HairyHarry

I just did a rear disc brake conversion on my 1993 Del Sol S yesterday and unfortunately, the brake pedal no longer works. When the car is off, the pedal is "stiff" but I can push it to the floor, and when the car is on, the pedal has very little pressure unless I slam on it (but still sinks if I hold it down). I had no issues with my brake components before the swap. I also bled all for corners in the PR > DR > PF > DF pattern until no bubbles were present, where I jacked up the rear when I bled the rear brakes raising it higher than the front and vice versa. Also, I've noticed that when I start the car, the initial idle is much higher than usual at 2000 rpm versus like 1400.

Should I re-bleed in a different sequence (maybe with the car on)? Or is this a compatibility problem? Like is the stock brake booster/master cylinder combo not enough for these rear disc brakes? The Del Sol S has the 2525 proportioning valve by the way - not too sure if this matters. I don't know what car these discs brakes originated from because the donor Del Sol that I picked them from is also an S model (meaning they were swapped onto it too). The donor Del Sol also has a much bigger than stock brake booster and master cylinder (brake lines are bent to fit) but with the 2525 prop. valve, and the brakes worked when I drove it.

Anyone know whats going on? Thanks. (I'm off to work so I may not respond for a couple of hours.)

muellersfan

Re-bleed in proper wheel order.

HairyHarry

Do you know what the proper sequence is for a USDM left-hand drive honda?

HairyHarry

So I've just read that you are NOT supposed to push the brake pedal all the way to the floor while bleeding the brakes because that could ruin the master cylinder. Can anyone confirm this?

tony_2018

link source.

mk378

That is sort of a wives' tale, but you have noted that the pedal sinks after you make a stop and hold the brakes on with steady pressure. That would mean either an internal leak in the master cylinder or an external leak somewhere. Air in the lines is different, the pedal will go all the way down on the initial press and the car won't stop very well.

HairyHarry

In regards to not pushing the pedal to the floor while bleeding? This tutorial mentions it: https://honda-tech.com/how-tos/a/hon...-system-374619

I've also seen a few forum posts too.

HairyHarry

Actually, the car was not driven at all. All of the issues/testing occurred in my garage. The brake pedal would go to the floor while the car was off -- it felt like there was some pressure but obviously not enough. When I started the car, the pedal had almost no pressure at all unless I slammed it with my foot, but would quickly revert back to no pressure sinking to the floor.

muellersfan

Proper bleed sequence of wheels is RR, FL, RL, and FR.

tony_2018

If you have debri in there yes it can damage the bmc. Do you have debri in your reservoir?

HairyHarry

Anyways, before I forget to update this thread, I did manage to solve the issue. All it took was re-bleeding the whole car again .

What I did was:
>Jack up all four corners so that the car was level in the air.
>Put a block of wood under the brake pedal to keep my assistant from pressing it to the floor.
>Bleed the brakes in the PR>DF>DR>PF sequence, making sure the master cylinder never went dry.
>Open the bleeder valve, tell assistant to press, close bleeder valve, tell assistant to let go -- doing this until there were no more bubbles.
>Did the Passenger Rear corner again just for the hell of it.
>Ta-Da, the pedal is now stiff as hell while the car is off and normal while on.

It turns out there was a ton of air still left in the lines going to the rear brakes. After getting it all out, the brakes now work like they should, and thank God the master cylinder didn't crap out. I guess compatibility isn't much of an issue because the disc brakes feel noticeably better/quicker than the drums, even though I'm using the stock 2525 prop. valve, booster, and MC. They might brake better if I upgrade the prop. valve, etc. but for right now they work just fine (and look good too), which is all I care about at the moment.

HairyHarry

Yes I found that out. Thank you.

HairyHarry

I think the master cylinder is fine now that I got the brakes working. It's only a year old so it shouldn't be too dirty.