Engine Stalling when Braking

[Rob_M]

Hey Guys,
I have a 68 427 Biscayne w/original power 4 piston disk brakes that has an issue when braking. After the car is fully warmed up, when I brake the engine stalls. As an example I will put it in neutral going 30 mph hit the brakes, and it stalls. If I take my foot off the brakes quick enough the engine will resume. It's as if I turn the key off and on quickly. It will even do this when in gear. Of course it dumps raw gas in the exhaust and I get a *very* loud pop out the back when I let up on the brakes.
I have checked for vaccuum leaks, blocked the vaccuum booster, adjusted the floats, (has a Holly), checked for loose wiring near my brake pedal and engine bay, etc - Nothing.
I am at a total loss on what is happening. I plan to replace the check valve that is on the front of the brake booster but like I mentioned earlier it still does it when the booster is unplugged & vaccuum is blocked. I have noticed it doesn't do it when the car is cold and when I go backwards.
Any ideas or thoughts would be greatly appreciated.

Thanks,
Rob Mansfield

[TDW]

Air cleaner cover just touching the coil wire when braking? Coil wire loose? The 12 volt wires, not the center coil wire? Bad connection at the horn relay? Ignition switch wire loose?

[PeteLeathersac]

Could the wiring be mixed up where the ignition feed is somehow connected via the under-dash brake light switch?.
The hot/cold difference is perhaps it's own problem but it's possible someone's wired things up so the reverse lights are supplying ignition power while backing up?.
Run a hot-wire + battery to + coil and see if it still happens when you step on the brakes?.

Goodluck!.
<<GRAEMLIN_URL>>/beers.gif
~ Pete

[SS427]

What about parked, running and the brakes applied. If it still does it then it is likely related to electrical. If not, likely fuel related or like Tony mentioned. I would also experiment with driving down the road and VERY gently applying the brakes though enough to slow the car over time. If it stalls, I would again look at electrical. If it does not, look for fuel related.

[Rob_M]

Well..... I'm a little embarrassed. After checking all the wiring, a friend suggested checking the floats again. Sure enough I had the springs in backwards!
<<GRAEMLIN_URL>>/smile.gif
Thanks for all of the assistance!

Rob M

[mockingbird812]

Looks like Rick gets the prize. Glad you got it figured out. Nothing to be ashamed about, most of us have been there before! There seems to be a healthy dose of folks 'round here willing to help out a fella when he's havin' issues! <<GRAEMLIN_URL>>/beers.gif

[TDW]

Glad ya got it fixed Rob. Are any of you Kazoo guys heading to Flint for the &quot;Back To The Bricks&quot; next month? Should be a real good show again.

[Rob_M]

Hey Tony - Probably not this year but I have heard good things about it. I will be at the Grand Rapids cruise though. I've been there every year since it started and it gets bigger every year. I usually park my car at Berger Chevrolet.... I've been to the Woodward cruise and I think the Grand Rapids one is bigger!

[Rob_M]

Well I was/am a little premature on the success of my repairs. The car is really doing it now - Every time I hit the brakes the engine dies. I bypassed the ignition switch in the dash but no luck. I went around the whole car while it was running and shook wires including under the dash but nothing.

I also installed another carb that I had, and the car still died while braking.

I have a MSD box and distributor so I'm wondering if I need to find another distributer to test that out.....

[njsteve]

Did you disconnect the brake light switch to see if the car still dies when the brakes are applied? Could be a 12v wire crimped against the firewall by the brake bracketry - when you apply the brakes, the bracketry shifts and grounds the wire and backfeeds the car into a 12v positive ground system.

When I pulled my 69 Z11 pace car apart I found a main power lead wire from the dash harness clamped between the brake/clutch pedal assembly and the firewall. It would have eventually caused one helluva electrical fire.

Also, one of the brake light bulb assemblies themselves could be internally shorting to ground when the power goes to the bulb. From experience I know the Mopars are extremely sensitive to a bad ground on the tail lights - so bad that they backfeed all the other lights in the car when the brakes are applied, if the ground is not good enough.

[PeteLeathersac]

What happens if you try starting the car while your foot's on the brake pedal?.

<<GRAEMLIN_URL>>/dunno.gif
~ Pete

[Rob_M]

The engine does NOT stall when I use the brakes going backwards, but it does stall when I use the parking brake to stop when going forward. That basically eliminates the brake light switch theory. I did check for any wiring interference and I didn't see any. I also checked the wires while the car was idling - shaking them and so forth and nothing. The car idles just great!

As an example, our driveway is at the top of a hill and if I let the car go backwards and hit the brakes it doesn't stall. Here's the interesting part, if I am going backwards and goose it a little the car dies. This strongly suggest that this problem only happens when the car is accelerated in one direction. Going in reverse and hitting the gas produces the same 'motion' (the car and occupants being accelerated toward the front of the car), while going forward and braking.

When I am driving the car and put it in neutral I can pump the brakes and the engine will start to stall and recover each pump that I do. When it is idling I can hold the brake pedal all day long and the car does not die. It also starts with my foot on the brake pedal.

I know this hard to believe but that is what it does......

I wired the MSD box into the battery, bypassing the rest of the car and it still does it. I assume that only leaves the ignition part at fault. One thing I did noticed is my MSD Blaster coil is mouinted sideways with the bottom of the coil facing the front of the car. I plan on trying a different coil to see what happens. After that I will reinstall my old distributor. (I installed a new MSD ignition this spring...)

At this point I'm just trying everything that sounds logical....

[x Baldwin Motion]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: PeteLeathersac</div><div class="ubbcode-body">What happens if you try starting the car while your foot's on the brake pedal?.

<<GRAEMLIN_URL>>/dunno.gif
~ Pete
</div></div>

Has the motor and trans been out recently? Sure sounds like some wire is being pinched somewhere during deceleration. Check all wires around back of motor, top of trans, starter, exhaust. What type of trans ? Sure is a puzzler. <<GRAEMLIN_URL>>/hmmm.gif

[njsteve]

Do you have all of those braided copper ground straps that run from the block to the firewall, and from the block to the subframe? Without those, the power will backfeed up into other circuits.

[Rob_M]

OK. Here are more of the 'things' that I tried with no success.
1. Changed the coil, didn't think it would do anything but I tried anyway.
2. Removed the brake light switch, same.
3. Spent time under the dash and went through all the wires and they all looked tight and connected. Nothing was near the brake pedal.
4. Looked at the wiring under the hood and it looked good there. I do have a copper ground coming from the firewall to the head and that was connected. I do NOT have any other ground straps though.
5. Car starts and idles beautifully when I have my foot on the brake.

The car has a manual transmission in it and there are no wires going to it. No backup switch or anything. This weekend I will install the motor to frame grounding strap. The thing is the car hasn't had that strap since I have had the car.....

Like I mentioned in my previous post, I took my ignition, (MSD box 6AL and distributor), and connected it directly to the battery which I assume, tell if I am wrong here, will bypass the rest of the wiring harness. When I did that the car still died. It makes me think the problem is within the ignition itself..... When the engine does die my voltage meter reads ~14 volts. If I had a bad ground would my meter still read 14v?

My next step is putting a different distributor in it.... I want to eliminate everything that I can....

Thanks - Rob

[PxTx]

I am a little suspicious of the distributor at this time. Why don't you pull it out and look it over. There could be a broken ground wire, and as the advance moves things, the problem occurs.

[Plowman]

Try the fire wall fuse block connectors [on the engine bay side]. I think there is a bolt that hold's half of it tight. See if it is loose. Also see if it is clean inside.

[PeteLeathersac]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Plowman</div><div class="ubbcode-body">Try the fire wall fuse block connectors [on the engine bay side]. I think there is a bolt that hold's half of it tight. See if it is loose. Also see if it is clean inside. </div></div>

I'm thinking this plug too and better yet may be undoing it from the engine side to inspect and clean the connections..
Some of these were a 3/8&quot; bolt head and the engine side splits into separate sections that go to their respective assys...engine, nose lamp harness etc..
Check any other connections @ the firewall too as perhaps the mechanical side of brake application is flexing the metal enough to alter a ground or connection somewhere?.

Have you tried remotely grounding the engine to chassis/body w/ a booster cable yet?.
Also was the ignition dash lite on regardless of key position when you hotwired the coil?.
Lastly, when it quits and you immediately check the carb is there fuel at first pump and lots w/ subsequent pumps too?.

<<GRAEMLIN_URL>>/beers.gif
~ Pete

[Rob_M]

Got it!
After going through everything I could think of, I thought about switching out the battery from my 'Honda'. When I started playing with the battery in the Biscayne the engine died. Sure enough, when I tilted the battery forward the engine died, when I tilted it backwards nothing. That was it. The only thing I could figure was there was a bad cell that would short out when it was tilted in one direction only. Strange.

Thanks to all for their comments and support. If nothing else, I am much wiser and know my car a little better. <<GRAEMLIN_URL>>/tired.gif


Rob

Go Green!!

[Xplantdad]

Interesting...thanks for sharing the final resolution. It may save someone else from the trials that you went through

[BARRY]

HI that is realy strange never heard of that 1 in a million

[x Baldwin Motion]

great, that was a real challenge. never heard of such a thing !

[2qwik2c]

I had the same problem with my 68 Camaro years ago. It would die when I hit my brakes hard. Tried everything but not the battery like you did. I gave up after awhile and just didn't hit the brakes hard anymore <<GRAEMLIN_URL>>/eek.gif .

[PeteLeathersac]

W<<GRAEMLIN_URL>>/hmmm.gifW that's a new one to consider for sure!.
Cool you finally got to the bottom of things!

<<GRAEMLIN_URL>>/beers.gif
~ Pete