Nose Dive When Braking

[FoMoCoBronCo]

1971 Bronco mostly stock- 302 bored 30 over; upgraded to C4, power steering, GM front disc conversion and Chevy astrovan hydroboost

This is the Front Disc Brake Conversion Kit I used: https://www.cjponyparts.com/front-disc-brake-conversion-kit-bronco/p/DBF48/
This is the Master Cylinder w/ adj. prop valve I used: https://www.cjponyparts.com/cj-clas...black-with-proportioning-valve-kit/p/BMC107B/
Hydroboost unit was a junkyard part and the bracket I used was off ebay.

I left the back brakes as drums, but I did replace everything with new parts and had a brake shop adjust the adjuster mechanism to get the pads in the right spot.

I left my original H-block plumbed in line, but not before I thoroughly cleaned the whole thing, removed the plunger & cleaned it. I even used the special tool to keep the shuttle centered while bleeding
https://www.musclecarresearch.com/brake-valve-tool?v=53

After installation and bleeding of the system, it works great. Only problem is that I get pretty extreme nose diving when braking. I tried with the prop valve backed all the way off, then slowly increased the pressure to the back brakes until the prop valve was bottomed out.

When I turn my headlights on, my brake warning light stays illuminated, when they're off, it goes out. (This may be an unrelated wiring issue lol)

I'm wondering if this is normal, if i need to add a metering valve or something else, or if there's something wrong with the way my system is set up. Any help is greatly appreciated. Thanks!

 

[Wild horse 75]

How old is your suspension? Your brakes sound like they’re working fine. My guess would be old shocks or weak springs.

 

[FoMoCoBronCo]

How old is your suspension? Your brakes sound like they’re working fine. My guess would be old shocks or weak springs.

Front shocks and springs are both brand new- they're not fancy (auto store aftermarkets)
Rear shocks are new; leaf springs are original

no lift

 

[ba123]

Sounds like maybe fronts working and rears are not.

Kinda like an endo on a bike when you just use your front brakes and make your back wheel come off the ground.

Maybe jack it up and make sure the rears are actually working? Although very different with driving force. Have a parking brake? maybe try applying the parking brake to the rear wheels and press the brake pedal at the same time to see if it still does it?

 

[Apogee]

Weight transfer under braking is going to be defined by several variables, not the least of which will be the wheelbase, center of gravity, spring/damping rates, suspension geometry, front/rear brake bias, etc. It's normal to get some dive under braking due to weight transfer, but without knowing the severity of what you're experiencing, it's a bit tough to say whether what you're seeing is normal or not. FWIW, my dive increased noticeably when I upgraded to CAGE long arms and softer front springs, but I also raised the CoG at the same time with a body lift, so I'm sure it was a combination of everything contributing to the increase.

The fact that your brake warning light is coming on may or may not be significant, so I'd slap a brake pressure gauge on it front and rear an see where things fell before I started to make any assumptions. If you don't have a high-pressure brake gauge, you could instead install the brake bleeding tool into the H-block and take it for a test drive so that you can say with confidence that the shuttle valve is staying put. I don't know off hand if the EB H-block blocks flow to the low-pressure side or not (some styles do, but my EB is a '77, so I've never messed with one), but someone else here might...you were digging around inside the block, so what did you see?

 

[73azbronco]

I remember the good old days you worried if it didnt nose down during braking...