Disc Brake Conversion. 1975 FJ40. Rear Brake proportioning Valve

[knuckle47]

So the title describes the project but there remains a question I would enjoy having a consensus of opinion on. How many of us use a rear brake proportioning valve. Some use it some don’t

Use it or not? Why?

 

[pb4ugo]

I run an aftermarket adjustable on both my 40's. I set it and forget it. Without it the rear brakes are overpowering, and will lock up easily.

 

[pb4ugo]

Here you go. It's a 75 with frt disc too

 

[Jdc1]

Decent discussion-

1975 FJ40 disk brake upgrade question. Proportioning valve? Yes or no?

all my fj40s with disc brakes had a valve from the factory,other than a short piece of brake line from napa to hook it up there is nothing to it .getting a valve shouldnt be to hard .the fsm shows where it goes

forum.ih8mud.com

 

[1911]

So the title describes the project but there remains a question I would enjoy having a consensus of opinion on. How many of us use a rear brake proportioning valve. Some use it some don’t

Use it or not? Why?

I use a Willwood proportioning valve just like @pb4ugo has. It still needs some adjusting; I have it cranked almost all the way down and my rear discs are still too touchy for my taste, i.e. they lock up before the front discs if I brake hard. I just got used to it and adjusted my braking style. One of these days I need to play with the valve some more and see if I can improve the bias.

 

[charliemeyer007]

Something like 80% of your stopping power is in your front brakes - the engine is above them and stopping puts more down pressure on the front end while unweighting the rear end.

 

[JohnnyC]

A prop valve will be needed because of the small front brakes and ginormous rear brakes.
The imbalance can be mitigated by upgrading to the bigger 4runner front calipers & pads with an aggressive semi-met pad, and using the cheapest ceramic pad in the rear.

best advise here

 

[Will615]

Does the choice of master cylinder have any bearing on reducing the rear brake power? Example 80 series master vs an 40 series master?

 

[knuckle47]

Something like 80% of your stopping power is in your front brakes - the engine is above them and stopping puts more down pressure on the front end while unweighting the rear end.

Motorcycles use the same process for braking…brakes suck until the weight transfer to the front tire gives it a powerful force

 

[pb4ugo]

On my 1st 40 decades ago, I think I used the wilwood valve and it worked great. On the red 40 in the pic, I used the summit version and cranked it all the way and it isn't as effective. I also need to rebuild my master and bleed the brakes better that might be contributing to the bias. I should know the results of master in a week or two. My 1st 40 the braking is even which I prefer. I don't want my frts to lock up 1st.

 

[wngrog]

I run an aftermarket adjustable on both my 40's. I set it and forget it. Without it the rear brakes are overpowering, and will lock up easily.

This.

City Racer sells a Wilwood.

 

[wngrog]

Does the choice of master cylinder have any bearing on reducing the rear brake power? Example 80 series master vs an 40 series master?

I use early non ABS 80 masters and they need a prop valve. 100%

 

[peesalot]

Well it depends on which disc brake conversion. I have a late 70 40 with a dual circuit boosted master cyl. I went with GM brakes using the larger bolt on csaliper up front and the metric ones out back. The metric ones can have the e-brake option and NO proportioning valve, works great, if I were daily driving it I would add the valve as when you panic stop the rear does lock but with 38's its a crap shoot anyway.

 

[Jdc1]

I use early non ABS 80 masters and they need a prop valve. 100%

With stock drums in the rear?

 

[knuckle47]

Thanks guys for the opinions….p valve it is!

 

[pbgbottle]

I use a prop valve and the 80 series master. Still can lock up the rears first.