L400 suspension lift - if you have it, make sure it's good

[Yukonflyer]

2. Rear brake proportioning valve

What it is/purpose : The rear brake proportioning valve assists in braking with varying weight loads in a vehicle.

For those who may not know , the rear axle on the L400's has a Brake Proportioning Valve fitted to it . The valve itself is rigidly mounted to the chassis. The rear brake line enters this valve and then is routed to the rear calipers. The valve has a lever on it that moves fore and aft. This lever opens and closes an orifice to limit the flow of brake fluid to the axle as the load demands . The other end of the lever attaches to the axle via a large coiled spring. When the vehicle is empty , the orifice is greatly restricted as the lever is pulled by the extended spring because the body of the vehicle is sitting high. This prevents rear wheel lock up when empty. As the load increases in the vehicle , the rear of the car lowers which takes the tension off of the spring and allows the lever to relax a little. This opens the orifice in the valve allowing more fluid pressure to reach the rear brakes giving more braking power.

I only seen one L400 with an extension. Probably because people don't know of the need to install one. The raised vehicle without an extension will have poor rear braking performance and increased front brake wear because the valve thinks the vehicle is lightly loaded due to the body sitting high, regardless of weight in relation to the axle height.

Solution : The typical extension should correspond with the amount of lift (ie. a 2" lift would need to have the spring attaching bracket moved up 2" to keep the spring at the correct angle).


So here's a question, How does using airbags to keep the rear from sagging under load effect this?
it seems to me that by using airbags to prevent the rear from drooping with a load in or a trailer on would reduce the effectiveness that the rear brakes are supposed to have when loaded and thus have a similar effect as a lifts. HD springs would also result in the same effect.

Thoughts? it'd be nice to do airbags or hd springs but not at the cost of effective braking
thanks

[thelazygreenfox]

YF
The proportioning valve can be adjusted to suit the new height.
This is my guideline:
adjust the pv till the rear brakes lock up driving downhill on a steep gravel road, then back off till the wheel don't lock. Check both rear wheels for skid marks on the gravel.

When you're finished post your experiences, with pics of course.
good luck
TLWF

[Firesong]

If your vehicle is level with a lift what is it going to matter with the valve

[macro]

If your vehicle is level with a lift what is it going to matter with the valve

Effectively you're making the valve "think" that the van has no weight in the back so the rear brakes don't need to work as hard. The valve attaches to the body and then to the axle with a spring. When you lift, it pulls those farther apart, having the same effect as an unloaded van.

The valve needs to be adjusted to compensate for this, putting the valve on a 2" block (or adjusting it manually) will set it's 'zero position' back to stock height so when you throw some weight in the back the valve does it's job and gives you more rear braking.

Does this make sense? I haven't had my coffee yet.

[Firesong]

Yup

[Chedder114]

I did the 2inch spacer lift, sent it in for a wheel alignment and my tie rods are to short now. Any ideas on why or what rods I'd need to suit the lift?

[Firesong]

That's strange.

Not sure why that would come up unless something was different on yours to start with.
Mine was a 1" spacer, but the heavy large coils putting it up about 2" total.
J

[Gandalf]

2. Rear brake proportioning valve

What it is/purpose : The rear brake proportioning valve assists in braking with varying weight loads in a vehicle.

For those who may not know , the rear axle on the L400's has a Brake Proportioning Valve fitted to it . The valve itself is rigidly mounted to the chassis. The rear brake line enters this valve and then is routed to the rear calipers. The valve has a lever on it that moves fore and aft. This lever opens and closes an orifice to limit the flow of brake fluid to the axle as the load demands . The other end of the lever attaches to the axle via a large coiled spring. When the vehicle is empty , the orifice is greatly restricted as the lever is pulled by the extended spring because the body of the vehicle is sitting high. This prevents rear wheel lock up when empty. As the load increases in the vehicle , the rear of the car lowers which takes the tension off of the spring and allows the lever to relax a little. This opens the orifice in the valve allowing more fluid pressure to reach the rear brakes giving more braking power.

I only seen one L400 with an extension. Probably because people don't know of the need to install one. The raised vehicle without an extension will have poor rear braking performance and increased front brake wear because the valve thinks the vehicle is lightly loaded due to the body sitting high, regardless of weight in relation to the axle height.

Solution : The typical extension should correspond with the amount of lift (ie. a 2" lift would need to have the spring attaching bracket moved up 2" to keep the spring at the correct angle).


So here's a question, How does using airbags to keep the rear from sagging under load effect this?
it seems to me that by using airbags to prevent the rear from drooping with a load in or a trailer on would reduce the effectiveness that the rear brakes are supposed to have when loaded and thus have a similar effect as a lifts. HD springs would also result in the same effect.

Thoughts? it'd be nice to do airbags or hd springs but not at the cost of effective braking
thanks

I feel the need to correct the information in this thread... it took a fair bit of consternation to reconcile and figure this out lol.
As clearly stated in the Mitsu brakes PDF, the lighter the load in the rear of the van the looser the spring is (and shorter it is), allowing the valve lever to relax towards the front of the vehicle, reducing brake line pressure post-valve, and braking effectiveness of the rear discs. This is also exemplified by giving the vehicle a 2" lift without compensating.

Now, where things get muddier is if we were to give the van a much bigger lift like 5-6", there is a point at which the spring will begin to be pulled tighter again even though the lift is increasing :p. In such a case, there is a chance that the rear brakes could be actuated harder as the load decreases, which would be the opposite of what we want because the most unloaded wheels would brake the hardest.

But, for all of us, as the spring tension is increased (spring pulled tighter and gets longer) and the valve lever is pulled towards the rear of the vehicle, rear braking is increased.
I will likely experiment with a pair of prop valves, eliminating the oem prop valve, to see if I can get more rear brakes safely, since the oem prop valve is likely past its prime, and regardless it does not properly differentiate between L/R wheel load/lift in offroad braking. Done properly there really should have been two valves, one for each side, to compensate bilaterally, in the oem design.

For testing, we have to unload the rear as much as possible by braking hard on a downhill pavement with excellent traction. The reason for this is, due to the vast majority of stopping power coming from the front brakes, the more effectively the front brakes deliver stopping power to the road surface, the more the rear is unloaded. Now, I'm not 100% up on how the ABS affects F/R brakes in our vans, so this is an additional factor. Even changing to stickier tires can change how much unloading of the rear tires occurs.

Of course, take great care when testing brake effectiveness, and do it incrementally in a safe location. Whew! Preachy today

[Khrolar]

Alright so here's something that I haven't found discussed anywhere, and I feel like digging up this old thread if the right place for it.

I recently installed overload springs on the rear of my L40., I did the brake booster adjustment and sway bar drops for the 1.5" of lift it gave me.

Last week I had the chance to view my deli alongside a few others. I noticed that what I thought was stock ride height in the front was actually a 1-2" lift. Does anyone have the specs for stock ride height from the center of the hub up to the top of the wheel arch? I can't find it anywhere!
But more to my point, after researching upper ball joint spacers, it seems there are 2 styles. A flat one with both sides parallel to each other, and one with a 2-5° taper on one side. The tapered ones make sense to me, as the upper controls arm is raised the angle changes.

Does anyone have some insight to this??

[thelazygreenfox]

Just lost my entire post. I took too long and had to log in again. Soooo lets try again. #$@^

I have HD front torsion bars, HD rear coils,2" BJ spacers, air bags etc. All delis have spring sag so have compensated with reindexing the bars and raising the rear as well. I tried aluminum coil spacers as well. I'm on my 3rd deli over 12 years and have experimented with all sort of things over the years. if there is a spec on axle to fender height please let me know, I've never seen one.

BJ spacers are a PITA. We need adjustable spindles as well to do a good (even 2" raise). The UBJ and LB Joints have a limited travel so whether flat or angled BJ spacers make little difference after 1 1/2" of raise. Butch once told me that was his upmost limit on deli raise. I agree with that as the deli suspensions just aren't made to raise more than that. Experiment with an unloaded front end and note the angles and movement on the BJ's at the extremes. Grease moves out of the BJ at the higher angles, boots break and BJ's stress to breakage with greater angles especially with 4x4ing and cut back upper stops.

Upper and lower control arms have rubber bushings that suffer when over worked, not to mention all the other bushings in the rest of the front suspension. Raising the deli creates a long list of parts that suffer.

i have a motorcycle rear carrier and a m/c trailer as well so needed HD rear coils and air bags to make for safe travel. They compliment the front end lift but wear a lot and are expensive to install and maintain. i do all my own work so cut costs a lot. Still many BJ's have changed hands with my delis.

This is my 3rd deli over 12 years and lots of experiments. My biggest problems are from braking and corrosion. All older vehicles suffer the same, zinc is a wonderful material but we lose lots every day and when it's going all the body including brakes suffer so if you're having probs with rusting or corrosion or brakes that's where it's from.

Thats my (rant) insight, had more to say but lost it when I signed in again.
have fun
Wayne