47-55.1 Master Cylinder/Booster HELP!!

[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.

[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.

[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 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]

Thanks again for the tips DsRaven. I'll keep everyone updated once I have more time to work on the truck.

[NeoJuice]

Last month my buddy came over and we got working on the truck. We first removed the U bolts then used the floor jack to lift the rear off the perches.

Once the perches were out we used the grinder to remove paint from the perches and diff. Put the perches back down on the leaf springs and lowered the diff back down.

We then did some side to side measurements until it was perfect and were able to move the 'pumpkin' up into almost the correct angle. We then installed the drive shaft and installed the c clamps to secure the drive shaft to the pinon. He then used his angle tool on the tranny, drive shaft and pinion yoke to get the correct pinon angle. Once that was set he layed a good tac weld to hold everything in place.

Once the tac welds were done we re-checked the angles and side to side and we then determined it was ready to go. He burned a good weld onto the each side of the perches to the diff. Once we cleaned up the welds we re-installed the U bolts into the lower shock bracket and torqued to spec. So now that job is done I'll shoot some black paint over the welds come spring time.