Driveline braking

[travismac]

Would mounting a disc brake on to the drive shaft multiply the braking ability at the wheels because of the gears? Or would the disc need to have a large diameter to overcome the torque coming back through the driveshaft from the coasting vehicle? Just another quick qusetion, that I think I already know. Are driveline brakes legal for the road? Or does there have to be a brake on each wheel? If it makes any differance it is on a 1 ton truck.

 

[ivymike]

The torque ratio is going to be roughly the reciprocal of the speed ratio, since wheels go slower than driveshafts the torque at the driveshaft is less.

The power dissipation requirement would be double for a single driveshaft brake vs two wheel brakes.

Also, having one wheel go airborne would make the driveshaft brake completely ineffective (differential).

 

[patdaly]

I would say InHiding's answer should drive the nail in the coffin on this one, I would also add I would expect to see a serious reduction in life of the Ring and Pinion, as all the braking force would be imparted to the coast side of the gears.

 

[patprimmer]

Also, there are more potential failure points between brake effort application point and the tyre contact patch on the road.

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Regards
pat

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[JBurgess]

Travismac-
I used to have a model t ford with transmission brake. It got really exciting on ice.
I have also seen Driveshaft brakes used for parking brakes on many trucks from the factory.
In Arizona drivehaft brakes are not legal for service brakes, we get hasseled for them on our rockwell axles on lifted trucks. There is not a clear answer if they are suffient for parking brakes as we are required to have the parking brakes hold 2 wheels.
They also generate a lot of heat, I assume because all the braking action is one rotor instead of two. But they require a lot less pedal pressure.
jburgess

 

[willeng]

travismac;

Use a small eddy current retarder if you wan't drive line braking, they are used on everything from mini-buses to prime movers. There ideal & can be 12 or 24v, look up Telma retarders they've got what you wan't.

 

[travismac]

Thanks for the info, It was the rockwell axles that got me thinking of this idea, and my old samurai that had the parking brake on the shaft. For the most part my truck stays off road or on a trailer, but it is nice to be able to drive it to the local playgrounds. Just in hindsight if the axles have mechanical lockers, wouldn't the brake be applied to both wheels?

 

[ivymike]

yep.

 

[patprimmer]

At least while the mechanical lockers are in the locked position.

It still has a larger number of points for failure between the drum and the tyre contact petch.

Regards
pat

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[carnage1]

most of the driveline parking brakes were failure prone, even people doing restorations insted of making hotrods usualy switch to a newer rear axel with the rear wheel parking brakes. driveline brakes arent well liked by most of the old car builders i talk to.

 

[GregLocock]

Landrovers used to have some sort of transmission brake as a park-brake. It had a somewhat lousy reputation, since over enthusiastic (ab)use would break the half-shafts. This rather bears out Pat's point.

Cheers

Greg Locock

 

[evelrod]

50's GM trucks (I had a '56 one ton step van---my 'hippie' years) had driveshaft brakes just behind the trans tailshaft. Not at all uncommon to see them with broken rear 'U' joints as I recall.

Rod

 

[76GMC1500]

Why use one brake on the driveshaft when you could use at the wheels?

Anybody watch American Hotrod? Did anybody see that Jaguar rear-end they put under the '56 Chevy, or have you seen a Jag rear end at all? The have the brakes up near the differential, and then have a drivehsaft going to each wheel.

Another problem I forsee with putting a brake disk on the driveline before the differential is that it isn't protected from all of that stuff on the road, especially water and dirt, that normal brakes are by the wheel.

 

[JBurgess]

76GMC1500

I saw american hotrod, but the rear end in the '56 had a drop out center section, I thought maybe a 9" ford in a custom setup? The inboard disc brakes would reduce the unsprung weight at the wheel.

Back to driveline brakes. With large tires (16r20) it is difficult to get parking brakes to hold on a incline. The reduction in torque require to hold is a big advatage. Another problem in converting to disc brakes there is a very limited selection of calipers that include a parking brake.

Jburgess

 

[Rob45]

76GMC1500 wrote:
"Did anybody see that Jaguar rear-end they put under the '56 Chevy, or have you seen a Jag rear end at all? The have the brakes up near the differential, and then have a drivehsaft going to each wheel."

What he described is of course inboard disc brakes, with the brakes mounted on the inboard ends of the axle shafts, and not remotely related to this discussion of DRIVEshaft mounted brakes.

Big problem with driveshaft-mounted brakes: what do you do when the u-joint fails?

 

[ZoRG]

If you are concerned about weight have you though about carbon-ceramic brakes? If I may ask, where are you getting your titanium rotors from?

 

[patprimmer]

I must say I am interested in the carbon/carbon rotor solution.

I know they are used in F1, so should be durable enough for a drag race car, and should significantly reduce the inertia of the wheel hub assembly.

I guess I will start with a Google search

Regards
pat pprimmer@acay.com.au
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[ZoRG]

Pat carbon/carbon won't work well for drag racing, they only have good braking at high temperatures. You will want to look at carbon/ceramic discs, they are slightly heavier than carbon/carbon 2g per cc vs 1.7g per cc. And go for 10000UK Pounds per wheel, discs and pads. You can get them for half the price if you are willing to machine it yourself, but you require diamond tooling, its almost as hard as silicon carbide.

If you are still interrested in Carbon/Carbon, you will require high density medium quality and a coefficient of friction .35 or more(Im sure you already know this), the cost is $250-$400 per kilogram, and should weigh around 2KG per disc and pad. Good luck in finding a manufacturer willing to supply you with low quantities though usually its 500KG minimum, there is one company I know off that sells them at US $1200 per wheel, pads and discs so alot more than the $250-$400 per kilogram but at least they supply low quantities.

Let me know if you are interrested and I'll provide you with the info on where to get it and save you some time. These are for only the discs, so you will have to make your own hats.

 

[rmw]

Since this thread is about driveline braking, and some consequences of driveline breaking have been pointed out, check this link for some serious consequences.

http://www.ntsb.gov/publictn/2002/HAB0219.pdf

This is a larger vehicle than the one in the subject topic, but the reactions where the rubber meets the road are the same, and this report helps explain it in a very technically detailled way.

rmw

 

[patprimmer]

ZoRG

Thanks for your help, but if the number of Zeros in the Carbon/Ceramic disk cost is correct, that makes them A$30,000 per wheel or $120,000 per car. That is way above our budget.

I may have hijacked this thread, but as the original question was about reducing drive-line inertia by removing weight from the brake system, I felt it was relevant.

I will start a new thread just in case an affordable solution comes up.

Regards
pat pprimmer@acay.com.au
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