Disk brakes on a pickup...

[pope_face]

Alright, I know there's a brake section, and I know this topic has been covered before, but I'm just trying to get a feel for how well this would work before I look for a writeup, and this is more truck related than a general brake question... so, what I want to know is: Can disk brakes on a pickup potentially be a bad choice over drum brakes?

 

I know that disk brakes offer more stopping power, but I'm curious as to the wheels locking up... I think I've read on here that that's one of the reasons disk brakes weren't used on the early Datsun trucks, because of the difficulty in proportioning the front/rear bias on an unladen vs fully loaded bed... I'd like to get disks, but if it's a choice between losing rear wheel traction when I'm just cruising or not being able to stop when I'm hauling something, then I'd rather keep my drum brakes...

[808DA6]

I haven't heard any problems from anyone i know w/ disc conversions. There's a bunch of different configs and my Hardbody setup has never locked on me. I'm also using a 7/8" dual master w/ a Z proportioning valve. :)

 

~Brian

[tnip]

well if you do disks in the rear you would need a prop valve anyway to prevent this... wilwood makes one that people on here have used... if i'm not mistaken.

[pope_face]

Ok, so as long as it's done properly and I use a proportioning valve, there shouldn't be any issues?

[mklotz70]

I used the combo valve out of an S10(disc front-drum rear). I never worry about it. We haul wood with it up and down some pretty good hills and brakes are low on the list of concerns :)

 

In the NL, I will use a wilwood adj since it's getting disc/disc and I won't be hauling anything with it.

[]2eDeYe]

The newer Frontiers are 4-wheel disc so I think you'll be ok with a proportioning valve. Maybe you could get one from a frontier...hmmm

[pope_face]

Awesome, thanks for the replies... Like I said, I wasn't sure how well it would work out, but it sounds like it'd end up pretty good. :D

[69FJWagon]

I have a 7/8 master in my wagon with 4 pot wilwoods up front and stock drums in the rear and have no problems with the rears locking up before the front and I dont have any type of proportioning valve and I have used them pretty hard from over 100 mph but I did notice that when I had 4 wheel wilwood disk set up in my 2 door 510 it did get a little tail happy under hard braking from anything over 70 or 80 mph using the same master and brakes as on my Wagon minus the rear set up, I guess it all depends on how you drive your truck I know Fineline has his 4 wheel brake set up on his 620 and he drives hard and uses his brakes just as hard and I dont think he has had any problems but I cant remember what he is using for a proportioning valve

[datzenmike]

I have a 7/8 master in my wagon with 4 pot wilwoods up front and stock drums in the rear and have no problems with the rears locking up before the front and I dont have any type of proportioning valve and I have used them pretty hard from over 100 mph but I did notice that when I had 4 wheel wilwood disk set up in my 2 door 510 it did get a little tail happy under hard braking from anything over 70 or 80 mph using the same master and brakes as on my Wagon minus the rear set up, I guess it all depends on how you drive your truck I know Fineline has his 4 wheel brake set up on his 620 and he drives hard and uses his brakes just as hard and I dont think he has had any problems but I cant remember what he is using for a proportioning valve

 

If this is the adjustable proportioning valve from Wilwood (I have one) here's what I've noticed. You can adjust the bias, front to rear and that's it. It is not automatically adjustable for different loads, you have to adjust yourself. If you have more weight over the rear tires, you can have more bias to the rear because more weight provides more traction so it is harder to lock them up.

 

Here's the problem: Sunny dry day, your brakes are adjusted so front and rears just lock-up together under panic stop. You throw 800 lbs of shingles in the back and head home. To avoid an accident you hit the brakes, hard! The front discs lock and you slide to a stop, the rears don't lock because of the added traction from the extra weigh. The bias setting is too light for the heavier load.

 

It should be load sensitive and automatic. The Pathfinders have one. The Chrysler mini van had one. The proportioning valve mounts on the rear axle frame and has a lever that connects to the body. As more weight is loaded, the body squats lower and the lever opens the valve to allow more brake pressure to the back drums.

[69FJWagon]

If this is the adjustable proportioning valve from Wilwood (I have one) here's what I've noticed. You can adjust the bias, front to rear and that's it. It is not automatically adjustable for different loads, you have to adjust yourself. If you have more weight over the rear tires, you can have more bias to the rear because more weight provides more traction so it is harder to lock them up.

 

Here's the problem: Sunny dry day, your brakes are adjusted so front and rears just lock-up together under panic stop. You throw 800 lbs of shingles in the back and head home. To avoid an accident you hit the brakes, hard! The front discs lock and you slide to a stop, the rears don't lock because of the added traction from the extra weigh. The bias setting is too light for the heavier load.

 

It should be load sensitive and automatic. The Pathfinders have one. The Chrysler mini van had one. The proportioning valve mounts on the rear axle frame and has a lever that connects to the body. As more weight is loaded, the body squats lower and the lever opens the valve to allow more brake pressure to the back drums.

 

ya i have a proportioning valve in my turbo car so I get that part (also have tilton drop down pedals with a balance bar adds a bit to tuning the brakes:confused:) and I understand the problem with the truck...now (thanks datzenmike) but i am also thinking that most of us own a lowered truck ...some lower than others and with anything much heavier than maybe a datsun engine the axel hits the frame so the load issue may not be that big of a problem... not much of a real load and I have found that with the 7/8 master it seems to be more rear biased anyway so if you are running disk up front and drum out back the improved brakes up front and more bias goin to the rear it should kinda equal out :lol: on a real note if you are worried about it install a proportioning valve set the bias without a load then go to your local home depot and get 200 or 300 lbs of sand and set the bias with the load and you would know that you have to increase/decrease rear brake a turn or 2 what ever the case maybe when you have a load

[datzenmike]

Agreed. I believe Keith Law's 510 has the adjustable proportioning valve mounted near the shifter. As he races and the gas tank empties he can adjust more to the front.

 

My truck suffers from EXTREME weight transfer to the front with resultant rear lock up even under moderate pressure. Usually the last few feet before stopping at a red light, which always got unwanted stares. I replaced the stock valve with a 720 4X4, no go. Had to drive with 3-4 car lengths around town, more in the rain. Best $50 I spent was the adjustable valve. With the rear full off, maximum 60% internal, I get the rears to just barely squeek equally with the front. Rubber marks are even and equal.

[pope_face]

Mike: Thanks for the suggestion... I think that's the solution I was aiming for when I first asked the question. If I go with disks, which is a possibility, I'll likely go with the automatic adjustable proportioning valve... I like the concept of being able to adjust it myself, but then you start getting into issues with weight increase/decrease as well as load distribution, etc... Not to mention full gas tank vs empty tank, as you mentioned above.

 

However, I'm wondering how well one of those automatic proportioning valves would work on our trucks... I understand the concept of it, but I figure it would have a lot to do with suspension firmness, weight of the rear when completely empty (including tank), percentage increase of weight when fully loaded as opposed to empty, etc... The amount of suspension travel would likely play a part in it as well... I know I'm being picky, but I'd just curious if someone has tried this, either successfully or not, or if my concerns are ungrounded...