355 Teves hydraulic brake delay valve leak

I also tried to unscrew the halves but couldn't. Seems that they have some very strong threadlocker but someone has actually managed to separate them (Jaguar XJS):

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This is as far as you can go and you still cannot remove any of the internals. The left part appears to be just a cover, and an adapter down to M10, after the right part has been (permanently) assembled in the factory.

Jaguar calls this part sometimes "Delay Valve" and sometimes "Pressure Reducing Valve". Someone on a Jag forum described it as "These have a rising rate so under light braking the rear curcuit would recieve about 95% of total system pressure for good feel and balance in everyday driving situations. But as pressure rises the rate of reduction increases." I don't know if this statement is correct, there is nothing in any of the Jag or Teves MK2 manuals that I have. Jaguar diagram:

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So, it appears that this valve is delay with some proportioning (pressure reducing). The level of proportioning of the valve is not high (just 6 Bar less on the rears compared to fronts) but this is sufficient for Jaguars as the "main" proportioning on them is achieved with much smaller rear brake pistons and pads. But in the case of the Ferraris, with the rear brakes being the same size as the fronts, more proportioning is needed and this is why, I think, Ferrari added another proportioning valve to bias rears further down (an adaptation of the available Teves system at the time to the Ferrari brake caliper concept).

I did some further testing on my Jag valve. Using a very small compressor (max about 4 bar), I blew air through it. I found that, when blowing in the direction of the arrow, I can easily hold the pressure with my finger on the outlet port so it seems that there is some pressure regulation action in the valve. When blowing in the opposite direction, there is no pressure regulation (hard to keep the pressure with my finger). Also, when I blew in the opposite direction leaving the other side open, I could hear something like "flip-flop" in the valve as I was opening and closing the air from the compressor.

I guess this means my spare valve is good.

 

I spent some time looking for the full info as to what exactly each of the two brake valves does but just found out that it is all int he 348 and 355 manuals. In summary, this is what they do:

1. "Delay Valve" (the hexagonal thing) - It provides a simple fixed step-down to the pressure going to the rear brakes of 8.5 Bar according to the Ferrari manuals and 6 Bar according to the Jaguar manual. I guess the correct reduction is 8.5 Bar because it is stamped on the valve. This step-down remains at 8.5 Bar irrespective of what pressure arrives at it so it is not any front-rear proportioning valve. It is part of the Teves system and it is there just to prevent the rear brakes starting to engage before the fronts.

2. "Valve Corrector" (the cylindrical thing) - This is the proportioning valve. Up to 25 Bar on the 348 (marked 5!25) and up to 20 Bar on the 355 (marked 5!20), there is no proportioning; once these pressures are exceeded, the valve will progressively reduce the pressure to the rear brakes to about 50% of the pressure going to the front brakes.

Sources of the valves:

"Delay Valve": Jaguar but only used are available; it is the same on 348 and 355 and, as long as the Jaguar valve has "8.5" stamped on it it is identical to what is in the Ferraris.

"Valve Corrector" (Proportioning Valve or Pressure Regulator):

For the 348 (p/n 136313) - BMW E30, p/n 34-33-1-152-494, stamped 5!25, same as what is on the 348 valve. Identical to the valve in the 348, plenty about at some USD 60-70.

For the 355 (p/n 157908) - I have not found any identical valve used on other cars. The nearest available are either the 348 valve (same proportioning rate but slightly later start of proportioning, 25 Bar instead of 20) or a Porsche 928/944 valve (~USD 300) which is 5!18; same proportioning rate as the 355 one but starts the proportioning at 18 Bar instead of 20 (small difference, not really an issue). However, its inlet port is a male M10 (it is female M10 on the Ferraris) so it would have to be mated to the Delay Valve with an adaptor.

 

BMW version stamped 5!25, I assume the threads are the same.

 

I just bought this one - https://www.ebay.com/itm/For-BMW-E30-318i-325e-325i-325iX-325is-ABS-Pressure-Regulator-Ate-34331152494/112421712508. Having had a number of BMW-s, including two E30-s, I know that practically all brake piping threads are M10 x 1.0 so it should be same as the Ferrari one.

 

I saw that, I read the recent negative reviews and just bit the bullet and bought form Turner. At least I bought with confidence, had one too many issues with unknown suppliers myself i'm sure it works out for others often.

 

I got a used 348 Pressure regulator and a new M3 one. The Ferrari one has a spring check valve on the exit side you can depress with a thin hex key. The BMW has none and the exit port is just a fine pin hole. Blowing in them they are also very different. While the pressure marking is the same the function may be different. If you look close at the one on the left (bmw) you can see the pin size hole as a black dot. The Ferrari one has a large hole with a spring check ball in it.

Miroljub, did you observe the same thing?

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I do not have a spare 348 proportioning valve but I received a new BMW 5!25 one a few days ago. It has number 164G7 stamped on the side opposite to where the "Ate" stamp is. It also has a pin hole at the exit port, in an internal brass piece.

I believe that the function of the BMW valve is the same although it appears to have somewhat different internals (perhaps a new Ate design/construction).

The pictures below show a disassembled Porsche 964 prop valve. In this design (appears same as the BMW one except it is 5!45), the spring loaded "semi-ball" is plastic and it is at the other side of the brass piece having the pin hole (you can see the white plastic piece looking in the inlet port). It can be depressed with a thin wire inserted through the pin hole at the exit port but I wouldn't try it in order not to scratch the plastic half-ball.

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Blowing into the Ferrari and BMW Pressure regulators is VERY different especially the back pressure. I wonder if its worth trying the BMW of the same pressure.

 

Here is the 348 one, quick hit with Impact and it came apart, it appears its identical.
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And here is the BMW

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The solution, open them both, grab the brass nozzle from the 348 and put it in the cap of the BMW regulator. The exit port of the brass nozzles are different, (see #32) that's the only difference and they remove easily and are set in with an o-ring. You now have a brand new Pressure regulator. Cost new Ferrari $3200. Used about $100. But who knows if its worn. A completely shiny newly created OEM one $75. New springs, O-rings, seals etc.


What is very interesting is the Pressure regulator can is not tightened down, if you do it will crush and hide the O-ring. To tighten it to the extent that the O-ring appears the same as it does before disassembly, its really only finger tight. It must be thread locked but taking it apart I did not notice any thread lock on the threads.


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Miroljub let me know if you notice the same thing regarding reassembly.

 

I will not disassemble my new BMW valve but I intend to, in a few months, remove the delay and prop valves from my 348 and check them. I will then compare (using a compressor) the operation of the 348 prop valve with the BMW one. I don't believe there is any functional difference between the BMW and 348 prop valves. They are both marked 5!25, meaning start proportioning at 25 Bar input pressure and limit the pressure to the rears at 50% of the fronts.

As for the steel ball you mentioned earlier that can be easily pressed in, I believe you referred to the steel ball in the Delay Valve (I can see one in my spare Jag Delay Valve) and not in the Proportioning Valve.

It seems that the sealing of he brake fluid in the prop valve is not by the threads but by the internal seals. In the case of internal seal failure, the fluid will probably start coming out pass the threads. The external o-ring is obviously not there to seal the valve housing but, I believe, just to prevent any leaking fluid from spraying around and possibly to also protect the threads from water/corrosion.

I can see that Eurospares offer the prop valve (in stock) at GBP 50. Could be the same BMW valve.

 

Some findings about a possible alternative for the Delay Valve (p/n 134597, £1,686.57, $x,xxx.xx, but not available).

A similar function valve ("Mopar") was used on Camaros and a number of other models of the late 60's and early 70's. It is called "Hold-Off Valve" and it was installed into the brake pipe going to the rear brakes on cars that had disc-disc setup. According to my findings, the function of the valve was:

"This valve was used to hold off pressure to the rear brakes so the front brakes would go on a split second before."

"Hold-Off, per Mopar terminology, set-point or "Cut-In", is 117 psi for std & tk, and 165 psi for PoPo/Taxi apps."

117 psi is equal to 8.1 Bar so it seems that its function is much like the Ate "8.5" (8.5 Bar "Cut-In") - delaying the "bite" of the rear brakes for a brief moment, i.e. until the input pressure reaches 8.1 Bar.

The Mopar valve comes in three versions but they are all probably same functionally:

1968-72 A-, B-, & E-body 1968-70 AMC AMX & Javelin, Disc Brakes, Rear Hold-Off Valve, PR104B
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1967-69 GM F-body, 1968-69 Chevrolet Nova Hold-Off Valve, PR104E
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67-68-69-70-Mopar-Charger-GTX-Roadrunner-B-body-Disc-Brake-Hold-Off-Valve, INL30106
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Obviously, they would need adapters to the Ferrari M10 x 1.0 fittings to "simulate" what the Ate 8.5 has. I have not found any adapters from 7/16-24 to M10 x 1.0 but adapters from 7/16-24 to 3/8-24 and from 3/8-24 to M10 x 1.0 are easily available. I have bought the valve shown on the second picture above (both ports are 7/16-24) so I will use two adapters at each valve port: 7/16-24 to 3/8-24 and then 3/8-24 to M10 x 1.0. Once I receive the adapters, I will rig-up the Mopar valve and, using a compressor, try to establish whether it "behaves" like the Ate 8.5. The spare Jag Ate 8.5 was holding the pressure of 5 Bar in the direction of brake fluid flow (since the valve opens at 8.5 Bar) and not holding in the opposite direction (brake release). I couldn't test it for opening at 8.5 bar as my mini compressor can't go that high.

 

FYI They use on of these valves on the GM A bodies as well when they have the optional disc brakes (I don't know the specs though). Way back in the day before I understood the function of this part it was impossible to bleed the rear brakes on my '69 GTO with the Mighty Vac method. Had to resort to time tested ask the girl friend to pump the pedal.

 

Same in the case of 348/355 - you cannot bleed the rear brakes with a pressure or vacuum bleeder. Furthermore, in addition to having your girlfriend pumping, you need to keep the ABS pump active.

 

Key powered on, not started, cant bleed rears without abs on the front you can, its not a function of that valve I believe its a function of the ABS pump or so I understand it. I always thought you could use pressure bleeder if the ABS pump is on. Maybe not.

 

On the Teves system the rears are controlled by the high pressure circuit. Accumulator must be charged and bake pedal depressed, not pumped, to bleed rears.

 

As Jonk said, the only way to apply pressure towards the rear brakes is to have the pump active and to press the brake pedal (I agree, not necessary to pump) sufficiently to open the mechanical valve in the MC that controls how much pressure from the pump/accumulator is applied to the rear brakes. Also, sufficient fluid pressure needs to be applied to overcome the 8.5 Bar opening point of the Delay Valve. Pressure or vacuum bleeders are simply unable to open the 8.5 Bar valve

 

I finally decided to use and adapt this delay ("Hold-Off") valve by Inline Tube:
67-68-69-70-Mopar-Charger-GTX-Roadrunner-B-body-Disc-Brake-Hold-Off-Valve, INL30106
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This is because it is for disc-disc brake systems and because I also found info that "it holds off the rear brakes for a split second" and that its opening pressure is ~ 8 bar. If this is all correct, it means that its function is very similar to that of the original 8.5 delay valve.

I got the necessary adapters and made it into an assembly that is just about the same as long as the original valve. Had to use two adapters at the inlet side as I could not find an adapter from 7/16-24 male to M10 x 1 female (and two adapters are actually better as they bring the overall length of the valve to what is needed). Below it is my spare Jag valve (capped / sealed with o-rings after I dried it for a couple of hours in the oven):
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The ports are staggered a bit but I don't think that would be a problem. Here's the pic of the hold-off valve attached to a new BMW proportioning valve:

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For the time being, I will keep the new assembly as spare. Once I decide to have a look at my existing delay & proportioning valves, I will put it in if I find the existing valves not to be in very good condition.

 

Crack in the flare of the break line?

 

No, still just keeping it for spare.