I like the 4 lug look and in the past have put 320i calipers on a 914. I recently put Volvo 240 calipers on my current 914 but…..I can’t get a firm pedal. This is what I have done so far to get rid of the air.
1. Opened the bleed valves while the wife pressed on the brake pedal. Closed the bleed valves before the wife released the pedal. I have used this technique for years…with success. Very effective.
2. Attached low positive air pressure to the cap on the brake reservoir and then opened up the bleed valves until no more air. Very effective.
3. Opened up bleed valves and used gravity to pull out the air. Didn’t get much air.
4. Opened up the bleed valves and while the valves are open, gently pushed up and down on the brake pedal. An auto mechanic said he used this as a last resort. Not much air.
5. Tapped the calipers with a rubber mallet and then tried all of the above.

Whatever I do now, I just get fluid. No air coming out but I know there is some in the system.

The Volvo calipers have three bleed valves per calipers and I made sure one of the bleed valves was at the top.

Interestingly, I get a firm pedal when I have low positive pressure being applied to the cap on top of the brake reservoir.

I thought the master cylinder might be bad but when I put the original calipers back on, and after 5 minutes of bleeding, my brakes are back to normal and firm.

I have everything except wheels for the five lug conversion but don’t want to admit these brakes have kicked my ass. Any thoughts? Help!

Are the calipers newly rebuilt? New seals have a tendency to pull the pistons back into the caliper until they wear in a bit.

From PMB's FAQ section:

"I've replaced my calipers with your new units and now I have a very soft pedal. Is there something wrong with my calipers?

Generally, no. This phenomenon is well known and actually explained in the factory manual.

The bore seal is responsible for pulling the piston back into the bore. The seal journal is slightly tapered which allows the seal to rock back and forth. New seals will act more aggressively than old seals. Your new seals are pulling your pistons back into their bore further than they had before. Even a few "thousands" of an inch can cause excess pedal travel. The standard venting clearance should be around 0.004" which is basically the thickness of a business card.

There are two procedures you can do to help bring your pedal back up:

1. Get a "decent" pedal by bleeding all of the air out of the system. We have a great article here on how to bleed your system http://www.pmbperformance.com/gravity-bleed.html. 914 guys and gals may want to try a pressure bleeder and an assistant method. Once you get a decent pedal, bed your pads. Even old pads can be re-bedded allowing them to work much better than before. We have a great article on "Bedding" here. Once you're done with the bedding process, you should have a much higher pedal. We always like to recommend doing a final bleed on the brakes prior to hitting the track. A good road workout can help dislodge air bubbles trapped in your system.

2. Remove the current pads from your calipers. Using an old brake pad backing plate or a piece of 1/4" plywood etc. Hyper-extend the pistons in the pad cavity and then push them back into place. This act can help lubricate the new bore seals and prevent the pull from the new seals.

Over time, your seals will continue to break in and your pedal will be firm as before."

IIRC, you have to let the air out all three bleeders. Also, the calipers should be oriented so one of the bleeders is at towards the top. I'll post a picture to explain in a couple of minutes...

I am not familiar with the Volvo calipers, but I have Wilwoods on one of my cars with two bleed valves on top. Each one bleeds half of the caliper body on that corresponding side.

If you just bleed one there is no way to get a hard pedal as you are bleeding only halve of the caliper. The other side will have air in it.

Probably be necessary to flip the caliper around to get the two bleed valve end up.

OK, diagram from page 500-1 of the Bentley manual for Volvo 240:

Click to view attachment

As you can see, there are two feed lines for each front caliper; upper line feeds the upper chamber, and top bleeder lets the air out of the upper chamber. Lower line feeds the lower chamber, and the remaining two bleeder screws let the air out of the lower chamber. Both feed lines need to be attached, and all three bleeders have to bled in order to get a solid pedal.

This diagram applies to all of the Volvo 240 Girling non-ABS brake calipers. Almost positive that the the ABS calipers have only a single feed line and a single bleeder on the front calipers.

Hope this helps!

Steve A-

Thought maybe I should send you this too... Not sure why, but Volvo has a specific brake bleeding sequence for their cars:

Click to view attachment

Probably due to the nature of their dual circuit system--may not be required for your set-up (depending on how you're running your lines), but thought it might come in handy.

I just did a new set of these a few weeks back on a P 1800
Girling dual circuit front calipers.
I used a power bleeder suction tool, hooks up to an air compressor.
Assuming you have a new dual circuit master cylinder, bench bled.
Use the proper volvo order above to get in close range using the tool .
Pump by foot for final bleed.

Top bleeder is one circuit
Inner and outer bleeders are the other circuit

Rich

Are these Volvo calipers dual opposing pistons or quad opposing pistons?

2 or 4 pistons?

A google search brings up both.


I've seen quad opposing pistons in many, many applications (almost every Toyota truck and most late model Porsches) but this is the first time I've seen dual circuits for the pistons in a single caliper.

Splitting the rear proportioning for each individual front circuit is very strange.

This makes a dual circuit master cylinder not "front and rear".
GM tried this on the X-cars (Citation).
That's where the "X" comes from, design of brake hydraulics.

I wonder if GM came up with this design due to Volvo doing it early than them.
I don't think anyone is using an X-pattern brake hydraulic system now.


Do your Volvo calipers have 2 feed entrances into each caliper?

If so, adding these to a 914 brake circuit will require significant routing changes to the stock hydraulic system which I would not attempt.
Minimum they will require a T to feed both circuits in the front caliper off a single line and the swept volume for the front pistons might be greater than the stock master can supply.
Rear system proportioning might be challenging as well.

I'd be very careful adding these to a 914 hydraulic system.
Personally, I don't think the dual circuit Volvo calipers will work properly in the 914.

Single feed calipers should work (bleed fine) but may have too much piston area for our small masters. This might feel like what the OP is experiencing.

Volvo did strange things with the provisioning on their cars in the early days.
They still are some of the most expensive parts available.
Blower motors are over 1K and fail quite often. Volvo customers ALWAYS think you're overcharging them for work on the cars.

I'd be fine without working on another one, ever...

Porsche parts are expensive, but modern Volvo parts are Ferrari/Lamborghini expensive.

Don't get brake fluid on you. It goes into your body fine but never comes out and is cumulative...

Bad idea...way too much piston surface area. The only reason you get a decent pedal with pressure on the reservior is because that low pressure has already moved the pistons hard up against the pads/rotor.

For reference (looking at only one side of the caliper)

Stock 914 front calipers with 42mm pistons = 2.14 sq. inches
911/BMW 320 caliper w/ 48mm pistons = 2.80sq inches
Volvo calipers w/ 38mm pistons = 3.51 sq. inches

Now multiply that by 0.010" or so and that's how much fluid volume you need to move between apply and release. You can do the same math with your master cylinder and determine exactly how much more calculated pedal travel you'll need, and compare with what you're experiencing to prove the case.

Those volvo calipers will require MUCH more fluid volume than either the stock or BMW 320 calipers....without about a 27mm master cylinder, you're not gonna get a reasonable pedal. Way too much caliper for the 914.

Front calipers with that much piston area will drastically reduce the effectiveness of the stock rears, because the fronts will lock long before the rears. This will actually reduce overall breaking performance compared to a properly functioning stock system. The rear calipers should also be upgraded appropriately, as well as the master cylinder in this case.

Agree with Pat and Zoom above, i didn’t see what MC you are using? Still the stock 17mm? Even a 19 may be a bit small for the 8 pistons up front, are the rears stock? On my -4 track car I have a 19mm MC feeding A calipers up front and M calipers in the rear, feel and modulation is great. I have 4 piston front and rears on my -6 and my 930 that use a 21mm MC.

Volvo used them since the 70s.

Personally I think its a great design, mainly focused on safety.
the first circuit is connected to both front and rear (similar to a 914)
The second circuit is stand alone in the event that you have a brake line failure between the front and rear.

Its like having two sets of brakes.
I found them challenging to bleed until I pretended it was two different operations...bleed circuit one, then bleed circuit two.

the do STOP the car...quite well.
They also appear to be bolt on for a 914 (same era, but I did not measure the bolt pattern or backspacing etc.
the rotors on the Volvo were also vented, unlike the 914.

if I was racing, I would certainly consider these to help eliminate heat issues for sure.

Rich

What I'm seeing from the diagram presented is one circuit is feeding either the top or the bottom of BOTH ft calipers and one rear caliper and vis-versus.

A failure on one circuit leaves you with 3 semi-functional calipers (fronts have 1/2 normal force in single side failure) which is far, far better than just the rears functional. It is not better than just the fronts working IMO.

This is why they show 2 (or 2 sides) on the prop valve.

To make that work properly you would need all elements of that brake set up including the dual lines from 6-way T to the front calipers and the dual prop valve.

As others have shown the caliper swept area is BIG TIME different and absolutely requires a larger master which makes the small piston rears even more unbalanced in the equation.

For me this level of brake manipulation is better left for much lighter calipers.

I will be going the Boxster route on my wild 914 and using the BMW caliper upgrade on the narrow 75 I'm building. As I'm using a 19mm master on this I'm hoping the balance will not be bad.

Can one of you numbers wizards check my math?
BMW Vs. 914 caliper +33% volume
19mm vs 17mm master +25% volume.

Versus a stock 17mm 914 the 19mm master and BMW caliper should have slightly longer travel and take slightly less pedal effort. This change should be minor at the pedal.
As the swept area of the BMW pad is 20%+ percent larger it should take less force at the pedal to stop the car versus the stock equipment.
I know an increase in pad area doesn't directly equal an increase in stopping power but it should be worth something IMO.

Is this change large enough to warrant adjusting the prop valve?

I will be using PorterField R4S pads all 4 corners and stock 914 rear calipers/rotors.

not sure what size the master is on a Volvo, but it did not look much larger visually...but it has two chambers of fluid, yet connected.

Quick google says the stock master for a volvo is 22MM.
The reservoir could easily be mounted up in the 914 location...and the master appears to be a similar physical size as the 914.

Nice part is that because this was used for so many years by Volvo, and because of the massive hobbiest volvo people out there...the parts are readily available, and will be for many more years.

I did read a very logical argument in a racing application to use two different and physically linked masters, but I think the 914 has no spare room for a descent solution like that underneath.

Rich

The first part of your statement is correct. Increase in swept area doesn’t equal more stopping power.

The two parameters that matter most to stopping distance are:

Effective radius (distance between hub center line and the center of pressure - assumed to be the center line of the caliper piston - for sake of discussion). This is largely a fixed number determined by part geometry and where the caliper mounts with respect to the rotor.

Coefficient of friction of the pad material and how much it changes (up or down) as a function of pad temperature. This is what you can most readily tune and control.

So, what you are saying is increasing the friction footprint by 20% makes no change at all?
This upgrade doesn't change the moment arm (distance from rotor center) at all, just the pads are longer in this case.

If so, this only gain from this set up should be longevity and it's not worth doing over the same pads (manufacture and pad compound) in the stock calipers?

But, in that case it should not affect F/R brake balance at all.

From a pure theoretical standpoint, footprint (area) of the pad doesn’t come into play

From physics: friction force = normal force (applied perpendicular to the pad) * coefficient of friction

Notice there is no term for area in that equation.

It is counter intuitive, but if you increase the area, the applied pressure gets distributed over a larger area and each portion of the friction material sees proportionally less pressure than it did with the smaller pad and therefore the larger pad generates the same friction force.

But what about tires you say - surely you agree larger tires create more grip?

Well the same equation applies for tires. However, as we have all learned about tires, there are microscopic interactions between the rubber of the tire and the asphalt that sort of “interlock” the rubber to the asphalt creating more grip than theoretical physics and the basic friction equations would dictate.

So let’s acknowledge that the friction equation has its flaws for viscoelastic materials like rubber and asphalt.

Organic brake friction material like Porterfield does tend to transfer to the rotor and we do get some shearing grip between the rotor and the pad SORT of like a tire but it’s only a very small fraction of what rubber does because the pad isn’t a viscoelastic material.

Now about the effective radius - generally speaking, when caliper piston size increases, that influences the effective radius. Sometimes negatively.

A larger piston usually means a thicker caliper bridge to resist the larger bending forces generated by the larger pistons. In order to keep it all fitting inside the wheel, the caliper piston has to move closer to the hub. This decreases effective radius. But, it gets offset slightly by increased pad pressure (assuming line pressure stayed the same and that you didn’t run out of master cylinder travel).

Brake “upgrades” get messy and complicated fast as witnessed by this thread.

In order to maintain proper front to rear brake balance it is best to increase both the front and rear calipers in the same proportion. And then of course, it may be come necessary to increase master cylinder displacement proportionally to insure that you don’t run out of pedal travel and can maintain equivalent brake line pressure.

You can't just look at the master diameter, you need to look at pedal ratio, stroke length, power assist, etc...

Regardless, I can't think of a single reason you'd need a caliper that big on a 914 using the stock solid rotor...

I assumed the rotors would be vented and someone is looking to improve braking.
I have not done a ton of track time in a 914 so I have no data on if/when the solid rotors on a 914 start to fail due to heat issues.

Seems like the Volvo brakes with the right vented rotor may help solve this issue.

An incredible outpouring of support. Ranging from “can’t do it”, “don’t do it “, “do it”. All responses considered. All good. I have had many, many sports cars over my years and belonged to many, many forums. This is the best.