rear brake pressure valves.

[adster]

Why is there 2 pressure valves on each side? Can't find any information about this? One is the normal in Line type of valve and the other has a bleed nipple on it.

[Andy_J]

Original design had 2 valves on each side, it was later updated to the 1 valve per side

[adster]

So I can replace my 2 with just one valve?
Which one do I need?

[Andy_J]

yes you can change the 2 valve per side set up to the single valve per side from a later model. Only worth doing if you have a problem with your current valves

You will need the valves from either a late SE or an S2

[theelanman]

I have done mine.....the replacement part is from the Esprit.....
You will need the fitting kit too.....iirc it was about £200

[theelanman]

Part number
A082J4495F £96.78.......
You will need 2 of these

[theelanman]

you will also need the 'p' clip fitting
082W6579F £2.86
2 of these too

[adster]

Would these be faulty if the brakes are pulling to one side, to the left and quite often the left rear locks up?

[Fredjohn]

Would these be faulty if the brakes are pulling to one side, to the left and quite often the left rear locks up?

I guess it is possible, but as the rear brakes only contribute c30% of the total braking force, it is more likely that the brake calipers are guilty.

Check all 4 calipers (front and rear) and ensure they are sliding freely. If they are not and they are seized/stiff then that is likely to be the problem. This is a recognised issue and there used to be a repair kit from Halfords for the sliders. May still be available, if not someone on here will know where from.

With regard to the balancing valve system, check the article on WikiLEC : http://wikilec.9600.org/index.php/Brake ... %29_Valves
Check also the WSM on how to deal with the sliding calipers.

Good luck

Fredjohn

[dapinky]

I guess it is possible, but as the rear brakes only contribute c30% of the total braking force, it is more likely that the brake calipers are guilty.

Jon,

don't forget they only provide 30% because of the limiter valve...... if it is faulty, and more presure is going to the affected caliper than should, then it will cause that wheel to lock.

If the valves are removed/bypassed, then the rear calipers would lock virtually every time you brake a bit hard.

The sliders which used to be available from Halfords were for the front calipers, and haven't been in stock for a few years - but they are still availlable from Lotus spares places (like SJ's), ebay, Big Red and other caliper overhaul specialists (about a tenner a set).

Personally, I think that if there is an issue somewhere in the system, then a full overhaual of everything from the master cylinder backwards is probably a good idea.

[Fredjohn]

Thanks for clarification Dave!

Adster: hope all this helps!

[Brit-Car-Nut]

Rock Auto also has the rear sliders available but they are listed under the GM cars that used them. Look at Chevrolet Lumina or Buick Regal or Pontiac Grand Prix.

Also see RAYBESTOS Part # H5043 $6.14 in the US or ACDELCO Part # 18K204 $13.79 in the US. Those are 2 pin kits but there are some 4 pin kits available if you do some searching.

These appear to be the new design to solve seizing but are steel, not aluminum.

RA also lists this 4 pin kit: BENDIX Part # H99 R Caliper Bushing KIT - CALIPER SLIDER PIN BUSHING REPAIR KIT USED TO SERVICE FROZEN CALIPERS $10.27 for a complete set of 4 with seals and other parts.

Here is a picture:

sliders.jpg

I think I have a few of those kits from earlier purchases (before the closeout prices) if anyone is in need.

[adster]

Could I get away with removing the valves with the bleed nipples on leaving me with the 2 original inline valves? As I reckon it's the other valves at fault, just by looking at them they look awful, quite rusty etc.

[Andy_J]

Not advisable, I would strongly recomend against it

[Fredjohn]

Check the parts catalogue. Think you will ffind all 3 valves have different part nos. You cannot remove one valve from a 2 valve system to create a single valve system.

[RayD]

The explanation is in the workshop manual, I'd attach a copy of the page but my computer is down.


Ray

[Fredjohn]

Here are relevant pages from WSM.













Hope this helps.

[dapinky]

Firstly, let me start with a serious disclaimer - any information entered here is purely 'food for thought' NOT a recomendation to perform ANY changes to the brake system as fitted to YOUR car, and based purely on my (limited) knowledge of braking systems - I DO NOT PRETEND TO KNOW MORE THAN THE LOTUS ENGINEERS WHO DECIDED ON THE BRAKE SYSTEMS FITTED TO THE ELAN M100.....

If you still have 'standard' brakes, then I would suggest leaving the system as described in the Workshop Manual (or make the changes as detailed in the above pages).

However - if you have 'upgraded' the FRONT brakes, but left the rears as OE spec (with or without the seperate hub conversion), then there are issues to be considered, which COULD involve the changes you are looking at.

The brake system was designed to give adequate (not necessarily 'good') braking of a 'standard' elan under a variety of conditions - this covers a heavily loaded car, an empty car, braking firmly, braking gently, braking at high speed, braking at low speed, removing a couple of mph, and coming to a full stop.

As you can imagine, designing a system to cover all bases is not a simple exercise, and 'weight shift' has to be fitted into all of the calculations to give a system which will work 'adequately' under all situations - designing a system for a pure 'track car' is far easier!

Anyway, the OE system allows for a certain percentage 'weighting' to the front brakes (where most of the weight is whilst braking), and to maintain the same percentage for as much of the time as possible, under all circumstances (it can't be done 100% of the time, but that's physics for you!).

If you 'upgrade' the front brakes - and this could be as simple as fitting different brake pads, or as 'complex' as fitting different callipers/discs etc (all of which give slightly different results), then common logic dictates that in order to restore the 'correct' balance, the rear needs some work doing to it as well.

There have been numerous threads/discussions in the past about the best way to do it, with thoughts varying between "it'll be okay as it is for what I need", through "I fitted better pads", onto "different callipers/discs"....

....however, another school of thought says that the rear pads/callipers/discs are fine for what they need to do - it is purely the 'pressure' which they work at which needs amending.....

...and if we can raise the pressure at a uniform and controlled rate (linear to the original proportions) relative to the upgraded front brakes, then 'balance' will be ruturned to standard(ish).

Now, the whole point of the brake limiters is to allow the whole pressure generated by the master cylinder to reach all four wheels up to 15bar pressure, thus 100% of the brake force is used at 'low' speed/braking force (the car shouldn't have too much weight thrown forward at that point)...

...then to allow an increase in pressure at 20% (for a 2/15 proportioning valve) or 30% (for a 3/15 proportioning valve) for the rest of the braking force applied.

...The 'top' pressure allowed to the rear is 65 or 70 bar - dependant on the brake limiter valve fitted (IF one is fitted).

If you consider that ANY brake system is normally 'limited' to about 75bar (depending on how heavily you can hit the brake pedal!), the limiter *could* be considered to be unnecessary.


Under 95% - 99% of the time you use the brakes, you will NOT hit the maximum figure before the wheels can lock up (track use & total panic emergency braking possibly excluded!!!) - and (as a bit of a guesstimate) I wouldn't expect brake pressures to exceed 40bar in 'normal' conditions, and as such, the limiter doesn't enter the equation at all.... so, in effect, you are just using the proportioning valve to keep the balance correct. (and in the early systems, this was a 3/15 valve).

As I said earlier, if you have got better than OE front brakes, then it may well be beneficial to actually use the 3/15 proportioning valves, as that will linearly increase the braking to the rear wheels and help the oveall balance of the braking, and therefore reduce the total stopping distance achieved.

In summary, removing the limiting valve *may* not have an adverse effect, and *may* have a beneficial effect if you have upgraded the front ones.

If the proportioning valves are not working optimally, they *can* be rebuilt, but new ones are availlable (at a cost) in either 2/15 or 3/15 values from Lotus.

As an alternative, then Peugeot fitted a 3/15 valve to some of their models, as did VW, but I have not been able to fully research the options (yet). There may well be a USA replacement unit aswell, but I'm still looking! (bearing in mind that many/most USA cars will need an adaptation to the current pipework as they probably have a UNF fitting, not a metric one).

[Brit-Car-Nut]

Excellent Discussion!

The US (GM Cars) usually attach the limiter directly to the Brake Master Cylinder which is why so many of the Brake Master Cylinders have huge bottom holes compared to the Lotus one when people go looking for a more cost effective replacement.

I believe all cars in the US went to metric after 1995, so if an in-line limiter is located, it might have metric fittings, but they might be a different size anyway.

[dapinky]

The US (GM Cars) usually attach the limiter directly to the Brake Master Cylinder which is why so many of the Brake Master Cylinders have huge bottom holes compared to the Lotus one when people go looking for a more cost effective replacement.

From the reading I have done, the VW and many GM (Opel/Vauxhall) fit the proportioning valves directly to the master cylinder, but the actual part is the same as the ones on the Elan, except the Elan has an 'extra' metal part of the housing which converts the male thread which would fit to the M/C into the M10 female thread....

...without having the parts in front of me to compare, I couldn't say for certain if the 'end cap' from the Elan ones would convert the others....

....there is definately a difference between ones fitted to cars with or without ABS (some are fitted remote, others to the M/C, and the difference in the opening pressures (closing pressures?) is relative to the exact model fitted - disc size, and/or drum brakes on rear axle - this is the main reason the 'easy to find' ones from the Opel/Vauxhal range are no good, as they don't reduce the pressure until you get to 30bar.

I was looking at something like these Dorman units, but can't find the technical specs for operating pressures (also, I don't know if the US ones will be rated in bar or psi)