View Full Version : Front brakes
05-05-2009, 01:00 PM
I have Monte Carlo disk brakes in the rear and 79-85 mini truck disk parts in the front. I also have a new Aisin big bore disk brake master cylinder and adjustable proportioning valve for the rears. I have found that even with the proportioning valve adjusted to max limit, the rears will lock up before the fronts on a gravel road.
At Moab last week, going over ledges and super steep descents, it felt like the rears were doing all the work and I had trouble holding it. At times the rears were locked up while the fronts were still turning, even with me standing on the brakes with both feet.
Questions: With the MC I have do you think I should add a 2lb residual valve? If so, do I add one to both the front & rear?
The pads look good on the fronts, is there anything I can do to improve the braking power on the fronts? Could there be something wrong with the front calipers that I'm not getting good clamping pressure? I don't see any leaks. Are there any calipers I can convert to that are an upgrade over the stock units? One person told me that converting to 4runner calipers will be a big upgrade in front braking performance. Any inputs on that? Is there a specific year range of 4runner caliper I should look for?
05-05-2009, 01:15 PM
Converting to 86-95 minitruck (including 4Runner) front brake calipers, FJ40 vented disks, and wheel spacers to correct the backspacing will yield superb brakes if paired with an FJ80 Aisin 1" MC and V6 minitruck vacuum booster.
With the 79-85 minitruck front brakes mounted in the rear, and a Front Range Offroad Fab manual prop valve (Summit Racing with metric fittings), I often consider getting interior windshield wipers to clear the nose prints off the inside of the windshield.
Yah, it stops.
No residual valve required.
05-05-2009, 08:06 PM
if your running the oem proportion valve. i recomend getting rid of it and installing a manual proportion valve. ( so you can fine tune your suspention to what feals best )
the reason the rears are locking up is because your valve is open 100% allowing greater pressure to the rear. which brakes surpurb on rear drums. but combined with disk brakes and you get "nose prints" or too much rear stopping force
toyota proportion valves are designed so that, with no weight in the rear of the truck the brakes are about 70-30 front-rear, and the more weight you add to the truck/runner the more braking forse is needed to stop the same. so the valve allows more pressure to the rear. so that the stopping force is felt the same regardless of payload:thumb:
to answer your Q better, the setup you have should be just fine, unless you are planning on running SCCA, the 89-95 v6 taco front 4piston calipers are my fav.. the master cyl you have is the best that im aware of.. it moves the most fluid.. if im not mistaken the stock proportion valve has 2 return lines.. if you wanted to get crazy, i'd pull all the lines off and run just one line back the rear and through the manual valve the hose to the axle then split to both calipers.. so that the brakes are much simpler you can also strip the front and run new lines and split and run equal length lines to both sides
05-06-2009, 09:33 AM
I dont have an OEM proportioning valve. I have an adjustable aftermarket unit. Even with this unit cranked wide open for maximum pressure limiting to the rear, I still have an issue with unbalanced braking.
I have the master cylinder shown in the attached photo. It is an aisin unit I got from JT Outfitters for $126.
I understand the impact of inertial weight transfer on the rear versus the front brakes. The issue I'm having is more than this.
In Moab, crawling down steep descents with virtually zero forward inertia, I would have to stand on the brake REALLY hard to hold the vehicle at full stop. You could hear the rear brakes groaning so you knew they were taking most of the load. You could also see at times where the rear tires were skidding on the rock and the front tires were still turning, again while standing on the brakes (literally) and the engine running so you're getting power boost.
Im wondering if this MC has a residual valve built into it for the rear but nothing to the front? If so, would that cause the rear brakes to apply much sooner and result in the fronts not fully applying? I know adding upgraded front brake components may yield a 15 to 20 percent improvement in clamping force, but I have to think the components I have, if functioning properly, should be working better than this.
Thus my question whether you think adding an after market 2 lb residual valve to the front circuit would be worth a try? Does anyone know of a brake chain store like Brakes Plus that has the ability to measure brake line pressure? If I could measure front versus rear line pressure I could verify its not a MC or line restriction issue.
05-06-2009, 10:14 AM
Im wondering if this MC has a residual valve built into it for the rear but nothing to the front? If so, would that cause the rear brakes to apply much sooner and result in the fronts not fully applying?...
Must be removed for rear disc brakes or the rear will drag:
05-06-2009, 10:32 AM
Must be removed for rear disc brakes or the rear will drag:
Mike-I think that applies if you have a MC that was setup for drum brakes, which would have had a 6 lb residual valve, that would make the disks drag since they are supposed to use a 2 lb residual valve.
05-06-2009, 11:51 AM
OK, I understand, I think.
I had to go outside for a walk after reading this to keep from getty dizzy :hill:
I'm not sure the booster should really be a factor in this since it just makes pushing the pedal easier. Whether the engine is running or not, if I am pushing on the pedal as hard as I can (seriously, like with both feet) it still seems like I should be able to get the front brakes, if functioning properly, to lock up at low crawl speed.
I'm wondering if I should just go ahead and get the JTO kit to put monte carlo disks and calipers on the front too?
I really want the peace of mind knowing if I go down any more steep declines in Moab that I can totally stop the vehicle with a resonable level of effort on the pedal.
05-06-2009, 12:54 PM
I called a guy I met a long time ago, who has been running a little brake repair shop out on the East coast for like 50 years. I described my front brake problem to him and it took him about 10 seconds to say:
"Check the rubber hoses that go from the hard line to the caliper. The older Toyota lines are notorious for losing strength over time so that when you push the brake pedal, they swell up like a balloon and all or most of the pressure goes there instead of into your calipers.":banghead:.":banghead:
I know those hoses are old and that would explain perfectly the symptoms I'm seeing. I'll let you guys know if this turns out to be the case.
He said if it isnt the hoses, it could be that one of the 2 cylinders in one or both calipers is frozen up so you arent getting full clamping. He said this is also a common problem back East with the salt and stuff especially on the older mini truck calipers. If they sit for awhile between uses I guess they can freeze up.
05-06-2009, 01:36 PM
I agree, I will replace the rubber lines no matter and am already working a deal to get some S12W calipers.
From another thread on MUD I'm following, it looks like the experts are saying you should use an OEM proportioning valve in addition to an after market adjustable unit because neither unit by itself has enough force to overcome the bias need because of the massive monte carlo calipers on the rear.
Does anyone have an OEM proportioning valve laying around they would be willing to part with? It should look like this:
05-15-2009, 08:21 PM
lol i was just about to reply :blah:
"how old are your hoses in the front"
then i actually read all the posts..
cheap and easy place to start.. also knowing there new is always keeps peace of mind.. :cheers:
05-16-2009, 02:17 PM
Yeah, the booster should not be necessary to brake. Definitely OEM systems are designed that the booster can fail and you still have a reasonable amount of leverage in the pedal that a little old lady can at least slow down. The booster though does adds a non-trivial amount of help. But with both feet a strapping fella like you for sure should be able to stop.
In theory, theory and reality are the same, but in reality, they are not... :lmao:
Just changing from the I4 vacuum booster to a V6 vacuum booster made a HUGE difference in my brake system. I had upgraded the front brakes, upgraded the MC, gone with fresh SynPower brake fluid, and it wasn't until I swapped boosters that I got the schnoz-reshaping brakes.
Also, the non-vented early minitruck front brakes are not as powerful as the later vented style. You should look into upgrading them.
05-16-2009, 04:25 PM
I've some of the newer Toyotas that have brake systems without vacuum boosters. Do those work any better with a non running engine than the vacuum type do?
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