I finally figured out why the 425 cad blew

[Longhorn Man]

Well, for those who followed the saga, you remember about 16 months ago when i was so happy that I was getting the longhorn on the road, only to blow the engine the next day.
Then, I located a 500, my wonderfull girlfriend sent me some money becouse things were WAY too tight at the time, and I got it all painted up, cracked it open to inspect it, slapped it in, and it has been my daily driver since last september, and my ONLY vehicle since November.
When the Locked up 425 came out, I didn't have time to rip into it to locate the problem. I saw piston skirt in the oil filter when i cut it open, it had no oil pressure after warming up, it was junk. It ended up locking up when i took it out for a drive...even though it was knocking and had no oil pressure. I wanted to clean up my dad's boat for fathers day, and I need the truck to do it with... figured it'd make it 7 miles.
I was wrong.

Well, since I installed the 500, I've never been able to get the tune right. I'd go a little this way, and the gassoline fumes would burn your eyes, a little that way, and I'd get pre-ignition rattling like you wouldn't believe. (93 octain) Even adding 2 CANS of octain booster, and it'd still ping like mad.
Even like this, it'd burn the tires to nothing. I've had a few members on here witness it... lytelredrydinghood, Neon Larry, I'm sure there was more... but none coming to mind... anyways, had plenty of power. Haulled dad's boat and would still out accelerate dad's mini van from the stop lights...even uphill.
Well, it's always acted like it's had a vacume leak, and I'd spend a little time every week or two messing with it, and got it doing OK... but never great.
I discovered last night, that one of the diaphrams in my booster is blown, and it's been driven all this time, with a HUGE friggen vac leak.
This explains the funny idle
This explains the pinging
This explains the brake pedal that was never quite right...but I couldn't put my finger on it.
This explains WHY THE $@% 425 BLEW UP!!! Massive lean condition.
When it chewed up the piston, i was on the freeway keeping up with morning northbound rush hour traffic. I was probably pushing 75. I had heard a little pre-ignition on the hills, but then again, you couldn't hear ANYTHING in that sucker at that time... the cherry bombs terminated RIGHT uder the cab.


I'm just lucky I haven't melted any pistons on this one.

I'm awaiting parts to convert to manual brakes, untill i can afford a new/reman booster. No more used ones. I've gone through 3 (plus the original bum one) on this truck... I thought this one was good. I got it from a board member, but I can't remember who. It was an as is sale anyways... he had no idea.

Long winded as usual, but at least now we ALL know...
The rest of the story.

[too much stuff]

I bet ya sleep better finally knowing...
Did you get through the silver book yet?

[Longhorn Man]

Actually, I'm probably gonna lose sleep, untill I can seal up that vac leak.


The solver book... I recieved it, sat down reading it, and didn't get up untill I was done. It wasn't what I was expecting, but it was well worth the read.

[TugOwar]

dang man. glad you found the problem.

[Longhorn Man]

I had wondered why the 425 was so kick ass one day, and then just torquey... and the 500 never felt as strong as the 425 did on some of the test drives. (before the booster went south)
So now, by this time next week, I should have manual brakes, and if not dead on tune.... pretty dern close.

[Ron 586]

I am damn glad you wrote that. I have been laughed at for years for pulling the brake booster line when chasing my tail on everything is new but it just ain't right vehicals. Glad you found it.

[Longhorn Man]

LOL, it only took me 10 months to finally pull that line and block it. It's amazing how quickly the idle calms down, settles to a nice, smooooth rumble.

[hexafamily]

Had the same problem on my '70 Buick 455 a few years back. Couldn't get it to run right for 2 years. Finally put a vac tester on booster and found the leak. Replaced it and now runs great.

[special-K]

Is a booster that you can hear exhale when applying brakes a sure bum deal?I`m thinking it obviously is,but never asked.

[Longhorn Man]

Hmmm, when I was a kid, my dad had a 78 aspen wagon with a 318. When you'd hit the brakes, it would his a little, and I have seen it from time to time since then, but I always remember that aspen doing it.
Becouse of that, I'd say no, it doesn't automaticly make it a bum item....but the rest of my brain says that's a bad thing.

[FormerMember]

A sure sign: You hit the brakes and hear a miss in the motor as it sucks air.

[kwmech]

I'm trying to figure out why you want to convert back to manual brakes after locating the problem?

[Longhorn Man]

maybe you missed the $$ part.
We don't all have a few hundred laying around... tossing a nonessental $100 piece at it would totally screw me all up. I have a trip I am saving up for, and other bills to take care of too.
One man's budget bolt on, is another man's entire budget.


Besides, I've owned both manual and power drum brake trucks... I really don't see what all the hoopla is about. Power is nice...yeah, but it isn't the first thing I would add like so many ppl here say it should. Maybe I have a stronger leg tham most... maybe most ppl are wusses, I don't know. I've just never seen much of a need.

[jacobs]

I perfer the feel of power brakes however I don't like the space they require. It's in the way for for a lot of engine mainancence and in a panic stop, I can't tell any difference. Maybe I just got a lousy rebuild from NAPA but I think I'll stay with manual brakes.

[67ChevyRedneck]

I drove the 67 for years with manual drums. Between the heavy clutch, brakes, and non-power steering, I got a good workout everday when I drove it! Your time will come man, I had to wait almost 10 years to do some serious work to my truck. Glad you figured out the problem!

[jrb71c20]

A sure sign: You hit the brakes and hear a miss in the motor as it sucks air.

My booster has been leakin air during braking....I guess this explains the runnin like a dog at the stop lights and the gas soaked plugs...awwwww hell. I'm glad I read this, thanks Longhorn Man

[Lemield]

Longhorn Man...You continually amaze me with your knowledge! I've been looking for what seemed like a vac leak on my C20 since I bought it.
I followed your advice and lo and behold....it looks like I have a leaky booster too.

Thanks Andy.....you are one of the reasons this board is so good!

[68speedalert]

For anyone concerned about their booster, here is the 'correct' way to check.

Pump the pedal a few times, KOEO. Pedal should be higher than normal. Start engine with foot on pedal. It should drop an inch or two after the engine starts.

Foot off pedal; turn off engine. Wait a a few seconds. Press on the pedal. Should get a least a couple of assisted applications (from the vacuum held in the booster). This will tell you how bad the booster is leaking. 2 assists, probably OK, 1 assist, getting close, 0 assists, get out the wallet.

If it fails any of these tests, remove the check valve from the booser. Do it with engine running. Engine should rev higher and should have STRONG vacuum at the valve.

Reconnect the valve and booster. Shut off engine. wait a few seconds. Remove the valve from the booster again, Listen for air being sucked into the booster when you do. If none, it's either a leaking booster (likely) or a bad check valve (you hope for this).

The booster on my truck will not pass all these tests. It does leak some, but it isn't large enough to cause the problem Longhorn Man had.

Use this as a guideline, most of our vintage truck's boosters leak some.

Sorry you had to find it the expensive way, Longhorn Man.

[67chevy2wd]

That was some very usefull information 68speedalert. I will have to try and remember that.

[Longhorn Man]

Originally Posted by Lemield

Longhorn Man...You continually amaze me with your knowledge! I've been looking for what seemed like a vac leak on my C20 since I bought it.
I followed your advice and lo and behold....it looks like I have a leaky booster too.

Thanks Andy.....you are one of the reasons this board is so good!

If I was amazing, i woulda noticed it a year ago...and an engine ago. But, at least you learned from my mistake. THAT'S what this whole board is all about. I blow up stuff, so you don't have to. (Hmmm...I see a signiture modification in there)


68speedalert;
You know, I've always felt my pedal didn't feel quite 'right' but I always figured I had a hyd problem or something... I basicly learned to live with it. The pedal feels like something inbetween power, and manual. I never bothered with the tests you described...why would I...my booster is fine, right?

[67chevy2wd]

Just look at it this way if the 425 wouldn't have blown up you probably wouldn't have gotten the 500. So in a way it was a learing experience with a blessing. Just now you will have to get a second job to feed the 500.

[Lemield]

Originally Posted by Longhorn Man

If I was amazing, i woulda noticed it a year ago...and an engine ago. But, at least you learned from my mistake. THAT'S what this whole board is all about. I blow up stuff, so you don't have to. (Hmmm...I see a signiture modification in there)

Don't sell yourself short....I'm pretty handy with cars/trucks/motorcycles and you have taught me a lot of stuff.

BTW....love the new sig mod!

[69TowRig]

Originally Posted by Longhorn Man

You know, I've always felt my pedal didn't feel quite 'right' but I always figured I had a hyd problem or something... I basicly learned to live with it. The pedal feels like something inbetween power, and manual. I never bothered with the tests you described...why would I...my booster is fine, right?

I put a used booster in my truck, but I did the power disc upgrade before the truck even drove, so I never knew what was "right". I will have to check mine, I can still push the pedal through the floor and not have enough brakes, plus the engine runs rough (but like I said, it hasn't run "pre-power" so I don't know if it will run better).

Thanks for the tip I will update later.

[68speedalert]

Longhorn man,

Ya know.....if you'd had some mufflers on the 425, maybe you would have heard the massive sucking sound coming from the booster!