Car won’t stop....UPDATE new brakes, still no

[Svtfreak]

Coyote with whipple suoercharger and 6R80 with factory mustang converter. Note that the converter and brakes all worked perfectly together before please. Some people say it’s not enough stall, but one experienced guy told me it would work great and it actually did. I wasn’t expecting that either.

Car starts and runs. Drives. But won’t stop. Used to stop barely touching the brake. Front locks up. Rear pushes through brakes and either slides front or sits and turns over. Rear brakes ain’t perfect but clamp so it’s hard with 2’ pry bar to turn over the axle. Like two hands and almost all my force hard. E-brake actuated with screwdriver on both sides until hit the caliper won’t stop them either. Only changes since it worked fine is it sat up awhile and new tune. Tune came from Lund via power by the hour. They say that all idle and part throttle trans calibrations are factory stock.

What’s wrong?

It slows the spin but won’t stop it. Motor bogs slightly but not half the idle speed like about half the axle speed if converter was locked up.

[Bob Cowan]

I also was not happy with the brakes. They worked, but if there was a bit of sand or water, it would push the front tires. If I shifted it to neutral, the brakes were awesome. I changed the torque converter, and that stopped.

The stock torque converter really does have too low of a stall speed for a light weight car. Raising that a little bit will really make some big improvements.

Also, the stock converter is good for about 500'ish hp. More than that will eventually cause a failure. You're between 600 and 650 hp. Changing to a better converter will increase reliability.

BUT, if I read this correctly, this all started after a custom tune. The stock converter is a lock up type. The point of lock up is controlled by the computer. I suspect the tuner lowered that lock up point.

[Svtfreak]

Thanks bob. Yes i agree with a lot of what you said. And was trying that one based on a knowledgeable persons recommendation. And, to my surprise, it worked actually. I don’t know why.

The tuner says they touch nothing at idle and part throttle. The brakes are working enough that they should stop the car (plus it did it before!)

I’ve thought through it and it dawned on me that I can put the factory tune back in it. While it won’t run right, it will run well enough to test this. That will alleviate tune, or prove the tune is it.

Update coming when I do that. If it’s not the tune, I may need help figuring out the culprit.

Bob, I see iou has a similar setup in a BdR whatever that is lol. What stall where you using?

[Gordon Levy]

Sounds like you need to reprogram the 6R80. The slip and lockup are set for a 3700lb Mustang not a 2400lb street rod and the computer is controlling the torque converter backed on converter slippage. It sounds like the street rod is so much lighter the converter isn't slipping like it would in the mustang and staying locked up.
I have brake systems if you want it to stop better.

[Svtfreak]

I just loaded the factory tune and it’s still doing it. So I have something weird. I know the brakes aren’t doing 100% what they should. So i guess it’s back to the drawing board on either brakes or converter or both. But I’m baffled why it didn’t do it 6 or 8 months ago?

[Arrowhead]

Sounds like converter lockup to me. A stock converter is no reason it won't stop at idle.

[Svtfreak]

Sounds like converter lockup to me. A stock converter is no reason it won't stop at idle.

First thing I thought also. But ruled that out. I can use the e brakes to just about stop the axles but the motor doesn’t bog down. It acts, to me, like the trans pressure is way up for some reason. PBH gave me some things to check. They say they’ve seen the valve in trans going to cooler stick and cause similar problems. So I’m gonna check the hose I’m using and that valve after Christmas sometime.

[Ray]

This is like the story where the mechanic couldn't fix the brakes so he made the horn louder.....

Not really familiar with your set up (have a carb'ed 302 in ours) but are you pulling enough vacuum?

Just a thought, after that, I'm out of ideas.

Good luck,

Ray

[Bob Cowan]

Thanks bob. Yes i agree with a lot of what you said. And was trying that one based on a knowledgeable persons recommendation. And, to my surprise, it worked actually. I don’t know why.

Bob, I see iou has a similar setup in a BdR whatever that is lol. What stall where you using?

BDR = Back Draft Racing

I installed a Circle D triple disc converter with a 3,200-3,400 stall speed. Made a huge improvement in brake performance.

[Svtfreak]

This is like the story where the mechanic couldn't fix the brakes so he made the horn louder.....

Not really familiar with your set up (have a carb'ed 302 in ours) but are you pulling enough vacuum?

Just a thought, after that, I'm out of ideas.

Good luck,

Ray

Hey ray. I have an ABS Systems electro hydraulic power assist system. It’s driven with a hydraulic pump, not vacuum, and very similar to hydro boost brakes. It’s a very cool idea, but I’ve had a few problems with mine, and they continue. I’m not confident in it right now. And you are correct. I definitely have to either perfect what I have or ditch it and do something else. And that is in the plans. But it is working well enough that it should stop the car (and it has stopped the car)

After much discussion several more knowledgeable people than myself, and a few tests, something is going on in my transmission that is raising the fluid pressure. The tuner is looking at if he can add that to the datalog so we can see the actual pressure. Meanwhile I am going to check a few things (like my temporary hose to cooler which maybe has swollen internal or collapsed? And the thermostatic valve in the cooler outlet port) that’s been know to fail and cause similar issues. We know the converter isn’t locked up so we look there next.

After I get this fixed, and can drive it, then I’ll plot a brake upgrade (or fix) course then we’ll do some road trials to decide if another converter is needed. I really liked how this one acted on the first drives though. But we shall see.

[NAZ]

Sum Ting Wong.

Read through this twice and still didn't see what I was looking for. Are you saying the brakes won't hold the car back at a stop or that the brakes won't bring the car to a stop from highway speed?

Do you know what your actual stall speed is (not the advertised stall or what the guy behind the counter told you)? Has that changed from when the converter was new?

If you're saying that it won't stop from highway speed with the trans in gear, have you tried it in neutral? That would eliminate the trans from the brake performance variable.

Have you at anytime before you noticed the brake performance degrading got the brakes so hot you could smell them? Such as going down a long steep grade using the breaks to maintain the speed limit.

Be advised that a street car converter is typically equipped with a sprag on the stator and the OEM style sprags don't stand up well to higher flywheel torque. I've seen them fail with ~500 lb ft and when they do the stall speed can be significantly lower. The car feels like it's taking off in high gear as there is no torque multiplication when the sprag fails. Theoretically this should not affect the ability of the brakes holding back the car at a stop but if the stall speed change puts it closer to the idle RPM it may have an effect.

[Svtfreak]

NAZ, it won’t hold it at a stop. Brings it down from ~35 mph just fine. They haven’t been hot at all.

The stock converter is supposed to be ~1800-2200. I don’t know what the actual is. But i know i can easily fit brake my mustang to 2000 rpm+ and this one is doing this at idle (~800 rpm, granted vehicle weight is less but stall rpm shouldn’t have dropped that much). Plus, this was not doing this before. That’s the big key, to me. As far as damage, it hasn’t seen any appreciable torque. All I’ve done is putt up and down my street a bit. Plus, these are living reliably with near 1000hp setups in mustangs so I’m fairly certain I haven’t killed it with abuse.

[NAZ]

Sounds like you're trying to troubleshoot an issue and don't have all the info you need. A key piece of that info is actual stall speed so you should consider determining what that actually is before going too much farther. It's very easy to do but it does not involve foot braking as that is not an accurate way to determine stall speed.

Here's a simple procedure from a major converter manufacturer you may have heard of so you're not just taking my word for how to perform this simple test: http://www.atiracing.com/links/faqs....mineStallSpeed

If your stall is less than 3000 you may not be happy with how the car stops at signals. I'd suggest you have a converter made that stalls closer to your max torque RPM. No, the engine won't run at that RPM all the time, doesn't work like that. Stall speed is affected by engine torque and your max torque RPM is at WOT, not at 18% TPS cruising down the highway. And since it's a lock-up converter it will couple the engine and trans during cruise anyway.

[Svtfreak]

NAZ, I agree and I will have to know that number at some point. But right now, it’s not an issue.

The issue is, something has changed. What worked before is not now. The stall speed has not changed. Nothing mechanical has changed from when it worked a whole lot better. That’s what I have to get reverses back to wheee it was so I can go about driving and testing and seeing if the converter and brakes will really work for me. Right now, something is way out of whack from where it was and nothing mechanical should have caused the change.

[JOP33]

Coyote with whipple suoercharger and 6R80 with factory mustang converter. Note that the converter and brakes all worked perfectly together before please. Some people say it’s not enough stall, but one experienced guy told me it would work great and it actually did. I wasn’t expecting that either.

Car starts and runs. Drives. But won’t stop. Used to stop barely touching the brake. Front locks up. Rear pushes through brakes and either slides front or sits and turns over. Rear brakes ain’t perfect but clamp so it’s hard with 2’ pry bar to turn over the axle. Like two hands and almost all my force hard. E-brake actuated with screwdriver on both sides until hit the caliper won’t stop them either. Only changes since it worked fine is it sat up awhile and new tune. Tune came from Lund via power by the hour. They say that all idle and part throttle trans calibrations are factory stock.

What’s wrong?

It slows the spin but won’t stop it. Motor bogs slightly but not half the idle speed like about half the axle speed if converter was locked up.

I am a little late to the game on this and only throwing this out because I had a similar experience the first time I put any appreciable mileage on the car. The brakes seemed to work fine at first then as I crept up to higher speeds I ran into the issue of not being able to stop completely - to the put I was having to use the e-brake. Once I made it back to the house, I ran the car on a back road and bed the brakes (as I should have done prior to taking it on the road), knock on wood, since then I have had good luck and no issues braking again.

[Svtfreak]

After some more playing and thinking, the brakes are getting worse. Everytime i mess with it, it gets more air in the system and the pedal gets spongier. So before i go any farther, I’m gonna pull the body off and redesign my braking system. The electro hydraulic system is coming out and gonna set up a tandem wolwood MC with remote reservoirs. I’ll prolly use the ABS systems aluminum ones. Either way, after I get the brakes tightened up and ensure they are working 100% right, then we’ll see how the trans does.

[Svtfreak]

Ok. I pulled out the electro hydraulic brake system and put a wilwood manual master cylinder. Checked all tubing, filled and bled the brakes good. Still won’t stop the rears from spinning. I have it on jack stands at the moment. The hydrostatic valve in the trans seems to be working right, I get good full flow out of the trans to cooler, and the cooler lines are clear. Hit the brakes, stand on them and the rear wheels still keep-a going. It does seem that it will make the car stumble now, just a touch, especially before it got warm and wasn’t acting quite right just after I started it after a reload of the tune.

That said, I know we don’t have a bunch of 6r80 folks here. But I could use some advice on how to confirm or rule out a locked up converter when it shouldn’t be. Or anything else. I have a call in to a local trans guy also. He’s supposed to be real good with these things.

Any pointers, advice or tips? This is my first auto trans build ever. No experience with these.

[Bob Cowan]

It's all computer controlled. The only way to know how and when it's operating, is to take it to a shop that has the right equipment. That's not hard to do, since there are millions of them on the road. Take it to a local trans shop and talk to them about it.

[AJT '33]

Ok. I pulled out the electro hydraulic brake system and put a wilwood manual master cylinder. Checked all tubing, filled and bled the brakes good. Still won’t stop the rears from spinning. I have it on jack stands at the moment. The hydrostatic valve in the trans seems to be working right, I get good full flow out of the trans to cooler, and the cooler lines are clear. Hit the brakes, stand on them and the rear wheels still keep-a going. It does seem that it will make the car stumble now, just a touch, especially before it got warm and wasn’t acting quite right just after I started it after a reload of the tune.

That said, I know we don’t have a bunch of 6r80 folks here. But I could use some advice on how to confirm or rule out a locked up converter when it shouldn’t be. Or anything else. I have a call in to a local trans guy also. He’s supposed to be real good with these things.

Any pointers, advice or tips? This is my first auto trans build ever. No experience with these.

OK, thinking outside of the box here, is it possible that your line going to the back got pinched somewhere? Or even possibly you have a blockage from something somewhere int eh line prior to splitting?? Just a thought.

[JimLev]

Have you checked the rear brake pressure with a gauge?
I'd think it must have something to do with the converter stall speed but you said it worked OK in the past.
I don't have your tranny. My 4L65e tranny computer uses a wire that connects to the brake switch which controls the lockup. Does yours uses a wire like mine? Check to see if it has power (or ground) on it when you work the brake pedal.

[Svtfreak]

I have a local trans guy gonna come put his computer on it. I can see trans fluid pressure and slip in my datalog but I don’t know what is normal and what is not. I’ve got a service manual but at 485 pages, finding info takes time.

There is no wire to the brakes. It is strictly throttle controlled. It won’t lock until 3rd year and should unlock when throttle lifts. Also, it is a modulating lock up. It can be locked, unlocked, or at any state in between. Ford racing was no help. Performance automatic, after the same brake discussion, says it’s eother the converter is stuck (he said it can actually still slip some when “locked”) of the valve for the converter lock up is stuck at some state partially on. The trans guy should be able to see that if that’s it (called for versus actual position and current draw of the valve are things he can see). Hopefully as soon as he gets a chance we’ll get that looked at.

As far as brake lines. One of the things I did was drain the lines and check them. No blockages. Fluid flows freely. I am certain the rear brakes are now working as they should, or very close to it.

The PA dude said it best. “It sounds like your converter is flashing at 5-800 rpm instead of 24-2700”.

[Svtfreak]

Trans guy came over today. We did a lot of testing. Nothing shows up as wrong. We even c clamped the rear brakes. While motor didn’t kill, it bogged down and got them real real hot, but they still turned.... geesh! The computer is showing slip so the converter is not locked up tight. We can get 480 slip in 3rd gear with brakes which he says in normal.

He has no clue. He thinks it’s either something stuck in the valve body or the converter bushing is burnt up. But that’s unusual cause usually they leak oil he said. First step is to pull the valve body and bring to him, let him go through it and check a couple items he said cause trouble (a “bridge” he called it between the body and the trans). Then we’ll go from there.

[FF33rod]

what a pain, it's going to be interesting to see what it is when you finally figure it out

Steve

[NAZ]

OK, I see you're still struggling so I'll try to nudge you once again for your own good. Have you checked to see what your stall speed is? It's a simple test but will either eliminate or confirm a problem with the stator and sprag. If a sprag fails it will significantly drop the stall speed of your converter and stall speed can make it hard to hold a car back during idle in gear. You have an engine with a power adder and sprag clutches are a known weak link with engines that make more than moderate torque. That's why you won't find them in drag race cars.

This is not theory but experience speaking.

Good luck.

NAZ, out...

[Svtfreak]

Naz, I couldn’t do that right now. It’s acting like the stall speed is at roughly 500 rpm. When you touch the throttle, the wheels respond. It is definitely not acting like it did when i first drove it. Not even close. I barely touched the brakes and the car would stop (and not turn the rear tires over). Being the 6r80, I can’t put it in high gear to do that test though. I have no way to force and hold it in 6th. In third though, it acts as though it flashes off idle. Like it’s already flashed.

The 6r80 is pretty reliable even at these power levels. And I haven’t even tested it yet. This thing hasn’t been beyond a neutrals throttle 15% blip and 5% when under load. It ain’t seen boost. This problem has been since I fired it up after installation of the blower. I’m not saying it ain’t a sprag (although I have no idea what that is in a trans lol) but judging by your description, it’s possible.

Keith told that trans fluid pressure is what unlocks the converter. I am wonder if a price of trash or something got in the line to the converter so that even though i have pressure, the full amount ain’t getting up there to fully unlock it (since it is a modulated locking converter).

Either way, I’m gonna get it. If Keith don’t find anything with the valves, the whole thing is coming out and going to him.

[Svtfreak]

Pulled the valve body today. (Got stuck at work last 2.5 weeks). Nothing broken or obvious. Other than a couple little small aluminum flakes in the bottom of the pan. The most worrisome is the ferrous dust on the magnet and a small amount in the pan. Extremely fine material. Trans guy said that shouldn’t be there. He thinks it’s converter clutch material (he called it that anyway). He thinks the converter is dragging and stuck in that position. He’s gonna go through the valve body and open the filter up and inspect it then we’ll plot a path forward.

Meanwhile, I have decided to redo how my shifter is mounted and do more like traditional style and mount it to the transmission, like prgmgr (Keith) has done. So I’ll work on that while half the car is apart and see if there’s a way I can pull motor only to swap out the converter.

[Svtfreak]

Trans dude just called. Said there’s nothing wrong in the valve body. All valves move free and the solonoid for lock up works fine. Absolutely nothing in the filter. Plan is to reassemble it and try again. If problem still persists, likely will try a new converter. Meanwhile, he has a brake clamping force gauge I’m gonna try just to see. Like I said though, we had c clamped the rear calipers and still didn’t stop it.