Brake M/C bore size question (1 Viewer)

[tdskip]

Good mornin, hope it’s been a good week so far and everyone is healthy and staying safe.

When I build my ‘68 rig I did a 4 wheel disc brake at up with a Lexus SUV brake M/C and a Mini truck booster. It worked well and had plenty of stopping power but was over boosted. The Lexus M/C failed after all of 1,000 miles and needs to be replaced so now would be the time to make any changes to address pedal effort.

I know there are oodles of options on how to do this but was curious if the brain trust here has any recommendations on difference MC options for less boost but still using the existing booster.

Thanks!

 

[tdskip]

Update - current M/C is a Lexus LX one inch bore unit.

 

[bikersmurf]

I have the same m/c with a stock 80 booster. Changing booster would likely make it worse.

A smaller bore M/C would require more pedal movement to develop the same braking force. That said, from a hydraulics perspective it would require less force. Braking would be less on and off though.

I’m very happy with the level of boost but it is very boosted.

I ran a stock ‘77 booster (equivalent to 4Runner) and a stock 40 master, and the brakes were much less sensitive. I’d suggest that. Be sure to switch the rear residual valve to a 2lb disc one (or remove both).

 

[tdskip]

Thanks for the reply.

I installed a Wilwood proportion valve, thanks to the good ideas here, so the front / rear balance is OK.

Sounds like what I am experiencing is normal for the set up then?

 

[1911]

When I build my ‘68 rig I did a 4 wheel disc brake at up

Mine (1980) is converted to 4-wheel disc brakes. I used my stock master for years until it failed, and didn't know how much better it could be - until (after research here on Mud) I replaced it with a non-ABS FZJ80 master cylinder and a City Racer booster. Wow! It was a night and day difference for the better. I don't remember the bore diameter of the FZJ80 master cylinder, but that combination really works well.

 

[GRM]

Make sure to run a non-abs master. The ABS unit requires more back pressure when you pull your foot off the pedal. Without the abs module it will collapse the brake lines.

If yours feels over booster, grab a 7/8” bore unit from a ‘88 4Runner

 

[bikersmurf]

I’ve got four wheel disc brakes. Stock Toyota up front and Chevy Blazer/.75 ton/Suburban in the rear. It weighs 950 kg in the front and 1050 kg in the rear. Willwood proportioning valve to boot.

It had tons more braking power with less input pressure. I can now stop as quickly as I want with the pressure of my big toe. It’s not prone to locking up... but it’ll lock all four wheels with a stab of two fingers on dry pavement at 30 mph.

 

[tdskip]

Thanks for the discussion and feedback.

Will try the slightly smaller bore.

 

[offrd63]

What size tires are ya running? I would change the booster to a single diaphragm booster from a Hilux/ 1st gen. 4runner. The 7/8 bore didn't work well with my 4 wheel disc set up and 37" tires. With my 1" bore MC, and the Hilux booster.
I still wouldnt mind if they hit a little faster/harder.
If you don't have one of these you should get one. I had mine adjusted by eye for years and when I finally got the booster tool my brakes went from OK to really good