72 4x4 poor front braking - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Chris183 · 03-12-2018, 07:39 PM

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?
Thanks Chris

hemi43 · 03-13-2018, 08:37 AM

Get new rotors and a good set of pads. EBC red stuff make a huge difference in stopping.

**jaros44sr** · 03-13-2018, 08:51 AM

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?

Chris183 · 03-13-2018, 10:17 AM

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.

Chris

hemi43 · 03-13-2018, 02:45 PM

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.

**jaros44sr** · 03-13-2018, 04:41 PM

Quote:

Originally Posted by hemi43

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

Chris183 · 03-13-2018, 04:57 PM

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

GM man · 03-13-2018, 09:52 PM

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?

hemi43 · 03-14-2018, 09:08 AM

Quote:

Originally Posted by jaros44sr

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.

hemi43 · 03-14-2018, 09:11 AM

Quote:

Originally Posted by Chris183

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. :-)

Chris183 · 03-14-2018, 08:43 PM

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.
Chris

**paul mora** · 03-15-2018, 09:51 AM

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.

Chris183 · 03-17-2018, 08:08 AM

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.
Chris

Chris183 · 03-29-2018, 11:55 AM

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.

Chris

SeventyOne · 03-29-2018, 01:10 PM

What camshaft are you running?

Chris183 · 03-31-2018, 05:10 PM

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.

Chris

03-12-2018, 07:39 PM	#1
Chris183 Registered User Join Date: Feb 2012 Location: Lindenhurst, NY Posts: 7	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? Thanks Chris

03-13-2018, 08:51 AM	#3
jaros44sr Senior Member Join Date: May 2006 Location: Philadelphia, Pa. 19454 Posts: 9,762	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? __________________ Semper Fi...Uncle Sam, you da man All parts offered to help are free, unless otherwise noted Dont try this stuff in my build thread, unless you have 55 years of mechanical OTJ training SAFETY FIRST AS usual, off topic They say your mind goes second, can't remember the first Jim

03-13-2018, 10:17 AM	#4
Chris183 Registered User Join Date: Feb 2012 Location: Lindenhurst, NY Posts: 7	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. Chris

03-13-2018, 02:45 PM	#5
hemi43 Registered User Join Date: Mar 2015 Location: Ontario Canada Posts: 1,526	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.

03-13-2018, 04:57 PM	#7
Chris183 Registered User Join Date: Feb 2012 Location: Lindenhurst, NY Posts: 7	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? Chris

03-13-2018, 08:37 AM	#2
hemi43 Registered User Join Date: Mar 2015 Location: Ontario Canada Posts: 1,526	Re: 72 4x4 poor front braking Get new rotors and a good set of pads. EBC red stuff make a huge difference in stopping.

03-13-2018, 09:52 PM	#8
GM man Registered User Join Date: Aug 2011 Location: Gainesville, Texas Posts: 127	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? __________________ 1972 GMC Jimmy 6.0/4L65 1972 Chevrolet long bed 1/2 ton

03-14-2018, 08:43 PM	#11
Chris183 Registered User Join Date: Feb 2012 Location: Lindenhurst, NY Posts: 7	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. Chris

03-15-2018, 09:51 AM	#12
paul mora Senior Member Join Date: Jan 2009 Location: huntington beach california Posts: 976	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. __________________ Pulatoy

03-17-2018, 08:08 AM	#13
Chris183 Registered User Join Date: Feb 2012 Location: Lindenhurst, NY Posts: 7	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. Chris

03-29-2018, 11:55 AM	#14
Chris183 Registered User Join Date: Feb 2012 Location: Lindenhurst, NY Posts: 7	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. Chris

03-29-2018, 01:10 PM	#15
SeventyOne Registered User Join Date: Mar 2007 Location: Oakland, Ca Posts: 1,382	Re: 72 4x4 poor front braking What camshaft are you running?

03-31-2018, 05:10 PM	#16
Chris183 Registered User Join Date: Feb 2012 Location: Lindenhurst, NY Posts: 7	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. Chris



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