A danger of Ride Rites, add-a-leafs etc.

[generubin]

I searched this website for any discussion of brake proportioning valves and was surprised, actually frightened to find no discussion of them.

There has been plenty of talk already on this site of overloading 1/2 trucks to the point of dangerous handling and braking. And there are those who will still use a mini-truck or 1/2 ton by adding Firestone Ride Rites or Add-A-Leafs.

Here is a serious braking danger to the occupants by the use of any rear suspension mod that brings the height of your truck up to normal although you have mounted a camper in it. On many trucks (most if not all Toyota's) there is a valve attached to the frame just above the rear axle. It is controlled by an arm/rod that is attached to the axle housing. Because the weight in the back of a pickup truck can vary from zero to a lot, the manufactures design this valve to proportion the braking between the front and rear of vehicle by sensing the location of the axle in relation to the frame. The more weight you put in the back of the truck, the closer the axle is to the frame, the more brake fluid pressure travels to the rear brakes to avoid a spin-out or rollover. Here is where the danger comes in: If you install a camper with Ride Rites or any other lifting device, you have fooled the brake system into thinking there is no weight in the rear of the truck (yet, of course there is and a lot of it!). When you brake hard the front brakes will do most of the braking, the rears very little, so the back of the truck will want to trade places with the front of the truck. Liken it to going down a steep hill on your bicycle and squeezing only your front brakes.

There is a simple fix but I have not seen a single person talk about it on this site. Before you mod your suspension, with the camper on the truck and loaded, measure the distance from the top of the axle house to the frame. After the mods make the same measurement. If say the difference is 2 inches, then you must raise the proportioning rod at the axle housing by the same 2 inches. This tells the valve to send more power to the rear brakes to compensate for your heavier load. Be sure you do this. Not to is a serious risk to your life in any emergency braking.

And don't even get me started on Ride Rites! Be sure to read the threads on 1/2 ton vs. 3/4 ton.

 

[Alex]

True for the Tacoma up to 04 model year.
There is no proportion valve on 05+ Tacomas.

 

[HERR42]

i am not aware of fords using them either.

 

[ntsqd]

ABS likely did way with these systems. My '84 Xcab has the LSPV (Load Sensing Proportioning Valve). With larger than stock tires and only a shell for a load the rear brakes still weren't optimized. After trying a range of adjustments I concluded that all of the way up worked the best. After testing this by wiring the lever-rod to the underside of the bed in the full up position I built the part below. I do not encourage anyone to go to this extreme, but it does work for me. (It is shown loose from the frame due to other work going on in the area. It is normally bolted tightly into place)

 

[Stan@FourWheel]

There was one thread on it awhile back.

I'm pretty sure it was Patrick Pevey that did the write up.

He also included pictures on a small bracket he used.


You are right in the fact nobody else has said any thing about it that I can remember.

And almost 100% of the customers I talk to day in and day out don't know anything about it.

I would bet almost any amount of money that any truck dealership will not know about this either.

If you go to 10 local truck dealerships and ask their sales staff and sales managers, I bet not many, if any at all, would know what it is, or if the truck has it or not.

I have never seen anything like it on my Ford F-150. But I think our Tundra in the shop probably does have one?

That said, we have never adjusted that valve on any of our company trucks, and I don't think any staff members have adjusted them on their personal trucks either ?

If someone has a camper on & off the truck regularly, I don't know what would be the best thing for them ?? Adjust ?? Or leave it alone ??

If they are going to put the camper on the truck, bolt it down, and leave it on the truck ALL the time, then it might make sense. But if the camper is only on the truck every once in a ahile, I can't see any customers bothering with. Wrong or Right ? I don't know ?

I have had truck sales reps tell their customers that the 1/2 ton truck they are about to buy has a payload capacity of 7000 lbs. I asked ... "that is 7000 lbs. towing capacity, right ?". They answered no, it can carry that much in the truck bed.

I even had a dealership tell their customer they were going to charge then $ 250.00 to take the tail gate off the truck for them ? Huh ? We took it off in the parking lot in 30 seconds with no tools.

It is always a good idea to do your homework and educate yourself.

We are all still learning here, that is for sure, and we have lots more to learn !




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[brett13]

True for the Tacoma up to 04 model year.
There is no proportion valve on 05+ Tacomas.

Not on the 07 and later Tundra's either. The manufacturers are using electronics these days, like Atari or the Space Shuttle.

 

[Alex]

Not on the 07 and later Tundra's either. The manufacturers are using electronics these days, like Atari or the Space Shuttle.


Atari <--- I miss that.

 

[leadsled9]

There is a simple fix but I have not seen a single person talk about it on this site.


I've seen it mentioned a couple of times.....but it never hurts to bring it up again. The small bracket makes quite a difference....at least it did for me.

 

[CJinCA]

It's been posted before. PVSToy did an excellent write up on it HERE . A quick search under brake or air bag will get results.

 

[Wilbur]

Quick question....would the same thing occur when using a weight distributing hitch to level the tow vehicle?

 

[ntsqd]

I would expect so. The same thing has happened, the weight is there, but the ride height has been artificially altered from where the weight would have normally put it.

 

[camelracer]

Quick question....would the same thing occur when using a weight distributing hitch to level the tow vehicle?

I would assume that if you have distributing hitch the load being towed will have its own brakes taking some of the load off the towing vehicle brakes.

 

[Lighthawk]

Just looked under my 06 Tundra AC TRD: There's no bracket/arm from the frame to axle, nor is there a valve.
I'm assuming the ABS electronic control has replaced the mechanical valve.

Andy

 

[generubin]

I understand your truck does not have the valve. I am not sure how ABS would circumvent the need of a proportioning valve as ABS is all about sensing differences in wheel speed and therefor sensing locking up brakes. How it senses the load weight of the bed of the truck is beyond me. Maybe someone else knows the answer to this.

Tundra thread about this: http://www.tundrasolutions.com/forums/brakes/32674-who-has-actually-adjusted-brake-proportioning/


Inexpensive bracket: http://store.fatbobsgarage.com/toyota-brake-valve-proportion-bracket-1987-2006-p8479.aspx

 

[HERR42]

the purpose of the valve is to determine what percentage of braking force is given to the rear.

greater load in rear (judging from sag) increases the portion.

antilock systems do this, and more.

 

[generubin]

LSVP= load sensing proportional valve

Newer ABS trucks do not have an LSVP.

Yes, I understand what ABS does, my question was, short of a difference of wheel spin or rotational speed differentiation, how does ABS sense the load and then proportion properly? I don't think it can. Whereas the LSPV was proactive (it made the adjustment in advance), the ABS can only be reactive and stop any brake spin after the fact, though quickly.

This LSPV is like having your truck in 4wd before you get stuck rather than slapping into 4wd or expecting a viscous coupler to engage once the truck begins to stick.

I have been a professional mechanic for years and I totally understand how ABS works. I don not see anyway it senses load proactively. ABS will give you proper braking in emergency but will not give the wonderful advantage of even wear between front and rear brakes like a LSPV. Anyone who can actually explain how ABS actually senses load, I am all ears.

 

[ntsqd]

My guess, and it exactly that, a guess, is that ABS rear brakes are set up for the max possible rear braking (i.e. at GVW on dry pavement). The ABS system then can "dial down" the rear brake response based on rear tire slip. So while it won't directly sense the load, it can still be effective in dealing with different loadings.

The ABS systems should have no trouble with not looking at relative wheel speeds, but more importantly at the relative wheel rates of angular deceleration. From those rates of change a prediction is an easy calculation. If the rears are decelerating faster than the fronts then the system can start "dialing down" the rear brake pressure before the tires actually stop rolling and skid

 

[generubin]

Makes good sense to me. Unfortunately requires a bit of tire wear to go about a fancy way of doing the same simple job that the LSPV did for so many years.

 

[HERR42]

variation in wheel speed is sensed many times per second. the calculation is based upon comparisons that involve fractions of an angular degree.
youre right, its reactive rather than proactive. which one helps in rain and ice?

abs is a good thing...i have less dents.....i did not say no dents.

if that mechanical valve.....an analog computer of sorts......is so good, then why are you having to defeat the design?

 

[generubin]

People where not defeating the design, they were just adjusting the valve to be correct with the change in ride height.