Seedy Al Posted July 22, 2014 Share Posted July 22, 2014 So have a customers car I am having a bit of a problem with, and after a fair bit of head scratching figured I would see if anyone has some other thoughts. The rear brakes are locking up under reasonable braking before the fronts are getting close. Car is a 1974 toyota crown, with a 2jz turbo. Brakes are mostly standard, so twin pot front calipers with solid disc, and drums in the back. Only mod that has been done is that a toyota surf booster and master cylinder has been fitted. Rear cylinders have been rebuilt, along with new shoes. Machined front rotors and new pads. Now. First thoughts would be to blame the only none original thing, the brake booster and master cyclinder. However, apparently the problem has been present since the car was original. Next thought is the brake proportioning valve. Which seems fair enough. So under the advice of a brake specialist, they removed the original valve, and fit a Wilwood brake bias valve in its place. $600 later and the problem is still there. There next thought was to try and under size the rear shoes. Which seems a backward step to me for two reasons. A: the brakes need to be at there best given engine upgrade. But B: I would have thought that making the contact area smaller would infact make the brakes more responsive as all the brake pressure would applied in one place..... But anyway they did that and it did not help.... So in my last thoughts I have been thinking about master and slave cylinder sizes. The original master cylinder bore size was 15/16. And is now 1 inch. Would assume this would make the brakes just work better all round. However. When the brakes were replaced in the back, apparently a set of slave cylinders that covered crown, and also corolla were put in. Which makes me think that maybe larger ones are meant to be fit, and tgat the combo of large master and small slave is causing to much of a problem. .... However apparently the larger crown option listed wouldn't fit..... So I don't really know. Is there anything I might have missed? One option left is I sold this guy a gs130 crown wagon. Am thinking maybe we need to fit the rear slaves and master cylinder from that. Along with the proportioning valve.... bore suze on that master is 1 inch also btw. Ok. Sorry for the novel. Just starting to pull my hair out... Hearts Seedy al. Quote Link to comment Share on other sites More sharing options...
sheepers Posted July 22, 2014 Share Posted July 22, 2014 dude check the pipes coming out of the master and check the seals are the correct orientation in the master. sounds like either the middle seals in the master are in around the wrong way or the pipes have been put on the wrong way round. 1" master will be sweet with the setup also. could be a pipe mixup? sounds a lot like it? Quote Link to comment Share on other sites More sharing options...
sheepers Posted July 22, 2014 Share Posted July 22, 2014 also, 600 for a willwood bias valve? what the fuck????? Quote Link to comment Share on other sites More sharing options...
bigfoot Posted July 22, 2014 Share Posted July 22, 2014 What about the proportioning valve? Would it require the surf one if its slightly different? Edit:you already covered that Quote Link to comment Share on other sites More sharing options...
downtrail Posted July 22, 2014 Share Posted July 22, 2014 a smaller master will apply more pressure as apposed to a larger one same with slaves. may be as you said incorrect rear slaves try larger piston ones if you can get. and also as above check that the lines coming out of the master are the correct way around. also may pay to check that the handbrake isn't on a tiny amount either may need adjustment. Quote Link to comment Share on other sites More sharing options...
cletus Posted July 22, 2014 Share Posted July 22, 2014 if you need to reduce rear brake, you need a smaller wheel cylinder, not bigger. adjust it coarsely with the wheel cylinder size, and use a proportioning valve to fine tune it. those wilwood valves dont have enough adjustment to fix it if the difference is too great now would be a good time to upgrade the front brakes to vented ones at least, if its going to get driven hard/pass a cert brake test it will probably struggle with solid discs also if the shoes have been contaminated with brake fluid or oil etc they can be 'grabby' even if they have been cleaned, as the shit soaks into the linings 1 Quote Link to comment Share on other sites More sharing options...
Seedy Al Posted July 22, 2014 Author Share Posted July 22, 2014 Pipes should be sweet coming out of master. Before the valve got changed we tried swapping them round thinking that was a possible. No change there, which got us thinking the valve was fucked. Admittedly have not checked the master as told the problem was present before it was all swapped for the surf stuff. Hand brake. Not a bad thought actaually. Might explain one thing I came across when reassembling the rear brakes, which was one side adjuster took alot more than the other.... And yeah. The valve included new lines and checking the brake pressure values. Which as said seemed a big waste of time... but made sense on paper. Quote Link to comment Share on other sites More sharing options...
sheepers Posted July 22, 2014 Share Posted July 22, 2014 I've run the 1" master with stock everything else and it works fine. Check the push rod in the booster too, if it's a fly shit too long it can cause all sorts of Fuck ups. If you want to run bigger brakes on the front then DBA272 rotors coupled with LN106 hilux calipers (equal piston dia ones only) are a bolt on option. Just have to redrill the mounting holes in the disk but that's child's play. Quote Link to comment Share on other sites More sharing options...
Mof Posted July 22, 2014 Share Posted July 22, 2014 A harder brake lining on the shoes would lessen the braking Lower the CoF Quote Link to comment Share on other sites More sharing options...
Bling Posted July 22, 2014 Share Posted July 22, 2014 I know fuck all about brakes really... but is it braking hard enough to lift the weight off the rear, meaning it locks them easily? Just a thought anyway, but the fact it's not been mentioned already leads me to think it's not related. But i'm keen to know if that situation is even a possibility or not. Quote Link to comment Share on other sites More sharing options...
Nominal Posted July 22, 2014 Share Posted July 22, 2014 Can you find out the ID of the original rear slaves, and compare that to the new ones actually fitted? Quote Link to comment Share on other sites More sharing options...
Seedy Al Posted July 31, 2014 Author Share Posted July 31, 2014 right so end of story Pulled all the rear end apart. Found a few problems. the internal part of the handbrake cable on one side was longer than the other, and they tried to balancce this out by welding in a bit to the mostache bar, so the shoes were not sitting all the back back to factory. Which explained to me why one side adjuster took so much more than the other. Solution. Swap the whole rear end with one out of a later model crown i sold him for parts.. turns out problem is all fixed. A bunch of money later for him tho. Quote Link to comment Share on other sites More sharing options...
yetchh Posted July 31, 2014 Share Posted July 31, 2014 Funny you start this thread as my 74 crown locks the rears up before the fronts.. fucken dodgy in the wet, had a few closies when I was driving it. I wonder how common it is/was.. also good you have a solution as I have a later model disk end to put in mine.. Quote Link to comment Share on other sites More sharing options...
Spencer Posted July 31, 2014 Share Posted July 31, 2014 Drum brakes are pretty simple its not a common crown thing they are just a normal setup. I mean drums they are a cunt to keep adjusted sometimes but there's no reason for them to be locking up if you service them and the proportioning valve is good. Quote Link to comment Share on other sites More sharing options...
yetchh Posted July 31, 2014 Share Posted July 31, 2014 Most of my cars have been drum rears and never locked up like the crown.. well, the fj55 used to lock the drivers front until I upgraded to disks Quote Link to comment Share on other sites More sharing options...
Spencer Posted July 31, 2014 Share Posted July 31, 2014 You should have serviced them. Honestly had lots of drum cars and the crowns nothing different, they are the same basic setup as every Toyota drum brake. Quote Link to comment Share on other sites More sharing options...
yetchh Posted July 31, 2014 Share Posted July 31, 2014 Have an ms85 rear end to install in the next 5-10 years anyhoo.. just seemed like a bit of a coinkydink that both rears locked up 1 Quote Link to comment Share on other sites More sharing options...
Seedy Al Posted July 31, 2014 Author Share Posted July 31, 2014 Yeah I have never had drum problems with a crown before. Especially like this. It pretty much all added up to a bunch of things being different sizes resulting in everything being up the shit and people doing dodgy fixes to try balance it out. Old cars equal old fuck ups. 2 Quote Link to comment Share on other sites More sharing options...
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