Upgraded brake problem (1 Viewer)

[deangeloni]

I always felt there is no reason to go fast if you can't stop, so I've invested a lot of time on my brakes. I couldn't stand the fj40 drum brakes, so I found an 62 axle and stole the front disk brakes, and got a rear conversion kit with the Monte Carlo disk setup. I also have a 350 SBC with a Saginaw pump driving a hydroboost brake assist, then into the steering gear box. The master cylinder is also brand new. The MC and hydroboost are from a Chevy 2005 2500HD. I've sat in my driveway watching a movie while turned my wheels back and forth at least 75 times in order to remove air from the steering pump system and not a hint of air bubbles. I've gravity and vacuum all my brake lines.

It just doesn't seem to stop like all the investment should do.

Any ideas?

 

[Pighead]

What is the inner diameter of the brake master?

 

[Jonathan Hanson]

If the pedal is firm and the system bled properly and the front/rear balance is good, it's possible your expectations are misplaced. My 1973 40 with Wilwood front discs and Monte Carlo rears doesn't stop any shorter than it did with drums—at least for the first few stops. The advantage of discs is in fade resistance and rapid water displacement, not (necessarily) shorter stopping distances.

 

[kudzugypsy]

Chevy hydroboost ...man that would throw you against the windshield in my old astro work van..I had to warn everyone who drove it

 

[deangeloni]

What is the inner diameter of the brake master?

 

[1911]

What is the inner diameter of the brake master?

This. The pedal length and travel and the master cylinder bore diameter (and I suppose the brake line diameter) must all be compatible and work together to get the right pressure and feel for the brakes. I have no idea what the specs are on the cheby stuff your using, but I bet it's different than what Toyota used.

 

[deangeloni]

If the pedal is firm and the system bled properly and the front/rear balance is good, it's possible your expectations are misplaced. My 1973 40 with Wilwood front discs and Monte Carlo rears doesn't stop any shorter than it did with drums—at least for the first few stops. The advantage of discs is in fade resistance and rapid water displacement, not (necessarily) shorter stopping distances.

That would stink. I would think the hydroboost benefit would account for something. I have the rear valve wide open for now, just to see if the rear would lock up.. nope it doesn't.

 

[deangeloni]

Chevy hydroboost ...man that would throw you against the windshield in my old astro work van..I had to warn everyone who drove it

LOL... That's what I was going for.

 

[1911]

View attachment 2315701

There you go - the best (in my experience) MC for a 40 is the non-ABS FZJ80 MC, which has a bore of 1". That cheby MC has a bore of almost 1.5" That is your problem right there.

 

[deangeloni]

This. The pedal length and travel and the master cylinder bore diameter (and I suppose the brake line diameter) must all be compatible and work together to get the right pressure and feel for the brakes. I have no idea what the specs are on the cheby stuff your using, but I bet it's different than what Toyota used.

I did make the assumption that pressure is pressures and if it was good enough for a 1/2 ton truck, then it would be able to push 62 series pistons and monte Carlo piston just fine . But, you know what they say about assumptions. I could be totally wrong on this one.

 

[deangeloni]

There you go - the best (in my experience) MC for a 40 is the non-ABS FZJ80 MC, which has a bore of 1". That cheby MC has a bore of almost 1.5" That is your problem right there.

Thanks for the direction. Let me pull it and verify..

 

[Pighead]

This.

TY 1911.
I've been driving around on 4 wheel discs for years now, but still using the old 4 wheel drum master (I rebuilt it, it still worked, so why not?).
Recently swapped in an 80 series master (smaller ID I "think"). Brakes seem much better to my SOP assessment.
So, yes, MC internal diameter and stroke length should be matched to brakes for best results.

 

[deangeloni]

Thanks for the direction. Let me pull it and verify..

Yep.. I wanted to make sure. Pulled and it is a 1.5.. I'm trying to make sense of it.. I bigger bore means more fluid transfer and wouldn't that mean better braking, or do I have it backwards. I thought with a bigger bore you need the hydro assist to push it arround but overall better braking. I just want to understand before I redo a lot of money and work. To be clear, your suggesting ditch the hydro and go with a standard vacuum and Toyota MC.

 

[deangeloni]

Yep.. I wanted to make sure. Pulled and it is a 1.5.. I'm trying to make sense of it.. I bigger bore means more fluid transfer and wouldn't that mean better braking, or do I have it backwards. I thought with a bigger bore you need the hydro assist to push it arround but overall better braking. I just want to understand before I redo a lot of money and work. To be clear, your suggesting ditch the hydro and go with a standard vacuum and Toyota MC.

I did some reading and your right... I'm going to take some measurements and see what I can do. Thanks everyone for all the input.

 

[Pighead]

As I sorta understand it...smaller ID moves less fluid but generates a higher pressure.

 

[deangeloni]

As I sorta understand it...smaller ID moves less fluid but generates a higher pressure.

As I read, your correct. Smaller diameter means higher pressure and quicker response. Sometimes touchy brakes... Larger diameter means less pressure, and more leg is involved.. I'm not sure if that's my problem. Even when I stand on the brakes, I get the hydro feedback, but still doesn't stop.. I'm going to have to meditate on this, drink a shiner Bock.... Im going to take a bunch of measurements and see if I can gain mechanical advantages, before I start swapping things.

 

[1911]

Larger bore moves more fluid, but takes much more pedal/foot pressure to push it. You will find that the chevy PU truck has a much longer brake pedal for more leverage.

If for some reason you wanted more responsive/touchy brakes, you could go with an MC bore diameter less than 1", but 1" works well in Land Cruisers with a vacuum booster.

 

[deangeloni]

Bad hydroboost out of the box... Put the old one back on and was night and day difference... I got a new one because it would get hard to steer into corners while braking at the same time.. a sacrifice in sharing steering and braking on the same pump. I read a bad hydroboost can do that, but after comparing the two, the old boost gets up to pressure in a second and pushes your foot up, while the new one just sat there.. thanks for all the help... I probably should have gone with a smaller bore.. that's good advice.

 

[deangeloni]

Update... Never underestimate the importance of tight pulleys. I thought the belt on the power steering pump was tight enough, but I was wrong. It's a pain when your by yourself, but I tightened the belt pretty tight and cured everything. It now locks up all four pretty easy.. it takes a little force, but I like that. I don't like driving trucks with touchy brakes and no anti-lock systems.. I like knowing when I need it, its there.. my FJ62 locked up on me one time when I braked hard and it wasn't a great feeling sliding out of control... Lesson learned, always tighten everything... again, thanks for all the help.