Tim Wright Posted August 30, 2018 Share Posted August 30, 2018 I received a lot of good feedback on my original post about my 89 Toyota Dolphin's front tires skidding on wet roads, gravel , and especially going downhill in reverse. Looks like the culprit is the load sensing proportional brave valve. From what I've gathered it sences the ride height of the vehicle and adjusts braking from rear to front depending on how much of a load it thinks the vehicle is carrying. The problem is with the Airbags lifting the rear of the vehicle up , the device thinks it's an unloaded vehicle and shifts most the braking to the front , causing poor braking and the skids. I really appreciated the help with some options of alleviating this problem and useful tips like using your parking brake if skidding backwards down a hill to keep things in control. So now my question is , " How much air should you put in your airbags " They say 90 psi max and I assumed the more the merrier. Since stumbling upon this phenomenon with the airbags I've lowered it to around 50. Still doesn't seem to do anything to the braking and some have spoken of these proportional valves getting stuck in the upward position , lending to most the braking coming from the front , when I need more in the rear. So any thoughts of a good psi for a fully loaded trailer ? I also drive on windy coastal / mountain roads and I'm pretty sure it cornered better with the higher PSI. Also , is this something a RV shop would tackle ? Is there replacement proportional valves available if mine is just stuck ? Anyone know of any shops who deal with this type of thing around Northern California / Southern Oregon ? Thanks for any help , I just want this thing to stop like it should. Quote Link to comment Share on other sites More sharing options...
WME Posted August 30, 2018 Share Posted August 30, 2018 (edited) Have you just tried bending the lever. About 1 ft from the valve just bend it up 8" or so. Keep checking the small button under the arm and make sure it is moving up. If this works then the valve is OK and just leave things this way. If no help then the valve may be frozen. Maybe remove it and try taking it apart and cleaning...After all its already broken? The sad news is a new one will have the same problem. Some folks have just removed it completely and used brake line blocks to to reconnect things. Edited August 30, 2018 by WME Quote Link to comment Share on other sites More sharing options...
markwilliam1 Posted August 30, 2018 Share Posted August 30, 2018 Unfortunately on my rig the valve was frozen and adjusting the arm was worthless! Quote Link to comment Share on other sites More sharing options...
Maineah Posted August 30, 2018 Share Posted August 30, 2018 Bypass the valve. The truck is always overloaded. What the valve was for was to reduce braking when the pickup truck truck bed was empty to keep the rear brakes from locking up. Now with a camper on it's back it is full loaded all the time think pickup with 1/2 ton of bricks in the bed. This probably will not fix your front breaking issue because going backwards rear brakes are not real efficient they are what's known as self energizing but going backwards they do not self energize. The front ones do not rely on the same principle so they apply full force no matter what the direction. There is a little science involved here with weight transfer and breaking also just remember the brakes are marginal in the best of circumstances, toy homes are not known for their superior stopping ability. Quote Link to comment Share on other sites More sharing options...
Homer Posted August 31, 2018 Share Posted August 31, 2018 Tim: Mine did the same thing although I have no airbags, I had to use the emergency brake (per previous owner) to stop until I fixed it. I bled the rear cylinders and all the lines and still had no breaks on rear, front always slid. Replaced the master cyl. Finally I took the proportional valve off, it was full of rust, cleaned it really good, put it back together, bled the lines again, still no brakes at rear. I think I pulled the axels in order to get to the rear brake shoes and wheel cyl. The cylinders were rusted tight, wouldn't move at all. replaced both rear cyls. with new ones and tied the proportional valve arm up ( "SUNRADER BOB" advised me to do this) I have rear brakes now and that has been around 9 years ago going on ten and still have great brakes. Wish you well on yours. Quote Link to comment Share on other sites More sharing options...
Maineah Posted August 31, 2018 Share Posted August 31, 2018 Yep mine worked fine for what they were too but it is important to keep your distance they are less than stellar in perfect condition. When I bought mine I went through the entire brake system at that time I bypassed the the proportion valve that way I knew I had all the pressure I could get on the backend of an overloaded vehicle. Because the weight shift of something like a toy home more breaking is placed on the rear unlike a car where close to 70% is on the front so yeah no breaking on the back is going to make the front work over time running the risk of lockup. Many years ago large dump trucks had no front brakes because they did virtually nothing. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.