to the diff.

I'm not sure how to proceed. If I maybe removed the drivers side running board I might be able to slide under there enough to get the measurements. But I still need to loosen off the u-blots to turn the diff. So maybe that might work and with the jack stands on the frame. I'm hesitant to jack on the pinion yoke.

Thoughts?

[dsraven]

here is what I would do.
-jack up using the rear axle as a jack point so the suspension stays loaded with the weight of the truck.
-put jack stands under the rear axle spring plates so the weight of the truck never leaves the springs but the axle becomes "unloaded".
-jack up the front end and place on stands or cribbing etc. watch how the rear axle sits on the stands to ensure it will not slip off.
-the unit doesn't need to be level, just high enough for you to get under it and turn the axle, weld etc
-once it is up on stands place some more stands/cribbing under the frame but not touching the frame. these are the "just in case things move" insurance policy.
-loosen the ubolts on the axle. since the axle is above the springs and the stands are under the spring plates the axle should turn relatively easy because it is not carrying a load. you could also put the park brake on, remove a wheel on the driver's side (the park brake holds better in the forward direction), and use something bolted onto the axle flange to help turn the axle. shouldn't really need to though. don't loosen the ubolts too much or the spring plates will wanna move around as well. with the wheels off you will have better light and room to work.
use a phone app or a digital angle gauge to check the angle of the trans output and then match that angle, in reverse, on the pinion. eg: if the trans angle is 3deg down then the pinion angle should be 3 deg up. you can also use the angle finder on the oil pan or trans pan as a guide.
-once you have the angle correct check to ensure the side to side dimensions are also correct and then tack weld the spring plates onto the diff. tighten up the u bolts, install the driveshaft and set the truck back down on the ground. move the truck back and forth so the tires move at least a turn, then check the angles again. sometimes the suspension will play tricks on you and not "unload" itself" when you jack it so that is the reason for the movement of the unit, to reset how the truck sits on the springs. you could simplify this by rolling the truck onto some ramps or a stack of 2 x 12's or something. since the truck will actually drive with the driveshaft back on it will be easier to accomplish this. this will enable you to do the angle recheck and ensure the truck is actually sitting at ride height with the suspension loaded as it would be normally. if you know somebody with a drive on hoist that would lend it for a few minutes that would also be great. I have also put down some ramps next to the curb and driven over that before, centered on the truck so you can slide under the unit while it is still "suspension loaded" and unchanged from the normal driving load the suspension would see when driving.
-if the angles are how you like then you can drive it back in the garage and get the spring plates welded onto the axle. like said previously, watch how much heat is going into the welds because the axle tubes will warp. all for naught in that case.
when all done get the truck sitting back on stands with the wheels off the ground and do a driveshaft check, just to ensure the shaft didn't get tweaked. it could have also bent the pinion shaft so watch for that as well.
you did get lucky, you could have been "pole vaulting" should that have happened on the highway. you know the Alberta road situation, not smooth anywhere, lol.
you may want to run the suspension through a full cycle and watch how much driveshaft yoke is slipped into the trans, just to make sure you have enough but not too much so it bottoms out on a big Alberta bump.
in one pic it looks like the brake hose took a hit. if it is chaffed you may want to replace it rather than chance it. I know, more brake bleeding. time well spent though if the hose is compromised.
post up some pics when done. we would all like to see how it worked out.

[NeoJuice]

DSRaven,

Thank you for all the tips. I appreciate you spending the time to write out that description. In my mind I just kept on running through scenarios on how I would get this process done. Should I do this or should I do that. Your tips helped a lot. I'll keep you updated on the progress.

I'll re-inspect everything under there rear to make sure there was no other damage like the brake lines, parking brake etc etc.

[NeoJuice]

DSRaven,

I just want to clarify before proceeding with these steps that the main key is to keep the load on the rear leaf springs. In your description you said "jack up the front end and place on stands or cribbing etc." So that means just some normal jack stands on the front frame correct?

As quoted "We want the load put on the jack stands under the rear axle spring plates so the weight of the truck never leaves the springs but the axle becomes "unloaded"

[NeoJuice]

So I had a little time on the weekend to work on the truck. I got the truck up on crib blocks in the front and front wheels off. I got the rear up on jack stands under the leaf springs.

The jack stands I have worked out good because on the height adjustment top plate it has a hole in it which the leaf spring alignment dowel/perch fit right down into, so the jack stand fits flush on the u-bolt plate. I also have additional blocks and left the rear tires on for extra safety.

Here is the kicker...... So I slide under the rear of the truck to find out what size the bolts are with my socket set. Grab my two foot breaker bar and go to loosen the first bolt and it was loose. It was like finger tight. I'm not even joking. I checked the other 7 bolts and they were the same way. I was like WTF! I would have expected them to be tightened up with at least an impact gun.

So the next steps are to loosed off all the bolts and turn the axel and get it aligned so I can get the perches welded on.

Buying someone else's project....expect the unexpected lol.