Does Air Suspension affect Rear Brake Load Compensator?

Anything and everything thing here
join a thread/start a thread
Post Reply
Sheriff
Posts: 84
Joined: August 25th, 2014, 5:47 pm
Location: Alresford, Hampshire

Does Air Suspension affect Rear Brake Load Compensator?

Post: # 18180Post Sheriff
June 16th, 2017, 4:29 pm

My rear brakes have been locking up when I've got the camper mounted, but are fine when demounted. I've found that my Hilux is missing the load compensator valve that is meant to prevent this happening, together with all the linkage that goes with it. This is a bit weird and no one I've talked to, including Toyota main dealers, can explain as this is standard fitting for the Hilux (and most pick-ups I think). If anyone can shed some light on why this might be please let me know.

I'm going to get the missing bits fitted, but it got me to thinking... if the load compensator valve, which adjusts the proportion of braking applied to the rear brakes, is actuated by sensing the amount of compression of the rear suspension caused by the load, and you fit air suspension that counteracts this compression, does that negate the effect of the braking adjustment? Has anyone had rear brakes locking up when their camper is mounted?
Guy
Karosser Camp 6L
Toyota Hilux 3ltr auto

User avatar
saDgit
Posts: 336
Joined: August 24th, 2014, 12:17 pm
Location: Aups, France (most of the time)

Re: Does Air Suspension affect Rear Brake Load Compensator?

Post: # 18213Post saDgit
June 18th, 2017, 6:54 pm

Sorry for the late response Guy - only getting online occasionally at the moment. When I fitted Air-Rides to our previous pickup the instructions that came with the kit were very clear that the compensator mechanism should be disconnected. I never did understand why that was necessary but I initially did that and then re-connected it before it went for an MOT (a definite fail if it's not connected). After that I just ignored the Air-Ride instruction and ran the pickup, with and without the camper, with the compensator connected and had no problems. Looks like somebody went even further with your Hilux and removed the compensator completely. I'd get the parts refitted and leave the compensator connected.
Martin

Previous demountables: Island Plastics 'Suntrekker' on P100, S.Karosser 'EC8L' on Ranger supercab, self-built pop-top on Ranger double cab
Current demountables: Rhino 'Safari' hardside on Ranger double cab

User avatar
zildjian
Site Admin
Posts: 22048
Joined: September 8th, 2013, 3:30 pm

Re: Does Air Suspension affect Rear Brake Load Compensator?

Post: # 18214Post zildjian
June 18th, 2017, 7:33 pm

The first camper we went to see long ago, owner told me the same, I confess I didn't really get it either and have never bothered
(if) I had an issue with brakes locking up I'd probably investigate it but since it's not happened on any of the three pickups so far
I've not had to.

so yes, replace the missing components>continue :D

User avatar
Toshbins
Posts: 237
Joined: October 22nd, 2015, 12:12 pm
Location: Between Reading and Oxford

Re: Does Air Suspension affect Rear Brake Load Compensator?

Post: # 18215Post Toshbins
June 18th, 2017, 10:17 pm

You would have thought that having the compensator connected would prevent the rear brakes from coming on so much. If the airbags raise the loaded truck back up to near normal height then the brakes will work as though the truck was unladen; I.e. Not come on much.

All the electronic gizmos that replace the compensator are also fooled by mounting a camper. By plugging in to the towbar electrics my Amarok thinks that I'm towing and adjusts all the parameters accordingly. I have proved that I can brake and swerve when some idiot pulled out on me so perhaps a camper and a trailer aren't so different in terms of braking behaviour.

Sheriff
Posts: 84
Joined: August 25th, 2014, 5:47 pm
Location: Alresford, Hampshire

Re: Does Air Suspension affect Rear Brake Load Compensator?

Post: # 18243Post Sheriff
June 21st, 2017, 4:38 pm

Thanks for your responses.

I took my Hilux to my Toyota main dealers who said they had never seen anything like it, but that the fittings all appeared to be original. They finally came to the conclusion that it must be because it is an Invincible rather than the standard model, and it has a bunch of electronic gizmos instead of the mechanical stuff (as Toshbins mentioned with his Amorak) . As they had never had any problems with an Invincible before none of the mechanics knew anything about it – not very helpful, but it pointed me towards electronic features.

So I had a search around the Toyota website and found that my Hilux may have EBD (Electronic Brake-force Distribution). This sounds like it is doing what a load compensator would do…

“Working together with ABS and Brake Assist (BA) , EBD responds to sudden stops by redistributing the brake force. Wheels with more braking effectiveness receive more brake force; wheels with less effectiveness receive less brake force, maximising braking power. EBD senses the weight transfer of the vehicle during cornering or braking, and adjusts braking pressure distribution to each wheel to maximise efficiency.
EBD is great when there's a heavy load in the back and a sudden stop is required. Sensors recognise the extra load on the rear axle, and EBD takes into account the extra weight and applies more braking to the rear wheels.


I don’t know where these sensors are or how they work, but the way my rear brakes lock up makes me think that the air suspension makes them overestimate the load and apply too much brake force to the rear.

So where do I go from here? Am I pumping my air bags up too hard (40 to 50 PSI)? Should I just forget about it, knowing that ABS on the rear wheels will kick in if they lock? And why am I the only Invincible driver who has this problem – do I just slam on the brakes more than others?
Guy
Karosser Camp 6L
Toyota Hilux 3ltr auto

User avatar
zildjian
Site Admin
Posts: 22048
Joined: September 8th, 2013, 3:30 pm

Re: Does Air Suspension affect Rear Brake Load Compensator?

Post: # 18247Post zildjian
June 21st, 2017, 7:05 pm

Hmm interesting,
I'm not especially surprised your Dealer was clueless, that seems pretty much default setting these days. I usually turn here to the HPOC massive for advice, you might join as a quick search I made earlier suggests its not a known issue

HPOC

Que
Posts: 45
Joined: January 26th, 2015, 9:57 pm

Re: Does Air Suspension affect Rear Brake Load Compensator?

Post: # 18251Post Que
June 21st, 2017, 9:23 pm

The simple answer to the immediate question is yes auxiliary air suspension can defeat the brake compensator.
The compensator valve biases the braking force to the front wheels when the truck is not loaded as that's where the greatest weight is in an unloaded state. This helps prevent rear wheel lockup during hard braking. With a full load over the rear axle (which increases the rear tyre grip) the brake bias is inreased towards the back wheels. The brake compensator "senses" the rear suspension deflection to achieve this fore to aft shift in braking force. If you pump up the rear suspension with the truck fully loaded , returning the vehicle to its non loaded height, the compensation does not occur making the vehicle more prone to rear end lockup. The air bags should really be used as helpers to prevent suspension bottoming out not to take over completely.
Why yours is locking up under load is an odd one if it's the rear wheels which are locking as it sounds as if your brakes are permanently in the loaded mode. Lead boots spring to mind :-)
Nissan D40 KingCab
Apollo Demountable
Weston-Super-Mare

Que
Posts: 45
Joined: January 26th, 2015, 9:57 pm

Re: Does Air Suspension affect Rear Brake Load Compensator?

Post: # 18279Post Que
June 24th, 2017, 1:51 pm

Hi Guy
I've been puzzling over this lockup issue and now having re read your info regarding EBD I can only think that your airbags are confusing the sensors but without info on how the system works it can only be conjecture . I know that on our Navara we initially ran the airbags at 3 bar also ( about 45 lbs) but after experimenting find that 1.5 bar or 21 lbs is perfect. It may be worth you trying say 7 lbs (1/2 bar) and doing a test run and see how it goes . Test the brakes and if all is well increase the pressure a little more until you experience lockup again. This will enable you to find the most appropriate setting . Hope you find the answer soon. Regards

Que
Nissan D40 KingCab
Apollo Demountable
Weston-Super-Mare

Sheriff
Posts: 84
Joined: August 25th, 2014, 5:47 pm
Location: Alresford, Hampshire

Re: Does Air Suspension affect Rear Brake Load Compensator?

Post: # 18283Post Sheriff
June 24th, 2017, 4:45 pm

Thanks for the suggestion Que, I was thinking of something along those lines - I'll try it next time I load up the camper
Guy
Karosser Camp 6L
Toyota Hilux 3ltr auto

User avatar
zildjian
Site Admin
Posts: 22048
Joined: September 8th, 2013, 3:30 pm

Re: Does Air Suspension affect Rear Brake Load Compensator?

Post: # 18331Post zildjian
June 28th, 2017, 3:34 pm

OK had some time this afternoon to search about and found this from Toyota owners


Image

load sensor

Post Reply