Guest jwelch Posted March 27, 2002 Share Posted March 27, 2002 Has anyone tried (with any luck) to adjust the stock 280Z proportioning valve? I've upgraded to the larger 2+2 MC and Booster and the rear drums aren't catching as well as before. I've adjusted the drums as tight as possible. When the rear wheels are off the ground I can't stop the rear wheels when applying the brakes with the car in drive. This is really bad. I've posted this before, as I originally thought it was the tranny. Any thoughts? Thanks Quote Link to comment Share on other sites More sharing options...
johnc Posted March 27, 2002 Share Posted March 27, 2002 The stock valve is not adjustable. I suggest you remove it and replace it with a short length of braided brake line as a test. Then find a nice, safe road and try braking hard from 40 then 60 then 80 mph. Caution: you might flat spot a set of tires doing this so start slow and if you get severe rear wheel lockup then its back to the drawing board. Quote Link to comment Share on other sites More sharing options...
deMideon Posted March 27, 2002 Share Posted March 27, 2002 Someone (some where..??) said that you could add brass washers to th stock proportioning valve. I thought they said to add 2 washers. Of course I don't remember if they said to add it to the front or back.... I do plan on testing this in about a month! Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted March 28, 2002 Share Posted March 28, 2002 I also have the 2+2 vaccum brake and master cylinder with the early 4x4 Toyota calipers with a JYZ proportioning valve on a non operating 280 Z project. THe QUESTION: should I remove the OEM brake proportioning valve???????????????????????? for the after market proportioning valve to operate properly. (Advice to any one on a project:Do not get more than 100 modifications going at one time)Now I want rear discs. In the middle of chasis modifictions / two fold:suspension/reinforcing with POR15 paint on about half of everything including my hands and the left one burned from welding from resting on the last pass. Quote Link to comment Share on other sites More sharing options...
CruxGNZ Posted March 28, 2002 Share Posted March 28, 2002 Tomahawk Z, On my '73 I just gutted the stock proportioning valve and left all the plumbing alone, less work. I'm assuming you can do ths on your 280Z too. Then I just plumbed in the APV into the rear brake line. That's it. Can I get a confirmation on this by anyone else? Can he do the same as I have done to my '73? !M! Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted March 30, 2002 Share Posted March 30, 2002 I looked right into that OEM 1977 280 Z Datsun rear proportioning valve and discovered that it is secretly connected to the front brake lines by brake fluid flow via spring and valve. Forum Research shows that a fellow member from down under added two brass washers to the rear proportioning spring to adjust less firmness in the rear brakes and taking a coil or two off the spring to stiffen the rear brakes (or vice -versa since this is Australia and every thing upside down to us). I am tossing the OEM valve and connecting the fore and aft lines with seperate connectors and plumbing that aftermarket rear brake valve somewhere around the master cylinder. I am hoping that I can also get adapters to adapt short brake lines from a donar vehicle to the after market rear brake proportioning valve. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 1, 2002 Share Posted April 1, 2002 What is the difference between OEM Datsun metric brake screw fittings and 1/8 inch brake pipe fittings??????I have this new JYZ proportioning valve via eBay purported to be a 1/8 inch inlet and outlet and found that my Datsun OEM male fitting "hand" screws into the female JYZ proportioning valve ports.(I did not force the fit)I suspect there is a difference such as the Datsun oil pressure sending unit metric fitting and the 1/8 SBC V-8 oil fitting....I tossed the OEM proportioning valve and found that the brass rear T fitting connecting the rear brakes could connect the front and rear brakes that formerly went into the proportionig valve. I cut off the body mounting hole section and polished two of the Tee's up and plan to plug the third hole of the Tee with a metric tapered brass plugs ....jwlech. I apologise for taking over your thread. Speedway Motors sells proportioning valves at $33 to 35.00 (cheapest I 've seen) if you do not want to add washer shims or cut springs for adjustment.I got my p. valve off eBay for about $15.00 total. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted April 1, 2002 Share Posted April 1, 2002 This is my understanding of the brake fittings. The 1/8" pipe threads are to be used to install a fitting into, and then the brake-line fittings screw into this fitting. The Datsun (metric) and the SAE brake fittings are straight cut (the 1/8" pipe is not), and are so similar, that it is nearly impossible to tell the difference when screwing them together by accident. In fact I had done this for years before realizing that there is indeed a slight loss of thread strength (which never showed up in stripped threads) when doing this. Now I remove the metric fitting (10mm 1.25 I believe) and replace (re-flare) it with the SAE fittings for all my aftermarket parts. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 1, 2002 Share Posted April 1, 2002 The Chassis Shop lists a straight brake line adapter for a metric bubble female to 1/8" NPT Male. Is tis the critter I need............. "metric bubble female" what the ************** Quote Link to comment Share on other sites More sharing options...
blueovalz Posted April 1, 2002 Share Posted April 1, 2002 I'm as confused as you on that one. Victoria British used to sell these adapters, but quit about 3 years ago. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 1, 2002 Share Posted April 1, 2002 GM has a 10 mm brake fitting but I do not know if it is straight or tapered or threads per inch. Quote Link to comment Share on other sites More sharing options...
RB30-ZED Posted April 1, 2002 Share Posted April 1, 2002 Ah, ive been miss quoted. Yes it was me that said that you can add some brass washers under the spring of the proportioning valve spring, But do not cut the spring shorter. Shimming the spring will raise the split point were the rear line pressure will be be decreased in proportion to the front, but not the amount it is reduced. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 1, 2002 Share Posted April 1, 2002 I'm running Toyota calipers up front on my '71, and have just added a 1980 MC. -I removed the rear prop valve, I doubt it's metering is even close to what it should be, especially with so much chnaged. -So I'll be running direct lines to each brake, and will add an adjustable prop valve (if needed)after some brake tests.... Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 4, 2002 Share Posted April 4, 2002 NEED help to solve this: Does Datsun have 10 mm "METRIC BUBBLE" brake line fittings???????????????? or standard 10 mm straight brake line fittings????? Quote Link to comment Share on other sites More sharing options...
Guest scca Posted April 4, 2002 Share Posted April 4, 2002 bubble is GERMAN........ VW etc jap cars use the normal inverted flare Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 4, 2002 Share Posted April 4, 2002 I just rebent lines for my 240. The lines to buy are 3/16" pipe diameter, 10mmx1.00, inverted flare. Don't try flaring them yourself...best to buy premade lengths and bend 'em. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 5, 2002 Share Posted April 5, 2002 With all your help, I have been able to re-educate myself and about every store clerk in "River City" (Eugene, Oregon)that deals in fittings on german bubbles,inverted flares and metrics.They just do not offer metrics to the public on a regular basis. A place called Pacific Rubber(????)............ can get me the adapters ,sleeves,etc. and do the inverted flares for me at $5.00 or less per piece.Now, not only can I talk about bubbles and inverted flares but I can eyeball and identify em .Right here in River City and friends, thats bubble with a capital B Quote Link to comment Share on other sites More sharing options...
Miles Posted April 9, 2002 Share Posted April 9, 2002 Testing and replacing stock brake proportioning valve in a 72 240Z: I recently tested my proportioning valve per the Haynes manual. Took the car up to about 30 mph and braked hard. The rear wheels locked up, but the fronts did not lock. The Haynes manual says to replace the proportioning valve if the front brakes do not lock first. Also, my 240z owners manual suggests that the proportioning valve should be replaced at about 30,000 miles as preventive maintenance. Has anyone replaced the stock proportioning valve ($86.00)? If so, did it improve braking performance by preventing the rear brakes from locking first? Thanks Miles Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 9, 2002 Share Posted April 9, 2002 Switch to an aftermarket adjustable brake propotioning valve. Speedway Motors has them at $33.00 in their new 50th Anniversary Catalog that is free. Very fancy catalog! Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 11, 2002 Share Posted April 11, 2002 I decided that after 30 years, that the stock proportioning valve on my '71 no longer served any purpose...especially with Toyota calipers up front, and the fact that it was supposed to have been replaced at 30,000 miles. I rebent new lines for the rear, and removed my valve. The car still locks up the front under heavy braking, which is almost normal. I plan on adding an adjustable proportioning valve on the front to balance it out. Quote Link to comment Share on other sites More sharing options...
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