2nd Gen prop valve?

Chris Wire

Chris Wire

New member
I'm getting ready to plumb my Tilton prop valve for the rear brakes and I was wondering whether or not most of you use or discard the factory prop valve.

Getting rid of it would certainly simplify the plumbing aspect of things, but I don't want to throw away a good piece of hardware if I'm going to need it later.

Any thoughts either way?

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Chris Wire
Team Wire Racing
ITS Mazda RX7 #35
[email protected]
 
Chris, I have a 1st gen RX-7 ITA/7 car & I eliminated the OEM prop valve. My prop valve was installed when it was a Spec-7 car & the valve had to be under the hood. I have left the valve under hood so that I don't dial myself out of a race. In IT the valve can be anywhere including within drivers reach. I use Hawk blue at all 4 corners with Mazda air ducts.

Have Fun
wink.gif

David
 
2 questions:
Is it legal?
How do you plumb it with the prop valve gone?

Thanks,

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Marty Doane
ITS RX-7 #13
CenDiv WMR
 
Originally posted by Eagle7:
2 questions:
Is it legal?
How do you plumb it with the prop valve gone?
Click to expand...

I hate that you can't cut/paste from the online GCR.

"Lines/hoses may be relocated and given additional protection. Brake fittings, adapters, and connectors are un-restricted. Brake system circuitry may be revised, but no modification or substitution of the original master cylinder, its location, or mounting is permitted........Brake proportioning valves may be used provided that they are of the in-line, pressure limiting type."

Therefore I say legal, as circuitry may be revised and the only item specifically forbidden is the master cylinder. Additionally, if you leave the OEM prop valve in, then you are limited to only adjusting the rear brakes between stock pressure and less. While that might be okay for a CRX or VW, I'm sure there as many or more cars that need MORE rear brake, not less. I see no basis for the rule if all the rule allows is further limiting the stock pressure.

As for the second question, the RX7 has one line for each front caliper coming off the front of the m/cyl, with a separate line coming off the rear for the back brakes. I will simply eliminate the valve and plumb the adj prop valve directly to the rear outlet on the m/cyl. Not too difficult.



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Chris Wire
Team Wire Racing
ITS Mazda RX7 #35
[email protected]
 
I removed mine. Ran new lines through a Tilton lever style bias adjuster. Works great. Comfortable adjustment when dry is either 1 or 2 clicks from full front leaving plenty of adjustment for when it rains. Hawk Blues all around FWIW.

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Chris Ludwig
08 ITS RX7 CenDiv
 
Thanks guys. Goes on the todo list. Tilton lever is already installed.

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Marty Doane
ITS RX-7 #13
CenDiv WMR
 
I think its legality is somewhat questionable so I would not do it unless there will be a clear benefit. I have a Tilton lever prop valve and in the dry always have it no more than 2 clicks from front. In the wet I will bring it back but I have never perceived that I did not have enough rear brake. If you do need more rear you can always go w/ a more aggressive pad.

Out of curiosity can one of you walk me through the fluid flow? From what I see, there are only 2 lines from the MC; one goes directly into the valve and the other appears to feed the LF brake. I assume all 3 lines from the valve are outlets, 1 rear and 2 front. One front goes directly to the right brake but the other goes back to the MC. It looks to me like that line may actually feed the LF, but why go through the MC? Chris, what do you mean 2 front lines from the MC; on mine the valve has 2 lines marked "F". What you are describing sounds like only the rear goes through the stock valve.

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Bill Denton
87/89 ITS RX-7
02 Audi TT225QC
95 Tahoe
Memphis
 
There are actually a couple different master cylinders and routings of the stock lines. Depending on which model you have, even among all the 5-lug cars.

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Chris Ludwig
08 ITS RX7 CenDiv
 
Bill,

I have three lines coming out of the MC. The car is an '89 GTU, but has been converted to 4 puck calipers. Now the car has not been on track yet, so I may still need to change MCs beforehand.

On the front, I have a line out of the bottom of the MC which runs to the bottom of the prop valve, out the top and over to the RF caliper. I have a line out the left front of the MC which runs directly to the LF caliper. I also have a line in the middle of the MC which runs to the bottom of the prop valve under the shuttle valve, comes out the top and runs back to the T-fitting in the rear.

I don't think the prop valve has any effect on the RF caliper, although I cannot figure out why Mazda would run it through the valve if it didn't. I am told that there is the potential for early RF lockup if I remove the valve.

Can anyone explain why a single MC feeding two identical calipers through separate lines would need a pressure limiting device to one side and not the other?

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Chris Wire
Team Wire Racing
ITS Mazda RX7 #35
[email protected]
 
***I am told that there is the potential for early RF lockup if I remove the valve.***

Chris, I am very curious why this early RF lockup would occure with no OEM prop valve on a 2nd gen while using a after market prop valve. Again on my first gen I elminated the OEM prop valve 5 years ago & have never had an early lockup of either front brake.

Have Fun
wink.gif

David
 
Chris Wire, I think it would be good for you and of interest to most of us if we could get this figured out before we run off and start messing w/ something we don't fully understand.

"I have three lines coming out of the MC. On the front, I have a line out of the bottom of the MC which runs to the bottom of the prop valve, out the top and over to the RF caliper. I have a line out the left front of the MC which runs directly to the LF caliper. "

Yes, there are 3 lines connected to the MC but we don't know if they are all outlets. My 2 lines on the front of the MC are reversed from yours: the one on the bottom goes directly to the LF and the one on the front L side goes to the bottom of the valve. ?

"I also have a line in the middle of the MC which runs to the bottom of the prop valve under the shuttle valve, comes out the top and runs back to the T-fitting in the rear."

That line obviously is the supply to the valve and the top one marked R is the outlet for the rear. By the same token, one would think that the 2 marked F are both outlets. That being the case, the one that goes back to the MC must be an inlet not outlet from the MC.

"I don't think the prop valve has any effect on the RF caliper, although I cannot figure out why Mazda would run it through the valve if it didn't. I am told that there is the potential for early RF lockup if I remove the valve."

"Can anyone explain why a single MC feeding two identical calipers through separate lines would need a pressure limiting device to one side and not the other?"

And which side it is apparently does not matter since mine and yours are reversed. If, as I theorized in my last post, the front of the MC is just a pass-through fed by the line from the valve, both fronts would then have been affected by the valve. That makes more sense to me except I don't know why one would go back through the MC.

Chris Ludwig, if you've done it, do you understand it?





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Bill Denton
87/89 ITS RX-7
02 Audi TT225QC
95 Tahoe
Memphis
 
Well, again, there are several different master cylinder configurations so what worked for me doesn't neccesarily transpose.

My car is setup like this: Bottom MC outlet to the left front wheel, passenger rear outlet to the right front wheel, and driver's front outlet to the rear wheels through the Titlton prop valve. All I can say is it works. I work the brakes over pretty hard and if there was an imbalance issue between the right and left front it'd be apparent. There is none. Only problem I've ever had is the spongy pedal that was well documented a couple months ago.

After looking through the factory manual the stock prop valve only controls the rear and has nothing to do with the right front. Still why the right front line runs through it is a mystery.

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Chris Ludwig
08 ITS RX7 CenDiv

[This message has been edited by C. Ludwig (edited April 04, 2005).]
 
The "prop" valve is actually a "proportioning" valve. It provides pressure to the rear brakes as a proportion of the pressure to the front brakes. In order to do this, it must sense the pressure applied to the front brakes, therefore the RF brake line goes through the valve but the prop valve has no impact on the function of the RF brake. By replacing this valve with a manual proprotioning valve (which I believe is the way to go) you eliminate this "automatic" proportioning and make it totally independent of what goes on at the front brakes, you adjust the rear brake pressure directly. This might require running a new brake line to the RF if you remove the stock prop valve.

One caution on 1st gens, I've heard, don't know if it is true, the the prop valve contains a check valve that is required if the rear DRUM brakes are to work properly.
 
backformore,

Your assessment sounds accurate. The RF line runs through the valve to set the baseline pressure that, in turn, affects the bias of the rears. In my AS Mustang, the valve also had a "shuttle" function, which separated the fronts and rears in the event the fronts failed, thus leaving some minimal braking in the event of a disaster.

bldn10,

Your post was a bit confusing. I have never seen a line run back to the MC on any RX7 I have looked at. Are you inferring that one of the lines running to the valve services both the RF and the rear brakes simultaneously? And the remaining line connected to the MC is a return of some sort? I'm just trying to see it as I understand your description.

To me, the simpler the better. I can get a female/female inverted flare fitting and simply connect the 2 lines leading to the RF. And by removing the valve, I can run pre-made -3 braided lines from the MC through the firewall to the Tilton, and then on to the rear brake tee. As I pointed out earlier, I would like to be able to get the max adjustment possible, rather than starting with the stock setting and simply reducing pressure from there.

The other thing to note would be not to bypass the valve running to the RF without disabling the valve completely. By eliminating the RF line from the valve and leaving the rear connected, the valve would have no reference from which to operate. I'm sure that would be interesting on track.
smile.gif


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Chris Wire
Team Wire Racing
ITS Mazda RX7 #35
[email protected]
 
"I have never seen a line run back to the MC on any RX7 I have looked at. Are you inferring that one of the lines running to the valve services both the RF and the rear brakes simultaneously? And the remaining line connected to the MC is a return of some sort? I'm just trying to see it as I understand your description."

Yea, that's what I was thinking. You've never seen a line go back? - "On the front, I have a line out of the bottom of the MC which runs to the bottom of the prop valve, out the top and over to the RF caliper." That's it. I was thinking that line was not an outlet from the MC but an inlet because the "bottom of the prop valve" is marked "F" as is the top, and I thought they were both outlets. However, w/ backformore's explanation, it may well be that the Fs on the valve are a passthrough just to sense the pressure. I.e. either one can be an inlet or outlet. And that also explains why the fact that yours and mine are reversed makes no difference.

"I can get a female/female inverted flare fitting and simply connect the 2 lines leading to the RF. And by removing the valve, I can run pre-made -3 braided lines from the MC through the firewall to the Tilton"

I get you on the front but 2 lines to the rear? From what? There is only the outlet on the bottom of the MC for the rear so why not just connect that line to the one exiting the valve going to the rear the same as the front?

Sounds like we got it figured out thanks to backformore but I'm still not doing it because I never run mine on full rear as it is.





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Bill Denton
87/89 ITS RX-7
02 Audi TT225QC
95 Tahoe
Memphis
 
Originally posted by bldn10:

(quoting me)
"I can get a female/female inverted flare fitting and simply connect the 2 lines leading to the RF. And by removing the valve, I can run pre-made -3 braided lines from the MC through the firewall to the Tilton"

I get you on the front but 2 lines to the rear? From what? There is only the outlet on the bottom of the MC for the rear so why not just connect that line to the one exiting the valve going to the rear the same as the front?
Click to expand...

Sorry, my description was a bit vague. I will run a single -3 braided hose from the MC to the inlet of the Tilton. Then from the Tilton I will run another -3 hose back to the rear brake tee fitting. Same as on my old AS car, worked great.



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Chris Wire
Team Wire Racing
ITS Mazda RX7 #35
[email protected]
 
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