front brake lockup

[Pfreen]

I have recently done my brakes, ie new disks, pads, drums and shoes.  They are now bedded in.  I put Mintex 1144's on the front.  The Mintex are much more predictable than the greenstuff pads I had on it.  The Greenstuff seemed to be grabby. I also replaced the drilled rotors with slotted rotors.  The drilled rotors made the brakes sound like my bicycle did when I was 12 when I put a baseball card in the spokes.

Anyway, I have a 7/8" master cylinder with Lockheed boosters.  The front brakes lock up way before the rears do.  A brake balance valve won't help since it reduces the rear brake pressure.  So, I was reading that most American cars use a brake metering valve in systems with front disc, and rear drum brakes.  I have never heard of a British car utilizing one.  Does anyone have experience using one?  This link https://www.freeasestudyguides.com/brake-metering-valve-test.html describes how it works.  It basically delays the braking action of the front brakes to match the braking action of the rear drum brakes.  Discs brakes act pretty much instantly and drum brakes have a delay.

I am thinking about installing this valve https://www.speedwaymotors.com/Brake-Metering-Hold-Off-Valve,8904.html.

Any thoughts or advice?  BTW, I know it is best to have the front lock up first, but I just want the rears to be slightly on the verge of lockup.

[jbcollier]

The problem with trying to get the rears to the “verge of lock-up” is that then they become very sensitive to rear loading.  The car might react completely differently depending on whether the gas tank was full or not, and be much more sensitive to road surface conditions.  If the rears lock first in an emergency situation, the car will slew around sideways.  This is never good and would be especially  undesirable in a mid-engined vehicle.

You have to be careful about increasing front brake power in a Europa.  The front end is light.  Weight has to transfer before full braking power can be used.  A sudden strong stab at the pedal will lock the fronts every time.  You squeeze the brakes moderately firmly and increase the pedal pressure as the weight transfers.  It’s a technique that requires practice.

That all said, a Europa’s brake balance can be adjusted somewhat by fitting different size of rear brake cylinders.  I believe they are available in 0.70, 3/4 and 7/8.  Maybe 5/8 as well.

Lastly, front and rear brakes are applied at the same time.  There is no delay.  However, one shoe of the Europa’s rear brakes is self-energized.  That does take a fraction of time to occur and leads to talk of drum brake “delay”.

[surfguitar58]

So you have boosters, reduced .750" ID master cylinder (standard is .875"/.812" stepped), AND high friction pads? You appear to be unique among Europa owners for having TOO MUCH stopping power. I agree with JB that delayed or reduced front braking action sounds like a bad idea for dynamic reasons. What about just going back to the OEM stepped master cylinder?
Tom

[Pfreen]

I have the stock 7/8” master cylinder.  The metering valve is used on American cars and I wanted to know if anyone has experience with them on British cars.  My car stops fine, I just want to make it better.  Everyone seems to want rear disc brakes, but I haven’t heard of anyone trying to make the drum brakes better.  Just a thougt.

[jbcollier]

Things that help brake efficiency:

- arc the shoes to fit the drum perfectly.  We used to do this in the old days.  You can easily do it yourself.  Remove the drums and lightly sand the brake surface.  Go for a ride and then remove the drum and check how much of the shoe is being used.  Sand off the high spots and repeat until you have all of the shoe making contact.

- make sure the shoes are properly adjusted.  Adjust until locked and then back off until just free.  This should be done before, and after, sanding the linings as per above.

-make sure you use brake shoes meant for a Europa.  They should have a different coefficient of friction over more common GT6 shoes.

[surfguitar58]

I have the stock 7/8” master cylinder...

Oop! Sorry Paul, my feeble brain saw 7/8" and read it as .75". Somebody should just put me out of my misery.
Tom

[GavinT]

Everyone seems to want rear disc brakes, but I haven’t heard of anyone trying to make the drum brakes better.

I recall talk years ago of using the twin leading shoe drum set up as found on the front of some Triumph Heralds(?) & Hillman Imps.

I don't know of anyone who's tried it, but would expect a twin leading shoe system to be more powerful.
That said, I wouldn't expect it to improve the delay.

Remember that the line pressure will be the same throughout the system so the delay is the wait time associated with getting the rear shoes to the drum - or at least it is with a single line master cylinder on my Type54/S2.

There might be some value in installing a residual pressure check valve in the rear line, though.
Anyone tried those?

[BDA]

Jensen Motors used the twin leading shoe rear brakes in their C production racing Europa back in the day.

[Nockenwelle]

Very interesting discussion. I had the same problem with my first Europa and never really get rid of it, especially in the wet. Interestingly all the contemporary test reports do not mention that problem so the brakes should have worked fine when new.

I also would like to stick with the rear brakes. There has to be a way to get them working. As mentioned above proper alignment of shoes and drums and the right mix of friction coefficient should help a lot. I never heard of those metering valves before, it sounds interesting. If I got it right they do the same like the braking technique described by jbcollier above.

[Pfreen]

This article, http://gglotus.org/ggtech/europa-brakeinfo/brakeinfo.htm describes the Europa brakes very well.  My hope is that the proportioning valve would eliminate the front lock-up during a panic stop.  I know that the best braking is accomplished by modulating the brakes, like anti lock brakes do.  However, I think that eliminating the initial front lockup may allow the rear brakes to lock up first.  If you can get to this point, maybe by front pad selection,  then a proportioning valve can be used to dial in the front /rear bias so the front wheels just lock up before the rears.
That is my thinking anyway.  The brakes are decent as they are, but I think they could be better.

[EuropaTC]

As a latecomer to the thread and also someone who's "nailed colours to the mast" and gone for rear discs, even so I'm intrigued by the idea of a device which slightly delays the front brake onset. It's not something I've come across before but if it's a standard fitment on US cars with Disc/Drums then I'm surprised it's not made it to the UK. (maybe it has, and I've just missed it ? )

A residual pressure valve in the rear line should have a similar effect because it keeps the drums just on the point of activation with (I think) a 10psi line pressure. Valves for discs are lower, 2psi on the ones I used.

I'm normally a fan of Golden Gate articles but that one is misleading, or at least it is if you skim it quickly like I've just done.  Elan front brakes for the 2 seater are pretty much the same as the Europa, it was the heavier +2 which has larger calipers/discs. The calipers aren't "similar but mounted further out" either, the Type 16 caliper has not only different mounting points but larger pistons, larger pads and is way, way heavier. 

However the Elan with knock-on wheels does have the heavier vertical links so is easy to fit the larger discs/calipers, and I've done it.

Still on the article, I also thought the S1/S2/TC all had the smaller rear drum widths with only the TCS going to 1.5", it seems illogical that Lotus would fit smaller brakes on the heavier TC after several years on the S1/S2. But I've never owned an S2 so is this something else that I've misunderstood over the years ? 

Finally a potentially controversial comment. I know the Road tests of the day praised the Europa brakes and we all know they work really well as standard in dry conditions if you think and apply the pedal with weight transfer in mind.

But that's something we've adapted to and if you tried to market a performance car with similar braking characteristics today then I think you'd lose. The designer thinks "the average Joe is going to stab hard on the brakes when he panics, so let's design the problem out", hence we have balanced systems and ABS these days.

Personally I'd prefer not to rely on my skill (?) to prevent lock up on a wet road when something unexpected happens in front. So if adding the device you've referred to, or a residual pressure valve to the rear lines makes it safer in that rare moment when your brain screams "stop !!!" and you forget all about gentle pressure first, then I'd go for it !

Brian

[cwtech]

I see three different devices being mentioned in this thread.  ...Each device has its own purpose.

A residual pressure valve (RPV) is used with drum brakes to prevent air from being ingested past the piston cups when the piston retracts.  ...The slight fluid pressure keeps the cups expanded to the cylinder bore.  ...The brake shoe return springs return the shoes, while brake shoe adjustment controls the amount of retraction.

A metering valve, aka hold-off valve, is used to allow fluid pressure to the rear drum brake circuit slightly before fluid pressure is allowed to the front disc brake circuit.  ....It does not limit pressure, but changes the "timing."

An adjustable proportioning valve is often used to control the RATE of pressure rise going to the rear brakes, in an attempt to balance front/rear braking.  ....It does not limit max fluid pressure.

[jbcollier]

S1/2 and TC use the same shoes and drums but different size of wheel cylinders IIRC.

[314159td]

Reviving a thread that's already on track of what I'm poking around.

I intend to toss type 14 calipers onto my Series 1 Europa*, which of course maybe started life with type 12 units.

Some napkin math says that swap would be a 25% increase in piston force for the same line pressure, further increasing the potential of a front lockup.
My car would have the same line pressure on the front and rear with a single circuit MC**, so I think a larger rear cylinder would help bring things back into balance. S1 was originally 3/4" rear, so a 7/8" unit may be suitable, but I can't seem to find these, only 7/8" in the TR style.***

With that issue and reading over some threads, it seems like an adjustable proportioning valve installed backwards would work. Reading through Willwood's excellent writeup here, it seems that installing a proportioning valve backwards/on the front circuit would allow the rears to receive full line pressure, then taper off the fronts after a certain adjustable point is reached. This would work in panic stopping events, and I think generally appropriate for how people have described the Europa's braking.
It seems like that would handle most (all?) the changes to the braking system caused by larger front calipers.

I've never had a proportioning valve in a car with mixed drums and discs****, so I'm unsure how the delay and self-energizing of the drums would play into this. A hold-off valve (as mentioned in the first post) in combination with the reversed proportioning system may have more impact on the "delay" felt at the rear brakes.

I don't think a proper combination valve would work here, as it would delay the fronts slightly but also only allow the rear pressure to be reduced, hence separate units so you can flip the proportioning.



*Type 12 cost more for new units, parts to rebuild old ones are tricky to find (pistons have been OOS for years), and my other car also uses 14 so may as well share a single spare pair. BPNW currently has 12s in stock, but I'm not going to rely on those always being there in the future.
**tried to fit a few different dual units, didn't work. Series 1 is much worse than 2 in that regard. 
***Ex: https://bpnorthwest.com/triumph/wheel-cylinder-875-trw-morgan-large-bore-tr4-to-tr6/
****yes, I know about rear disc conversions for the Europa. Later problem.

[EuropaTC]

I can't answer the question on proportioning valves and what you say sounds logical, but rather than guessing I think I'd ask Willwood for their comments.

The braking balance as standard is generally praised in dry conditions, it's wet roads when the real problems come along where you don't get the weight transfer. The snag with deliberately allowing the rear brakes to come on first is that you could end up with the rear end locking so you'd be swapping one problem for another. And of course you'll only know that on a wet road with a panic stop....

One thing I would add is that if you increase the piston diameters is that you'll also increase pedal travel, more so if you managed to fit larger rear cylinders. Not a deal breaker, but something to consider when re-designing the system.

In the UK, ANG classic cars list the type 12 pistons, I don't know if it's an old listing and they still have stock but it might be worth an email.

https://www.angclassiccarparts.co.uk/products/triumph-5981/triumph-13001500-fwdtoledo/brakes/brake-caliper-piston-type-12-triumph-1300-68