Hydro-boost with Disk/Disk Prop Valve

[LS short box]

On my Mustang project I didn't have power steering so just one resivisor for the hydro boost. With the C5 discs it would put your nose up against the windshield until you got used to it.

[jeffahart]

Originally Posted by 67 twins

If I remember correctly(and I may not) GM trucks from the 80s had this before they,went to ABS

Ya, GM called it a "Height Sensing Proportioning Valve". I have one in my garage somewhere. Just one more contraption to battle with, never set it up. My axles and hydro-boost are off a CUCV. So I had Boyce Equipment send me everything brake related after I got the axles. And I specifically asked for that part/contrivance to be sent also... I don't know why!

j

[57taskforce]

My K20 has a front dana 60 and hydroboost. I’ve still got drums in the rear for now until I can get my hybrid old school 14 bolt with 2001+ 14 bolt rear disk setup installed. One thing to remember is the front 60’s use more fluid than the 44’s. To do this swap right you really should swap to a to square body K30 master cylinder which has the appropriate bore for the dana 60 calipers. My pedal was instantly more mush after the swap and all the air is out. The brake warning light in my truck isn’t hooked up currently so I have no idea if this could be your issue, but if you have the original master cylinder it definitely could be something to look into. In my mind if the valve is looking for a certain amount of pressure on the front and it doesn’t see it because the pistons in the calipers are different sizes, it could trip the valve. As for the reservoir mentioned above it’s likely for the pump. I didn’t need one but it took me a little bit to get the power steering bled, I had to fill it with the engine running to keep it from cavitating the pump and foaming up from the reservoir bad.

A little friendly reminder from forum staff. If guys are trying to help answer your questions or offer things that could help, there’s no need to be a jerk because you deem the information unhelpful.

[Orange Crate]

Originally Posted by jeffahart

Ya, GM called it a "Height Sensing Proportioning Valve". I have one in my garage somewhere. Just one more contraption to battle with, never set it up. My axles and hydro-boost are off a CUCV. So I had Boyce Equipment send me everything brake related after I got the axles. And I specifically asked for that part/contrivance to be sent also... I don't know why!

j

My hydro is also from a CUCV. I agree that the height type would be just one more contraption to have to troubleshoot if things get sideways. On an adjustable valve I could mark where it is best for loaded and unloaded.

[Orange Crate]

Originally Posted by 57taskforce

My K20 has a front dana 60 and hydroboost. I’ve still got drums in the rear for now until I can get my hybrid old school 14 bolt with 2001+ 14 bolt rear disk setup installed. One thing to remember is the front 60’s use more fluid than the 44’s. To do this swap right you really should swap to a to square body K30 master cylinder which has the appropriate bore for the dana 60 calipers. My pedal was instantly more mush after the swap and all the air is out. The brake warning light in my truck isn’t hooked up currently so I have no idea if this could be your issue, but if you have the original master cylinder it definitely could be something to look into. In my mind if the valve is looking for a certain amount of pressure on the front and it doesn’t see it because the pistons in the calipers are different sizes, it could trip the valve. As for the reservoir mentioned above it’s likely for the pump. I didn’t need one but it took me a little bit to get the power steering bled, I had to fill it with the engine running to keep it from cavitating the pump and foaming up from the reservoir bad.

A little friendly reminder from forum staff. If guys are trying to help answer your questions or offer things that could help, there’s no need to be a jerk because you deem the information unhelpful.

The master and prop valve were "supposedly" for a disk/disk set up, that is why I wanted to confirm a disk/disk prop valve part number from a known good working system.
I will in the future use the approved provided method of categorizing posts.... or this one...

[57taskforce]

What I’m trying to tell you is that you can put any proportioning valve you want in it, if the master bore isn’t spec’d for the size of the pistons in the calipers and a few other variables you are going to have problems, it might not always be with the dash light but there are other things that can come up as well. What I should have added in my post above and didnt orate very well is that yes you have disk disk master but I would make sure you have the right bore. That’s what I was trying to say in referencing the K30 master. It’s been a long week of 12’s, my brain isn’t as sharp as it usually is. I still believe this could be why you are tripping the light.

[Orange Crate]

Originally Posted by 57taskforce

What I’m trying to tell you is that you can put any proportioning valve you want in it, if the master bore isn’t spec’d for the size of the pistons in the calipers and a few other variables you are going to have problems, it might not always be with the dash light but there are other things that can come up as well. What I should have added in my post above and didnt orate very well is that yes you have disk disk master but I would make sure you have the right bore. That’s what I was trying to say in referencing the K30 master. It’s been a long week of 12’s, my brain isn’t as sharp as it usually is. I still believe this could be why you are tripping the light.

Well you might just be right about that. The only real way to check is to replace the current MC. I did some quick numberings and a 1 inch bore MC volume compared to a 1.25 bore MC is a change of 53% (K30 MC is 1.3" bore). Also measuring the piston diameters of the two calipers (D44 v D60) the change in volume is 16%. There are a couple of MC's available 1" bore, 1.125" bore, 1.25" bore and then the big boy K30 at 1.3" bore. These are all stock Chevy offerings so I assume the connection to your favorite booster would be standard. Someone please check my numberizing if you are bored, I used a stroke of 1.5 inches for the brake piston (I know that isn't realistic but the percent change would be the same). I also used a MC stroke of 1.5" again just for the percent change. (D44 piston = 2.830, D60 = 3.05)
Someone above mentioned the parking brake on these calipers. I activated it randomly during the (many, many) bleed sessions just to make sure there were no air pockets hiding but you never know right? I'll let it sit a couple days and bleed again to see if anything shows up. As soon as the light comes on the pressure at the rear disappears just like it's supposed to....Ok, choose your catagory or

[57taskforce]

One other thing to remember when switching masters is the pushrod length that activates the master, think the part that physically connects to the brake pedal linkage. GM over the last 50 years has used at least two different sizes that I know of. In my case my hydraboost is from an 09ish Silverado and the master currently on it is a reman for a ‘72 K20. They play fine together. If you mismatch the push rod lengths typically the brakes won’t release all the way.

[HO455]

Originally Posted by 67 twins

If I remember correctly(and I may not) GM trucks from the 80s had this before they,went to ABS

One ton Toyotas from the late 80's and early 90's had them too. Good idea until they fail. Which in my experience was always after you unloaded a bunch of weight out of the back. Then valve would stick in the truck loaded position and the rears would lock up every time you braked. While driving in the rain I had a couple of spin outs trying to baby one home from Lewiston ID. That was a long miserable trip I hope to never repeat.

[Orange Crate]

Originally Posted by HO455

One ton Toyotas from the late 80's and early 90's had them too. Good idea until they fail. Which in my experience was always after you unloaded a bunch of weight out of the back. Then valve would stick in the truck loaded position and the rears would lock up every time you braked. While driving in the rain I had a couple of spin outs trying to baby one home from Lewiston ID. That was a long miserable trip I hope to never repeat.

Ya, it's under the truck in the salt and ice an snow so that helps.....darnfangled contraption I say....now if a fella had one under the warm hood that had two settins' one a fer TK8EZ and one a fer Yerfien...

[KQQL IT]

Did you try the original pv2 proportioning valve?
Disc on a d60 lugnut4x4 kit.
Said no prop valve changes necessary.



Also why i asked what calipers you had, the site made mention of not all re pop calipers are good.

[Orange Crate]

Originally Posted by 57taskforce

One other thing to remember when switching masters is the pushrod length that activates the master, think the part that physically connects to the brake pedal linkage. GM over the last 50 years has used at least two different sizes that I know of. In my case my hydraboost is from an 09ish Silverado and the master currently on it is a reman for a ‘72 K20. They play fine together. If you mismatch the push rod lengths typically the brakes won’t release all the way.

Thanks. I do have a small amount of play before the pedal moves the pushrod, not much maybe .050" or so. because of geometry that translates to about a 1/4 travel/play at the pedal pad.

[Orange Crate]

Originally Posted by KQQL IT

Did you try the original pv2 proportioning valve?
Disc on a d60 lugnut4x4 kit.
Said no prop valve changes necessary.
Also why i asked what calipers you had, the site made mention of not all re pop calipers are good.

My master and prop are from a corvette, don't remember what year. So disk/disk engineering? I think maybe 57Task has it right. The volume change from D44 to D60 is 16% for the front, not all that big of a change but maybe the limit for the master (volume wise) I have is say, 10% or 12%. It's a SWAG (scientific wild ash guess) but the light will come on at the END of the pedal movement and then is intermittent from there on until it is reset. The pressure drop (turns the light on) could be there at the end of the stroke when the master runs out of fluid to move into the rear circuit, but still has fluid movement to the front circuit. I would really need to find the difference in volume between the original rear drum wheel cylinder and the new rear disk calipers to make this a complete trouble shoot OR I could just buy another master with a larger bore and report back. I chose this master & prop valve combo because of the volume for a disk/disk but....not so much right? I was trying not to "shot gun" this problem because everything in the system is new, so then I would have two sets that are new (spares!).