Aviator857

I've bleed my brakes with Evey technique known and they are still softer than I expected. I do not see any air bubbles with the "one man" method. I've bench bled the master. There is no leaks.

I have 4th gen master
Thirdgen booster.
4th gen front brakes, take off calipers, new pads and slotted/drilled rotors.
Willwood prop valve.
earls braided lines up front.
But I haven't done the drums yet out back. (debating on what I want to do with the rear end)

So is it that I'm driving drums with a disk master?
They pump up hard with no vacuum to the booster, but with vacuum it's super soft. Could it be the booster? Even before this swap I always thought the brakes were softer than I would like and that was 100% stock. Stops the car fine they just feel soft and have more pedal travel than I expect.

daferris

iTrader: (8)

Are the rear brakes adjusted? if they are loose (too much travel before they hit the drums) you will have a lot of pedal travel...

Aviator857

Yes, rears are adjusted. Drums and shoes have very few miles on them, so there isn't a groove in the drum.

Zach/90\irocZ

iTrader: (6)

get new booster or used one and see if there's a difference could be a leaking booster and bound to happen as many don't change them lol

Aviator857

I was leaning toward that direction -- the booster is original to the car (well I haven't changed it and I've owned the car since 1997).

OK I see rock auto has ac delco's and Autozone has one-- I do have the booster from the 2k car but the center part doesn't bolt up to the 89 car...
Well as we say in aviation time to spend another aviation monetary unit. (AKA $100 because in aviation everything is at least 1 AMU LOL).

QwkTrip

iTrader: (22)

https://www.thirdgen.org/forums/brak...rakes-ls1.html

Aviator857

Thanks... So I'm thinking I can weld a washer to the push rod then grind it down so it's .100 longer than before.

Or I guess I could massage the firewall and use the 4th gen booster.

QwkTrip

iTrader: (22)

Don't just make some random length. It needs to be right. Master Power Brakes sells a tool to measure depth.

Aviator857

I'm guessing I can return the booster I ordered the other option is to just order a disk/disk master made for the car). But I'm guessing one should actually re pin it anytime you change it. I've got micrometers etc so I can measure it, my question is more will welding a washer on and grinding it off be good or is there a better option.

Zach/90\irocZ

iTrader: (6)

I used full 4th gen system so didn't have to do all that
I'm sure difference is felt using 3rd booster and 4th gen valve which is only people IIRC that needed that part to be longer
there is more play in the movement of the fire wall when pressing the brakes as well
solution is if you have a strut brace is to fab up a brace to hold prop valve to prevent play

Zach/90\irocZ

iTrader: (6)

https://www.thirdgen.org/forums/brak...r-mc-help.html

there's a lot of good info with a little searching

Aviator857

Interesting, when I tried fitting the 4th gen booster the center boot was too large to go through the firewall hole and I saw that most people only used the master. I have the booster from the donor car. I guess my search skills failed, I had seen the post you linked to but not the one Qwktrip did.

I'm not running the stock prop valve and the mounting bracket I made for the willwood holds it pretty stationary. I don't yet have a strut bar, I was waiting until I had the LS1 swap done before I bought that and the rear suspension parts. I don't like the idea of mounting a brace forward to the strut tower though, in a wreck that is liable to transfer a lot of force from the strut tower area into your foot...

scooter

iTrader: (11)

I don't think so, it isn't a steering column that is in direct line to any part of your body. The pedals are low, and the direction of energy in a head on crash would be at your waist, since that is where the pedal bracket actually is.

Aviator857

Not something I'm going to debate here but without actually modeling the car in mechanical desktop or catia and running virtual impact tests to verify, it its not something I would trust.

Zach/90\irocZ

iTrader: (6)

lmao well aren't you fixing brakes to prevent a crash aka better stopping power lol if you worried about that maybe you shouldn't be modifying your brakes and keep it stock

lmao this is too funny lmao ha ha a

#cuzracecar

skinny z

Something to consider is the difference (or potential difference) between a disc master and drum master where the later will incorporate a residual check valve to keep pressure applied at all times. It's been demonstrated that without a check valve the shoes don't maintain contact with the drum. As a result every application of brake pedal has to take up the slack created as the shoes are drawn back by the springs.
There are different parts numbers for the OEM disc/drum vs the disc/disc master cylinder. Bore sizes are certainly different so the amount of fluid pushed into the brake lines will also be different. It may also indicate the presence of the aforementioned check valve.

Lifted from the internet:
Typically a disc brake system is going to require more fluid to operate properly, so a disc brake master cylinder will simply hold more fluid than a drum brake master cylinder. On a drum brake master cylinder, you will also have residual pressure valve to maintain a certain amount of pressure at all times

Zach/90\irocZ

iTrader: (6)

https://www.thirdgen.org/forums/brak...son-pedal.html

should be helpful to put into picture what skinnyz referring too

Aviator857

On the stock parts is the check valve in the master cylinder or the prop valve. The check valve makes sense. I'll check the booster pin this weekend, if that doesn't work I'll know it's the drums and will ignore it until swap to disks on the rear. I still need to finish buttoning up the dash but didn't want to do that if I had to pull the booster again

skinny z

My understanding is that it's in the MC and not the prop valve.

Below is a (copied) GM service bulletin regarding pedal feel and MC options for the early 3rd gens. It demonstrates that without enough consideration, swapping calipers, master cylinders and prop valves could result in all manner of different operating behaviors. The J65 option mentioned below also uses a unique prop valve.

Section: 5 (V)
Date: Mar., 1984
Subject: REDUCING BRAKE PEDAL EFFORT ON CAMAROS WITH FOUR WHEEL DISC BRAKES

Model and Year: ALL 1982-84 CAMAROS
TO: ALL CHEVROLET DEALERS
The higher brake pedal effort associated with 1982-84 Camaro cars equipped with four wheel disc brakes may be a source of some customer comments. The J65 brake system was designed with a low pedal ratio for reduced free travel and a firmer and higher effort pedal for the high performance buyer. Owners of J65 equipped Camaro cars not sharing this interest and desiring reduced brake pedal effort can be accommodated by replacing the original production master cylinder assembly with the appropriate J50 master cylinder unit specified below.

Sort of your situation in reverse.

Aviator857

Ok I see willwood has a 2lb and 10lbs check valves.

https://www.wilwood.com/MasterCylinders/MasterCylinderProd?itemno=260-13707

So my plan is to:

Check booster pin tollerance
Go ahead and throw on the rear disks
If it's still soft put 2lb check valves.
though unless the 4th gen abs box had internal check valves that shouldnt be needed.

I've never gotten too deep on brake haudrallics design...

Thanks I've got a game plan now.

QwkTrip

iTrader: (22)

You don't use a check valve with disc brakes. Wilwood sells those things for people with funky designs where the master cylinder is lower than the brakes and fluid will drain out of the brakes back to the master.

skinny z

True. Once you make the move to 4 wheel discs, there are no check valves required.
With your 4th gen MC, you should be good to go on the hydraulics. Investigating the pushrod is something you'll still need to address.

scooter

iTrader: (11)

Yeah, for real, lol

There is nothing to model. There is nothing to make it worse. If something is hitting you so hard that the strut bar is pushing the master into the firewall, it's going to happen with or without a brace that's an extra inch or two in front of the master. If all that happens you're going to have way bigger problems than the brake pedals hurting you. If you feel like that, you probably shouldn't modify the car from stock at all

Aviator857

So I replaced the booster pin with the pin from the 4th gen booster, the tip has a different shape and it has a collar that rests on the plastic/composite part vs just fitting inside it. I then found I had one of those faucet repair kits that had a bunch of different thickness washers. I found a combination that gave me the right thickness. Used clay initially to check depth that the set up was off.

At any rate this was a vast improvement, I can still feel the drums expand out but that feels different, it isn't complete mush for the first few inches of pedal travel now. Once I get around to do the disks in the rear (I will do that before any real driving is done) it should be rock solid.

Though I'm thinking I may want to modify the rod to the pedal assembly. With the 4th gen pedals and the tick clutch master adjusted out the clutch is just a tad higher than the brake, and the brake is just a tad higher than the gas. Raising the brake pedal up some would make heal/toe operation easier, but there is plenty of authority now and I'm no where near the bottom at full brake engagement (can't press the pedal any further down).

As for the brace from the STB to the master cylinder all I will say is I went to one of the top 5 engineering schools and weigh mods on a risk/benefit scale. There are certain mods I think outweigh the risk. I could be wrong and it could bite me one day. There are mods I don't think the benefit outweighs the risk, again I could be wrong as its just a guess without modeling it or crash testing it. All mods should be done under the risk/benefit mind set, otherwise you are just do things for the sake of doing them.

Now if someone can show a 25 foot (or some non trivial amount) stopping distance reduction from 100mph simply by installing a brace on a 100% dialed in braking system on a thirdgen I could be persuaded. Other cars have alot of flex and it may actually help, I hear on the 4th gen it does. I do appreciate the suggestions and help, feel free to laugh at my expense, but unless you have test numbers I will ignore any other posts about the brace.

Zach/90\irocZ

iTrader: (6)

its more of feeling then performance and there wont be any hardcore testing done as far as brakes @87350IROC has the most legit data I seen on brakes on this forum and thread is mainly about the feel of the brakes vs the performance and I highly doubt that changing the pin is changing the feel vs drastically improving the braking distance maybe I over look something in your response but its all about the good confident brake feeling that modern performance cars have and that every inch amounts to large improvements , and with the risk etc. that's very dependent on the drivers abilities to fully utilize the new performance put a inexperience driver in the seat of a race car and he be no better than he was in a Prius and can have and or be very dangerous in either car and can or wont fully utilize full capabilities of either car I understand your reasoning but I don't think it needs modeling to assume if your crashing where pedals will be push in you either shouldn't be driving that fast and or it was some freak accident it doesn't take rocket science to improve a thirdgen performance lets be real we are not re inventing the wheel here if you want the best feel then a lot of thing come into play like I said and every little bit counts on a 20+ year old car and that every little bit has multiple and duplicate threads thru out this forum .

https://www.thirdgen.org/forums/brak...der-brace.html

Aviator857

Even ignoring crash worthiness do you really want to conduct any flexing and vibrations in the strut tower into your brake booster mount? I can put a lot of pressure on the pedal before I notice any deflection on the master. The car may be old really shouldn't matter, there is no rust on the structure, the spot welds are solid etc.

Pedal feel is subjective, and I get it, its a cheap way to increase pedal feel. On a race only car I would have no issue doing it. No matter how good of a driver you are you can't control oncoming traffic, the small offset head on collision is the most common fatal accident. It usually occurs on a blind hill/curve when someone drifts over the center line on you.

Something like the booster pin delays your effective reaction time due to the "play" at the top. Firewall deflection reduces the effective force until you reach the limit of the deflection reducing the amount of force applied during the first moments you hit the brakes and increasing the time to full force applied. Both will increase stopping distance even if the ultimate maximum brake force is the same. A firmer pedal/booster mount would make for more consistent feel. If I were to do it though I would make a mount that comes up from below the frame rail, has a small poly bushing connected to an adjustable rod so that I could preload it downward (or weld in thicker metal on the firewall), a mount cantilevered off the STB honestly is trying to control deflection from the wrong plane.

I think I have the brakes dialed in now though, it isn't quite 2018 Z06 territory but it is better than factory.

skinny z

Excellent.
Be sure to follow-up when you have the discs on the rear. I've added LS1 front and rear to a former disc/drum car and maintained the original master, booster and prop valve. What I can say about this is that although the stopping performance has greatly improved, I'm not terribly impressed with the "pedal feel" either. I have the J65 prop valve (purchased from FlynBye Performance) but have yet to install it. My thinking is that it will change the characteristics of the package as a whole as suggested by the service bulletin posted earlier. Whether that also includes a J65 master cylinder (if such a thing exists) I can't say.

scooter

iTrader: (11)

It's not all just that though, it's stress to the sheet metal, over time it will crack, as we have seen from people who don't do the auto to manual clutch master conversion properly.

Aviator857

I'm using Wilwood 4444/30 260-11179 prop valve, cut and re flared the front lines with the right line nuts, found an adapter for the rear line since its such an odd size. I always thought the disk/drum factory prop valve was suspect on this car. Since the weight of the car is different than the 4th gen, and the calipers are so different and I obviously didn't use the ABS module I assumed that I would need something adjustable to dial it in.

I'm still trying to convince myself to drop the money on a ford 9" or 8.8 is why I'm procrastinating on swapping the rear brakes. Though I could throw the rear end from the donor car into the 89 in an hour or so... it may be worth doing that for now... especially since it would allow me to go ahead and solve the e-brake issues (I didn't cut the bracket from under side the donor car before sending it to the recycles).

Zach/90\irocZ

iTrader: (6)

8.8 will do just fine but if your not dropping clutch on slicks and or a aggressive driver 10 bolt can last as no sticky tires will loss traction before diff breaking etc you can get the brackets and parts cheap junkyard etc only issue with donor car if its 4th gen rear is rear wheels will be moved out some and if on stock wheels makes car stance look weird

if you look at post above even tho more modern calipers have more pistons to apply pressure to the disk the overall volume pistons is all very similar to the factory single piston caliper but better braking performance is due to the more surface area pressure applied to the larger disk

ABS is possible to put into a thirdgen custom abs rings need to be made to press on the rear of disk and rear abs is all included with rear axle and custom plumbing of abs system couple years back a guy custom made abs rings

https://www.thirdgen.org/forums/brak...ossible-2.html

Aviator857

Mentioned the abs module only because the 4th gen doesn't have a independent prop valve. I have no desire to attempt abs install.

I'm aware of the rear diffence, but the factory 2.7x ratio rear has to go. It would be temporary until I decide on the rear I want to buy.

Zach/90\irocZ

iTrader: (6)

yea big project lol

yea just swap 4th then as for the rear it def comes down to preference wont go wrong with either one and far stronger than the 9 or 10 bolt
8.8 would be the cheapest and most bang for buck and strength comparable to any other rear upgrade