GM Proportioning Valves investigation for compatibility

[bobbrown]

The valve could fail in either position but the chances are it would fail closed which is probably the safer option as rear wheels locking before the front is not a good thing unless you are rallying when this is sometimes desirable. Handbrake turns and using the handbrake on a stage to get around tight corners are examples of what happens when you apply the brakes to the rear not what you want when you are not expecting it.
They work like this
There are in effect two pistons of unequal size as the pressure rises then the differential pressure cause the piston assembly to move towards the pressure inlet at a point around 15 bar the valve starts to reduce the pressure on the down stream side. As the pressure on the upstream side rises the force on the smaller piston increases and allows the valve to open and once the force on the larger piston is equal to or greater than the smaller one the valve is shut off. When the pressure is released the shut off valve allows the pressure to be released.
The ratio is dependant on the differance in the piston sizes which is what I am keen to see with regards to the Vauxhall valves, the main spring will set the pressure the valve starts to operate at in this case ours start to operate at 15 bar.

[bobbrown]

Not sure if this has gone a bit off topic in as much as Candles was after thoughts regading the Wilwood bias valves, no doubt a moderator will be along to correct it if this is this case.

Onward and upward

I have mangaed to get the material spec sorted EPDM
DO NOT use standard nitrile rubber O rings as they are not suitable you have been warned.
I think to get the correct sizes I will send the company that has come back to me the two I have as samples and let them measure them once I have done my comparisons.
If they are a standard size then they will be about £1.00 for 4, 2 big 2 little, if they are a non standard size then they are £3.50 for 4 if we take 50 of each or they come down to £1.00 if we take 250 of each.

[saska]

Measured the two "O" rings and they are as follows
smaller one is 3.75 mm id and 1.8 mm cross section
larger one is 7.1 mm id and 1.8 mm cross section

Thanks Bob. I'll add to the Wiki. Could you also measure the seal and I'll add that too.

It is very important to select the correct material as some materials are not compatable with brake fluid! so do not just pick them out of a box of standard O rings

Amen. Was thinking of EPDM -- widely available in many sizes and recommended for use with brake fluid. Kalrez would probably be the best, impervious to damn near everything, but isn't readily available in many sizes.

[bobbrown]

Good news and bad news

Firstly I think I have an early OEM valve and it is likley to be a 3/15 not the later 2/15 to confirm this I would need a later valve.
The valve I brought of fleabay is very close, every thing is the same with one exception and that is the spring which is stronger and may be the reason for the 3/35 stamped on the out side.
Change the spring with the original and you should have a 3/15.
I have a supplier looking into these valves and he is going to look at some of the others they have to see if there is one stamped 3/15 or even better would be 2/15 as there are 7 different valves in the Nova range so I think the chances are looking good

These are available but in what numbers I do not know as he said they are not fast movers and are stacked up high in the warehouse.

I'll post some pictures later.

Bob

[Steve A]

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

[bobbrown]

To progress this to a conclusion I need to know how many people would be interested
I have the spring spec to convert a Vauxhall valve at 3/what ever to 3/15 so I can get the springs made
Spring rate 4.58 N/mm
33mm long
14.1 od
10.9 id
16 gauge wire diameter
7 coils ground ends

I have a wholesale supplier that may be willing to sell his stock all be it limited of Vauxhall valves so that may give us 50 or so
I can get the end that allows the valve to be fitted in the fixed pipe work made to eliminate the problem with stripped threads
Cost at a calculated guess about £35.00 each for a complete replacement unit.

Bob

[DeeAitch]

To progress this to a conclusion I need to know how many people would be interested
I have the spring spec to convert a Vauxhall valve at 3/what ever to 3/15 so I can get the springs made
Spring rate 4.58 N/mm
33mm long
14.1 od
10.9 id
16 gauge wire diameter
7 coils ground ends

I have a wholesale supplier that may be willing to sell his stock all be it limited of Vauxhall valves so that may give us 50 or so
I can get the end that allows the valve to be fitted in the fixed pipe work made to eliminate the problem with stripped threads
Cost at a calculated guess about £35.00 each for a complete replacement unit.

Bob

Count me in for a pair

[Specky]

Two sets please Bob (4 in toto)

do I get my old one back or the 20% discount we never discussed....

I'll get me coat....


TTFN

[John_W]

Bob,
I'm in for a pair, please.
Also happy to buy more for long term storage if needed to get the numbers up.
John

[Dico]

A pair for me please Bob.

[Specky]

A list me thinks:-

1. DeeAitch
2. Specky
3. Specky
4. John_W
5. Dico

[scottswatches]

1. DeeAitch
2. Specky
3. Specky
4. John_W
5. Dico
6. Scottswatches (1 pair)

[BFG in the BRG]

Oh Oh another list

1. DeeAitch
2. Specky
3. Specky
4. John_W
5. Dico
6. Scottswatches (1 pair)
7. BFG in the BRG (1 pair please)

[RayD]

Have you all got the 3/15 valves fitted?

I thought if you were going to change them you’d go for the later 2/15 ones and do away with the pressure control valves.

I have the D100J6025F 2/15 valves fitted on a 1992 SE as in Pic 1 (215)

Ray

[bobbrown]

RayD,
There is not a solution with in the Vauxhall range for a 2/15 valve or at least I have not managed to find one and I do not think they are available from Lotus but could be wrong.
If you have upgraded fronts then the 3/15 valves are a better option as they restore some of the braking to the rear and they are what Lotus fitted in the first place.
If you have upgraded front brakes it is worth noting that you are going to lock the fronts with a lower line pressure and probably long before any shut off valves come into play.
Not being privy to the reasons why they were changed and there are a number of reasons, cost, supply and of course a change to the brake characteristics. As they did not force the change with a recall or alike, only when the 3/15 valves were faulty I do not see there being any problem fitting 3/15 valves.
Any one know when the change was implemented?

proportioning valves relationship1.jpg

1. DeeAitch
2. Specky
3. Specky
4. John_W
5. Dico
6. Scottswatches (1 pair)
7. BFG in the BRG (1 pair please)

[Monty]

I`m sure mine are the same as Rays and don`t have the seperate limiting valve and mine is on a 1990

[saska]

Think I'd prefer to go with a 2/15 solution even if it meant trying to rebuild the current bias valves.
Whilst having a new component is v. desirable, Lotus recommended replacing the 2 types of 3/15 installations with the single 2/15 valve. I'd have 2 pairs of new 2/15's in a NY Minute.
Were I doing Normas then I could well see doing a 3/15 since the Norma is 51lbs lighter (mostly at the front) than an SE but I'm doing an SE & S2 so would much prefer 2/15.
Effectively the difference between 2/15 & 3/15 is 10% when brake pressure is above 15 bar (which is anything more than mild braking) -- 80% front/20% rear vs 70% front/30% rear.
Lotus must have had evidence for recommending 2/15.

Since BobB has already provided the O-Ring dimensions, I'd really appreciate it if someone could measure the sealing washer shown in the picture below:

brake_bias_valve.gif

[bobbrown]

I'm dropping this and not doing any more work on it.

[saska]

I'm dropping this and not doing any more work on it.

Not quite sure if this is due to my comments but anyway; my reading of the Service Notes is as follows:
All of the 3/15 systems either had an additional limiting valve or an additional proportioning valve to deal with heavy braking conditions.
1. Pressure limiting valve at 70 bar upstream of the 3/15 valve.
2. Pressure limiting valve at 65 bar upstream of the 3/15 valve.
3. Pressure proportioning valve (70:1) upstream of the 3/15 valve. Reduces any increases above 70 bar by 70:1.
Replacing any of these dual valve systems should be done with a single 2/15 according to Lotus.
For info: 70 bar = 1015 psi and is v. hard/emergency/clenched buttock braking territory imo.

[RayD]

Tony,

I don’t think there’s anything wrong with your comments.

Bob,

I understand what you're saying about the extra capacity that could be applied to the rears once the fronts have been upgraded ... It is also mentioned here.

I assumed the reason for the change to 2/15’s was they were having the rears lock up with the original system. The logic behind the assumption ... PV’s are to stop the “problem” of the rears locking ... in the manual it says if you're have a “problem”

The balance may be nearer and more desirable with 3/15’s for all we know.

It may be a good idea to collect more information on MOT or any other brake test figures, for cars with the various upgrades and the various valves.

If 3/15's are being fitted on a car with 2/15's and no PCV's it might be best to try it on one car before going into mass production.

Ray