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Old 08-19-2019, 11:59 PM   #1
bigblockmark
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Default Brake questions.

My G body has never had great brakes, just OK. Chased it for a while then just got used to it.

Would like to revisit my combo and see if I have wrong parts or just not getting brakes bled well enough or maybe pedal ratio wrong, or?


Master cylinder. Strange Mopar style. 1.125" bore. #B3359.

Firewall mounted on Auto Fab aluminum adapter.

Front brakes. Wilwood Dynalite. 10.75" rotors. 4 pistons 1.75" diameter. Rebuilt a couple times chasing drag issue, still the same. #140-1033-D.

Rear brakes. Strange 11" 4 piston. #B1708WC.

Pads have been changed a couple times. No difference.

First pump of pedal is not that strong, second is better but not
what you would expect. Line lock holds fine. I don't get that near cars in front of me in case the first pump does not stop it quick. Stops at end of track OK., but can't really lock up the brakes if needed to. A little hard to stage with this set up.

My bleeding procedure is pump brake pedal, open furthest away bleed with line going into jar below level of brake fluid, when pedal goes to floor, tighten bleeder. Repeat until no air comes out. Repeat for all 4 bleeders on caliper, move to next furthest caliper and repeat.

No residual valves. Have proportional valve but no adjustment helps this condition. Flexible brake line is minimum length.

1.125" bore master cylinder is what Strange and Wilwood both recommended and I have had other cars with this same set up that worked fine. 4 piston calipers are pretty well standard parts.
Don't really know what pedal ratio is.
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Old 08-20-2019, 12:11 AM   #2
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Default Re: Brake questions.

When I switched to manual brakes I had to relocate my pedal push rod up to the next hole to increase the pressure on the master. You may have did this already but I didn't see it in your post if you had.
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Old 08-20-2019, 12:20 AM   #3
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Default Re: Brake questions.

Don't remember which hole it is in. It had manual brakes when I got it. I did add the aluminum adapter for the Mopar master cylinder so it is possible it was in the wrong hole and I just repeated a possible error. Thanks.
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Old 08-20-2019, 07:42 AM   #4
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Default Re: Brake questions.

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Originally Posted by BBC Malibu View Post
When I switched to manual brakes I had to relocate my pedal push rod up to the next hole to increase the pressure on the master. You may have did this already but I didn't see it in your post if you had.
This is the first thing to check. G-Bodys were powerbrake cars so it may be not enough ratio. Second, put a residual valve in it and it will eliminate the first pump. I understand for a drag car yeah a residual valve MAY add drag, but if you drive it on the street at all you need to have them.
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Old 08-20-2019, 11:09 AM   #5
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Do not waste time guessing, get a psi gauge, thread it into the caliper and confirm the brake pressure. Then if low, change the pedal ratio. Then after you have got past this critical step, we can talk about bracing the master cylinder to eliminate firewall flex Last we can talk about how Wilwood brakes are not much if any better than stiock disc brakes.

Last edited by classracer; 08-20-2019 at 11:13 AM.
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Old 08-20-2019, 12:39 PM   #6
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Default Re: Brake questions.

I'll agree with classracer. I'll also add that i've gone down to a 15/16 bore with good results. As for stock vs Wilwood its all about weight reduction.
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Old 08-20-2019, 01:32 PM   #7
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Agreed, the wilwood drag racing brakes are all about weight reduction, not better braking over OEM GM disc brakes.
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Old 08-20-2019, 01:43 PM   #8
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Default Re: Brake questions.

This car already had Wilwood brakes front and rear when bought it in 2010. I later changed to Strange rear 4 piston disc brakes looking for better stopping. (Had to clearance the calipers for wheel room, 7" back space.) Made no difference. I would have changed front brakes too, but the stock steering arms had already been modified for the Wilwoods (hole drilled thru for extra bolt). Strange does not make a front brake for the G body stock steering, I don't think?

The Wilwood Dynalites are not rated for over 125 MPH and 3000#. More of a Pro Street deal.

Master cylinder bore, 7/8", 15/16" versus 1.125", does come up a lot. I thought more bore gives more volume so should be full pressure first pump, on 16 pistons, but will be less pressure. That was the brake manufactures reason also for going bigger bore. I don't know what the bore was on the stock cast iron master cylinder was, but the 1.125" bore made no difference. Maybe stock master cylinder was for power brakes and that makes a difference?

Last edited by bigblockmark; 08-20-2019 at 01:45 PM.
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Old 08-20-2019, 01:53 PM   #9
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Default Re: Brake questions.

If you can get a heat gun on each rotor when you get back to the pit it might give some insight into what is going on. Mike D.
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Old 08-20-2019, 02:36 PM   #10
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Default Re: Brake questions.

Quote:
Originally Posted by bigblockmark View Post
This car already had Wilwood brakes front and rear when bought it in 2010. I later changed to Strange rear 4 piston disc brakes looking for better stopping. (Had to clearance the calipers for wheel room, 7" back space.) Made no difference. I would have changed front brakes too, but the stock steering arms had already been modified for the Wilwoods (hole drilled thru for extra bolt). Strange does not make a front brake for the G body stock steering, I don't think?

The Wilwood Dynalites are not rated for over 125 MPH and 3000#. More of a Pro Street deal.

Master cylinder bore, 7/8", 15/16" versus 1.125", does come up a lot. I thought more bore gives more volume so should be full pressure first pump, on 16 pistons, but will be less pressure. That was the brake manufactures reason also for going bigger bore. I don't know what the bore was on the stock cast iron master cylinder was, but the 1.125" bore made no difference. Maybe stock master cylinder was for power brakes and that makes a difference?
Mark, you need to know what the current pedal ratio is. PERIOD

And if you have the room on the brake pedal to drill a hole closer to the pivot, but keeps the mc pushrod level, then by doing this, you'll increase your pedal ratio.

I like as close to 7:1 as possible. You need to get as much pedal ratio as you can, this is important.

Then look at going to a smaller bore master cylinder. The smaller bore will increase the pressure at the calipers.
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Old 08-20-2019, 04:54 PM   #11
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Default Re: Brake questions.

Pedal ratio is key. I will say this, I run a large bore GM front caliper (they work) and 4 aerospace rear calipers. Aerospace 1.125 master instructions shows they want you to T both sides of the master together. I called to question if that was a misprint, and they said no. I also checked front a rear pressures, and was surprised to find my rears way low on pressure, as the way you turn your proportioning valve is not necessarily the way you would think. After verifying front and rear pressures, and bleeding with a professional brake bleeder, the pedal was decent, but not as good as I expected. I drove it like this for two summers (and many 145 mph passes) and just accepted it. I damaged a rear flex hose this past month, and after changing, and re bleeding the rears, the pedal has never been so good! Rock solid, and braking with much less travel, and effort. Chances are, if your pedal is less than stellar, you probably have a pocket of air floating around somewhere.
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Old 08-20-2019, 06:53 PM   #12
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Default Re: Brake questions.

If you have a stock G body brake pedal you should have 2 holes... the upper is for manual brakes. I have a manual brake MC adapter that looks kinda like the TRZ adapter... not sure, it was on the car when I bought it. It angles the MC so that the rod attaches to the brake pedal above the power brake hole but below the factory manual brake hole. I have had stock front and rear brakes and they have worked fine. I now have stock front and big ford drums on my Strange 9", they still work fine, although the rears will lock up now.
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Old 08-20-2019, 07:17 PM   #13
Mike Beck
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Default Re: Brake questions.

Bet you the pedal is not in the right hole. On both of my 3rd Gen F-Bodies I had the pedal modified by Ed Quay, did a friends car also, but his aluminum adapter and master cylinder, all three cars are perfect! I had tried using the stock location on the brake pedal, wouldn't even trust stopping in my own driveway! If your pedal doesn't have another hole, then find one that does, or find where that hole should be located. Stick a pressure gauge on there now and you will see why the brakes suck.
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Old 08-20-2019, 08:24 PM   #14
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Default Re: Brake questions.

Wilwood Dynalite calibers flex like crazy they make pedal feel soft and tilt the piston/pads and actually loose braking power if you give them too much pressure.

stuff i wound helped my 4 corner dynalite brakes

tighten caliber bolts
residual valves
dont push pedal too hard funny feeling when you loose braking power when you push pedal harder
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Old 08-20-2019, 09:02 PM   #15
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Default Re: Brake questions.

Another vote for pedal ratio

Recently bought a 85 Monte SS roller that was owned and raced by quite a few people with good results lol

Plugged an engine in the thing and it was barely raceable , brakes sucked ass !!!! Pulling the pedal was a pain in the ass and yes, the ratio was totally off !!! Factory power disc position with manual master. None of the previous owners caught this ???? Quick drill and brakes were awesome !!!!
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