Spongy brake pedal, ABS?

Thank you for your prompt response, Joe.

I followed the recommended sequence, but as the vehicle was an Australian-release Honda MDX, I had to start from the front right. I selected the US equivalent Acura MDX as the option was not available while feeding the vehicle details.

I conducted the test you suggested and found that the pedal was very firm at the first 1/4th travel (with the engine off) and it did not go all the way to the floor even with full force. I also tested the pedal's firmness before connecting the lines to the MC during installation, plugging the out ports and pumping the brakes. The pedal remained very firm even when the engine was on.

My question is whether it is safe to assume that there is no internal leakage in the MC after it has been successfully bench-bled (bled until no air bubbles were visible).

So far, didn't get the ABS error light.

Hi Joe,

I used the Foxcom NT630 Plus scanner to automatically bleed the ABS system. After that, I bled all four wheels again. However, the issue still persists.

I am wondering if the brake booster is faulty. Normally, a damaged diaphragm would cause the brake pedal to become very hard, but in my case, it feels spongy. Can the diaphragm be damaged in a way that causes the pedal to go all the way to the floor?

If I disconnect the vacuum hose from the brake booster while the engine is running, the brake pedal becomes hard to push.

I am eager to receive your response.

Regards

Hi Joe,

Thank you for your suggestion. Unfortunately, I have not been able to find a new master cylinder for my model, which has the part number 46110S3VA11. I have searched everywhere but to no avail. I was able to locate a used one, but I am experiencing the same issue with the brake pedal traveling to the floor. When I bench-bled the second-hand part, I did not notice any leaks, but I suspect that I may have damaged the plunger rubber seals while doing so. Is it possible that pressing the plunger all the way down, causing it to travel through the unused area, may have caused damage to the seals? If this is the case, I am willing to wait until I can find a replacement.

Thank you for sending me the picture. My part number is 46110s3va11, while the Acura MDX part number is 46100s3va11. I noticed that the reservoir in the Acura MDX is sitting on the master cylinder, while in the Honda MDX, it is connected with hoses. In the Honda MDX, there are two plastic connectors on the rubber grommets that connect the hoses. Both MCs have the same outlet size, which is 14x1.5mm. However, I am unsure if all other specifications match. If they do match and the hose connectors can be attached to the rubber grommets, I would be interested in purchasing the Acura MDX master cylinder. The Honda MC appears difficult to dissemble and I couldn't find the bore diameter. I understand that the bore diameter in Acura MDX is 1.06"

I have attached images of my current master cylinder for reference. I would appreciate any information you can provide on this matter.

Hi Joe,

That is the correct part, but it's quite expensive, costing around AUD 641.00 including postage, while the Acura one is around AUD 100. I was able to dismantle the master cylinder of the Honda MDX and found that the bore diameter is 1.06", which is the same as that of the Acura MDX master cylinder. The plastic connectors were also detachable. I need to confirm the following three things about the Acura:

1) The outer diameter of the cylindrical portion that enters the booster is 43mm or less.
2) The distance between the center of the mounting holes is 89mm.
3) The distance between the center of the outlets is 67mm.

I am currently seeking the specifications of the Acura MDX MC. I will update you once everything is confirmed.

Regards

Sorry, Joe, I forgot to mention that I live in Australia.

I have attached pictures with measurements marked for your review.

Hi Joe,

It has been a while since we last talked. You mentioned that you would like to visit Australia. Welcome to Australia. Here's some important information about the country. Australia is a diverse nation with people from different ethnic backgrounds, a majority of whom are not very religious. Unfortunately, over a third of the country is desert, and almost 90% of the population lives within 50 kilometers of the coast. In Australia, people drive on the left side of the road, and vehicles have right-side steering. The country doesn't manufacture cars due to the high costs involved, so most vehicles are imported from Japan, Korea, Europe, and the USA.

Australia is known for its beautiful beaches, rainforests, and captivating cities. The distance between major cities is around 1,000 kilometers. It's currently winter with daytime temperatures around 15 degrees Celsius and nighttime temperatures around 5 degrees Celsius. In spring and autumn, we experience very pleasant weather. If you need more information, please let me know. You also can find information about tourist destinations by exploring the country online.

Let me jump to the issue I'm having with my brakes. I found a secondhand master cylinder (MC) from the same model, which was involved in an accident with damage only to the back of the vehicle. Before removing the MC, I tested the brakes and they were working well with no spongy pedal travel.

I bench-bled the MC using only a vacuum pump without pushing the flange at all. After installing the MC in my MDX, I bled all the wheels, used a scanner to bleed the ABS, and then did the final bleeding for the wheels. I placed a 50mm thick timber block under the pedal to prevent it from travelling to the floor, during the bleeding and to make sure there were no full strikes at any time.

However, the result remains the same. The brakes work, but the pedal doesn't feel hard, and the timber block is still present.

Could the ABS have become faulty because the reservoir went dry earlier?

Thanks, Joe. I am eagerly anticipating Ken's response.