Rover SD1 Brake Calipers

[Bendder]

Hummm.... I wonder why the 4 pots that I have are not the same dia as the Vitess? Could the cup dia of the non vented SD1's be different than the vented Vitess ones? I got mine from Rimmers.

Mark
1977 TR7 FHC
1978 TR7 FHC
1980 TR7 DHC
1980 Rover SD1 4.0L

[Beans]

Sorry, got the SD1 and Princess caliper mixed up [:I]
Bigger piston area is certainly better

<center>
<font color="blue"><i>1981 TR7 FHC Sprint (better known as 't Kreng)
1981 TR7 DHC (not very well known yet, but back on the road)
Also a 1980 TR7 DHC, 1980 TR7 DHC FI, 1981 TR7 FHC
http://tr7beans.blogspot.com/</i></font id="blue"></center>

[Marko]

if you want to calculate the stoping force of the brakes , it is verry simple math(8. grade of elementary school ).



so where do we start....

lets say that you push your brake pedal with the force of 50N. the pedal is built like a lever , force on your foot * the length of the whole pedal = the force on the brake master cylinder* the length from the uper pivot of the brake pedat mounting to the place where the master brake cylinder is conected to the pedal. boost ratio of the standard tr7 servo is 2.3 : 1 . now you got the force on the master cylinder piston surface. that force * the area of the brake master cylinder is = to the pressure in the system. ,that pressure is acting in the whole hydraulic system,and pushes the caliper pistons outwards. so that pressure * the total area of the caliper pistons = the normal force between the pads and the rotor . normal brake pads have coeficient of resistance 0.5-0.6. Ft = Fn * mi( greek letter mi)
so the force of resistance is equal to the normal force ( the force on the caliper pistons ) multiplyed by the coeficient of resistance.
now we got the force of the caliper that acts on a "lever" that has the size of the brake disc to produce a moment that stops the wheel from spining. but that "lever" isn's calculated by the whole disc diameter!!! you have to measure from the middle radius of the brake pad, that is the efective radius of the brake rotor. the brake pad area is not important for the braking force, for example you produce the same brake moment with the brake pad of 1cm^2 and 1000cm^2. but the 1cm^2 pad will overheat instantly and fade( loss of coeficient of resistance , rapid wear of the brake pad) and the 1000cm^2 won't.
now you have calculated the brakeing moment of the brakes., now its up to tires to be able to tranfer that moment back into force that stops the car.( moment/distance of the lever = force).this is calculation of the brake system , now the problem with the weight trenfer during brakeing is aditionaly calculated,and the amount of brake pressure reduction in the rear brakes...

[Beans]

Have a look at this site ...

http://www.forum.triumphtr7.com/topic.asp?TOPIC_ID=6056

<center>
<font color="blue"><i>1981 TR7 FHC Sprint (better known as 't Kreng)
1981 TR7 DHC (not very well known yet, but back on the road)
Also a 1980 TR7 DHC, 1980 TR7 DHC FI, 1981 TR7 FHC
http://tr7beans.blogspot.com/</i></font id="blue"></center>

[Bendder]

OK. I have been doing some more reading about brakes. I have come to the conclusion that bigger is better in some way's... If we want to increase braking in a street/daily driver we would have to increase force at the caliper. That being said a 7" vacuum booster such as the TR7 should make about 800psi so would it not stand to reason that going with say a 9" booster such as the SD1 unit making around 900psi would incerase that clamping presure? This would not do anything as far as brake fade goes (sloting could help reduce off gasing and fade a bit here) but unless your alway's in the twisties or using the car for track day's this should not be to big a deal. I went out to the garage and did some quick measuring and the SD1 unit looks like it should fit in the space although it would be tight. This increase in clamping force at the caliper should realy improve breaking even with the stock 2pot calipers add in some better pads such as green stuff and bingo better breaking but fade may become more of an issue as heat would increase and the pads and rotor's would not be able to dissipate it if you start getting hard on the brakes repeatedly. If we go one step further and add in some vented rotor's the fade is reduced (sloting could help reduce off gasing and fade a bit here also). To go vented we need to have different calipers such as the Princes 4pot or Volvo 240DL type but this just add's one more plus as the pad size increases. Possible problems though could be a lac of volume in the master which can be overcome by using the SD1 master which is 7/8" vs the TR7 at 3/4" they both have the same stroke so ther are not any pedal issue's I can think of but pipping is on the opposit side. If the problem of volume for the calipers was not an issue then we gain because the smaller master puts more force to the caliper than the lager one, though you would have a longer pedal travel to fill the bigger caliper, this might be a problem. So if "bigger is better" is applied here if there were space permitting then why not find a dual diaphram booster that would increase clamping force even more. Many type's are available in 7,8 and 9" making as much as 1200psi that's 33% increase right there in clamping force. Coupled with say some Vitesse vented rotor's and 4pot calipers and againe Greenstuff or yellowstuff pads should make for some through the windshield braking. Keep in minde I am thinking Sd1 stuff as I am going with the five stud setup from the SD1 all around not to mention I have a buch of spare bit's about.

Some topic's I have been reading

http://www.ebcbrakes.com/automotive.html
http://www.mpbrakes.com/uploads/documents/optomize.pdf
http://www.mpbrakes.com/uploads/documen ... ooster.pdf

Mark
1977 TR7 FHC
1978 TR7 FHC
1980 TR7 DHC
1980 Rover SD1 4.0L

[Marko]

nice page, someone spent some time to make it.

its a bit too cartoonish for my taste but its nice

[Dave Dyer]

Bendder (Mark)

Not really brake related, but you mention you have the SD1 5 stud setup, I can see how the fronts struts could be used, but what about the rear, are you running a complete rear axle from the Rover ?

Thanks, Dave

[Jolyon39]

To get the Rover 5 stud pattern on a TR7 diff

Pull the 1/2 shafts out of the Rover diff, have them shortened and they fit straight into the TR7 Diff. I understand you can use the back plate off the Rover diff to allow you to mount the larger Rover rear drums and shoes as well.

Jolyon

[Bendder]

Dave,

Jaylon is exacly right. I have used the SD1 axel's and had them annealed and then cut new splines and re hardened which are not as strong as the original rolled splines but then againe I'm not running the kind of power that will stip them clean. For that matter I was informed by the shop that cut them that many pro modified dirt tracker's use there service and have had no problems with the cut slpines and they run a hell of alot more power than we could ever get from our motor's. So I called a friend of mine who races a pro modified and asked him what he thought...low and behold it was the shop that has done 3 set's for him!! nedless to say they did mine also. Jaylon is also right about the backing plates for the rear brakes. The SD1's are 1/4" deeper and the drums have a more square front face so the shoe size is 2 1/4" vs the TR7 @ 1 3/4" both are the same dia. the Sd1 shaft's are much beefier by not having the bell cut in them right inside the bearing mounting flange and are tappered from the bearing to the splines. The measurment from the axel flange that the backing plate mounts on to the outer edge or mounting surface of the drum is unchanged from the TR7. Bingo, bigger brakes and five studs.

Mark
1977 TR7 FHC
1978 TR7 FHC
1980 TR7 DHC
1980 Rover SD1 4.0L

[Dave Dyer]

Thanks Mark,

I'm hoping to do the same with regards to the 5 stud conversion. I didn't realise it was so involved. But thanks, I didn't realise the axle shafts had to be annealed, cut and rehardened.
Are you using the SD1 Servo and Master cylinder as well ?

Dave

[terryjm1]

In my experience the problem with TR7/8 brakes is not the lack of pressure/force of the pad to rotor. The problem is that the pads and rotors overheat and lead to extreme brake fade and subsequent disc warp.

The solution is vented rotors. I have spent the last several months having adpaters made to mount vented Escort discs on the TR7 hub just as JClay did. Also, I have been working with a local machinist to plug and redrill volvo 4 pot calipers. He is just about ready to start knocking them out. He built a fixture to fit on a mill to assure the drilling will be accurate. This fixture is costing me some bucks. However, while the 4 pot caliper looks cool and certainly helps, the key is thicker vented discs.

For those of you that are reading this and are waiting to send the calipers to be plugged and re-drilled, I think he should be ready to go any day now. He is a machinist with 20 years experience and does the work when he can fit it in on his days off. Sorry it is taking so long.

Terry Merrell
St. Louis, MO

[terryjm1]

Also, I think I have found a Saab master cylinder that is a 7/8 bore, has the piping in the correct places, and bolts up to the TR7/SD1 booster. I will post when it is installed and let you know if it is worth the effort. With the 4 pot calipers I am hopeful the larger bore will offset the difference and I will end up with the same pedal travel. By the way, brand new with plastic reservoir at $100 shipping included.

Terry Merrell
St. Louis, MO