proportioning valve (solution) - cheap rear brake 'upgrade'

[lotusflasherman]

My Subaru Forester has proportioning valve linked to lower rear suspension arm so when the rear lifts it increases the bias to the front brakes - now that's the way to go Mr P.

Yes, but Subaru nicked the idea from the British!

It is a standard fitment on the Dolomite Sprint - but it is also one of the first things I removed from every one of the (16) Sprints I have owned - no-one ever seemed to get them to work properly once they were about 2 days old!!! A standard flexible hose replaces the complicated (and heavy) unit above the rear axle and then by fitting different front/rear brake systems you can set it up however you want it (depending if it's for road, race or rally).

(and I'm pretty sure that Triumph didn't invent the concept, but they seemed to be the first company to totally destroy the idea that they were a great addition to the car!!!!)

Must be getting senile Just remembered the Dolly Sprint was rear wheel drive so why did it have a bpv? Not usual to worry about locking up the driven wheels at rear in that era.
My dad had a Triumph 1300TC that was fwd (worst car he ever bought as engine far too small for weight of car) and I expect the bpv was standard fitment to those fwd variants (1500 etc) and they just overlooked taking it off the Dolly Sprint..

[lotusflasherman]

OK, but I don't think Dave did his mod to deal with a difference between a weak OS that failed the MOT and a working NS that passed. He does say "It will allow you to easily pass the MOT test – just wind up the pressure for the test, and put it back down again afterwards (I DO NOT RECOMMEND DOING THIS JUST TO GET A ‘PASS’ - - FIX YOUR BLOODY BRAKES PROPERLY!)."

I still think it's important that you get both rear brakes working in a similar fashion and then whatever bias from front to rear you choose it will be the same OS to NS. I would not advise having different ramp curves to deal with your difference between OS & NS, otherwise you'll have a car that wants to play hopscotch under heavy braking. Where in 'South East Essex' are you? I'm in South Suffolk/close to North Essex (Colchester) so if you need a hand give me a shout.

Yes adding the adjustable valves just to pass the MOT would be foolhardy

I need a new valve, the adjustable valves are available, cheaper, and will do a better job when set up correctly, so for me it's a no brainer

I've now removed the old valves and need to make a platform for the valves to sit on, then I need to find somebody that can knock me up some new brake pipes

I've got a flaring tool and always keep a few coils of Kunifer (copper-nickel) pipe. Flares easily, bends nicely and doesn't ever rust.

[dapinky]

Must be getting senile Just remembered the Dolly Sprint was rear wheel drive so why did it have a bpv? Not usual to worry about locking up the driven wheels at rear in that era.
My dad had a Triumph 1300TC that was fwd (worst car he ever bought as engine far too small for weight of car) and I expect the bpv was standard fitment to those fwd variants (1500 etc) and they just overlooked taking it off the Dolly Sprint..

The bias valve on the Sprint was unique to the model - the earlier 1300/1850 (and later 1500) didn't have it - it was more of a load/weight device (simple spring and lever system) on the rear axle.

The whole car is under-braked (by modern standards - but it does make the Elan system feel very good!), the only way they could get the Sprint to stop even remotely adequately was to fit much larger drums at the back than the other models - then it needed the valve to keep the rear working when the weight shifted from back to front.

It wasn't an issue on competion cars with harder suspension, but the standard car was intended as a luxury saloon with ride to match.

Obviously, it seemed like a much better idea than designing a whole new brake system to actually work! (using modern parts it is a fairly simple job to fit vented disks and callipers from a Sierra, Escort or Golf) - and the works car has an OE vented kit using bespoke parts based on the ubiquitous (in its day) princess callipers.

[CalElan]

Always wanted a Dolly Sprint - about 15years back I looked at quite a few but most were very rotten.
Still a regret to have not had one.. funny that!

[Steve A]

I've got a flaring tool and always keep a few coils of Kunifer (copper-nickel) pipe. Flares easily, bends nicely and doesn't ever rust.

Thanks for the offer Phil, but given your location it's probably easier if I find someone local to make some up.
I have done it before but I can't remember where I got all the parts from.

[lotusflasherman]

I've got a flaring tool and always keep a few coils of Kunifer (copper-nickel) pipe. Flares easily, bends nicely and doesn't ever rust.

Thanks for the offer Phil, but given your location it's probably easier if I find someone local to make some up.
I have done it before but I can't remember where I got all the parts from.

Don't like being dependent on others so have always made my own. Quite easy so sure you can too - tool here, similar to mine but mine has a cast handle with a flat section to clamp in a vice which makes it easier to use..
http://www.ebay.co.uk/itm/Brake-Pipe-Flaring-Tool-Powerhand-PH-BFT-316-3-16-/151035636166?pt=LH_DefaultDomain_3&hash=item232a6ce9c6
& pipes and unions here www.ebay.co.uk/itm/Copper-Nickel-Kunifer-Brake-Pipe-25ft-Roll-3-16-24-Metric-Male-Female-Ends-/261748138837?pt=LH_DefaultDomain_3&hash=item3cf167a355

Only tricky bit is difference between single flare and double flare but instructions will guide you...

[vinnie]

Can you give me details of the bais valve and were to get them. I upgraded fronts with PNM calipers and disc replaced rear hub with new OE refurbished calipers new s/s braided hoses all round bleed bleed bleed bleed. Mot result front 288 fns 275 fos rear 71rns 74ros placed 100kg in boot went back retest 95rns 93ros . Ithink that the upgrade as unbalanced the bais and this looks to be the best solution

[dapinky]

Can you give me details of the bais valve and were to get them......

If you mean the adjustable ones which I used, then there is a link in the first post to these.

[Steve A]

Mine are now on the car, I've gone for your settings of 2.5 turns for weakest pressure (Dave) as a start point, the retest will be done tomorrow so wish me luck

The job was fairly straight forward, I mounted my valves on 10mm thick nylon which is fixed to the chassis via 2 X 6mm tapped holes that are already there (so no drilling required), the nylon gives clearance to the adjusting knob.
I only need to changed two brake pipes as the new valves are around 50mm smaller in length.I also counter bored one of the value bodies as they are not handed so the cap heads look the same both side.

[dapinky]

Doesn't look too dissimilar to mine - except i used Aluminium brackets not nylon - but the theory is the same!

The pipes dictated where the valve sits (withinn reason) and it was all about getting them out of the way but accessible (knobs).

Hope it goes okay tomorrow - depending on how accomodating your tester is, it is an ideal time to balance the two valves whilst it's still on the rollers.

[Steve A]

You can all relax it passed
I didn't have to adjust the valves as they were very close or as the man said "spot on"
I tried some "vigorous braking" before the test and all seemed to be well balanced.

Now to do some driving and falling in love all over again

[HIBUTK]

All: This setup is a good idea! My two cents on proportioning valves for the Elan rear. Had cleaned originals awhile back. I’m running Wilwood 4 puck calipers on the front and their 12.19” rotor with Bob’s rear setup with hi-spec calipers and the Elan front rotors. All rotors are slotted and cryogenic treated. Ran a track day at Sebring and fried the Raybestos ‘race compound’ pads in about three laps over several sessions each time. Switched back afterwards to street pads of the Porterfield R4S. Checked 3,000 miles later and the fronts were worn .150” and the rears .015”.

I purchased a gauge and adapter set to check the pressures. From my notes in May of 2013 - the rear proportioning valve is 0 – 15 bar at full force, over 15 bar equals .2 times the pressure per the factory manual. I’m going to use psi instead of bar as that is what our gauges are calibrated in (USA). The info I had from the Stainless Steel Brake Company with their adjustable proportioning valves was the calipers don’t function well under 600 psi (41 bar?).

With the stock proportioning valve in place I took readings between the valve and the caliper. Medium pedal pressure resulted in readings around 200 psi. Full hard pedal pressure were 375 psi, comparable to the factory manual. Measured between the master cylinder and the proportioning valve it read 825 psi or a 450 psi drop. For comparison, the fronts read 1,100 psi on full hard pedal. Not sure if they should have been the same. Wilwood says 1,250 psi max at their calipers.

I installed two of the adjustable valves, one on each rear line – see photo, and checked the pressures coming out to the caliper per the turns on the valve . As 375 psi was not doing any good, I arbitrarily set the rears at 575 psi. Almost two years later, but no track days or autocrosses, I checked and the rears had not much more wear, so I raised the psi to 700. Just normal spirited driving and no real testing has been done since the increase.
Just some numbers to consider if you make these changes.
mike k

[muley]

My MOT tester casually mentioned that the owner of the other M100 he tests removed the valves completely...

..and it made no difference to the effectiveness of the brakes (from his perspective)




Jim

[Candles]

I had a crack at this in 2010. Here's the old thread with some science:

Old Prop Valve Thread

Sorry the images have gone - the intervening years have lost them in internetworld...

The update to the saga is that I still have the valves just poking out between the seats and under the roll bar, they work fine, it passed an MOT the other day (on rollers) so there must be some rear braking effort and I've driven it a fair bit without issues. Once I took it onto wet grass and checked I could get everything to lock up, but aside from that I've applied no science to the setup of the valves, I've just got them on minimum braking to the rear.

[Candles]

IMG_1217.JPG

Found it! Aren't computers brilliant....

[dapinky]

...and there was me thinking I had come up with a novel solution, when all the time it was 'just' another recycled idea ....

Candles, I honestly couldn't remember your thread - I wish I had found it, it would have saved me doing a load of Maths ('cos Bob did it and said you were wrong!).

Mike, it's interesting to see the pressure numbers (I understand bar far better than psi, but can visualise psi far better than bar, so I like the scales used!) - and it would be good to get your impressions of how different the car feels with more or less at the rear wheels whilst driving, not just static on a roller.

Anyway, it appears that MY super-dooper 'new' idea has now been done by (at least) 3 original thinkers, and however many copiers - surely we can't all be wrong in the thought process? (but still waiting for Bob to enter the conversation and tell me i'm wrong - especially as Ray Dodd agreed with my theory).

It also seems that it has been measured/tested in 3 different ways for effectiveness....

...Mike used pressure, Candles used rollers, and I used a deserted airfield.

I think that if you take some of each write up you will see that we all ended up with the same adjustable valve (having looked at the pressure characteristics), 2 placed it in OE possition, 1 placed it for 'easy-reach' (but you'd have to ask how often it gets touched - unless you track the car a lot, when it is VERY wothwhile).

We all went through a similar thought process to get there.

We all tested it differently, but came to the same result.

3 very different braking systems were used -

Mikes - USA car with Wilwood/Hi-Spec
Candles - UK car with whatever brakes he currently has (always messing, that boy )
Pinky - UK car, OE callipers, narrow-bore master cylinder

[Candles]

For your study, mine are:

Front: Wilwood 4 pots on the small setup to go under 15" wheels
Rear: Dormans on grooved/drilled rotors

[neil1849]

Came across this modification thread just after my M100's rear brakes scraped through the Mot. So I decided to replace the messy and complicated Lotus rear prop valve and pressure limiter by carrying out this conversion. I used the very same valves recommended in this thread and I am sorry to say that the results were abysmal. The car pulled violently to the left, due to a locking left rear, and no end of adjusting the valves would cure the problem. Put the car on an Mot brake roller which confirmed the road test findings.
Now given that the whole braking system had been rebuilt and that the car previously pulled up in a straight line, I suspected the valves to be at fault.To confirm this I replaced the aftermarket prop. valves with straight through brake pipe, albeit temporarily. With this set up the car pulled up straight once more until both rears locked up, which was quite easy to do.
This exercise proves that some method of proportioning front to rear brake pressure is essential on the M100. Plus the original fitment rear brake calipers are more than up to the job, so in my opinion rear caliper upgrades are totally pointless and unnecessary. Even more so if one has uprated front brakes because the rear will tend to lift even more. Somewhat like braking hard on a motorcycle, as the rear wheel lifts from the road the rear brake becomes less effective up to the point of it being useless.
I now intend to fit a single prop. valve but one which has two inlet and two outlet ports so that the diagonal dual circuit system can be maintained. This valve is mucho expenso, over £350, compared to the single screw/knob type but not too bad when compared to the Lotus prop. valve system. If it does the job then I will be happy, especially given that the original Lotus system is largely unobtainable. Will post results along with details of the valve used once the job is complete.

[muley]

I fitted some adjustable valves to the rear

1. Willwood style. 1st one was fine and is still on the car Couldn't get another one that worked! Tried three from supplier ~ all bad ~ gave up.

2. Sundealy style off eBay. Fitted fine.

Went for MOT.

Massive fail on the Sundealy. Worked with the garage to try adjustments and we broke it in very short order ~ with a good hard shove on the pedal it started leaking round the spindle.

Pics and solution to follow.

Mind how you go

Jim

[dapinky]

Hmmmm....

As it appears that 2 people have had recent issues with this piece of mechanical bodgery (engineering!) I thought it best to revisit my setup......

..... no leaks evident, and so out for a drive to a suitable test area (Pembroke is blessed with old airfields, and the one at Carew is local and ideal!!).

All appears to be as it was when fitted, and car brakes in a straight line, with no major upset when braking on a bend.

The MOT isn't until the end of next month, so I'll have to wait and see what the numbers are showing.

For the 2 'failures' I would be interested to know exactly which valves have been used, and failed - and if it is the same as the ones I have fitted, then I'll strip and examine mine to see if there is any internal indication of wear/failure.

I can only really say that I am still happy with mine, and have no problems to date - but if there is an inherrent problem with part of the system, then I will investigate it.