ANY ISSUES WITH BIGGER REAR DRUM BRAKES?

[TIMINATOR]

My 87 Turbo Coupe Ltd. came with a 7 1/2" 2.41 geared rear end, and I assume the last owner had a good, or nefarious reason for changing it. I replaced it with a bolt in 9", 31 spline axles and good posi, and 11"x 2 1/4" brakes instead of the 9 1/2 x 2 stockers. I figure I can stall it higher on the footbrake launch, not a bad thing, and it came without brakes anyway. I assume others have done this, so my question mainly is will this upset the brake balance enough to cause problems? Will I need a proportioning valve? Or mebbie bigger disks on the front? I am not the guy that puts huge brakes on everything, I don't see the need. My other GNs stopped just fine with the bigger tires I had on them and stock brakes, but stalling it up pushed thru the stock brakes easily.
I never had any problems with my 1968 454 8-71 blown Nova, that originally came with an anemic 6 cyl. and tiny front drums. I had the same rear brakes on the 9" that I put in it.
I am just finishing up the new motor, so I figure if I need something, I would order it now.
The Nova ran 9.60s @ 141, but I only expect mid 10s with the Buick, and I'm not gonna do a roll bar, just stiffen the frame.
It, like the Nova, is just a street car, but both of the dragstrips are now gone.
TIMINATOR
P.S. it ran good, but was kind of lazy under 35 mph or so....

 

[dynoman]

I have a 9" with drum brakes and Wilwood 6 piston 12.1" rotors up front . I didn't change anything with the proportioning valve and all is good . I'm also on vacuum brakes .

 

[TIMINATOR]

Oh yeah, I'm on vacuum brakes too.
I think if I ended up having to prop valve it, I would lose the ability to stall it up, and that's why I bought the big brakes to begin with.
The Nova had a STOCK DUALLY 13" convertor in it to make it easier to hook on a narrowest tire. It still stalled that to about 2400 rpm! Gotta love the Roots blower torque! That combo with 3.73 gears went the 9.68@ 141. One pass, no roll bar.....
TIMINATOR

 

[1986 Buick GX1]

It seems like I’ve seen prop valves with an adjustable orifice to limit the flow to the rear during a panic stop so the back doesn’t lock up, but will allow max pressure after a few seconds.
Maybe I was dreaming, but pretty sure I’ve run across one.

 

[TIMINATOR]

Now that sounds like exactly what I'm looking for!
Max pressure for max stall and spool, and no lockup during panic stops!
Mebbie someone will chime in, or I'll call the different brake companies. I didn't think anyone made such a thing.
THANKS FOR THE INPUT!
TIMINATOR

 

[SS/GN]

Never had a problem with larger rear brakes. Adj prop valve might be good to put in to have some adjust-ability when you are doing the project.

 

[Chuck Leeper]

I think if I ended up having to prop valve it, I would lose the ability to stall it up, and that's why I bought the big brakes to begin with.

"Back in the day", there was a "jump valve" that would allow full line psi to bypass the prop valve. Haven't seen one in many moons.
Some of the other old farts may recall it.
Here's the Wilwood on my 8T6. No jump valve.

I had over 2000 psi available with the HB. No issues with stock TR brakes on the ft.

 

[TIMINATOR]

"Back in the day", there was a "jump valve" that would allow full line psi to bypass the prop valve. Haven't seen one in many moons.
Some of the other old farts may recall it.
Here's the Wilwood on my 8T6. No jump valve.
View attachment 390636View attachment 390636
I had over 2000 psi available with the HB. No issues with stock TR brakes on the ft.

What size rear brakes do you run?

 

[Chuck Leeper]

What size rear brakes do you run?

On the 8t6 it's a 9" with stock 11" drums.
On the last 55, same combo. Both are with hydraboost.

 

[TIMINATOR]

Thanks! Cool! I won't worry about it then...
TIMINATOR

 

[Warp6]

"Back in the day", there was a "jump valve" that would allow full line psi to bypass the prop valve. Haven't seen one in many moons.
Some of the other old farts may recall it.

Hydroboost is what it was called, I think. Here's mine I sold several years ago. Never installedit

 

[TIMINATOR]

I finally got my Cometics, just not from them. I can finally put the heads on and finish assembly. Then we will see what the brakes do. As I understand, the adjustment knob on the prop valve controls the maximum pressure to the rear brakes under all conditions, yes no?
That would prevent rear lockup in a panic stop.? The bypass over pressure deal if automatic, would be good, or I could possibly use a normally closed solenoid valve (opposite of what a line lock valve is) as a " full pressure, spool up bypass" around the prop valve if needed.
I will make calls to brake guys, probably, Benny at Baer, I've known him since the 1980s! He prolly knows the answer, or who does.
I'll post with results.
Thanks for the input so far!
TIMINATOR

 

[Mr.Spool]

I finally got my Cometics, just not from them. I can finally put the heads on and finish assembly. Then we will see what the brakes do. As I understand, the adjustment knob on the prop valve controls the maximum pressure to the rear brakes under all conditions, yes no?
That would prevent rear lockup in a panic stop.? The bypass over pressure deal if automatic, would be good, or I could possibly use a normally closed solenoid valve (opposite of what a line lock valve is) as a " full pressure, spool up bypass" around the prop valve if needed.
I will make calls to brake guys, probably, Benny at Baer, I've known him since the 1980s! He prolly knows the answer, or who does.
I'll post with results.
Thanks for the input so far!
TIMINATOR

Good news get that motor together !
Moving more pressure to the rear will hold the car at the line.
That's where the car is truly held if it's a footbrake car.
It may try to come around you if you try to get stupid with the car or perhaps in rainy weather.
I have personally never had an issue and those drums hold great with alot of psi to them.
Test the brakes yourself on your car and see how it behaves

 

[SCOOBY DOO]

I used S-10 rear wheel cylinders, line lock, all long pads and replaced the flex hoses with Russell braided lines. I could hold any RPM on the line I wanted.

 

[TIMINATOR]

My Nova and chevelle was setup that way. My best friend worked at an industrial truck brake and clutch rebuilder. We did that to all of our cars and customers stuff too. We called them "Billy brakes" (his name!).
The great thing about 9" is that you could get wheel cylinders to fit from 7/8" to 1 3/16" in .030 or .060" increments. We never added or changed a prop valve on anything, just wheel cylinders, with drum or disc fronts.
Getting excited for the motor, it's been out of the car since January 2020!
Buisness has been smoking hot, covid supply issues, wife also died first week of January 2020, I caught covid while at her side in the hospital, got remarried in November 2021, been running my Harley dragbike, sold it, now, BUICK TIME! Finally got all the parts, 'cept the custom roller, I put in a 212/212 off the shelf Comp roller and 1.65 rockers for now. If it runs 14 flat or faster, I'll leave it in there. LOL!
TIMINATOR

 

[SCOOBY DOO]

Please be careful on the streets...as it fucks the rear brake bias and the ass end will come around on you in a panic stop on the street. Ask me how I know.

 

[SCOOBY DOO]

I've got 3 bikes...including a Harley 2006 Fatbob with larger pistons, intake and exhaust mods. I'm truly sorry for your loss.

 

[TIMINATOR]

Recently sold my 9 sec. V Rod Destroyer, back/ neck problems from getting hit at a stop lite at 50 mph in my TRUCK! , Old bat didn't see a 3/4 ton silver, lifted GMC truck sitting at the red lite on a 4 lane intersection, at 7:30 A.M. In the summer, clear, dry, no other traffic.
I can call her an old bat because I'm 70, and I still drove the drag bike until recently.
My 2017 HD Breakout Pro Street makes 136 hp on the motor on 91 octane. 10.90s with a perfect launch on an Avon roadrace tire. It's my regularly driven street bike. I have always had sleepers, as I have been known to street race,a bit, or so, OK more...
Cops always go after the noisy jap bikes, or flashy, noisy cars.
Thank you, Scoob, she rode a 127 HP. 2004 Screamin' Eagle Deuce that ran mid/ low 11s. We regularly dragraced all 3 bikes, and we were getting a divorce when she had her heart attack. She hid her condition from all of us, and had a cardiologist that I and no one else knew about.
TIMINATOR