Brake Hold off valve

[Capt-Culver]

What do they do? Are they absolutely needed when converting from drum to disc? Educate me...

 

[Frank Mopar]

A proportioning valve is needed on the back brake line to limit pressure to the rear brakes if that's what your taking about. Never heard it called a brake hold off valve but I've been wrong before

Tell us what your doing and someone can better help

 

[Capt-Culver]

I have a proportioning valve for the 2 lines going in and 3 lines going out. But, when I converted to disc brakes, I purchased a new line set. The new line set had an "S" shaped line from the proportioning valve going to the back...that line stopped just short of the torsion bar crossmember. Then from there, another line going to the back. I bought the set from Right Stuff. The set didn't come with a hold - off valve. Doing some research, it appears that I may need one. This valve would be completely different from the proportioning valve. just not real sure what it does.

 

[Capt-Culver]

https://www.summitracing.com/parts/...MIm9DA0LiQ1QIVTGp-Ch205A4GEAQYASABEgL1DPD_BwE

 

[Frank Mopar]

One line cone from the MC to the rear and splits off at the rear end. The proportioning valve needs to be anywhere in that single section before the split. Hopefully it has a knob on it to adjust the pressure. Not sure what you have

 

[PurpleBeeper]

CORRECTION - See 440+6's & Bruzilla's posts below mine... I don't know who's right, but it's something like that.

Ahhh... I've seen this recently. Mopar used a proportioning valve AND a "hold-off" valve (the other name for this escapes me at the moment). Anyway, some of the newer (say '74+ or something like that) are combined, both valve in one. The older ones (like on my '70) have these two parts as separate pieces. Your picture is of one of those two pieces for the older style.

Here's where I don't know much..... I "think" the proportioning valve adjusts pressure front vs. rear just like Frank Mopar is saying. I "think" the "hold-off" valve creates a 1/2-second delay or something like that to delay the back brakes just a little bit, making the front brakes kick in first, and preventing you from locking up the back brakes first making you skid out.... I "think"

 

[440+6]

Hold off valve delays pressure to the front until the back are making contact.
Proportioning valve limits the pressure to the back.

 

[Bruzilla]

A proportioning valve is needed for any car that has disc brakes on the front and drums on the back. The reason is the disk brakes pads are essentially always in contact with the rotors, while the pads for the drums are not in contact. Without a proportioning valve, the front brakes will engage first. The valve enables the rear pads to engage the drums a second before the front pads engage the rotors.

Think back to when you were riding bikes, and rode with your first set of hand brakes. You learned quickly to never just squeeze the front brakes as the rear of the bike would rise up and at best the back of the bike would swing to one side or another and at worst you could flip over. It's the same deal with cars. If you engage the front brakes before the rear, the momentum of the car can cause the rear to swing to the left or right, and that would be bad.

You often hear people saying "I got rid of my valve and everything is fine", but there are people who A: have discs front and back, B: are people with drums front and back, or C: people who haven't had to come to a really sudden stop yet.

 

[1967coronet440]

A proportioning valve is needed for any car that has disc brakes on the front and drums on the back. The reason is the disk brakes pads are essentially always in contact with the rotors, while the pads for the drums are not in contact. Without a proportioning valve, the front brakes will engage first. The valve enables the rear pads to engage the drums a second before the front pads engage the rotors.

Think back to when you were riding bikes, and rode with your first set of hand brakes. You learned quickly to never just squeeze the front brakes as the rear of the bike would rise up and at best the back of the bike would swing to one side or another and at worst you could flip over. It's the same deal with cars. If you engage the front brakes before the rear, the momentum of the car can cause the rear to swing to the left or right, and that would be bad.

You often hear people saying "I got rid of my valve and everything is fine", but there are people who A: have discs front and back, B: are people with drums front and back, or C: people who haven't had to come to a really sudden stop yet.

I thought even with 4 wheel disc you needed to have a proportioning valve, am I mistaken?

 

[magvan]

No you dont need a hold off valve. The hold off valve delays the front brakes for a Split Second making the rear brakes ACT first. The car stops more level with a hold off valve and will have a very slight nosedive without it. I put one of my van when I converted it to disc brakes I did not put one on my Coronet.

 

[Capt-Culver]

Thanks! I have the proportioning valve. I just didn't know if I needed the hold off valve in conjunction with the proportioning valve.

 

[Bruzilla]

I thought even with 4 wheel disc you needed to have a proportioning valve, am I mistaken?

You should have one. You always want the rear brakes to engage first, but with all the wheels having the same brakes the valve isn't as important as when you have a disc/drum combo.

 

[Bruzilla]

Thanks! I have the proportioning valve. I just didn't know if I needed the hold off valve in conjunction with the proportioning valve.

I believe a hold-off vale and a proportioning valve are the same thing.

 

[Capt-Culver]

I believe a hold-off vale and a proportioning valve are the same thing.

According to this, they're 2 separate things. Sounds as if I don't need it though.

http://www.getdiscbrakes.com/rmb6801