Bora hydraulics question

The low pressure warning light has started blinking on my 1972 Euro 4.7 Bora.
I performed the residual pressure test and am able to get the headlights to cycle through 8 complete times after shutting the engine down.
I was hoping it was just the sending unit so I picked up a replacement from MIE and swapped the old one out. No luck, the light is still blinking.
Any thoughts on what the next trouble shooting step should be.
Much thanks for any help.
~Tom~

 

Tom,

When where the brake accumulators rebuilt and the main accumulator replaced? If more than 10 years (or you do not know when it was done) then it is time.

Tip: write the date on the brake accumulator when they were rebuilt ... makes it easier next time around.

If the brake accumulators were recently rebuilt then I would start by replacing the main accumulator, perhaps the last one was siting a long time on the shelf.

Ivan

 

Hi Tom---

I think Ivan provides sound advise.
However, the fact that your headlights are still good for 8 full cycles, bothers me.
Remember that on a 1972 Factory Euro 4.7 Bora (like both our cars) the same low pressure warning light also functions as the hand brake warning light.
Take a look at the hand brake switch first.

Let us know!

B.

 

Thank you gentlemen for the replies.

Boralogist, I will check the hand brake switch this morning. I assumed, perhaps incorrectly, that the hand brake would give a solid red light and not the blinking one that I am getting.

Ivan, my thinking was similar to your advice in swapping out the accumulators, starting with the main one. When I pulled this car out of its "barn", about this time last year, I was told that all three accumulators were rebuilt sometime during its 8 year slumber. That definitely points to them as possible suspects.

 

Well it seems that Boralogist correctly identified the problem. The hand brake switch was faulty and is now repaired and all is quiet with the lights. I does seem odd that the hand brake warning and the low pressure warning would be the same blinking light but I guess they had their reasons for this set up.

Ivan.
I'm thinking that I will leave the accumulators alone for this driving season and deal with them next winter. Hopefully they will cooperate with this plan.

Thank you again for the help,
~Tom~

 

Tom,

I know you already did the headlight test but in my humble opinion that test is close to meaningless in an emergency. If your engine was to stop while going down a long hill having operational headlights will be the least of your concerns What you want to make sure is that the hydraulic system has enough reserve pressure to stop the car.

A more meaningful test is to bring the system to pressure. Stop the engine for 5 minutes. Pump the brakes, you should feel some pressure being released. Anything under 10 pumps is time to refresh the accumulators. You should be able to get 20+ brake pumps on a good system.

Ivan

 

Ivan,
I value your opinion and will perform this test immediately. I spoke with MIE regarding the accumulators and they have them in stock ready to go. Do they deteriorate over time without usage and should I inquire about the build date of their units?

 

They do deteriorate over time and I forgot to ask Stuart at MIE how long the accumulator I bought from them had been sitting. I recently replaced the main accumulator on my Bora since the system was not holding pressure overnight. Although the car passed the 10+ brake pump test I felt it could be better. The MIE accumulator made a significant improvement.

Ivan

 

Hi Tom, Ivan, Bob, et al.
Late to the "party", and I see you solved the problem, but I wanted to add this piece of experience in case someone comes searching for this topic in the future.

The same 'blinking' happened in my Bora and it turned out to be air in the brake caliper(s).

The 'low hydraulic pressure / brake failure' warning light would blink on for a split-second every time I applied the brakes. It made logical sense: For an instant the system had to pressurize the air before hydraulic brake action could occur. An inspection revealed some brake fluid weeping from the calipers. So it was easy to diagnose it. Bleeding was easy with a snug fitting surgical tube applied over the caliper's top nipple to catch the runoff - just keep the main green LHM reservoir topped off, and I found it was easier with the engine running so as not to deplete accumulator pressure whilst bleeding the air out.

Glad MIE has you covered for accumulators. As a side note, Dave Burnham Citroen out here in Delanson NY rebuilt all my accumulators for easy money. It's the rubber diaphragms that fail and need replacement, not the steel shells.

Cheers, may we all enjoy the driving season!
- Art

 

Art,

I never had the light come on even once in Nevada when the diaphragm in a brand new main tore and put nitrogen bubbles into the fluid making a creme de menthe like milkshake. But periodically I had to bleed all four corners because I would notice that the grabbiness increased and the calipers weren't all engaging simultaneously. So put that one on your annual to do list.

 

Thanks Bob,
It's interesting what kinds of things can happen to the high pressure LHM system. My air situation was accompanied by the same 'grabbiness' of the brakes. LOL, I've created my own 'Creme de Menthe' shake by bleeding the LHM too aggressively. Best to do it slowly.

What's definitely on my particular To Do List is a rebuild of the rear brake calipers so they stop weeping LHM.. and it ain't going to rebuild itself, so I'd best get going.

Happy Spring to all, - Art

 

weeping calipers is not cool. But the next time you see Dave ask him about the phenomena I described. All components were in tip top shape. I used to have a favorite road to take the Bora on about 25 minutes from my place in SF. I ran the piss out of the car in some spots with lots of braking. It was there that I could detect the uneven braking, not gawd awful like when there's a large amount of air or nitrogen from the accumulators in there. When braking for a curve at 110 mph on a two lane road you notice braking anomalies quite distinctly!

If I bled the calipers slightly it would go away but it did come back after a while.
I suspect Dave has an answer ...

 

I'm coming back to this thread,
My Bora has developed the need for its brakes to be bled annually. Very little sign of any loss of LHM, an d not much air - but for two years running the 'low pressure' light blinks on for the first split second of braking, after I bring it out of winter storage. I know, it's telling me "don't store me all winter!"

..upon bleeding, I find just a wee bit o' air in the LHM brake lines. This year the blink came on AFTER I had braked, so I bled them and it was clearly only the fronts that had some air bubbles.

Easy enough to bleed out, just thought I'd mention it here.

I reviewed it with Dave Burnham and I'm doing a 'wait n watch' approach. I noticed one single drop of LHM hanging from he HP accumulator, 4 years since rebuild.

I'll update again if anything more interesting develops.
- Art

 

My suspicion is nitrogen permeation of the rubber in the accumulators.

My car doesn't have the flow limitation device that some cars do so I can crack open a bleed screw and push a lot of fluid out into a jar. So that's what I did.

It's annoying isn't it. I don't remember if the warning light ever came on? I think I would have noticed that.

I once lost the main accumulator on a long road trip due to a torn membrane. I could still stop but the compression of the nitrogen made the brakes weird. I'm sure the light must have come on for that.

Are your accumulators relatively new or older recharged ones?

 

Thanks for the remarks, Bob.
Carter at DBCitroen rebuilt the accumulators about 4 years ago. Dave feels it's possible they're letting go. So I wiped it clean and will monitor the slow drip.


RELATED TOPIC: Hydraulic Brake Light Switch...while I have you here - another question:

Must one bleed LHM into the hydraulic brake light actuator switch in order for it to function? If so, before or after installing, and how? I notice there is a small allen screw on the top, near the contacts. Maybe this releases air out the top? I inspected the old "bad" switch and the function of this allen screw wasn't apparent.

I installed a new one, and it's not working. Dave and Carter aren't available to answer this question today.

BACKGROUND:
My LHM brake light switch failed. There is 12V power with ignition on to the hot side of the switch, but the circuit doesn't close upon operating the brakes. I installed a toggle switch temporarily, and hold it in my gear-shift-hand to flip on the brake lights when driving (the Bora had an important date I could not miss, hence the ungraceful temporary fix). The brake lights work in this mode, so the problem is isolated to the LHM pressure switch.

I received two spare switches from MIE.
Installed one of the replacements today.
No joy.

What gives? Do they need a bleed? Are they that unreliable right out of the box?

In the meantime, I'll drive the '65 Plymouth.

If there is no bleeding, I'll crossly fingers and install the second switch I ordered.
- Art

 

This is a strange problem. I've replaced several Bora and Khamsin brake switches and never did anything special such as bleeding them.

Although unlikely, the spare switch could also be bad. Loosen up the threads (so that the switch leaks) and put paper towel around the switch. Apply the brakes and see if you get pressure to the switch. I've never seen blockage to the switch but I guess anything is possible.

Ivan

 

Thank you for sharing your experience - and that's a good idea, thanks Ivan. It did dribble a decent amount of LHM when I made the switch from old to new.. But easy enough to try it again. (PS - Thinking of you yesterday; an acquaintance sent me a link that your argent Mistral Spyder is for sale....

Ciao, - Art

 

Answer to the hydraulic brake light switch problem: The new part failed right out of the box.

I put in the second one I had ordered as a spare, my son blipped the brake pedal to prove I had pressure, installed it - and it works just fine.

I'm sending the first new one back to MIE for an exchange, I still want a spare. I think I'll test it first though, when it arrives.

Ciao,
- Art

 

Glad to hear that you solved the problem. I should have also mentioned that the switch that activates the headlights is the same as the brake light switch therefore as a test you can swap them and see if the problem moves.

The Mistral spyder is going to the Bonhams auction at The Quail Lodge. Fingers crossed ....

Ivan

 

Gosh Art that's not fair. You're having all the luck and fun!

I've never had a problem like that. I would think that bleeding a large volume of LHM out of the braking system would flush out all the bubbles in spots like that though.

Glad you're fixed up now.

BTW, I didn't see the shift link bellows anywhere on MIE's website. I wonder what they're selling now and what it looks like.

 

Sorry to reactivate this old Bora thread and to use it for my Indy 4900 braking issue, but I thought it was not worth opening a new one to make my case as it seems closely related.

My Indy 4900 has basically the same LHM braking system than in the Bora or the Khamsin, except that the LHM hydraulics are not used more extensively for other systems such as seats, lamps, clutch or steering.

My car recently came back from a 2.5 year restoration process.
Unfortunately, braking is all but straight and smooth: actually, there are violent pulls on the right when pressing the braking pedal.
I also noticed that the large central red warning light for low pressure in the hydraulic circuit as well as the smaller one for the hand brake flashed from time to time when driving.

The LHM spheres were reconditioned (new membranes) as part of the restoration process but that was done 2.5 years ago, and the car was not used since then.
Just before passing its Technical Control test, a lack of braking balance between front and rear was diagnosed and corrected (rear brakes were not activated).

Do you think that the most likely cause of the current issue might be air bubbles in some of the callipers as described in this thread? That could be easily solved by bleeding.
Or could it be a more serious issue such as a failing membrane in the main accumulator or the spheres, or seizing pistons in the callipers?

Thanks for your help.
Serge

 

I would start with an extensive bleed and BTW since this is a brand new system recently filled I wouldn't toss out the bled LHM fluid. Catch it in pristine clean containers. But DO NOT put it back in the system WO letting it sit enclosed for at least a day because you may introduce bubbles.

If that doesn't seem to help then make sure your main accumulator, I assume that system has one?, isn't leaking. I had an incident on the road where the plastic button at the top of the main accumulator cracked, pierced the bladder and I had a foaming mess.

The lights are concerning. It sounds like your system cannot maintain adequate pressure. Is the pump cycling on and off all of the time?

I never had violent pulling on one side but I could detect uneven braking at times and a bleed always helped that out.

Your situation sounds much more serious. Are you confident in the condition of your calipers?

 

Thank you Bob,
Actually I don't know what is the overall condition of the whole system right now.
I intend to bring back the car to the mechanics who made the restoration for an exhaustive check-up of the braking system.
Bleeding is certainly the first step, hoping that it may allow recovering a sound system.
But as you suggest, all the critical components should be carefully inspected.

And yes, it has a main accumulator as seen on the diagram (part nr. 117) and picture below (the big black sphere above the green stuff):

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Hi Staatof,
Sorry, this is out of context, but previously in this thread, you mentioned a favorite drive to wring out your Bora, some 25 miles from San Francisco. I was born & raised there, but have since moved slightly South to Skyline Blvd, near Alice's Restaurant. I was wondering where you favorite drive is?

Many Thanks, RF.

 

Skyline Blvd ! I'd leave SF via a quick jump onto the 101 skyway in SF (no longer there! ) Then over to 280 and go south exiting @ 92 and going west till I hit 35 and run down that. Many, many times. I never got nailed. But I didn't do it on the weekends and always off hours. Other places were in Marin County or the Delta around Stockton via highway 4 which was very different way back then before the enormous build up. My good friend George Marin who died last year had it even better than I. They used to drive to Monterey and back for dinner from Berkeley and he went like hell. He had a Cord Sportsman in HS and then a Gullwing plus a whole lot of other cars over the years. The Bora was his last true exotic. He drove an AMG Mercedes until the day he died @ 84 from a stroke. California was a wonderful place to drive back then. It's a lot harder to do now. Now it's only about the scenery for the most part.