Rear Disc Brakes

[EuropaTC]

If I recall, the spreadsheet for the Europa suggests that a stock front disc is best paired with a 34mm rear calliper.
I've been tempted to go for a 36mm calliper and use an adjustable proportioning valve to trim the rears. One other advantage of this is that one could open the valve further for a wet track.

Strangely enough, during our latest lockdown and prompted by the topic being raised here again, I took a fresh look at my set-up and came to the conclusion that a 36mm piston was certainly worth looking at.  (that's with 266mmF, 258mm R discs)  In theory it should have both locking around the same time but even if the sums are wrong then as you say a valve could trim it back a touch. But it's cold here and so I've done nothing other than idle thoughts and browsing Ebay.

Incidentally I tried the G force recording after a few guys on here told me that in the 20th century we had such things as phones & tablets which could do such things. I used a free app called "Physics Toolbox" (or something like that) which gave accelerometer graphs.  The most impressive was off scale but I think that had something to do with the tablet flying off the passenger seat and ending up down the footwell.....   

Brian

[Pfreen]

My big complaint about my Europa TCS brakes is that the front brakes lock up way before the rears, if I can even get the rears to lock up at all.  I have a standard TCS brake system (lockheed servos, front discs, rear 1.5" wide rear drums, standard master cylinder).  I have never experienced brake fade in the Europa, although I have never had it on a race track.

So, does the rear brake disc conversion actually solve this issue? Do the rear brakes actually lock up?  Any feedback would be appreciated since I would not consider changing to rear discs unless it did.  If the rear disc conversions did this, I would consider it.  However, I have not heard anyone claim that. 

In my perfect world, with no bias valve, the rear brakes would lock up prior to the front brakes.  A rear brake bias valve would be installed and then could be adjusted so the front brakes lock up slightly prior to the rear brakes.  This adjustment would also be very much a function of the brake pad/shoe material and their temperatures, since the coefficient of friction of the brake material are not constant over temperature. 

I have looked at this issue and have the following thoughts to improve the rear braking power and improve brake balance.

Install rear discs, but space and available calipers are limited with standard 13" wheels.  Will they lock up the rears before the front brakes allowing the use of a bias valve?

Change pad and shoe materials.  My experience is the greensuff pads really made the front lock up early.  I currently run Mintex 1144 pads, which I really like except they squeal.  There is not a lot of options for the rear shoes except if I want to rivet my own brake shoes.  I run standard shoes.

Find a larger rear brake drum cylinder, which is difficult because of the self adjuster ratchet being part of the cylinder.

I have thought about installing a 3:1 servo in the rear circuit and keep the 1.9:1 servo in the front.  They are currently both 1.9:1 servos.  BP Northwest has the 3:1 servo for $159.  Obviously, a rear bias valve would be needed for this.

Install a bias valve in the front brake circuit.  This is not recommended by the bias valve manufacturers but I do not know why.

Install a residual valve in the rear circuit to improve the drum brake response time.

So basically, I would like to be able to adjust the F/R braking bias which is not possible right now unless I install a bias valve in the front circuit to reduce the front braking pressure.

Any other ideas or thoughts?

[jbcollier]

The correct way to adjust brake balance on the fly is with twin masters and a balance bar as adjustments remain constant.  Adjustable bias valves are not consistent performers and need to be checked before each critical use.  I would strongly recommend NOT using an adjustable bias valve in the way you describe.  YMMV.

[SwiftDB4]

I would agree with JB. Bias valve isn't as consistent as mechanical balance bar and dual MC. Yes you can get the rears to lock up with the right components. My S1 has Wilwood 4 pots all round (1.75" F and 1.375" rear). I have 13" wheels and I believe the rotors are 10" front vented, rear solid. With balance bar adjusted to rear I can lock up rears on track days. Of course it's preferable to have the fronts lock up slightly before rears for stability. Is all this necessary for street driving? Probably not.

[EuropaTC]

So, does the rear brake disc conversion actually solve this issue? Do the rear brakes actually lock up?  Any feedback would be appreciated since I would not consider changing to rear discs unless it did.  If the rear disc conversions did this, I would consider it.  However, I have not heard anyone claim that. 

Not completely, but then again you don't want the rears locking first. 

I've added 2 screenshots below. The first is the OEM disc/drum TC, the rear brakes are the same as the S2 and not as large as the ones you have. This shows pretty much what everyone knows, you can lock the front brakes very easily at less than 1G and the rear drums never lock. (the lock is where the dotted line crosses the solid line, Front is black, Rear is red)

The next is 232mm F, 240mm Rear disc.  I don't know what everyone else uses and that combination wouldn't fit with my 13" Cosmics but it was very close and I reckoned it could be made to work with minor adjustment.   That will lock the rears in theory, but still after the fronts and at over 1G.

Whether these numbers are spot-on accurate or not I have no idea, but using the same data it does illustrate how you change the brake balance with rear discs. Larger discs don't really alter these ratios but they do reduce the pedal pressure significantly for a given brake force.

Brian

ps - actually I can confirm the rears will lock, I tried it on our gravel drive to see if I could get 4 skid marks ! ("you little kid" as my wife said)

[BDA]

Is there anything you haven't measured or calculated on a Europa, Brian?!

I'm curious where your got all those numbers and calculations?

[EuropaTC]

Is there anything you haven't measured or calculated on a Europa, Brian?!

Fuel consumption, running costs and "hobby spends".......      never a good idea to have it written down. 

I'm curious where your got all those numbers and calculations?

Mostly from road tests. the manual. etc.  I have been known to take bathroom scales to the workshop to weigh wheels/tyres, but only when the coast is clear (wife out shopping)

The original drum calcs/data were from Richard's original spreadsheet which I just copied over.

[Pfreen]

JB

Many, many cars have adjustable rear bias valves.  So, I respectfully disagree.  If you are talking about my mention of putting the bias valve on the front circuit, I don't know and it is not recommended by any of the bias valve manufacturers.

I agree that twin master cylinders with a balance bar is best, but difficult to implement.

Also, would you agree the rear brakes lock up way before the front brakes?

[JR73]

Banks balance bar pedal box with twin master cylinders (lid removed at time of pic). Hydraulic clutch option also available.
Fibreglass reinforced in area where pedal box is mounted.

[GavinT]

JB

Many, many cars have adjustable rear bias valves.  So, I respectfully disagree.  If you are talking about my mention of putting the bias valve on the front circuit, I don't know and it is not recommended by any of the bias valve manufacturers.

I agree that twin master cylinders with a balance bar is best, but difficult to implement.

Also, would you agree the rear brakes lock up way before the front brakes?

Forgive me for butting in.

In general, the thinking is that if the fronts lock and the rears don't, limiting the front brakes to match the rears via a bias valve likely leads to an overall reduction in braking.
More to the point, it doesn't address the actual issue which is insufficient rear braking.

From a short trip around the inter-webs, I didn't find complaints with adjustable proportioning valves but I did for the fixed OEM 'combo' variety. Happy to be educated on this.
It may also be that there's undoubtedly tons of OEM fixed valves travelling the countryside and a stark minority of aftermarket adjustable valves presumably used by enthusiasts.

Yes, difficult to implement twin masters.
There are a number of 'hanging pedal' kits around but I prefer the ergonomics of the floor hinging pedals - seems a more natural movement because it keeps the heels planted. I also want to retain the front plenum.

It's possible to buy the balance bar unit separately to install in, say, a replacement brake pedal, but that means rearranging the real estate on the front of the T section for the MC's. Not insurmountable, I'd guess, but I'd also want room for a clutch MC as well. That might get crowded.

Somewhere along the way we should discuss the stiffness of the various options. A stiffer pedal & MC mounting results in better feel under the foot and thus, easier modulation.
I suspect the Banks overhead pedals as per JR73's pic are mounted to the top of the chassis (?) and probably reasonably stiff.
The stock pedals bolted to the rear 'flap' of the chassis through the fibreglass floor probably less so.

[GavinT]

  (that's with 266mmF, 258mm R discs)

Are these inside 13" wheels?

[Clifton]

Yes, difficult to implement twin masters.
There are a number of 'hanging pedal' kits around but I prefer the ergonomics of the floor hinging pedals - seems a more natural movement because it keeps the heels planted. I also want to retain the front plenum.

It's possible to buy the balance bar unit separately to install in, say, a replacement brake pedal, but that means rearranging the real estate on the front of the T section for the MC's. Not insurmountable, I'd guess, but I'd also want room for a clutch MC as well. That might get crowded.

A top hanging pedal follows the arc of your leg better than floor mounted (not my opinion). I kept floor mounted and used a dual master as I didn't want to cut out my frunk. If you want tandem masters you can make it work.

 I wish someone would make a billet tandem adapter. I have seen them for other makes. It would solve many problems for Europa people.

[EuropaTC]

  (that's with 266mmF, 258mm R discs)

Are these inside 13" wheels?

No Gavin, 13" would be very optimistic 

I'm using 15" wheels. I haven't checked but would imagine that 245mm (GT6) and 240mm would be about the best you could get with 13" wheels. My Elan has the GT6 discs/caliper on 13" steels and it's a tight fit.  I'd guess 245/240 would be the best you could hope for with standard rims.

Brian

[jbcollier]

An article on proportioning valves:

https://centricparts.com/getmedia/d958a29e-4ebf-41fd-931f-bf7e4451801b/brake-proportioning-valves.pdf

[Nockenwelle]

This is a very interesting debate which I follow closely. Valuable input from all sides. I had exactly the same problems with my first Europa which I restored some 30 years ago. The front brakes locked up very early especially in the wet. Very scary. I even tried to fix the issue by fitting a Tilton proportioning valve in the front circuit like suggested by Pfreen. With the bias forcefully shifted to the back it was indeed possible to lock the rears first even on a dry road. But the pedal force was really high and the deceleration not impressive. It felt like pulling the handbrake while driving. As we all know not much will happen in an Europa . I kept the valve as the braking performance was slightly better with a some bias shift to the rear. But it was a far from ideal solution and I wouldn't do it again.

What puzzles me is that in all the old road tests no tester ever mentioned a bad brake balance on the Europa. They frequently achieved a deceleration of 0.9 g and had no complains concerning the braking performance. Of course back in the late 1960s the brakes were much worse in general but I can't imagine that the brake balance on a new Europa was as bad as we experience it today. My thought is that it must have something to do the friction coefficient of the older materials and the braking system being in a 'new' condition.

Now that I'm restoring another Europa I will face the same problems once more. I would really like to keep the drums so I need to get them working. First I will meticulously make sure that the whole system is setup 100%. The drums will be turned, balanced and the pads bedded in using emerald paper. I also may fit bigger slave cylinders to the rear if I think I need to shift the brake balance to the rear. That would have the same effect like adjusting a balance bar.

JBs comments concerning 'threshold braking' is very helpful. Especially as the response time of drum brakes is slower than disc brakes. It may have something to do that there is a spring that pulls the shoes away from the drum. As a resut there is more dead travel to overcome compared to a pad nearly touching the disc. That's where fitting of a residual valve could help by keeping the pad closer to the drum surface. I will give it a try as those valves are not very expensive.

Another reason for the slower response time of the drum could be that a drum brake has a 'self servo' effect. The leading shoe is forced by the rotating drum into the direction of the drum and increases the brake power. But this takes a short while so adds another small delay. I have no idea of how to overcome this effect except for fitting disc brakes to the rear.

Klaus