Rear brakes (MOT fail)

The ACL is the luxembourgish (national) automobile club. Some years ago, they started to offer MOT for young- and oldtimers. This year was a first for me to try this service out. Unfortunately, my car failed the brakes test due to a rotten rear wheel cylinder. When I disassembled it, I found a completely blocked cylinder at the rear left. I made my shopping list:
rear wheel cylinder - Hitec H27270 (19mm)
rear brake shoes - TRW GS6125 (38x203mm)
shoe fitting kit (springs) - Hitec H7514

The cylinder is measured inwards and not at the stub protruding, the shoes measurements are simply measured width per length of the brake pad glued to its carrier. The next post will be about the reassembly.
Cheers.

Brake circuit design (without math)

Warning! Don’t touch your brakes unless you know what you are doing. As with other safety relevant components in your car (steering, suspension a.s.o.) your life depends on it. What I describe in the following is about my car. You may find information suitable for your application, but I can in no way be made responsible for anything happening to you,  your car or anybody (anything included) getting in your way as you drive, brake or trying to.

Components list
Front:  HiSpec 4 piston aluminium brake calipers, M16 bolt pattern, ventilated discs 245x20mm
Rear: standard Ford 9” drums
Pedalbox: highly modified OBP
MC’s: Girling type (see text for diameters)
Fluid reservoirs: Aluminium with level sensor
Fluid: ATE DOT4
Tubing: Cunifer
Flaring-tools: K-tools

My car had hanging pedals from stock. I went to floor mounted pedals during the rebuild and redesigned most of the braking system. Although you could do this with mathematics, starting from caliper diameters over pedal ratios and needed volume, I had some of the components already in place and had to adapt everything around. Anyway, the brake pedal now operates two separate master cylinders for the front and rear brakes, I stayed with the cable operated clutch. The pedalbox has been purchased from rallynuts.com

                                                

This particular model has a square recess where a chassis rail is present in most kitcars. Thus, it can easily be adapted. Although it is intended to be floor-mount, I welded brackets on to the chassis for a secure fixing. The kit comprises a bias bar, brake fluid reservoirs, hoses and two master cylinders (MC):
- diameter 0.700 intended for rear brake circuit
- diameter 0.625 intended for front brake circuit

As my particular set-up showed, those values are not applicable for me. Both MC’s are too spongy for the front circuit and pedal travel therefore is too long. The pedal even hits the bulkhead. The smaller MC is all too big for the rear circuit which results in a very hard pedal. Further on, I will check whether I will insert a pressure relieve valve to accommodate with the rear brakes.

Assembly  
For some reason, and I can only guess it is because of safety matters, manufacturers and resellers of brake components don’t give a lot of information about the assembly and set-up of their products. Maybe they prefer professionals to do those installations to prevent us amateurs fiddling around. On the other hand, the more good information I have, the better and safer my modifications will be.

The first problem I encountered was how to assemble the bias bar. It is not obvious, at least not for me, how to do it, unless somebody tells you. The clevis is mounted first, and then the master cylinder’s pushrod is bolt on. This rod can rotate, if you have enough space, you can rotate the whole MC to bolt it to the clevis (prior to plumbing). If you mount the clevis to the MC’s pushrod prior to fit it to the bias bar, it is impossible to mount them both. As soon as you screw in the second clevis, the first one is screwed out. Sounds funny? It is!

Above diagram shows how to align everything to start, further settings will show alterations.

After that, you have to be familiar with the function of that bias bar. I found a very good explanation in a UK forum http://www.locostbuilders.co.uk/viewthread.php?tid=171423 . Hopefully this thread will be reachable with above URL forever.

This diagram explains how it works, but … you must know that while pushing the brake pedal, you start braking on one MC, which then becomes the pivot point together with the big internal olive of the bias bar. Only then force is applied to the second MC and the braking process goes on. Now you can set up the system to suit your driving or legal regulation i.e. the front brakes should lock before the rears. In above you can see that the front MC pushrod is not as deeply bolt into the clevis as the rear MC.

Design
The front brakes need more fluid for operation since the brake pistons are of a larger diameter. This means that the front MC needs more travel for a given MC diameter. There are some possibilities to achieve this:
- set the bias bar askew as of start of pedal movement (see above 'no pedal effort'-position)
- shorten one of the pushrods (not recommended)
- put a spacer under one of the MC’s to put it away from the bias bar (see below)

To start the design for my car, I had the following set-up with the new pedalbox:

The approximate pedal travel of 124mm must suffice to activate the front brake until block and even leave some place before hitting the bulkhead, which leads to problem number 1:
- the 0.625 MC intended for front brakes needs too much travel and the pedal hits the bulkhead
- the 0.700 MC intended for rear brakes used up front for trial wasn’t big enough either

 
Solutions
- order a 0.750 MC and try (order placed March 5, 2013, arrived March 12,2013)
- alter the pedal ratio or bring it nearer to the driver, both need major mechanical alterations (will do if no success with above solution)

Possibilities to reduce distance between pedal and bias bar / MC and bias bar:
 - Put in washer when mounting MC
 - Shorten pushrod
 - Screw pushrod further into clevis
 - Manufacture specific clevis

Further design is only feasible once problem no.1 (pedal hitting the bulkhead) has been solved.

Some TEE (trial and error engineering) to follow...
2013 03 18  

Yesterday, we put in the 0.750 for the front brake circuit and the 0.625 for the rear. The pivot is set completely to the left side (front brake). Problem no.1 is solved, the pedal not hitting the bulkhead anymore. After bleeding both circuits, it is not obvious that braking is ok because pedal travel is reduced by the whole setup and I don’t know if the front brakes get activated enough for a full stop or block.
Next thing to do: try to further reduce pushrod length off the rear MC (bolt it further into clevis). I have to design a little tool to grip the pin holding the protective sleeve and turn the pushrod. I will turn it into the clevis as far as possible without blocking the bias bar movement (tonight). Next option will be to recess the rear MC mounting. Pedal travel is around 100mm for now. With a ratio of 5:1, this gives 20mm piston travel (max is 25mm). 

I measured the piston travel from rest to fully applied and found 25mm (1” … ?).
2013 03 20  

Thoughts …
The pushrod of the rear MC was already bolt in at its max, no further setting possible.
Next weekend, I want to assemble the car for roll out and do some testing outside. Therefore I need to mount the scuttle and plumb the water circuit ready, fasten the suspension bolts once the car rests on its wheels, and maybe some other smaller jobs.
2013 03 23  

Short roll out with 0.750 front and 0.625 rear, I can block the front wheels but haven’t seen if the rears block first, second or if they block at all. Next time I will have Max or Pit (or both) to watch the wheels. Ideally, it is possible to do the fine setting. Pedal feel is quite ok and I look forward to the final setup. 
2013 09 20 (engine rebuild in between)  

Pedal feel is quite hard for full stop, but ok for normal operation.
Car passed MoT (SNCT-Sandweiler). Note that for some technical controls (depending on countries), the bias bar has to be blocked and dash mounted knobs permitting bias adjust on the fly are prohibited.
In conclusion
Although my approach was far from being scientific, I managed to design the brake circuit to operate the already existing braking gear. Selection of MC’s was by trial and error (and some swearing), but one should be able to resell what isn’t needed or keep it for other projects. At the time of construction, universal Girling style MC’s cost around 25.-£. Click labels at the end of this post to see more about braking on this blog.

Cheers.

New front bearings

When assembling the new wheel hub and bearing, I wasn't happy with the amount of grease they had put in the factory. So off again for some good greasing! While I'm at it, I folded the retaining brackets to secure the disc bolts (pics show before and after, look near the bolt heads).

Taking of the hub gives a different view of the speed sensor and further explains how it can count the disc bolts. But after all those nice pictures, you have to get dirty and reach for the big grease pot.

The crown nut is used to set the bearing. Not too tight because the heat will expand the bearing and it can seize. The securing pin is folded to both sides.

Use brake cleaner to clean all the parts from excessive grease or other gunk. And now have a look at that grease cap. No new grease cap supplied so I had to use the old one. Well, it had a life before and you can see it!

Cheers.

As the book says

Front MC with clevis, than bias bar and second clevis.

 

Rear MC bolted onto clevis.

Parts arrived and I decided to assemble everything as the book says for the second try. That means the 0.625 master cylinder up front and the 0.700 for the rear brakes. The bias bar is set in the middle and everything has yet to be adjusted. Next step is bleeding to chase the air, probably early Saturday morning.
Cheers.

Brake circuit - design start

Not as easy as expected. Bolt on the pedal box, bleed the brakes and off we go? Naaaah ... Some more parts ordered at rallynuts.com.
List:
A bigger master cylinder sized 0.750". I expect the pedal not hitting the bulkhead after fitting it.
A new bias bar. I modified the first one for a rigid setup. That was an error! It doesn't work.
A bias valve. If the rear circuit still gets too much pressure, I can set it to lower figures.

I have to admit, when changing the hanging pedals to a floor mounted pedalbox with bias bar and two separate master cylinders, I hadn't learned enough about the brake system to properly design it. Now that I have learned how things work, I want to do it right. I also started to write a complete design report to be published once the circuit completed and ... working!
Cheers.

Brakes - more work to come

After fitting the brake master cylinders and bleeding the air, it appears that the rear MC is way too hard and the front a little bit too soft. With diameters of 0.625 at the front and 0.7 at the rear, the values are quite common but apparently don't suit my set-up. I will have to look for information and calculate the whole thing before ordering one (or two) other MC's.

Bleeding the old-fashioned way ... still what I prefer. Old school.
Cheers.

Have a brake

Brake system is ready to be filled!

Both seats fixed but attachments for the shoulder straps are too near to the headrests. Some more mod!

My (patient) wife "caught" me straighten up the tools ... never enough tools. I need more tools!

Cheers.

Fix to flex

And here the finished connection from the fixed brake line to the flexible line. This is the driver's side (LHD), some more bending has to be done around the steering column.
Cheers.

Flexible

Finally some work done in the new workshop. New flexible brake line shown here with full steering lock, still some excess length to evitate stress on the unions.

Where the unions will meet inside the engine compartment, shown here is the old female union.

 

My first (selfmade) double-flare to connect the fixed line with the flexible line, new union is M10x1.
Cheers.

Rear brake pipe

The original brake line going to the rear drums was a little bit too short, so it had to be redone. After a few hours of bending, from underneath and above the car, adding the connectors ... here we go.

Alongside the gearbox and then it disappears around the clutch, connected to the brake master cylinder. Brake pipe bending is not my forte and some of the bends have to be revisited.

Quite a frustrating result after three and a half hours of labour ... I had to mount those posh brake fluid reservoirs to make me happy again.
Cheers.

Pedalcar

The clutch cable routing shows that the cable is quite long. Connecting it to the pedal is not complicated and there is enough remaining cable for adjustment. I wanted to keep the clutch cable operated and not add a piston and convert to hydraulic.

The pedals mounted with the throttle operation finished, the clutch pedal to be adjusted and the brake pedal to be modified. I decided to alter the original adjustment system for ease of use. With all three pedals in place, it is possible to choose a spot for the footrest destined for the clutch-foot. Not much room left, but I really want to try fitting one for comfort during long journeys.
Cheers.

Brake pipe flaring

To achieve a perfect sealing of brake pipes, the ends have to be flared. Different standards are used and therefore, the aforementioned kit offers the possibility to manufacture different flares. First step is to cut the pipe to the desired length.

Even a well done cut should be deburred to avoid chips entering the pipe and block the fluid.

Then choose the right inserts by comparing with the pipe you want to reproduce. In this case, the pipe is 4.75mm and the flare is DIN.

The tool is assembled with everything needed to compress the copper/nickel pipe at it's end(s).

Pipe from the left stuck in the matrix, hydraulic screw with chosen punch, handle to turn, above grip to hold the tool by hand. There exist other flaring tools to be placed in a vice, this one has the advantage to be taken to the car. First try:

On the left compared to the old flare, on the right a different flare (double bubble) for trial.

Although this is no rocket science, I really have to warn everybody not owning the right skills or tools to let this work be done by professionals. I'm doing it on my own for the love of tools and the feeling to have achieved something by myself. If you're not sure, leave it to a specialized workshop.

Cheers.

The LOFI principle

... or, why you have to put first into the chassis what you last took out. Clear? LOFI stands for: last out first in. Some of the brake lines mount easier with the engine out, so after a little attention with Scotchbrite, the first part of the brake system went in (T and RH brake line).

 

Where possible, I will re-use the old brake lines. For those not fitting in the new installation or in bad shape, I will replace them with new ones. To do this, you need a flaring tool kit and some special spanners (flare nut crowfoot wrench), new brake line and... keep those old lines, they are precious templates.

 

Mounting the pedalbox took me almost all the Saturday afternoon. The accelerator pedal mechanism is now ready to receive the clevis linking the bowden cable to the throttle.

 

This meant grinding and drilling to assure the clevis to move freely when activating the throttle pedal... which I hope doing a lot !!! After the mod I repainted the machined end with chassis paint.

Cheers.

Remote brake fluid reservoir

What? Well, that's the name. If the brake master cylinder has the reservoir not fitted directly to it's body, you are free to place and fix it where you want. When ordering the OBP pedalbox, I wasn't aware how big (and ugly) those reservoirs could be. Holding them in my hands, it was clear to me that I will never mount them into my car. Then a long surfing search began and I found above reservoirs in the U.S. of A. Order placed and curious to see how long it will take them to arrive here and what taxes they will add to the announced price. I added the plastic fantastic reservoir to compare. No poll needed.
Cheers.