explain stall convertors and trans brakes to me

[briggs&strattonChev]

Hey guys, how does a stall converter work? Say, if you have a 2500 rpm converter, the car wont move until it is revved to 2500? Ive also heard that it will move the car normally, but if you hold the brakes it wont lock up until youve hit the 2500. Im pretty sure there isnt a sensor that goes to the brake pedal, so maybe that last one isnt true? Also, is a trans brake electrical? How do they work, and if it is electrical, can you rev it to whatever you want and get it to lock up with a button or switch or something? What is a better system, the converter or the brake? Is the trans brake more expensive im guessing? Ive been wondering this for a while now, please help if you can.

Briggs

[Roothawg]

Have you ever heard a car that sounds like the rpm's are going faster than the car is actually moving, at low speeds?
The stall lets the rpm's build up allowing you to get it closer to it's power band.

Example: The Fly has a 3500 stall convertor, it will move under it's own power but at low rpms it kinda slips a little until you reach that magic number then it hooks up.
Make sense?

[briggs&strattonChev]

ok, but if the cars powerband is from like 0-2500, a convertor would be pointless? My dad is building a t bucket (well actually its an overland body, but same concept) and he's running a fairly mild but not stock 355 and a turbo 350. Hes been told that it would be stupid to not have a converter of up to 3500 in the car. Is there any reasoning to that or is it nonsense?

[Tinbender]

Is he going to drag race the car? If not he has no need for a high stall converter. In that light of a car he won't like it on the street. I have a 2200 converter in my stude. It's what GM used in some of the hotter factory cars. Works great, don't notice it in normal driving, but it helps, slightly off the line. It was under 100.00.
A trans brake locks up the trans so you can bring the car up to the stall on the line, without it rolling, then you release it to launch. Again, not something you would use on a street car.

[Thirdyfivepickup]

Further on the trans brake... it locks first and reverse against each other. It is solenoid operated... usually a pushbutton off of the steering wheel or shifter. Don't want to accidentally hit that button in motion...

My cousin had one in his "street car" blown BBC prostreet GTO 800hp range... called it a trans break because he went through 4 transmissions in one summer. Took out the brake and its been good 5 years.

[four-thirteen]

a transbrake is an electrically activated solenoid in the transmission, attached to the valve body. When activated, it engages both first and reverese gears in the tranny, locking it up. when it is realeased, only first gear is engaged.

its used to launch a drag car very hard, because you can engage the transbrake, and floor the throttle, and the doesn't move. let go and the full power goes to the tires, instantly.

the term "stall converter" is used by laymen to describe what is actually called a high stall converter. all converters have a stall speed. stock converters are usually around 1500 to 2500 for stall speed.

definition: stall speed: stall speed the number of RPMs that a motor will rev to, with the tranny in gear, and the car not moving, with the motor at WOT.

you can check the stall speed of the converter in your car very easily. Just push very hard on the brakes, and floor it. whatever the tach revs to, is the stall speed.

now you might say to yourself, hey, i bought a 2500 stall converter from so and so. i put it in my car and checked the stall speed like you just told me to. it only reved to 2200 rpm. whats the deal? when they make a converter, they don't know if it is for a 250hp motor or a 700hp monster. and horse power affects stall speed. a 2500 stall converter will not be a 2500 stall converter behind a 250hp motor, it will be less, and it wont be a 2500 converter behind a 700hp motor, it will be much more.

and get this! there is no industry standard for stall speed ratings. their ratings are totally arbitrary. one manufacturer's 2500 stall converter might be more like another's 3500 stall or vice versa.

my recomendation for converters and stall speeds? call a good manufacturer like DYNAMIC or G.E.R. and tell them your combination, and have them send you the converter best matched to your motor, of have one custom made to fit. off the shelf parts will always get you off the shelf performance. well built well matched parts will make you run the numbers. David

[Paul]

I just went through this myself

when I first put my present drive train together the cam dude said my combo would work best with a 2500 stall speed converter. ok cool.

worked great but, related or not, the transmission shit the bed.

guy behind the counter where I bought the replacement transmission said with my combo the 3000 stall converter would be the hot ticket.

with the only slightly higher advertised stall speed the rpm's wound too high too fast and the rush was nowhere.

put a new 2500 stall in and man she really came alive.

I would listen to the cam guy.

Paul

[JOECOOL]

Opinions are like assholes ,everybody has one. My opinion is do not do business with GER.I don't think I have heard of one or two people who were satisfied with their product. I also heard that the better business beauro kicked them out because of hundreds of conplaints.
The stall speed is a particular consistent guess.A 1100 hp car will stall different than a 350 hp one. Also you don't determine stall by stomping on the brake and the throttle at the same time. The correct way ,according to several convertor manufacturers is to get rolling in high gear and mash the throttle . This is called flash rpm and is what most race convertors are sold by.
A higher stall convertor will make your transmission run considerably hotter.A good convertor builder will want all the info on your car and will make the convertor fit it. The only way an off the shelf convertor can say 3000 stall or whatever is they are guessing what it's going to be used in.A 4300 lb wagon will stall different than a 1600 lb. roadster.
Trans brakes come in two different styles.A reg. brake and a Pro brake. A reg brake works only when you push the button,a electric solenoid opens a valve that allows reverse to engage.It only works when the gear selector is in low gear. A pro brake replaces the reverse valves altogether and when engaged applies reverse. The pro brake by not using the stock passages and valving is then able to release the fluid more rapidly and therefore cut reaction times down. These are normally used on cars running a Pro tree therefore they are called Pro style brakes. The problem with a pro brake is the new circutry for the fluid bypass's all the safeguards in the valvebody and will engage reverse anytime ,at 120 mph in the traps,anytime. Pro brakes by design will always have to be engaged to make the trans go in reverse,if you need to back up you will have to hold the trans brake button all the time your backing up.
In my opinion trans brakes have no business on a street car. But I could be wrong!

[alteredpilot]

as far as the stall in a t bucket is concerned, if you put a low stall convertor in the thing, being so light, it is a chore keeping the thing to stay put at stop lights and such.
with a stall as low as 2500, even at idle, youre already way up on the convertor and the car wants to creep and lurch. and while it may not seem like a big jump, if you go to a 3k or 3500 it is more well behaved in gear at idle and a little less touchy/jumpy out of the gate.

[Paul]

which takes us back to the opinion side of things..

about testing stall speed,

I thought the way was to block the car from moving and with the transmission in gear bring the rpm up untill the motor stalls. that rpm is your stall speed.

all I know is from my own very limited experience,
with my high torque low rpm motor in a light weight car
with moderate rear gears and slicks
I like the slightly higher than stock stall speed converter.

Paul

[Rand Man]

Stall speed is an aerodynamic term. The inside of the converter housing looks like two fans. Fan blades work a lot like airplane wings. By altering the pitch of the blades you affect how the fluid “stalls” inside. The simplest way to explain why one would alter the stock setting is to relate the automatic transmission to that of a manual trans. When you hop-up an engine, you often move the power band up in the RPM range thereby taking away low-end torque. With a manual trans you might rev-up the engine as you engage the clutch, so you don’t lug it down and possibly kill it. A properly chosen torque converter converts the twisting force of the motor to forward motion for the car. This must be done in an RPM range that matches the weight of the car to the output of the engine. A trans-brake is like standing on the throttle and popping the clutch. If the car isn’t specifically set-up for that you’re gonna have trouble.

[Crosley]

Very interesting comments


Briggs&Strattonchev......... I'll repeat one item posted here:

as the weight of a vehicle goes down ( lighter) the stall RPM of the converter must go UP to avoid the car wanting to creep against the brakes.

A bone stock 327 or 350 chev motor in a T bucket with a 2500 RPM stall converter will drive & feel normal as a 3500 pound car with stock converter & engine. If you cam the engine up , you need more stall in the converter in the T bucket.

[JOECOOL]

One way to increase stall speed is to go to a smaller diameter or a smaller engine H.P. convertor.
For instance a 4 cyl. vega convertor is smaller in diameter and will give a higher stall than a 11 inch from a 454 on the same engine.You also have the advantage of reducing weight similar to putting on a light flywheel .
A stock type vega convertor will last a very long time in a moderate H.P. ( 450 to 470 ) in a light car. They will not last at all with a brake.The last one I bought was about $45 exchange ( rebuilt) and ran in a street strip nova for 3 years .Just my opinion.I could be wrong.