Unconventional Proportioning Valves: Thoughts?

[Candles]

After 10 years of ownership, I've been through the following saga with brakes:

Stock, with various seized elements.
Stock, repaired and on new sliding pins.
Stock, EBC greenstuff, grooved rotors, reconditioned rear calipers (SJ's) with EBC blackstuff pads. SS braided hoses.
Wilwood 4-pot fronts
Wilwood 4-pot fronts with Dorman rears
As above with new master cylinder

Throughout all of the above changes, I could get a good pedal, lock a wheel (normally front left first) and pass MOTs. The car always exhibited a weird pull to the left. This winter, I decided that I would replace the only original part remaining: The proportioning valves. I figured that with a non-stock setup, a non-OEM valve would be a better choice:

So, I thought I would install them with cabin access so that they could be set up by the driver on a roller brake tester running the rears. Here they are:


The pipes are diverted here:


and route up through holes in the battery-bay floor. The pipes then go from the valves, down through a hole into the chassis box, then aft to the original joins for the braided flexible hoses. I plan to re-make the pipes from the join to a connector mid-way down the car as I don't like the look of the hand-bent steel pipes adjacent to the wishbone attachment.

Accepting that by changing the brakes at all, I am beyond all the; "Oh, you know better than Lotus?" types of comment, what do people think of this modification? I can tell you that it functions, the car brakes in a straight line, and with a guessed proportioning setup, it passed an MOT.

The unwelcome (to me, with skinned knuckles and greasy hands) footnote to the story is that, 10 years on and despite all the changes, before each MOT I have to remove the rear calipers and manually adjust the handbrake bite point so as to pass the MOT with 'reserve travel'. I can't wait for Bob's next run of rears!

Candles.

[rip]

That must have been a major mod to fit the valves there?
I can definitely see the point of changing them though: Upgrading the front brakes will theoretically put the system out of balance.
Better rear brakes helps balance this out, but surely the stock valves are there to stop the rears doing too much in the first place? Therefore if the front brakes work better, you should simply be able to fit less restrictive valves?

If you just want to increase braking performance, an alternative would be to upgrade the rear pads. In the UK, Greenstuff appear to be the only option for this.
However, if you search US sites for the alternatives which use the same calipers, there are a lot more available. I am fairly certain that you can get Redstuff & Yellowstuff in the correct size & you can definitely get Powerstop Evolution.

[Monty]

Great work Mr Candles, IIRC Dave in the USA did this on his Track Elan but had the adjusters under the drivers seat.

So the New BMC didn`t solve the left front locking up so has fitting these adjustable valves solved this ?

[bobbrown]

I see some problems with this Wilwood brake bias adjuster, it does not match the OEM bias valves very well as it is rated to reduce the line pressure by 57% max and I'm not sure at what point it starts to reduce the line pressure.
There are others available that are closer to the OEM ratio but still slightly high, the AP racing ones are 0.325 which is close to the early valves but still higher than the later OEM valves at 0.2.

09_CP3550-14_Perf_Graph_1.gif

If you look at the graph then there only needs to be a small adjustment to get to a 15 bar start point and then it follows a 0.325 ratio as the pressure rises, now you would need some playing around to get them both the same, probably why competition cars are split front to rear not diagonally and only one pipe to the rear brakes and a single valve.
AP do make a lever valve Link that is twin port so could be used but is still not ideal.
If you look at the OEM items then they are designed to start to operate at 15 bar and reduce the pressure from that point by 80% on the 2/15 valves. and 70% on the older 3/15 valves
I think the original valves were off a Nova, Corsa A or Astra but not sure which one and an adapter was screwed in the end to fit them in the fixed pipe work instead of directly in to the master cylinder.
If I could sort out which one it was then these are still available as a GM part or aftermarket the latter at a reasonable price around £20.00 each.

If the front brakes have been upgraded then you could increase the pressure to the rear but the relationship would still need to be the same or similar.
I would be inclined to treat this carefully as you could quite easily over brake the rear and end up in a complete pickle with the rears locking before the front, may not happen in the dry but on a wet road after a protract dry spell could be down right dangerous.

Bob

[RayD]

... and with a guessed proportioning setup, it passed an MOT.

Candles,

Did you get the brake test figures from the MOT ... they may indicate where you had the valves set.

Ray

[Candles]

Ray,

Sorry I didn't; with the state the car was in, I paid as quickly as I could, grabbed the certificate and ran to the post office to tax it, laughing.

[bobbrown]

Did you get the brake test figures from the MOT ... they may indicate where you had the valves set.

Ray

Ray,

The brake rollers used for a MOT do not show the balance front to rear they only show left to right on each axle, the figures that you get at a MOT station depend on a number of factors from the state of the brake rollers, the tyres, weight, the amount of pressure applied to the pedal etc etc. To see what the balance is front to rear you need to check all 4 wheels or put a pressure gauge on the line so you can replicate the pressure for the front and rear.

I have managed to get a new Nova/Corsa/Astra proportioning valve off fleabay for a fiver so I will carry out some test with a couple of pressure gauges to see what these actually come out at and to see how they differ from ours in terms of fitment.

Bob

[Steve A]

This is what this site should be about, it's interesting and helpful to others, none of that negative and boring

[Doug]

[Sy V]

It's destined to become another LEC classic thread. I think I'll pull my sun lounger a bit closer so that I don't miss anything and help guard the OP's nucleus.

[Candles]

Monty,

The front left still locks up first, but I think this is due to the weight distribution. According to my mate, who did a road safety course with the Cops, they used to find that a lot before ABS at the scene of an accident where the car only had a driver on board. So, if you think, I always stop pressing the pedal when I hear a tyre lock, so if the above is true, then I'll only ever see the front left lock-up, until I find a willing passenger!

[RayD]

The brake rollers used for a MOT do not show the balance front to rear ...

Yes, Bob ... I was asking because it doesn’t show the balance front to rear.

Ray,

Sorry I didn't; with the state the car was in, I paid as quickly as I could, grabbed the certificate and ran to the post office to tax it, laughing.

When you get chance give them a ring while they still have the details.

Hopefully your rear readings are around 100.

Jay's (Monty)
Front 330 350
Rear 100 100
Handbrake 120 130

Ray's
Front 300 300
Rear 100 100
Handbrake 200 200

Ray

[Jackonicko]

I like the positioning of these new valves - they're much less likely to get full of gunk and crud.

Good work by BB on the Nova item, too.

[bobbrown]

I like the positioning of these new valves - they're much less likely to get full of gunk and crud.

Lets not lose track of the fact the Wilwood valves are by no means ideal and I do not see how the internals of the current valves can get full of "gunk and crud" unless you are running contaminated brake fluid.
The one I opened up to get the O ring sizes was as clean as a whistle on the inside, dirty and a bit of corrosion on the out side but that is to be expected after the years it has been sitting exposed to the elements.

I have asked the question of a couple of O ring suppliers to quote for suitable O rings in a material suitable for the application should be cheap enough.

[Coupeboy]

I am watching this thread with a vested interest in a solution. Whilst I have swapped one of my valves for an unknown mileage/age unit, and got a positive result, my suspicion is that 15+ year old valves are suffering out there and I would like longer term comfort that I can leave it alone for a while yet. A solution that offers either a rebuild or a replacement of alternative origin is keenly sought. I would suggest a site 'recall' to make everyone aware if and when solutions are on the table. In other words, if a solution or two is offered then these should be publicised as a 'sticky' or whatever the web techo speak is. The thought of several of these cars zooming around (never mind in the wet) experiencing strange braking effects possibly attritributable to failing/failed valves is quite alarming. The MoT does and will pick up uneven rear pressure distribution (beyond an acceptable margin) but has a dormancy of a year for it to worsen and catch you out when you need the brakes (happened to me). As a matter of course, we should all check/clean/grease brake sliders annually (prior to the MoT) and note any rear lock-ups/yawing as an alarm bell to sort out potentially failing proportioning valve(s). On the solution of rebuilding these the Lotus Manual does not recommend this. In the absence of new (Lotus) units being available, there is no reason why a rebuild should not be persued so long as there are foolproof instructions for a rebuild (body torque values, o ring material spec etc) and you feel competent to trust your life to this (probably why Lotus does not recommend it). All power to Bob and others looking at this.

[RayD]

The front left still locks up first, but I think this is due to the weight distribution. According to my mate, who did a road safety course with the Cops, they used to find that a lot before ABS at the scene of an accident where the car only had a driver on board .....

It’s a good tale Candles but nevertheless unlikely.

If it were true it would happen on all similar cars. It would continue to happen after the advent of ABS - only you would feel/hear the ABS action instead of the tyre locking up.

If you were trying to cause it to happen on purpose, what could you do? ...

I’m sure people can think of others but here’s a few ...

Have less air pressure in the right rear.
Have two different tyres on the front.
Have a less grippy tyre on the left front.
Have a softer spring on the rear right.
Have a failed shocker on the rear right.
Have a twisted chassis.
Have two different springs on the front.
Fit adjustable dampers and set them differently.
Have adjustable spring platforms at different heights.
Have the suspension geometry set wrong.

and the things you've addressed ...

Have a faulty master cylinder.
Have a permanently open proportioning valve on the rear left.
Have a permanently closed one on the right.
Have different pads on each of the fronts.

Ray

PS ... Have you rang up for those brake test figures?

[Steve A]

Good research Bob, this is a long term problem no one else has managed to crack.

[Candles]

PS ... Have you rang up for those brake test figures?

I asked. Because I'd told them it had a LSD, so they didn't burn it out on the brake rollers, they used a decelerometer, so no figures. Probably why it passed! I'm going to 'hire' a bit of time at a local garage and try and set the whole car up better as it is somewhat unscientific at the moment. It appears I am a good guesser though!

Candles.

[RayD]

PS ... Have you rang up for those brake test figures?

I asked. Because I'd told them it had a LSD, so they didn't burn it out on the brake rollers, they used a decelerometer, so no figures. Probably why it passed! I'm going to 'hire' a bit of time at a local garage and try and set the whole car up better as it is somewhat unscientific at the moment. It appears I am a good guesser though!

Candles.

Thanks Candles,

Take your time between now and then as the back brakes would have passed even if they were a mile off - proportionally.

You'll understand what I mean ... instead of say 300F/100R they would have passed if your guess had landed them at 300F/200R (If it's possible in the range of adjustment)

Ray

[Elantastic]

I like the positioning of these new valves - they're much less likely to get full of gunk and crud.

Lets not lose track of the fact the Wilwood valves are by no means ideal and I do not see how the internals of the current valves can get full of "gunk and crud" unless you are running contaminated brake fluid.
The one I opened up to get the O ring sizes was as clean as a whistle on the inside, dirty and a bit of corrosion on the out side but that is to be expected after the years it has been sitting exposed to the elements.

I have asked the question of a couple of O ring suppliers to quote for suitable O rings in a material suitable for the application should be cheap enough.

Did anyone ever find a supplier for the sealing ring that goes onto the screwed end of the proportioning valve?