Soft Pedal

[C. Ludwig]

On my 2nd Gen ITS car I've always had a bit of a soft pedal. This year I'm determined to rid myself of it. Everything in the system is new or rebuilt. New master and rebuilt calipers. Nothing is leaking. I've bled until I'm blue with ATE. A fellow 2nd Gen racer helped me with bleeding last year without much results and the pedal in his car is right. So at least he knew what he was doing. So I don't think it just needs bled. Funny thing is if the car is running and I have my foot on the pedal it's mushy but as soon as I shut the car down the vacuum bleeds out of the booster and the pedal comes up. Is that right or does that indicate a problem with the booster? It's the only thing that's not new. It's original to the car and has never been touched. Opinions? Thanks!

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Chris Ludwig
08 ITS RX7 CenDiv

[instigator]

ludwig, try starting from scratch. Remove all of the lines from the master cylinder. Cape them off. Bleed the ports. start the car. Do you have a good pedal? If not the problem lies in the master cylinder or booster. If you do have a good pedal connect one line bleed the caliper or calipers it operates. Start the car is it good or bad. If good remove and re cap and bleed, Connect another line and repeat this process until you check all of the lines seperatly. You should find your problem that way. By the way have you checked to make sure your calipers float smoothly on their guides? Please let me know if you find your problem.

Kurt IT7 #00 and #59

[C. Ludwig]

Good idea. Never thought of isolating each component. The rears float well and the front pistons are free as well. Now where would one suggest finding plugs for the master cylinder? Guess I could throw a ball of weld on the ends of some spare fittings?

BTW, I quickly figured why the pedal goes hard as soon as the engine is cut. I had replaced the soft vac hose from the hardline to the booster and forgot to install the check valve. Put one in and now the pedal stays soft when the engine is cut.

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Chris Ludwig
08 ITS RX7 CenDiv

[John Herman]

Chris, Might want to check the structural items of your system for any cracks or excessive flexing; firewall, brake pedal arm, attachment points to body, bolts tight, etc.

[ddewhurst]

Chris, with this soft thing, think about your age.

Is your 2nd gen master cylinder is similar to the first gen. What I mean is the 1st gen master cylinder is one round cylinder with two seperate pistons atttached/machined to a common shaft. The piston at the rear of the master cylinder is for the rear brakes. The piston at the front is for the front brakes. With a 1st gen when you bleed the brakes you start with the R.R, then the L.R. & you have a HARD pedal....... Now when you go bleed the R.F., then the L.F. you have SOFT pedal. What happens is that with the rear fully bleed & a HARD pedal the front piston can not travel far enough, push enough brake fluid to allow you to bleed all the air out of the front line/lines. The rear piston is solid & does not allow the front piston to travel the required distance to eliminate the air. My solution to the SOFT THING (I am older than you ) was to install a speed bleeder in each caliper & a speed bleeder with a short piece of tubing attached in the rear line (I have only one line going to the rear) at the master cylinder area. After beeding the rear & haveing a HARD pedal, take the master cylinder pedal cover off, insert the master cylinder speed bleeder hose into the master cylinder, just crack the master cylinder speed bleeder open, & now bleed the front. Now with the master cylinder speed bleeder cracked open the rear fluid flows back into the master cylinder & the front piston travels full length allowing the front air to be bleed out of the front brakes. One man/woman job & your THING will be HARD.

Your THING will be HARD if you had air in your system. If the issue was not air your thing will still be soft. Soft is not good...

Have Fun
David

[C. Ludwig]

I played with it a good bit last night and it has to be air in the system I'm not getting out. If I pump it enough it firms up. Guess we'll get back to bleeding again.

I'll check the structural items John. Thanks for the input!

Dave, I dunno about your soft thing... When I see you in St. Louis next week let's just not mention this conversation?

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Chris Ludwig
08 ITS RX7 CenDiv

[This message has been edited by C. Ludwig (edited March 03, 2005).]

[ddewhurst]

Chris, from my experiences a person can bleed the brakes untill hell freezes over on a 1st gen Mazda & the brakes will still be soft. If your master cylinder is similar to the 1st gen get five speed bleeders & make it a final fixed issue. After I put in the previously explained speed bleed system the soft pedal has NEVER shown up again. I don't bleed between sessions because the pedal is always hard.

Have Fun
David

[This message has been edited by ddewhurst (edited March 03, 2005).]

[backformore]

Here is another thing to check. Make sure your clearances are correct between the master cylinder and the brake booster as well as the pedal adjustment. I had a soft and long pedal on my second gen and as we adjusted the pedal freeplay, both problems improved. I sold the car shortly thereafter and I don't recal if that fixed the problem, but it certainly improved it.

[C. Ludwig]

Pedal adjustment is one thing I went over last year and it was good. I'll check again though. Never hurts.

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Chris Ludwig
08 ITS RX7 CenDiv

[bcarter]

Dave,

I also am an old fart, with occasional SPS (soft-pedal syndrome) in my 1st gen. I win a bunch of races, so maybe I don't need the darn brakes, but...

So, I need a little clarification on your speed bleeding technique.

First off, where do I get the speed-bleeders, and second, can you clarify what you do with the whole set-up..particularly the part about the master.. Please feel free to e-mail me, racing(at)wheatbuckley.com and maybe I can ask you some specific questions.

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G. Brooke Carter
Wheat Buckley Racing
# 10 Challenge Car
2004 Class Champion
Calgary, Alberta


[This message has been edited by bcarter (edited March 03, 2005).]

[ddewhurst]

Brooke, I will e-mail the more specific details.

[C. Ludwig]

Well, I'm learning all kinds of things. There are two rod adjustments in the pedal linkage. One from the pedal to the booster (knew about that one and checked it sometime ago) and one from the booster to the master. Checked it last night. It was a few mm short but lengthened it up and the results were the same.

We adjusted the rod in the booster last night then began bleeding again. Again the pedal was very solid with no vacuum but as soon as we fired it the first 1/4 travel produces a very soft pedal.

Now I have 3 sets of factory manuals for 2nd Gens and I finally went there for help last night. Turns out there are two sets of bleed screws on the rear calipes. How many times have I had this and other 2nd Gens apart and never realized this. The manual says to bleed from the bottom if the calipers have been rebuilt. Gonna try that one tomorrow...

BTW, cages make it a huge PITA to work under the dash and my head still hurts.

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Chris Ludwig
08 ITS RX7 CenDiv

[MaxEnergy]

This topic is very timely but I don't have much to add. I too am stumped by a very similar situation but I know it is not like that on all 2nd gens. I bought my ITS car from Andy B who post here often and the pedal is firm and solid ALL the time, even after I have rebuilt the calipers a quick bleed and it is firm and stays firm. 2 of my very good friends have been fighting the exact problem mentioned above, we have replaced, the master, the ss lines, the calipers, adjusted the pedal and bled gallons of fluid and can't get it to firm up without a couple quick jabs of the pedal. With the engine running the pedal is even lower and mushier. I'm not sure how the booster could be the issue but it is the only thing we haven't replaced as well.

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Jamie Kekeisen
86 ITS RX-7 NER
92 325IS under construction

[reisertracing]

Novice question, what are the sizes of bleeder screws on a 1985 Mazda RX-7?
I found speed bleeder screws for sale at Pegasus Racing, but don't know the size to order.
Any help will be greatly appreciated!

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Johhny R.

[ddewhurst]

Johhny, I also have an 1985 RX-7 1st gen. I went to the garage & measured a OEM bleeder which I had 4 in a package. The diameter measured .266 inches. I purchased my speed bleeders at Pegasus & they have 7 mm & 10 mm.
7 mm X .03937 = .276 (that works)inches. 10 mm x .03937 =.394 (to big)........ As best I could measure my OEM bleeder has 24 or 25 threads per inch which would make the metric thread 1.0 mm.

If you buy the Pegasus 7 x 1.0 mm part number 3266-12 you should be in good shape.

Have Fun
David

[C. Ludwig]

Success!!!!

After all this time! I guess it was the 2nd bleed screw on the bottom of the rear calipers. Here's to reading the instructions. Bled from those first and got quite a bit of air. Then went back and re-bled everything. Pedal is now firm at the top of the stroke with vacuum applied to the booster. Now that I have a firm pedal it'll probably totally screw up my feeling for the brakes. I won't know how to act.

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Chris Ludwig
08 ITS RX7 CenDiv

[Dick Elliott]

10mm equals 25.38 thds per inch. The metric # (in this case, 10mm)is the length of one thd, or aprox .0394. Heavy on the aprox!!!! Hope this helps. DICK

Originally posted by ddewhurst:
Johhny, I also have an 1985 RX-7 1st gen. I went to the garage & measured a OEM bleeder which I had 4 in a package. The diameter measured .266 inches. I purchased my speed bleeders at Pegasus & they have 7 mm & 10 mm.
7 mm X .03937 = .276 (that works)inches. 10 mm x .03937 =.394 (to big)........ As best I could measure my OEM bleeder has 24 or 25 threads per inch which would make the metric thread 1.0 mm.

If you buy the Pegasus 7 x 1.0 mm part number 3266-12 you should be in good shape.

Have Fun
David

[23racer]

I had the same problem with my car (1988 chassis) and found a different issue that needed to be looked at. On mine I was still running the stock proportioning valve. After changing the rear calipers at the track, my crew couldn't get the rear brakes bled. We went around and around the car numerous times and the best we could do was a very mushy, loooong pedal.

Finally in frustration I wacked the proportioning valve with a hammer and the next time the rear brakes bled properly. It turns out, after talking to an older race mechanic who had worked on 2nd gen RX7's back in the dark ages of Firehawk, that the stock proportioning valve has a fail safe. If you whack the brake pedal down with no resistance in the rear brake lines, the proportioning valve's shuttle valve will slide fully to one side and stick there until released either manually, with some fluid placed in the lines/ calipers or by a quick rap on the proportioning valve.

Don't know if this will help, but now that I know this I have had it happen twice more and been cured with a slow pedal depress and a quick light tap on the proportioning valve.

By the way this year I have removed the stock valve and gone to a Wilwood valve.

[ddewhurst]

Chris, thanks for posting your success results....

Have Fun
David

[paulydee]

Hey Chris,

I am glad to see that you got your brakes squared away. I knew about that lower bleed port but frankly I have never used it so it never occured to me that it could have contributed to your problem. See you at IRP I assume?

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Paul D'Angelo
73 ITS CENDIV
Indy Region
http://www.iridiumracing.com