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jgkurz

Toyota 4x4 Braking problem

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jgkurz    11

Hi Folks,

 

I have a braking problem I'm hoping to get some input on.

 

First let me give you some background. My car is a 77 280Z that I have upgraded to the S12W Toyota 4 piston calipers with 300ZX vented rotors on the front. The rear has 240SX calipers with 300ZX rotors. All calipers are remanufactured with new high quality rotors. All brake lines are Goodridge with a Wilwood adjustable proportioning valve from Modern Motorsports. The MC is a new 15/16 unit with ATE® Super Blue fluid. I am reasonably confident that the system has no air in it since the pedal is good and solid.

 

There are a couple symptoms to my problem. First is the perceived fade I get compared to previous Z’s. It may be the larger 15/16 master cylinder but the brakes just don’t seem to grab as well as I had hoped. This is with both KVR Carbon Fibre and Porterfield R4S pads. I’ve tried both brands on all four corners.

 

The second problem is my front right brake locks up under EXTREME braking. If I’m doing a hard stop after going through the traps at the drag strip or on a road race track, the front right will lock up prior to all the other brakes. What’s strange is the car brakes evenly and acceptably in all other situations.

 

 

I’m thinking about going back to the 7/8 master cylinder to troubleshoot the fade but I’m not sure where to start with the lock-up problem.

 

Any suggestions would be appreciated.

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jgkurz    11
there is a problem with your left front caliper.. return it

 

This assumes that you cleaned everything properly (pads and disks).... contamination will cause this as well...

 

 

I think they are under warranty so I may do a swap. I might try one more bleed on that caliper alone to see if it helps before I tear things apart.

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Nigel    5

How did you hook up the adj. proportioning valve? On '73 and later Z's the stock proportioning valve uses pressure from the front right brake line to modulate pressure to the rear brakes. If you gutted the stock proportioning valve like a lot of people will mistakenly tell you to do (because they assume that it's the same as '70 to '72 Z's), then this could mess things up.

 

Nigel

'73 240ZT

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Zmanco    13

I've already got the 4x4 calipers up front and am getting ready to switch to the 240SX calipers in the rear. On my '73, what do you recommend to put in place of the proportioning valve? Are there any unions (don't know what else to call it) with several female threaded holes that I could put in place of it? I'm hoping I don't have to put in new lines.

 

Also, would there be any issue with running the rears off of one side of the fronts as is done with the stock system on the '73? There would be an adjustable proportioning valve inbetween. I know the pressure SHOULD be the same throughout the front brake circuit, but theory and reality don't always line up :)

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jgkurz    11
I've already got the 4x4 calipers up front and am getting ready to switch to the 240SX calipers in the rear. On my '73, what do you recommend to put in place of the proportioning valve?

 

I use a Wilwood generic valve, lines, and fittings that I purchased as a kit from Ross at Modern Motorsports. The kit was all inclusive and had all the parts ready for installation in my 77 280Z

 

Are there any unions (don't know what else to call it) with several female threaded holes that I could put in place of it? I'm hoping I don't have to put in new lines.

 

You will have to add the prop valve inline with the brake line that feeds the rear brakes. To do this you will probably need a new braided line from the distribution block. I have a 280Z so the 240Z may be different.

 

Also, would there be any issue with running the rears off of one side of the fronts as is done with the stock system on the '73? There would be an adjustable proportioning valve inbetween. I know the pressure SHOULD be the same throughout the front brake circuit, but theory and reality don't always line up :)

 

The recommended approach is to have full pressure going to your front brakes and an "adjustable" lower pressure to your rear brakes. Even in the OEM system you still had a prop valve that reduced pressure to your rear brakes.

 

 

BTW, I fixed the problem I described when I started this thread. The front driver side caliper was defective. I did a warranty exchange then re-bled the system. That fixed the problem. Strangely, it was like I could never get the air out of that old caliper. Now it works great!! :burnout:

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