6R80 transbrake tech discussion

Thought maybe I could get others thinking. This really isn't a difficult thing, so background on how the trans and transbrakes in general function. Someone might want to attempt this themselves.


Any transbrake you buy is going to raise line pressure in order to increase the amount of torque the elements can hold. By elements I mean clutches and bands. There are no bands in this trans, so only clutches. Some want to say raising the line pressure is bad, well they can think that if they want, I disagree.

Also any transbrake is going to have a limit to the amount of input torque it can hold. I mean think about it, don't tell me I can bolt up a blown nitro hemi to your brake and it is still going to hold, there is always a limit. This can be increased by line pressure as mentioned above, or by increasing the amount of clutch plates in the elements which are holding when on the brake. I said increased, because while you can raise the limit, there is still always going to be a limit, the point is to have the limit out there high enough to make the brake a usable tool with a given combination.

If you've never used one, don't think it is like dumping the clutch in a manual car. There are some similarities, the suspension stays relaxed, the driveline isn't loaded behind the trans, but the "hit" is not as hard as a manual trans.

Next lets look at the elements in this trans and how they might be used as a brake.

1. Forward clutch. This is applied when high current is routed to SSA. This is used for forward gears 1 through 4.

2. Direct clutch. This is applied when LOW current is routed to SSB. This is used for reverse, 3rd, and 5th.

3. Intermediate clutch. This is applied when high current is routed to SSC. This is used for 2nd and 6th.

4. Low/reverse clutch. This is applied when LOW current is routed to SSD, and SSE is ON. This is used for 1st and reverse.

5. Overdrive clutch. This is applied when LOW current is routed to SSD, and SSE is off. This is used for forward gears 4 through 6.

Next, possible ways to lock up the trans.

We really want reverse and 1st gear at the same time to do this.

So reverse has the direct and the low/reverse applied.
1st has the forward and the low reverse applied.

First logical conclusion would be just apply the direct in 1st gear. I've tried that, and technically it works, so it is a transbrake, but the holding capacity is very low. I'm sure this could be improved by adding clutch plates, but I think the object here is to avoid that, even though that maybe isn't all that practical.

There might be some combination where a clutch is released to accomplish lockup, then reapplied when the brake is released, I haven't investigated that and wouldn't even consider it. It's much harder to apply than it is to simply hold, and this sort of method is going to lead to a greatly increased probability of trans damage.

So what else do we have to work with that we can add? Only things left are OD and intermediate. Due to the way SSE controls whether SSD controls either the L/R or the O/D, those two are mutually exclusive, so we can't work with the OD without losing the L/R, which we need.

So intermediate is it. It needs high current to apply. Either a circuit needs to be built to supply this, or a circuit needs to be rerouted to do it. In 1st gear the only circuits that are high go to the forward which we need to have, and the direct which is actually holding the direct released. This is what I do, I connect the circuit for SSB to the intermediate, and SSC to direct. Then causes the direct and the intermediate to apply.

There's still an upper limit where it won't hold, north of 4k RPM in the case of the car I tested with. Anyone that tells you they don't have a limit, well they're working with the same trans I am, unless they've added clutch plates, explain how they can possibly hold more torque.

Here is a transbrake which doesn't raise line pressure, and no calibration is needed. I do firmly believe this to be less optimal then the raised line pressure version we will be track testing which does require calibration. I only break into 2 wires from the trans, then there's the 2 wires to power the relays.

So is the raised line pressure one wired differently or it is the same with a modified tune?


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SSPSTANGBANGER said:

So is the raised line pressure one wired differently or it is the same with a modified tune?


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It has this same wiring, plus additional wiring to raise line pressure. I also got an idea for a safety feature today that I think I can add to it.

According to the data sheets Bosch relays engage in 10ms and release in 15ms, and in all the testing I have done that has proven itself to be quick enough to not set any codes regarding SSB or SSC, hence no calibration needed for this portion.

Thanks for the info, now its figuring out how to wire inline with my n2o setup.

Also noticed the wiring shows a 2 step is this needed in order for the brake to work?

2 step is completely optional, but I would always want one so you can set it at the RPM you want and just put it on the wood without thinking about it. The Coyote specific MSD one is a very easy install and works really good too, that was a big part of me footbraking to 1.48 60'.

Are you using a push button to activate on a third relay?

BV600 said:

Are you using a push button to activate on a third relay?

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You can see the pushbutton in the schematic near the ground, no additonal relay needed.

Ah Perfect don't know how I missed that, somewhat got it figured out wired into the nitrous though
When you testing it at the track?

They're open next week unless weather, so that's the plan. Have tested best we can on the street for now.

You going to little river? If so I may come out to see it in action!

Contrary to popular believe reverse is not exatly ideal in a transbrake. The gear ratio for reverse is much higher than first gear and is able to apply more torque, that makes holding first gear harder. Reverse is usually easiest to manipulate to get a tbrake though. Usually just have to apply the reverse band over the forward clutch. People usually think in their head you need a forward and reverse to have opposite pull for it to work. Just ain't so. In all reality holding any gear other than first will make a tbrake work as long as it's not the same gear ratio as first gear (never will be). Then the gear ratios will fight each other trying to turn at different speeds, and when they can't,.... Whamo, you have a brake.

Line pressure. The pump is going to do what it's going to do. It's the valve bodies job to regulate the line pressure to the tranny. The line pressure is the term used when referring to the ENTIRE tranny's main source of pressure. If you modify a circuit to receive more pressure, you haven't raised the line pressure. Even if you open that circuit all the way, it will still be limited because the line pressure itself has not changed. So when some says "line pressure" is changed, any builder will think the entire tranny is seeing more pressure overall. This is when other circuits have to be regulated to keep from pushing a converter forward. Arbitrarily raising line pressure can be bad. Ever have a shift kit? All it more or less did was change the line pressure in the tranny for firmer shifts.

Tbrakes do raise line pressure also. It helps the clutch and servo apply more pressure for holding power. There are problems like cracking cases, seals and pistons that can be hurt by excessive line pressure, so there is a limit. The 6R80 has huge drums and clutch, that are deep so they hold a good amount of steels and clutches from the factory. Hence their stock strength. After market steels and clutches we can fit 18-21 steels and clutches. Because of the drums physical size in diameter, there is a lot of contact surface for the clutches. So line pressure doesn't have to be raised in the tranny one bit.

As far as what holds and what doesn't Chris's car has held up to 6psi on the brake. Well north of 600ft/lbs to the tire no problem. He didn't release on 6, for fear of carnage lol. It has a quick, clean release with no signs of negative effects yet. As far as a limit, we haven't seen it yet. But it's a purely bone stock tranny other than converter and tbrake mod. If others have limits something's wrong. It's always wrong to assume because you can't do it, someone else can't, or is lying.
Hopefully the brake w 3 relays holds above 4k. But looks like not? Again RPM means noting when talking about a brakes holding power. It needs to hold back torque. 5-6psi from a boosted car is MUCH harder to hold than an N/A car, especially if on the two step. The reason that drawing doesn't hold is because it's WRONG.

63T-Bolt said:

Be cool. But the relays are going to suck dick for reaction time between release of the brake to actual forward movement. Then add in the fact the reverse fluid system isnt designed to exhaust its clamping fluid circuit fast, id imagine you'll see some burned up transmissions from it.



Imagine slipping the clutch at wot for the first 20ft in a stick shift car..... that is what your basically doing to the reverse clutches or band when the trans is not built with a trans brake in mind.

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I don't understand autos well enough but this is from another forum discussing this mod...^^^

There are two things to that since he's right.
A normal valve body modified for a brake takes those things into consideration to release properly.
Second is that he is again assuming like most that reverse is the gear used. So while he's right, it doesn't apply here

Now hitting with a lot more torque via forced induction and still good.

BTW release time on those relays is .015. Yes you can buy solid state relays if you want, they're out there. I used the last of what has been in my toolbox for 25 years or so.

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63T-Bolt said:

Regardless what gear is being used fluid has to be exhausted when its releasing its clutch pack or band. Period end of discussion. ... its being clamped by fluid, the fluid has to be exhausted to remove applied pressure.



On top of that depending on the apply piston design you can again create issues. Certain type piston packages just dont react as fast as others. Thats why a 4r70w will never have the release time a power glide until someone designs a new reverse drum and piston. Again its part of the package deal when dealing with its design. Its also why piston modifications are made so the reverse clutches dont drag when the brake is released.



With the relay pack they have done.... they wont release in .015..... can take that to the bank. Its part of them odd electrical issues that are created when your talking about collapsing a field. Not energizing it..... but when you actually try to remove power and ope. The contacts back up. What happens when your removing power from a clamping circuit with a coil is pretty damn cool, but also something that can slow a brakes release time dramatically.




all of this is very basic trans brake operations.





someone could slap a brake valve body into a stock 4r..... it will work. Just like this. But the trans wont live half as long as one thats built with its operation in mind

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Yes fluid still has to be exhuasted, nobody's disputing that. But we're using a circuit designed for faster release than reverse. A foward gear. If a forward gear didn't exhaust fast enough on a shift it would drag and burn up. If the car is forcing past the clamping just before it completely releases we'll see it on tear down. Until then not much we can do except beat on parts until something goes and diagnose from there.

We'll have a better idea of the release when we look at duty cycle on the bump box and how the car reacts. But on a stock tranny w a few bucks in parts, not asking it to be a pro tree capable tranny yet lol. Building a heavy hitter right now and tryin to decide if Inwant to go thru and figure all that out and what will break w real power put to it, or just slap a 4L80E from Jake in that bitch.

For once I agree with Dustin on something. My thoughts on the int and direct clutches were that each of them applies and then releases 2 different times as the car goes up through the 6 gears. This is also why I wouldn't consider trying to use the OD clutch for anything, it comes on in 4th and never goes off on an upshift. Yes it has to dump if you downshift to 3rd or below, but we also know how painfully slow the kickdowns are in a stock calibration.

And yes accelerated clutch wear would not be surprise. It's a stock transmission with a transbrake after all. Expecting ANY stock transmission to have a normal lifespan with a brake is completely unreasonable.