TR6 tr6 rear disc brakes

[amcboy]

This could be an alarmingly long post, but I'll be briefer than usual.

Depending on how you use your brakes, most of the stopping power comes from the front.

Most fixed bias systems are 70/30 to the front.

We ran adjustable bias on a (granted, heavier) road-race car and ran closer to 90/10 front bias. And places like Mid-Ohio where there is giant transitional braking areas even more was dialed into the front.


Consider the weight transfer when you brake.

All that mass landing mostly on the front end...


Considering we are talking about shear values and not tensile values on the TA hub bolts from braking, calculations could be made to see what the average loading is per bolt/stud. I'd expect this value to be pretty low (really).

Now, moving the hub further from the TA will add tensile differential to the fasteners and the TA.


IMHO the hub should be where designed and any bracketry should be outboard of the hub.


I'd also install a manually adjustable proportioning valve and set the differential for the intended use.

 

[Tinster]

Shear values on the T/A studs yes but there is also an "overturning"
moment of the steel studs in the aluminum.

Think of the steel stud as a telephone pole anchored in soil.
As you increase the height of the pole you must then increase
the depth of the pole buried in the soil. The exposed portion
of pole is in shear; the entire pole has an "overturning" moment
as well. I am thinking it is approx 4:1

Extending the length of the six T/A steel studs should require
a proportional increase in the depth they are anchored into the
aluminum trailing arm. I know for three studs, this is
impossible.

But then, I ain't a wrench, as everyone knows.

dale :shocked:

 

[amcboy]

Good point.

You could do a "body fit" on the portion that goes through the hub to load the hub flange a little with those forces.

Not so convenient though.

And hard to assemble...


Hmmmm, must ponder....

 

[BobbyD]

Darn.............I forgot completely that I added his conversion to my site. Glad to see that it's helping ya'all out! And noooo.....I haven't done the conversion. I'm keeping the drums with a beefier wheel cylinder.

 

[tr6lover]

hi guys, didnt mean to start such a controversy by posting that. i want a cheaper alternative with less maintainence. disk brakes work very well, better than drums for their ability to self clean and cool reducing brake fade. due to more surface area you could get more stopping force with a disc than a drum but you are correct about having a portioning valve to increase the force. honestly for even stock drums and all stock parts in the back it adds up quick then you also have to adjust all the time. in addition once you decide to go aluminum drums, kevlar brake shoes and morgan wheel cylinders it adds up. by going with discs you can easily and cheaply replace parts. as far as braking force applied to the trailing arm i believe thats rubbish, the mounting points are all the same and all taking the same load, although the clamping force is applied differently to the wheel it still applies the force to the trailing arm the same way through the same points, yes if you extend the studs out farther it will change the load some, but not significantly and this has been done successfully before. there are many benefits to rotor/caliper set ups which originated on aircraft and this is why jaguar decided to use them on cars back in the 50's and this drastically reduced stopping distances, just a thought for everyone saying this could not possibly reduce stopping distance....
Randy

 

[swift6]

The advantage of disc brakes is that they cool better, so less likely to overheat under extreme conditions. But my experience is that the front discs will overheat first even with drums out back, so any upgrades should start in the front, IMO.

You'd overheat more often too if you did 85-90% of the work. The rear drums on a TR just don't work very hard. So with a stock M/C set up your money and effort would yield much better results by improving the front brakes over the rear.

 

[swift6]

hi guys, didnt mean to start such a controversy by posting that. i want a cheaper alternative with less maintainence. disk brakes work very well, better than drums for their ability to self clean and cool reducing brake fade.

Don't see it as controversy, just good discussion. Just because we don't agree with you doesn't mean its controversial. :wink:

Less maintenance? A set of shoes on a TR should last through a few sets of front pads. Seems pretty low maintenance. Unless you don't like adjusting them occasionally. How often do you imagine changing pads on a rear disc conversion. With a conversion that would make use of the extra ability, you would be changing pads on the rear probably twice as much as you would shoes. Equalling more expense and more maintenance.

If your experiencing rear brake fade now, you've got other issues.

due to more surface area you could get more stopping force with a disc than a drum but you are correct about having a portioning valve to increase the force.

If you measure shoes vs pads, I' think you'll find that the shoes have more surface area. Its the hydraulic pressure to that surface area that provides the actual force. Which is why changing the rear wheel cylinder has the effect that it does. Even adding an adjustable proportioning valve in to increase the pressure will yield better results with the drums without making them overheat. Racers have to do this all the time.

honestly for even stock drums and all stock parts in the back it adds up quick then you also have to adjust all the time. in addition once you decide to go aluminum drums, kevlar brake shoes and morgan wheel cylinders it adds up. by going with discs you can easily and cheaply replace parts.[/qoute]

Don't forget weight as an additional cost. The disc conversion will likely weigh more right at the wheel. Especially when you add in the parts to allow a functioning handbrake. Now if you could put the discs inboard (like Jaguar did) then you could negate that weight cost. Otherwise, the more weight out at the wheels will affect handling.

there are many benefits to rotor/caliper set ups which originated on aircraft and this is why jaguar decided to use them on cars back in the 50's and this drastically reduced stopping distances, just a thought for everyone saying this could not possibly reduce stopping distance....

Jaguar used them on their race cars first while Triumph used them on their production cars first (then took their production cars racing :wink: ). They also designed their brake systems for 4-wheel disc brakes. As I said earlier, if you re-configure your entire braking system, disc brakes will improve/decrease your stopping distance. If you just install them without altering the master cylinder proportioning then they will not. I think we have all agreed on that part though.

One more thing to keep in mind. Insurance liability. Fundamentally altering the braking system on your car could have dire consequences if you should ever be found at fault in an accident and they know you 'altered' your braking system. Just something to keep in mind.

 

[TR3driver]

i want a cheaper alternative with less maintainence.

Well, opinions vary, obviously. Mine is that the stock drum brakes require virtually no maintenance, and parts are cheap. I don't think there is any kind of cost justification for a conversion unless you are planning on doing several hundred thousand miles.<div class="ubbcode-block"><div class="ubbcode-header">Quote:]due to more surface area you could get more stopping force with a disc[/QUOTE]Even if that were true, you couldn't use more stopping force ! A locked wheel provides significanly less stopping power than one that is almost, but not quite, locked. Thus the goal should be to have both ends lock at the same time (then hold them just under that point for maximum braking). The original TR3 rear drums actually worked too well, leading to several reductions over the years to reduce premature rear lock up.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:] but you are correct about having a portioning valve to increase the force.[/QUOTE]No, the proportioning valve only reduces the force, in order to keep one end from locking up first. It does NOT increase the force.<div class="ubbcode-block"><div class="ubbcode-header">Quote:] then you also have to adjust all the time.[/QUOTE]If you are having to touch the adjustment more than once every 20-30,000 miles then there is something wrong, IMO. I check mine every 10-12,000 (when I do the rest of the chassis lube/service) but only go another click on the adjuster maybe every third time I check them. <div class="ubbcode-block"><div class="ubbcode-header">Quote:]as far as braking force applied to the trailing arm i believe thats rubbish,[/QUOTE]Well, make up your mind. Are you going to increase braking force or not ?<div class="ubbcode-block"><div class="ubbcode-header">Quote:]just a thought for everyone saying this could not possibly reduce stopping distance....[/QUOTE]I won't say it couldn't possibly ... but IMO if there is any improvement at all, it will be from subtle factors like improving front/rear balance for the tires and suspension mods you use; or improving brake modulation near the limit. Which of course doesn't mean you shouldn't do it, just be realistic about what to expect.

Just please <span style="font-weight: bold">don't</span> follow me & my drum brakes too close

Oh yeah, don't forget you also need to change the MC to one with a larger reservoir for the rear brakes.

 

[milemarker60]

I guess I'll chime in on what I found experimenting with rear discs on my TR6/M3. Keep in mind I ran my tests with the Modified BMW S50 M3 Engine (325hp), R200 Diff (3:54), CV-Joint Axles, M3 Tranny (.85 OD in 5th), 225/45/17 Falken Azenis RT-615 Tires, TR6 Master Cylinder, DOT-5 Fluid, Toyota Vented Front Disc Conversion and no body panels at all (light...).

For my baseline I used the Aluminum Drums, Morgan Wheel Cylinders and Carbotech Bobcat compound pads and shoes. Then I installed my rear disc brake conversion from a well know racing enthusiast that has used it for over a decade on the track with no mechanical issues or degradations. It incorporates a set of Willwood Billet Calipers and I also installed Carbotech Bobcats on these. At this point I also installed a Willwood lever-style proportioning valve on both the front and rear systems poking thru the front of the foot well where I could adjust the f/r bias inside the car with ease.

Stopping distances are irrelevant since the car was about a ton lighter without the body panels. I did run the tests with up to 500lbs of weight distributed throughout the chassis on some of the runs. Overall, I had a 5%-10% reduction in stopping distances with the discs on the rear depending on whether they were heated up or cool. Most importantly, the initial grab was significant leading me to believe in an emergency situation, I may just have an even greater advantage. In addition, I noted no significant fading issues with the discs as I purposely heated up both set-ups and ran them hard thru some aggressive twisties.

I figured with the stock MC I might need to play with the front/rear bias and messed around with it extensively. Interestingly enough, I found that leaving both the front and rear "open" netted the best results both in cool and heated conditions. Bear in mind that this was not a track scenario but I did run the car thru the paces. Even a slight reduction in front bias would cause the rears to grab too hard in a corner increasing understeer too much and reducing the rear bias I could never get them to adequately bite in straight or twisty driving.

My conclusions to this point on my car are to leave the system "open" with no bias adjustment and indeed, there was a significant increase in braking performance. I did drill out the mounting holes on the trailing arm and put in steel inserts and where possible, ran longer bolts in (can't remember how many of them allowed for a longer bite). My system does not allow for a true emergency brake so I have installed a "park-lock" valve in-line to the rears so the button sticks up thru my floor board where I can easily engage it. This info probably won’t translate to a stock TR6 mostly due to my tire/wheel set-up as this is the most obvious difference on my car that would affect the braking performance.

I am anxious to get all the heavy panels mounted so I can see if the bias needs to be tweaked with the proper weight hanging off the tub. I’m not going back to the drums so no further comparisons will be attempted as I am very satisfied with the change I made at this point. If I start breaking rear trailing arms as some have proposed, well, I’ll revert. But as I said earlier, I didn’t invent the system and it has many years of proven reliability in a much more demanding environment than I plan to run in. Are they necessary, no. Do I feel that they will enhance my safety with my modified TR6, yes.

Dave

 

[Andrew Mace]

...Jaguar used them on their race cars first while Triumph used them on their production cars first (then took their production cars racing :wink: )....

Actually, Triumph first experimented with disc brakes in (IIRC) 1955 at the ill-fated 24 hours of Le Mans, where they tried Girling, Lockheed and Dunlop discs on different team cars. So technically, Triumph also tried them first on their race cars.

 

[tr6lover]

hey dave, that sounds interesting. the whole purpose behind what i want to do is for simplicity and any possble gains in braking performance. i keep my rear drums adjusted and it just seems to me they are not up to the task. granted i have not changed my rear hoses yet and it could be possible that over time they have swollen inside and restricted flow but overall i would be happier with discs in the back. i have by the way modified my front brakes, toyota calipers and slotted rotors. i am confident in the fact that i wont just lose my brakes or hubs, i mean really, if the hubs just break under normal breaking they have no place on any road car, drums or disks. i believe that if it had not been for cost triumph would have used discs to begin with.