craigw
Need a Spot
Reged: 01/14/11
Posts: 3
Loc: ca
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Hello,
I've got a 1985 toyota 4runner. I've had it for 12 years but in the last couple years the brakes have developed this problem.
The brakes need bleeding, I bleed them and all is good. Within 3 weeks the medal is mushy again.
I have replaced the Master Cylinder, Booster, and the flex lines are extended length plastic coated braided stainless steel.
I see no evidance of leaks.
Any help would be appreciated.
Can the rear proportioning valve go bad and cause these symtoms?
Thanks.
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OOP'S
Roll Me Over
Reged: 04/14/00
Posts: 4230
Loc: Roseville, CA, Gateway to the ...
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The answer to the question is yes.
Is this how you are bleeding them?
"...This is from the FSM and it works great..."
1. Drivers side rear
2. Passenger side rear
3. Passenger side front
4. Drivers side front
5. LSPV (Load sensing proportioning valve)
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David Fritzsche
1990 Ex-Cab V-6,5-speed, with a few mods
04.5 CTD Dodge 2500 Ram--Tow Rig
Roseville, CA
"Serenity through Sobriety"
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craigw
Need a Spot
Reged: 01/14/11
Posts: 3
Loc: ca
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yes, that is the order that I'm bleeding the system.
So you think that the LSPV could be bad and would cause the system to need bleeding every few weeks - Is there a way to test it before dropping $250 for this dealer only part?
Thanks
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OOP'S
Roll Me Over
Reged: 04/14/00
Posts: 4230
Loc: Roseville, CA, Gateway to the ...
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Quote:
yes, that is the order that I'm bleeding the system.
So you think that the LSPV could be bad and would cause the system to need bleeding every few weeks - Is there a way to test it before dropping $250 for this dealer only part?
Thanks
I really do not know how you would test. It seems like if it were bad it would be leaking. I would not spend that much on something that I was not sure if it were bad or not. Which wheel are you getting the air out of?
As far as the LSPV I would go to a P-N-P and see if you can find one or an adjustable proportioning valve, that is what I did when I put the disk brakes on the rear. Dave'z Offroad Performance. has a complete set-up for a pretty good price. The only other thing you will need is a plug for the "T" fitting that is in the PS front wheel well. You remove the return line from the LSPV and replace it with plug.
Dave'z web page:
http://www.davezoffroadperformance.com/
This is what it looks like and where to find it on his web page.
http://www.davezoffroadperformance.com/forum/viewtopic.php?f=3&t=52
Edited by OOP'S (01/15/11 09:48 PM)
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4Crawler
Toyota 4-Wheeling Forum Moderator
Reged: 01/12/00
Posts: 12144
Loc: N. California. USA
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The FSM lists a detailed test procedure but it seems to require some specialized equipment. Could try temporarily bypassing the LSPV and see if the problem does not reappear after a few weeks (rear brakes will touchier with no pressure reduction - will need one union and one line cap to bypass the valve). Or I have my old '85 LSPV (has bad the rod cut down) that I no longer use, contact me if interested. Or you could install an aftermarket (Wilwood) manual proportioning valve in place of the LSPV for under $100:
- http://frontrangeoffroadfab.com/nfoscomm/catalog/product_info.php?cPath=27&products_id=57
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r.c.brown@ieee.org
TruckEditor@tlca.org
Project: 4Crawler
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Adam F
Forum Moderator
Reged: 01/29/01
Posts: 11592
Loc: Cincinnati, OH
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Are you loosing any fluid? I wouldnt think the prop valve would be bad unless its leaking.
Have you checked and adjusted your rear brakes? Maybe the self adjusters are not working right or something, and they keep backing themselves off? Check the adjustment when you have a good pedal. Adjust them to whree they just start to rub. Then wait until you get a soft pedal, and check the adjustment again. If they have backed off you found your problem.
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88 4R, 350 V8, R150 5 speed Sold 
97 4R, stock, daily driver
98 Sienna, kid and dog hauler, wife's ride
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craigw
Need a Spot
Reged: 01/14/11
Posts: 3
Loc: ca
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I notice no leaks anywhere. No loss of fluid. I get air from all 5 places.
The rear adjusters being bad would cause the pedal to travel more but it wouldn't put air in the system would it?
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KF6ZPL
Recreation Advocate
Reged: 02/15/00
Posts: 3945
Loc: Lakeside, CA
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As you have replaced the master cylinder, done the bleeding and still have air in the system (with no loss of fluid), you may not have done a complete system bleed.
If you properly bleed the system, you should have no air in the system.
As you appear to have air in the system, you either have a leak or excess air that you have not been able to bleed out.
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John Stewart
Editor - 4x4Wire.com
4x4Voice
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OOP'S
Roll Me Over
Reged: 04/14/00
Posts: 4230
Loc: Roseville, CA, Gateway to the ...
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You could also have a caliper or wheel cylinder that appears to be fine. They are not leaking fluid to the outside but when they retract, the cups could be sucking air in. This does not happen very often but it can. When I was in High School, I was working, on a friends 55 Chevy that had the same symptoms, we changed the MC and all the soft lines and it still did it. I put four new wheel cylinders on it and the problem went away. There was no evidence of a bad wheel cylinder.
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David Fritzsche
1990 Ex-Cab V-6,5-speed, with a few mods
04.5 CTD Dodge 2500 Ram--Tow Rig
Roseville, CA
"Serenity through Sobriety"
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Brian894X4
Trail Leader
Reged: 05/14/01
Posts: 6767
Loc: Gresham, Oregon
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I believe you can suck in air at a very small leak point, without necessarily blowing a lot of noticable fluid out. As I recall, this tends to happen where the soft lines connect to the hard lines. You might check these connections over really well. Make sure all connections are sealed good, especially since you've replaced things like the MC and some of the brake lines.
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