Air bag and tire pressure

[rruff]

i’m still trying to find out what the right height is from the ground to the middle of the rear fender above the tire, mine is about 40 inches, but it seems a bit high to me, I’m thinking more like 38 inches is about right

Til the front and back match.

 

[gaylon]

Til the front and back match.

Ditto - I am shooting for level front to rear and side to side. You could measure from the ground to the fender opening above the tire, if you are on flat ground - any measurements will require being on a flat surface , of course.

 

[So Cal Adventurer]

For what it’s worth, with the TUNDRA, I’ve read and been told by various reliable sources, the truck is designed to be 3/4-1” higher in the rear for handling purposes. Also, the traction control works optimal like this.

I did some testing with mine, and the truck handles noticeable better with a slight rake, about 1”, the steering is more nimble, yet more stable.

Hard to explain really but do some testing on your own and try it out.

Also, shouldn’t be using the bags for “lift” persay, moreso as a supplement. If you’re using the bags for lift, you’re in a crappy predicament if one fails Offroad and the truck will be all lopsided until it’s fixed

My .02

 

[gaylon]

For what it’s worth, with the TUNDRA, I’ve read and been told by various reliable sources, the truck is designed to be 3/4-1” higher in the rear for handling purposes. Also, the traction control works optimal like this.

I did some testing with mine, and the truck handles noticeable better with a slight rake, about 1”, the steering is more nimble, yet more stable.

Hard to explain really but do some testing on your own and try it out.

Also, shouldn’t be using the bags for “lift” persay, moreso as a supplement. If you’re using the bags for lift, you’re in a crappy predicament if one fails Offroad and the truck will be all lopsided until it’s fixed

My .02

I have a 15 tundra and I will give a little forward rake a try. I am very impressed by the four wheel drive and traction control system in my truck, by the way. Hardly ever any wheel slip.

 

[So Cal Adventurer]

I have a 15 tundra and I will give a little forward rake a try. I am very impressed by the four wheel drive and traction control system in my truck, by the way. Hardly ever any wheel slip.

Cool, I’ll bet you’ll be surprised how much nicer the steering/stability is with a little rake.

And yeah, I’ve been off-roading my whole life and owned probably more than a dozen Toyota’s and agree, the traction control system in these things is freaking amazing. Was my first truck with it and was skeptical but I’m totally sold on it and absolutely love it. It impresses me each time i go out.

Cheers

 

[Vic Harder]

For what it’s worth, with the TUNDRA, I’ve read and been told by various reliable sources, the truck is designed to be 3/4-1” higher in the rear for handling purposes. Also, the traction control works optimal like this.

I did some testing with mine, and the truck handles noticeable better with a slight rake, about 1”, the steering is more nimble, yet more stable.

Hard to explain really but do some testing on your own and try it out.

Also, shouldn’t be using the bags for “lift” persay, moreso as a supplement. If you’re using the bags for lift, you’re in a crappy predicament if one fails Offroad and the truck will be all lopsided until it’s fixed

My .02

I bet the brakes work better too. The brake load sensing proportioning valve also cares about how the truck is loaded. Leveling the truck with a load fools it into thinking you have no load, so you won't be getting the full braking ability of your truck. Check out this video, Tundra focused, to see what I mean

 

[So Cal Adventurer]

I bet the brakes work better too. The brake load sensing proportioning valve also cares about how the truck is loaded. Leveling the truck with a load fools it into thinking you have no load, so you won't be getting the full braking ability of your truck. Check out this video, Tundra focused, to see what I mean

Bingo, exactly correct sir!!

The 80 and 100 series Land Cruisers were SUPER sensitive to load and brakes.

 

[rruff]

Leveling the truck with a load fools it into thinking you have no load, so you won't be getting the full braking ability of your truck.

Wait, that seems opposite...? When you have a load the rear will be low. So Cal is saying to raise the rear so the truck sits more like it's unloaded.

 

[Wallowa]

I bet the brakes work better too. The brake load sensing proportioning valve also cares about how the truck is loaded. Leveling the truck with a load fools it into thinking you have no load, so you won't be getting the full braking ability of your truck. Check out this video, Tundra focused, to see what I mean

Watched the video..interesting...but why block the rear of the front wheels when you jacked up the back of the truck [on stands] to keep it from rolling? Sloped driveway?

 

[Vic Harder]

I'm no expert, but... The brake load sensor is designed to sense load. If load ==> then more brake at rear. If you level the truck WITH a big load, then your rear brakes are doing nada. The proportioning valve needs to be adjusted to THINK you have a big heavy load, even if it sits level.

 

[Squatch]

I've got a thread on this subject around here somewhere. I have adjusted mine as far as it will go. But recently got a 2" bracket to lift the assembly at the axle. I normally lift the truck about 2" with the airbags. I'm going with steel upgraded springs so when that is done I'll install the bracket. And do a final adjust on the brake valve adjuster.

 

[So Cal Adventurer]

I've got a thread on this subject around here somewhere. I have adjusted mine as far as it will go. But recently got a 2" bracket to lift the assembly at the axle. I normally lift the truck about 2" with the airbags. I'm going with steel upgraded springs so when that is done I'll install the bracket. And do a final adjust on the brake valve adjuster.

If you’re in Socal and need either 2 or 3” spacers for the bags lemme know. I switched to the cradles and have both size spacers if you want/need them

 

[Squatch]

Thanks I'm on the other coast and have cradles as well.

 

[Wallowa]

I'm no expert, but... The brake load sensor is designed to sense load. If load ==> then more brake at rear. If you level the truck WITH a big load, then your rear brakes are doing nada. The proportioning valve needs to be adjusted to THINK you have a big heavy load, even if it sits level.

Vic,

Thanks for the input.

All this is beyond my technical knowledge of the Tundra system...but intuitively if system needs to sense a "loaded" condition to activate the rear brakes, then the rear of the truck will be lower than the front to register as a loaded vehicle...load in rear, sags suspension; not in the 'raked' position [man, that term takes me back to the '50s!]..how does the sensor register the "load"? By a leveling system? I am trying to understand with the system under discussion how much rear brake is applied in relation to the front, under what conditions and how are those conditions determined by the on-board system? I find this topic very interesting and hope to learn from it.

I have had vehicles of course with proportioning valves but they only split the braking force front to rear at a prescribed constant rate on all applications of the brakes...and I thought that 70% of the stopping power is generated at the front as vehicle decelerates...in any event my '05 Tundra has drum rear brakes and it handles the braking with a fully loaded '16 Hawk and lots of other gear on-board just fine. As mentioned the adjustments you make in speed and brake application once you recognize that stopping distance will be longer with the load is the best way to stay safe...anyway, that is how I handle it..

Phil

 

[Vic Harder]

Vic,

Thanks for the input.

All this is beyond my technical knowledge of the Tundra system...but intuitively if system needs to sense a "loaded" condition to activate the rear brakes, then the rear of the truck will be lower than the front to register as a loaded vehicle...load in rear, sags suspension; not in the 'raked' position [man, that term takes me back to the '50s!]..how does the sensor register the "load"? By a leveling system? I am trying to understand with the system under discussion how much rear brake is applied in relation to the front, under what conditions and how are those conditions determined by the on-board system? I find this topic very interesting and hope to learn from it.

I have had vehicles of course with proportioning valves but they only split the braking force front to rear at a prescribed constant rate on all applications of the brakes...and I thought that 70% of the stopping power is generated at the front as vehicle decelerates...in any event my '05 Tundra has drum rear brakes and it handles the braking with a fully loaded '16 Hawk and lots of other gear on-board just fine. As mentioned the adjustments you make in speed and brake application once you recognize that stopping distance will be longer with the load is the best way to stay safe...anyway, that is how I handle it..

Phil

Phil, I'll paste some links below that talk about this valve, what it does and how to adjust it. The bad news is that doing it "right" requires tools that the average shade tree mechanic doesn't have.

The worse news is, that even if you did, it might still not be adjusted optimaly.

The good news is, that if you have 4 wheel ABS, this might not be a big deal. I'm not sure on that one though.

Yes, your front brakes do about 70% of the braking. If you put a load in the rear of a stock truck, it will sag in the back, and the valve will put more pressure onto the rear brakes, because the extra weight allows more brake before the wheels break loose. If you compensate for the weight by leveling the truck in any way, that extra braking to the rear does not happen. What does happen is that you lose some of the possible stopping distance reduction because the rear brakes are under utilized.

WORSE would be if you overcompensated, or adjusted this valve for a "loaded" state. This would be super for a loaded camper/truck. BUT, if you then took OFF the load and re-leveled the truck with air bags or whatever, the adjusted valve is pushing way too much on the rear brakes, and they will lock up, causing the back end of the truck to get very loose and possibly causing a 180+ degree turn when you least expect it.

http://www.tundrasolutions.com/forums/suspension-axles-brakes/4227-load-sensing-valve-adjustment/
http://www.tundrasolutions.com/forums/1gen-brakes/150481-rear-brake-and-proportioning-valve/
http://www.proactivate.com/tundra/brakes.html

I hope that helps. If it were my rig, I would test the braking/handling on an icy surface and adjust it there to work well at low speeds. That should translate well to proper braking at speed on dry/wet pavement. Our local car clubs teach driving skills on a frozen lake, perfect spot for this kind of tweeking.

 

[jimjxsn]

Keep in mind that the mechanical LOAD SENSING PROPORTIONING AND BY–PASS VALVE went away on Tundras around 2005 or 2006.

See these links for more details on those systems -
http://www.proactivate.com/tundra/brakes.html
http://www.tundrasolutions.com/forums/knowledgebase-archive/16919-info-tundra-load-sensing-propotioning-pass/


On my late model Tundra it is describes as -
Star Safety System
Power-assisted four-wheel Anti-lock Brake System (ABS) with Electronic Brake force Distribution (EBD), Brake Assist (BA), TRAC (Traction Control), Vehicle Stability Control (VSC), and Auto LSD. Active Traction Control (A-TRAC) on 4WD.

More info on Electronic Brake force Distribution (EBD)
http://www.import-car.com/electronic-brake-distribution-emerging-technology-offers-service-opportunities/
http://www.tundrasolutions.com/forums/1gen-tundra/118339-do-all-tundras-have-load-proportioning/

 

[Squatch]

Bottom line is that if your truck is sitting higher than factory for the load in the bed that the little cable thingy on the rear axle either needs to be raised or adjusted to think it has.

As the truck settles from a heavy load the cable to the proportioning valve is moved to allow more brake line pressure to the rear brakes. This is a mechanical system that work off of ride height. If you raise the truck after loading the camper with air bags then the cable isn't being pulled enough. The truck brakes think the truck is empty. And the front brakes are doing all the work.

Some good links in this thread.
http://www.wanderthewest.com/forum/topic/12993-tundra-brake-question/

If you are raising the truck 2" with the air bags then this little bracket should do the trick. Rear braking may then be too much when unloaded though.
https://bilsteinlifts.com/shop/toyota-tacoma/1995-2004/brake-proportioning-valve-bracket-kit/

 

[jimjxsn]

Here is pvstoy's discussion of this from back in 2007. I seemed to remember this from back in the cobwebs of my mind...







When you raise the rear with the air bags you are now telling the truck that it does not need the extra braking force to the rear for the added weight.

This is what I did on two, Toyota Tundra’s. On the rear of most Toyota's is a diagonal bar from a valve to the rear diff. The bar allows the rear brakes to get more brake bias (force) to adjust for the load you put on the back. You add weight the bar moves, so then a valve opens more. Since you pump up the air bags the truck levels off and the so the valve closes as with no load. The system would not know it needs more rear braking force to stop. That's right the front brakes do more of the work.

I made an extension bracket that will extend the height where the diagonal bar attaches to the rear diff. Just a piece of flat stock steel works. Not too thick so you can use the same bolts. How much you need depends on your load and spring condition.

To find the spacer length needed: without the load (camper) on the back measure the height difference from the bar at the valve (near the frame) and the center of the round pivot at the differential. That will be you’re no load height and the brakes will work fine. Now add the load (camper) and average running weight to it. Now measure again the two reference locations. If you have air bags already you can flatten the air bags and drive around the block to settle the spring’s then measure.

You will notice the bar became flatter some. Let’s say you had a drop of two (2) inches. When you pump up your air bags to level the truck, you will want to make a spacer that you can raise the bar two (2) inches at the differential. All we are doing is keeping the bar at the same angle as before raising the rear with the bags.

This bracket works well if you have the camper on and off a lot. I can’t speak for other truck manufactures how they handle theirs; I’m just a Toyota guy.

Too much braking force on the rear with out the load will cause the rears to lock up on an icy road . The Dealer or a trusted mechanic should have pressure gauges that they can measure your brake bias and set it properly. I take no responsibility for improper brake adjustments. You should decide if you need to take action and make proper adjustments.

 

[So Cal Adventurer]

Here is pvstoy's discussion of this from back in 2007. I seemed to remember this from back in the cobwebs of my mind...






When you raise the rear with the air bags you are now telling the truck that it does not need the extra braking force to the rear for the added weight.

This is what I did on two, Toyota Tundra’s. On the rear of most Toyota's is a diagonal bar from a valve to the rear diff. The bar allows the rear brakes to get more brake bias (force) to adjust for the load you put on the back. You add weight the bar moves, so then a valve opens more. Since you pump up the air bags the truck levels off and the so the valve closes as with no load. The system would not know it needs more rear braking force to stop. That's right the front brakes do more of the work.

I made an extension bracket that will extend the height where the diagonal bar attaches to the rear diff. Just a piece of flat stock steel works. Not too thick so you can use the same bolts. How much you need depends on your load and spring condition.

To find the spacer length needed: without the load (camper) on the back measure the height difference from the bar at the valve (near the frame) and the center of the round pivot at the differential. That will be you’re no load height and the brakes will work fine. Now add the load (camper) and average running weight to it. Now measure again the two reference locations. If you have air bags already you can flatten the air bags and drive around the block to settle the spring’s then measure.

You will notice the bar became flatter some. Let’s say you had a drop of two (2) inches. When you pump up your air bags to level the truck, you will want to make a spacer that you can raise the bar two (2) inches at the differential. All we are doing is keeping the bar at the same angle as before raising the rear with the bags.

This bracket works well if you have the camper on and off a lot. I can’t speak for other truck manufactures how they handle theirs; I’m just a Toyota guy.

Too much braking force on the rear with out the load will cause the rears to lock up on an icy road . The Dealer or a trusted mechanic should have pressure gauges that they can measure your brake bias and set it properly. I take no responsibility for improper brake adjustments. You should decide if you need to take action and make proper adjustments.

Great explanation. I will need to check my 2014 Tundra but I don’t recall messing with a proportioning valve on the rear axle like I’ve done on prior trucks.

As far as i remember, it was just 2 small brackets moving the brake lines only. But I’ll double check

Thanks for great post

 

[Wallowa]

Yup, excellent posts and information sources...I will tinker with our Tundra/Hawk to see if I can dial this in..first time I have encountered an active proportioning valve that adjusts the front/rear brake bias based on the height of the vehicle bed.

Still the original suggestion mentioned to put a "rake" on the truck seems backwards if that means having the back higher than the front by raising the rear of the truck...

Again, I appreciate the discussion and shared experiences.

Thanks,
Phil