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chevy p-30 brakes

lonfu
Explorer
Explorer
Had to replace my front rotors and pads and master cylinder. Bled all wheels and all working fine. Then they started dropping again to the floor. I noticed last trip after a hard climb through the nevada mountains at the top of the pass that the rear brakes were non existant and the fronts were grabbing hard at the bottom of the pedal travel. I had to stop and let the moho cool down so I boondocked at the top of the pass. Next day going down the hill all was good again. As the engine heated up my brake function started to reduce effectiveness, especially the rear disc pads.

When I got home I pulled the wheels and the rear pads and calipers were working correctly. Traced the brake lines and found that they run parallel to the exhaust manifold for about 6 inches where they connect to the master cylinder. The brake lines for the 6 inches are only 1 7/8 inches from exhaust manifold. The fluid was boiling before it was even entering the ABS system. Of course the DOT3 was boiling and then cooling causing water vapor to form in the brake lines and mastercylinder.

This a very serious manufacturing defect that Chevy refuses to address. To repair, I made a heat shield from some light steel to protect the brake lines and master cylinder. I bolted it on to the main frame channel. Then I've replaced the brake fluid with DOT5.1 rather than DOT3 as the shop manuel states. The boiling point of DOT5.1 is much higher than the DOT3. Don't bother with DOT4.

In order to correct this engineering mistake, you must do both, heat shield and upgrade to DOT5.1, just changing to the more expensive fluid will not solve the problem, it will just put off failure for a little longer. Do not use DOT5, it will not mix with the DOT3 or DOT4.

In searching the net I found very little solutions for this very dangerous and common problem. Apparently chevy was aware of this problem when they sold to workhorse. No recalls have been made at this time to correct this problem. Failed front rotors are a common symptom of the boiling brake fluid problem due to the fact that the rear brakes are disabled by the hot gas in the rear line so all the stopping responsibility is thrown on the front rotors and pads. Then the over heated boiling brake fluid freezes the front rotors and "wallah" no brakes at all!!!





May your black water hose never break! Life Charter member since 89
27 REPLIES 27

lonfu
Explorer
Explorer
1998 p30 chassis, 4 wheel disc with hydraulic brake boost from the power steering pump. Replaced the master cylinder with a bench bleed. Replaced the hydraulic booster. Replaced all 4 brake calipers. Checked the very short flex brake lines, no expansion obvious. Changed to dot 5.1 or super dot 4. Problem is a spongy brake pedal with no ABS light. I've vacuum bleed and power pedal bled the system several times with clean airless brake fluid coming out. Total of one gallon of fluid. I've tied down the brake pedal for a couple of hours to let air out of the lines to the ABS module. Original service manual says to bleed like regular brakes. No special method for bleeding the ABS module. My tech2 code reader, when I go through special functions, reads that it "can't connect to ABS module". No ABS light.

So, I assume that the ABS module is not tech2 compliant and it won't work. Yes, I have pumped the brake 4 times to bring the system to 35 psi, held and then tried to connect. Tech2 reader works for all other functions. Other sites have suggested that the tech2 will not work on the p30 chassis ABS brake module.

BUT I STILL HAVE SPONGY BRAKES, WHICH INDICATES AIR IN THE LINES...

I can only assume that there must be air trapped in the ABS module. How do I get it out? I don't see any obvious bleeder valves on the module. I do see a hex head bolt/cap that sits flush with the body that is inaccessible without removing the entire module.

It is a real head scratcher for me??? Anybody have any suggestions as to what direction to go here??
May your black water hose never break! Life Charter member since 89

lonfu
Explorer
Explorer
Just got back from another walk about. 1400 miles. Drove over Donner pass in the sierra's. Brakes functioned perfectly. No brake fade, pedal stayed consistent, felt like stopping power was all there. New rear pads really made a big difference I could hardly tell my toad was there!

Engine temp was running 192 until I got to vegas, down town in stop and go traffic, the ambient temp got to 114, AC on, engine temp went to 220 mechanical. As soon as I got out of the down town traffic ambient dropped to 104 and engine temp to 200. As ambient dropped so did engine temp, stabilized at 192 degrees. Sounded like the fan clutch was doing it's job. Fuel mileage over the sierras and back was 8.25mpg. Fernely nv to Kingman az just below 11mpg. I think all the repairs were worth it.
May your black water hose never break! Life Charter member since 89

lonfu
Explorer
Explorer
Brian in Michigan wrote:
Ionfu, Your lucky to get yours to kick in at 200*. Mine once it gets a degree or two over 185* my fan starts to kick on and will not kick off til it's below 184*. Once the outside temp is 80* or more it will kick on and stay on. This is with two different clutches. I put in a recored radiator 5-6 years ago and it was great for a year or so then the kicking on and staying on started happening. I had sealed up the front end so all air goes through the radiator.I have a 185* stat in it and the engine runs right there,


This is an update, Fan clutch starts to cut in about 190 but is full engauged at 200, this is on my mechanical gauge. The temp climbs to 210 before it starts to drop again, I'm usually going up a pretty steep grade. I installed new a ETC and my tech2 now reads that it runs at 199 degrees where as before it was reading 177 degrees. My mechanical gauge reads 192 when driving on flat highway.
May your black water hose never break! Life Charter member since 89

lonfu
Explorer
Explorer
After a trip, my brake pedal got lower again. Brakes worked ok, but the pedal got lower as if the brake adjusters were frozen. Heat issue's solved but.........

First replaced the Master brake cylinder, again. The current one was 5 years old. Bench bled MC. Bled all wheel calipers with DOT5.1. It didn't help with the low pedal at all.

I pulled the rear disc brakes apart and guess what? There are no rear brake adjustors. None at all. The front and rear disc pads just wear and the pedal gets lower until you can't tolerate it anymore! What a great design!!! Duh!!!

I replaced the pads, but found that where the inside brake pad is installed into the caliper frame, the upper slot, had a groove worn into it by the brake pad. I emery clothed all my caliper to caliper frame surfaces and installed anti-seize. (silver silicon grease) That grove could cause the brake pads to hang up. Old pads were still at %50.

Bad news, the only way to repair those grooves is to replace the caliper frames. I would have to pull the axles to do that. It ain't broke, so.....

Road tested and set brake pads. Stops fast and straight. It raised the brake pedal level a whopping 2"!!!!! Leaving on a trip on Thursday for 10 days or so. All through I have only 20k or so on the front I may replace them too since I now know there are no brake adjustors in the system. Have to do that when I get back.

So, if you are having problems with your P30 brake pedal p30 stopping power, look to your rear disc brakes for answers before you replace your Master Cylinder. If you have p30 rear drum brakes, I'd pull the rear drums and clean your self adjustors/backing plates to make sure they haven't rusted or gunked up so bad that they are not functioning. I wouldn't be afraid to sand the brake shoes lightly to remove any glaze that has built up.
May your black water hose never break! Life Charter member since 89

lonfu
Explorer
Explorer
update on p30 brakes. Found the hydro booster was leaking from the front seal, replaced it with a rebuilt unit. Seems to have solved the slightly low pedal lately.
May your black water hose never break! Life Charter member since 89

BrianinMichigan
Explorer
Explorer
Ionfu, Your lucky to get yours to kick in at 200*. Mine once it gets a degree or two over 185* my fan starts to kick on and will not kick off til it's below 184*. Once the outside temp is 80* or more it will kick on and stay on. This is with two different clutches. I put in a recored radiator 5-6 years ago and it was great for a year or so then the kicking on and staying on started happening. I had sealed up the front end so all air goes through the radiator.I have a 185* stat in it and the engine runs right there,
1990 GEORGIE BOY 28' 454 4BBL, TURBO 400 TRANS,
CAMPING: WHERE YOU SPEND A SMALL FORTUNE TO LIVE LIKE A HOMELESS PERSON.

lonfu
Explorer
Explorer
Got a different style of fan clutch from AZ. It works correctly, starts to kick in at 200 and is fully engaged at 210 to bring the temp back down to 195 then starts to cut out. It is a slightly different construction than the first one from AZ and the follow up one from Napa, both of which failed. AC Delco parts are now made in the big C so no different quality than those at napa, AZ or O'reillys. Noticed this last trip that the hydro boost is leaking from the front, guess time to replace it.
May your black water hose never break! Life Charter member since 89

onebull
Explorer
Explorer
You might try the AC Delco, have maybe a little better luck with it but I do carry a spare. It may be the 15-4949.

lonfu
Explorer
Explorer
Just got back from another 2k walkabout. Drivers side panel was installed at the factory, I made and installed the panel on the passengers side. The panels are actually splash guards to prevent rock and water from the wheels being thrown up on top of the engine. convertors have been replaced, muffler is not restricting. High exhaust manifold temps for this engine are normal, what is not normal is the stupid !@##$ fan clutch not engaging early enough to prevent overheating going up even small grades.

Installed new fan clutch from napa. It doesn't engage until coolant temp hits 220 degrees, should start engaging at 205. It looks identical to the one from autozone, look to be the hayden brand, just repackaged. Guess I got another faulty fan clutch. Doesn't anyone out there make a proper fan clutch that won't fail? Only has 1400 miles on it..... any suggestions on a good brand?

It sure is nice having front and rear brakes again!
May your black water hose never break! Life Charter member since 89

lonfu
Explorer
Explorer
Ok, finally got a long trip in, brake line shield functioned perfectly. put 3k on, I now have 126k on the 98 chevy chassis. The brake fluid didn't boil and back and front brakes both worked perfectly. Took it up a 8000 foot grade and when I got to the top brakes still worked perfectly. Had a 3100lb toad on the back. So, check your brake lines to make sure they do not pass close to your exhaust manifold like mine did.

Yes, I have stock manifolds, yes they get hot when I'm going up a 8000foot grade. Of course I don't go up a 8% grade at more than 35 mph and I'm lucky if I can go that fast.

Dang gone new fan clutch went out just as we climbed the last hill for home. Only 3k miles on it and the temp spiked to 220 and the clutch quit roaring I could hear when it went out. I hate changing that thing out. Good news is it the part is covered by warranty.
May your black water hose never break! Life Charter member since 89

enblethen
Nomad
Nomad
Another thought!
have you tried to reduce the exhaust heat?
My rig came with metal panels attached to the radiator supports, along the top of the frame rail, back to near what would be considered the firewall to funnel air over the exhaust manifold/headers and exhaust pipe.
Another thing to look at is the exhaust system. Originally there was 2 inch pipes coming off the manifolds into the wye pipe then 3 inch to muffler and tail pipe. Restrictions can cause heat build up in the system that would radiate outward.

Bud
USAF Retired
Pace Arrow


2003 Chev Ice Road Tracker

enblethen
Nomad
Nomad
I had Banks system installed right after I got my rig. It does not get overly hot pulling grades. You cannot pull them with wide open throttle and expect not to have problems. Exhaust has not been an issue. W have pulled over passes well over 7000 feet.

Bud
USAF Retired
Pace Arrow


2003 Chev Ice Road Tracker

lonfu
Explorer
Explorer
Thought I'd add this for enblethen, I don't drive over 50 mph. My gas mileage drops to much when I do. I run the engine at 2500rpm up a hill. My chevy 2500 exhaust manifolds do the same thing. The brake lines are less than 2 inches away from the exhaust manifold. This is my 3rd p30 chassis, just never looked for the brake line issue before.
May your black water hose never break! Life Charter member since 89

lonfu
Explorer
Explorer


Brian, here is a pix of the heat shield that I made. Look at how close the front brake lines are to the exhaust manifold. No wonder my brake lines were boiling.
May your black water hose never break! Life Charter member since 89