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Old 03-12-2018, 07:39 PM   #1
Chris183
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72 4x4 poor front braking

I'm having trouble with my front brakes they don't want to lock up on a hard stop. The backs have no problem. I was able to force the proportion valve to trip and reset so I think that's good. When I checked the front hydraulic pressure the most I can get is 800 psi. at the caliper and master cylinder. Is this normal or on the low side. I got the same after bench bleeding the master cylinder and lines. Does anyone have any thoughts?
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Old 03-13-2018, 08:37 AM   #2
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Re: 72 4x4 poor front braking

Get new rotors and a good set of pads. EBC red stuff make a huge difference in stopping.
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Old 03-13-2018, 08:51 AM   #3
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Re: 72 4x4 poor front braking

800psi seems like enough, but I have never seen an actual number posted. Curious to see how you plumbed a gage into the system, as I want to mount the gage permanently in my dash. any pics?
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Old 03-13-2018, 10:17 AM   #4
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Re: 72 4x4 poor front braking

Thanks for your input. I did put on a set of rotors and pads from Wilwood but I'm willing to try another set. I bought a brake pressure gauge kit that came with fittings that mounted in the bleeder holes and I a used a couple of fitting from Ace Hardware to mount it to the master cylinder. In the gauge instructions it has a range of 1200psi to 2400psi for most cars with front disk brakes. I would like to find out what the range is for a 72 Blazer before changing any more parts. I do have 33 x 21.5 R15LT tires. The guy from Wilwood said he had the same on his with no problems. I bought the gauge kit from Amazon part #SSBA1704.

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Old 03-13-2018, 02:45 PM   #5
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Re: 72 4x4 poor front braking

Wilwood has many different compounds in heir pads. The vehicle that I put EBC red stuff pads on also had wilwood calipers with their "street" pads. I noticed a huge difference.
You might be at the limit with the 72 calipers ( I assume that's what you have) and those big tires. When I did my Blazer, I used bigger rotors and 2003 dual piston calipers, and I'm also running 33's. It stops on a dime.
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Old 03-13-2018, 04:41 PM   #6
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Re: 72 4x4 poor front braking

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Originally Posted by hemi43 View Post
Wilwood has many different compounds in heir pads. The vehicle that I put EBC red stuff pads on also had wilwood calipers with their "street" pads. I noticed a huge difference.
You might be at the limit with the 72 calipers ( I assume that's what you have) and those big tires. When I did my Blazer, I used bigger rotors and 2003 dual piston calipers, and I'm also running 33's. It stops on a dime.
Nice idea on the rotors and calipers, I'll start sourcing parts. where did you get your parts from? saw the mods in your build
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Old 03-13-2018, 04:57 PM   #7
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Re: 72 4x4 poor front braking

Yes I still have the 72 setup on the blazer. That sounds like the way I need to go. Were you still able to keep the stock wheels?

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Old 03-13-2018, 09:52 PM   #8
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Re: 72 4x4 poor front braking

It sounds like there's something wrong with your proportioning valve or maybe your calipers or there is air in the lines. For your rears to lock up but not the front is weird, but for a cheap stab at it , try flushing your fluid with new brake fluid. It can make a difference too. Did you clean your caliper pistons up when replacing your pads?
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Old 03-14-2018, 09:08 AM   #9
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Re: 72 4x4 poor front braking

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Nice idea on the rotors and calipers, I'll start sourcing parts. where did you get your parts from? saw the mods in your build
All standard items from NAPA. The only custom piece is the backing plate that holds the caliper.
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Old 03-14-2018, 09:11 AM   #10
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Re: 72 4x4 poor front braking

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Yes I still have the 72 setup on the blazer. That sounds like the way I need to go. Were you still able to keep the stock wheels?

Chris
Keeping the stock 15" wheels was a must, and that's was the biggest issue trying to fit these big brakes in those small rims. It does fit with some tweaking here and there, but barely. I have less than 1/8 gap between the caliper and the rim, but clearance is clearance.My truck is a 70 so I went from drums to disc using the original hubs, but if I had a 72 with original disc brakes, I would use the 72 disc and try and fit a modern dual piston caliper on it. :-)
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Old 03-14-2018, 08:43 PM   #11
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Re: 72 4x4 poor front braking

Thanks for all your suggestions. I'm going to go through the system again the only parts that are still on the blazer when I got it was the proportion valve and calipers. So I will put on a new valve and look to up grade the calipers. I think Wilood makes a dual piston caliper that fits. I will let you Know how I make out. If you think of any other suggestion please let me know.
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Old 03-15-2018, 09:51 AM   #12
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Re: 72 4x4 poor front braking

I was running front and rear disc with 15 in rims and 31in tires on my Blazer for years. Think it is just not strong enough to stop the Blazer and lock up the wheels. I switched to hydro boost system and all my problems were solved Dump the vacuum system install a hydro boost and all your problems are solved.
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Old 03-17-2018, 08:08 AM   #13
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Re: 72 4x4 poor front braking

Thanks, I will look into the hydro boost also. I still would like to know what the brake line pressure should be if any one has that.
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Old 03-29-2018, 11:55 AM   #14
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Re: 72 4x4 poor front braking

I thought I should give everyone an update. So I went through the brake system again, bleeding and adjusting everything with little improvement. So to see what would happen I brought the blazer up 30mph shifted into neutral and stepped on the brakes. Well all four wheels locked right and stopped on a dime. So I guess I'm looking at a vacuum problem. The booster passed the pedal test, then I checked vacuum. It turns out that I have 15" (A little low but not bad) in park at 1000 RPM and only 9" ( Way to Low) in drive at 750 RPM
and when I put a vacuum gauge on the booster the Vacuum goes from 15" to 0" in 15 seconds. I assuming the booster is bad and I have some other vacuum issues.

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Old 03-29-2018, 01:10 PM   #15
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Re: 72 4x4 poor front braking

What camshaft are you running?
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Old 03-31-2018, 05:10 PM   #16
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Re: 72 4x4 poor front braking

I'm not sure what you need off cam card. I will do my best.
Comp Cam part #260H-10
Valve gross lift .440, duration @ .006 Tappet lift 260
Valve Timing Open Closed
@ .006 INT : 24 BTDC 56 ABDC
EXT : 64 BBDC 16 ATDC
These Specs Are for cam installed
@ 106.0 Intake center line
Intake Exhaust
Duration @ .050 212 212
Lobe Lift .2930 .2930
Lobe Separation 110.0

I called Competition Cam and the tech support told me I should be getting 16" to !7' of vacuum.

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