Notchback brake upgrade

[Variant]

Greetings all

Notch has now done about 500 miles since the brake upgrade so everything should be nicely seated to allow a proper brake test to be carried out.

Before moving on the the actual test I made some calculations regarding the smaller diameter pistons of the new EMPI calipers. The original ATE T3 caliper uses 42mm pistons while the EMPI - which is actually a copy of a Girling T1 caliper, uses 40mm pistons. 2mm less in diameter doesn't sound like much but it means 9.3% less force exerted onto the brake pads than the 42mm piston for the same force applied to the master cylinder. On paper this means that one would now have to push the brake pedal harder by a few kg's to generate the same force as the 42mm piston. It also means that the distribution of total force between the front & rear brakes changes by 2.8% toward the rear. As stated in an earlier post - I really can't feel any of this when driving the car - these brakes are a lot lighter and crisper than those on my Squareback which still has the original ATE calipers. Maybe its because the notch weighs less than the square...

On to the brake test. It was done at Safety Brake & Clutch in Randburg using a Bosch brake dynomometer. The machine expresses the braking effort in kg of each road wheel as a function of the incerease in torque on the motors driving the car's wheels as the brakes are applied. Maximum brake effort is achieved just prior to the brakes locking up and causing the wheels to slip on the rollers. Consequently the higher the weight on the axle being tested the higher the indicated maximum brake effort. In the case of a rear engine car where more weight is on the rear axle the rear brakes will therefore indicate a higher maximum brake effort than the front brakes. The opposite will occur when testing a front engine car. This simple test does not show whether the balance between the front and rear brakes is correct although this can be determined if a load cell is available to measure the actual force applied to the brake pedal. None of the brake shops I contacted have such a thing... Anyway, brake efficiency is calculated as the percentage of the total braking effort from all 4 wheels divided by the vehicle's test weight - which is the unladen weight plus that of the driver/technician doing the test.

Total brake effort in kg
----------------------------- x 100%
Vehicle test weight in kg

Figures for the notch are as follows:

645 kg
--------- x 100% = 63.24%
1020 kg

According to the technician who performed the test this figure is very good for a conventional non-assisted brake system and may even improve further as the pads/shoes bed in further. It also complies comfortably with UK MoT requirements.

[retrovan]

Well done
Always good to know that should you need to stop,.... you can...

[Variant]

A few posts back I mentioned having issues with EMPI discs. This has now been resolved and the following for info:

It appears that a certain batch of these discs were not machined and inspected properly so the hub is too small for the outer (small) wheel bearing and cracked as soon as the cone was tapped into position. This happened three times in succession!!!

IMG_0661.jpg

According to SKF the outer diameter of this bearing should be 39.878mm, plus/minus 0.009mm. For practical purposes I've accepted this as 39.88mm with a 0.01mm tolerance. I then measured a number of different bearings - Timkin, FAG, SKF as well as a few no-name-brands - and found them all within the above specification.

IMG_0797.jpg

Unfortunately I could not find any specifications for the hubs from VW or elsewhere but I did have two replacement discs, also from Brazil but bearing the VW logo, which measured 39.85mm - using an inside micrometer. The EMPI discs measured 39.64mm & 39.76mm respectively. The latter being a disc that didn't crack and the measurement was taken after the bearing cone had been removed - with considerable difficulty.

The discs were then sent to a prescision engineering works to have some material removed. This was done using acid instead of machining. The hubs now measure 39.82mm & 39.84mm respectively and the bearing cones located normally.

IMG_0786.jpg

This highlights the importance of carefully measuring all close tolerance parts before proceeding with any assembly.

[Variant]

After the Notch came to a few grinding halts today I removed both front wheels to inspect the brakes. Found the left outer pad completely worn away, left inner 2.5mm, right outer 5mm & right inner 3mm. Never seen disc pads wear this unevenly before. These are the original EMPI pads that came with the calipers and they have done only 9 600miles. Way back when I did the brake test, the left brake was working harder than the right brake and by the looks of things it is still the case. I've bled the brakes a few times in between and I am positive that there is no air in the system. Wonderin' what could cause this... Different friction materials on the pads, unequal size pistons... I've replaced both front brake hoses at the time of the conversion so it couldn't be that either. Blockage - kink in a hard line maybe?

I hate ATE brake pads BTW - they squeal like stuck pigs, but this was the only set I had handy.

[Variant]

It has been a while since I updated this project. The Notch has done approximately 24 000 miles since i did this brake system upgrade. I believe that is a fair distance to evaluate and report on the performance of the different components used. Lets start with the EMPI universal brake calipers: Basically, they're rubbish. The piston seals are not compatible with DOT 4 brake fluid. The latest EMPI catalogue even contains a warning that only DOT 3 brake fluid should be used in those calipers. That's not a solution as DOT 3 brake fluid is only required to have a wet boiling point of 140°C and it does not take long for brake fluid to absorb enough water for the boiling point to decrease to this value. Disc brakes are easily capable of reaching this temperature & causing the fluid to start boiling which leads to brake fade. I did experience this on one occasion while driving down the Vanryhn's Pass. Also, the piston seals swell when they react with DOT 4 brake fluid causing the pistons to become sticky which leads to unequal brake pad wear as well as frequent pulling to one side - even under light braking. The caliper pistons are 40.6mm in diameter. This is a very odd size which none of the brake shops I consulted were able to locate seals for, meaning that one is unable to replace the rubbish quality seal with something better. It appears that the EMPI universal brake caliper is designed to be used until once and then discarded. Not what I had in mind... So I bit the bullet and imported a set of 42mm ATE-type calipers from Custom & Speed Parts in Germany. They arrived last week. These calipers are beautifully made and are exact copies of the original ATE calipers that VW fitted in the factory. Just to be sure, I popped out one of the pistons and confirmed the piston diameter at 41.995mm.

The plan was always to convert to a dual circuit brake system by installing a tandem brake master cylinder but I delayed this part of the conversion for the sake of sorting out the caliper issues first. I had a rebuilt tandem MC and associated plumbing ready but while in the UK last year I sourced a brand new genuine ATE tandem master cylinder for the Type 3 from JustKampers. Cost me an arm and a leg but it is also a beautifully made piece of kit. And so I spent three days this week installing all the brand new components. The front brake lines were also replaced as the original ones were too short to reach the ports on the new MC. An extension had to be fitted to the rear brake line for the same reason.



Here the installation of the new dual circuit brake fluid reservoir and the feeder lines to the master cylinder can be seen. The 8mm lines were made from samples by Quick Hydraulics in Silverton. They also supplied the 4mm bundy tube for making up the new brake lines. The blue Viton hose came from Volkspares in Jetpark.





These two images show the installation of the new master cylinder and brake lines from the top as well as the bottom. Note the extension fitted to the rear brake line. This proved to be a bit of a challenge as the line was badly bent by some genius in the past and a piece broke off when I tried to straighten it. So I had to purchase a pipe flaring tool for putting a new nut & double flare on the line before fitting the new extension to the MC.



Here is the completed installation with new brake light harness installed as well.

It took some effort to bleed all the air out of the system and once this was done we conducted a careful road test on a quiet street. Obviously the brake pedal feels different than before and is still a bit springy as the new brake pads are still running in but the system appears to be working very nicely. Once the pads have settled themselves I'll do a proper brake test on a dynamometer and report the results.

[Tony Z]

Thanks for the update.
Question, your new MC, is it the same size as the old one? How different is the feel after going from 40 to 42mm pistons?

[Variant]

Thanks for the update.
Question, your new MC, is it the same size as the old one? How different is the feel after going from 40 to 42mm pistons?

Yes it is. The master cylinder is 19.05mm in diameter and the stroke for each piston is 15mm. The pedal feels slightly heavier than before as it is pushing two separate hydraulic circuits but is still easy to operate.

[calooker]

The shortcomings you have experienced with EMPI products is no coincidence, I have been down that road, and learnt the lesson. I will not use any mechanical Empi components ie: engine, brake or suspension, even if I get them for free.

[Piet]

Sorry for the hijack, but how would one do the calculations to know what size piston to use when replacing front drums with disks?

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[Variant]

Sorry for the hijack, but how would one do the calculations to know what size piston to use when replacing front drums with disks?

Sent from my GT-I9190 using Tapatalk

No hijack...

Theres no need to on the Type 3 as the nerds at Wolfsburg did that for us when they switched to disc brakes. The following specs for the Type 3 from 1966 onward:

Master cylinder diameter: 19.05mm (whether single or dual circuit brakes)
Caliper piston diameter: 42mm
Rear slave cylinder diameter 22.02mm

Hope this helps.

[retrovan]

....... to know what size piston to use when replacing front drums with disks?..........

The smaller the MC is and the bigger the slave cylinder is, the easier it is to push the brakes and you can get the car to stop fast with very little effort.

BUT

The combination above will need more pedal travel, to stop the car.

But as you change to Disk brakes, the slaves do not normally travel much distance, so it does not matter.

If you really want to calculate it, then you take the oil displacement of the MC on full stroke of the pedal, and that must divide into the 4 slaves, or vise-versa.

Herman

[Variant]

Now that the brake pads have run themselves in nicely and I've bled the hydraulics again to be sure all the air bubbles are out of the lines, I am very happy to report that the braking action is much more progressive than before when the pedal is pushed gently; but will stand the car on its nose, with the tyres protesting, when stomped upon. The pedal feels different because it is pushing two separate hydraulic systems now, but does not require significantly more effort to operate than before. I'll let it run for a bit longer and then do a proper brake test. Will be interesting to compare the data with the previous setup.

[Piet]

Retrovan you say "But as you change to Disk brakes, the slaves do not normally travel much distance, so it does not matter."

My problem is the "not much distance". Is there a formula that will tell me that with x amount of pressure (regardless of the size of the the piston) the drum breaks will expand by y and the disk will compress by z? Or is it all by trail and error?

[retrovan]

Your normal brake shoes move away from the drum by a good couple of mm when not used, the disk brake pad moves away less then a mm, so to move it forward is only a few cc and you have full brakes.

Yes you can measure it, this is called fluid dynamics and it is simply that when you move oil from a 20 mm dia. cylinder for 5 mm, into another cylinder, the result will be a cylinder of 40 mm will move approx. 2.5 mm at double the pressing force that was applied to the 1st cylinder.

So if you calculate the volume of oil in the MC, and divide it into the volume of the slave 's, you will get a ratio, if you now take the movement of the MC, and apply the ratio, you will get the movement of the slaves.

BUT. the force applied to the MC, will be equal to all the slaves, only calculated by their size differential.(ie 20mm MC & 20 mm slave = same force, 20 mm MC & 40 mm slave = double the force)

So the smaller the MC, the less force you need to apply, to move and create a higher force in the slave cylinder.

The other factor you need to remember is that normally the shoe brake has a double piston slave of approx. 22 mm, that means it has a total surface of 44mm, so if your disk brake only has a single piston acting on one side only of 40 mm, you are worse off and need more effort to stop.

These are approx, as there are other factors like losses, and expansions that take effect.

Herman

[Piet]

Your normal brake shoes move away from the drum by a good couple of mm when not used, the disk brake pad moves away less then a mm, so to move it forward is only a few cc and you have full brakes...

Herman

Thanks Herman for the knowledge shared. The way I understand is almost like using a long lever to move a rock. The longer the lever the longer the travel but the easier the effort. The confusion in my mind is the mixing of disk and drums. I guess it is best to go for a tried and tested solution.

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