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pbarcher

Odd brake pedal travel

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Hi All

After a complete suspension/brake/bearing/seal/bushing project on my 73, I have an odd problem with brake pedal travel.

When I apply the brakes from moderate speed, the pedal doesn't engage until it is approximately even with the gas pedal. At that point the brakes work well but the side of my foot hits the gas. This didn't happen before all the work I had done. When the car stops, if I pump the brakes once the pedal height returns to "normal" which is about .5 inches higher than the gas. This is where the pedal used to engage.

The calipers have been completely rebuilt, master cylinder has been changed (even though a new one was installed two years ago), pads changed twice, rears completely rebuilt with premium products, system throughly blead, etc. However the Master Vac is original to the car. I've owned this car since new, so I'm very familiar with how the brakes used to work.

Any thoughts?

Peter

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First, bleed the master if you haven't already done so. Second, search "reaction disk" if bleeding the master doesn't work.

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Thanks all. I'll bet that the shop didn't bleed the master on my '73, which was replaced very recently. Can it be bled on the car?

After two recent drives through the Virginia countryside, I discovered an oily fluid on the plastic carpet protector under the brake/clutch pedals, which I think must be brake fluid. Does this mean that the brake booster is bad? It is original to the car. Braking seemed to be OK but I took it easy once I realized that something was leaking.

If the master vac needs to be replaced, is there any difference in the quality of the rebuilt units offered by our sponsors and the national chains?

As always, your suggestions and advice are appreciated.

Peter

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Thanks all. I'll bet that the shop didn't bleed the master on my '73, which was replaced very recently. Can it be bled on the car?

After two recent drives through the Virginia countryside, I discovered an oily fluid on the plastic carpet protector under the brake/clutch pedals, which I think must be brake fluid. Does this mean that the brake booster is bad? It is original to the car. Braking seemed to be OK but I took it easy once I realized that something was leaking.

If the master vac needs to be replaced, is there any difference in the quality of the rebuilt units offered by our sponsors and the national chains?

As always, your suggestions and advice are appreciated.

Peter

If your oily fluid is brake fluid it is more likely from the clutch master cylinder. Another possibilty is oil from the speedometer cable. Our car ('73 240Z) had an oil leak in the transmission that pushed oil through the speedo cable and it leaked out at the back of the speedo and onto the floor inside the car.

Brake fluid and gear oil are very different in look, feel, and smell so you should be able to tell which it is without too much difficulty.

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Thanks all. I'll bet that the shop didn't bleed the master on my '73, which was replaced very recently. Can it be bled on the car?

As always, your suggestions and advice are appreciated.

Peter

Didn't see your question answered: Yes, the master cylinder can be bled on the car. Actually make that the master cylinders. The front and back brake system hydraulics are completely physically separated from one another. The master cylinder needs two bleedings if both the front and rear brake lines have been disconnected for servicing.

Chris

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Here let me toss this idea out for discussion. Assuming the pedal feels firm, but the position is low, maybe the problem is a rear brake adjustment issue?

If the car still has the OE type drum brakes and the pedal gets higher when pumped it could be too much free play at the rear brake shoes. Pumping the pedal quickly will take out the freeplay giving you a higher pedal. The rear brakes have a 10 psi residual pressure valve built into the master cylinder. When the brakes are pumped quickly the valve doesn't let all the fluid return to the master cylinder. Repeated pumping restores the brake pedal level to the higher position.

Another issue that can come from doing a brake job is the rear shoes may not have the same radius as the drums. When you turn a brake drum the radius changes slightly. If the shoes are made for an OE diameter drum, only a very small contact area on the shoe will touch the drum when the brakes are initially applied. As the brake shoe wears it will wear to the larger radius until the shoe fully contacts the drum. It is possible that the shoe has worn away that small contact area requiring the brakes be adjusted.

Years ago when most all cars had drum brakes and turning brake drums was common, brake shops had a tool that would re-arc the brake shoes to fit the turned/resized brake drum radius. By re-arcing the brake shoe to properly fit the turned drum radius the friction surface (in therory) would make full contact with the drum when the brakes were initially used and there was no wearing in period. Today, where brake drums are almost always replaced and not turned, it will be hard to find a shop that has the tooling to re-arc brake shoes to properly fit a turned drum.

Edited by Dave Patten

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I believe that the speedo cable is causing the interior leak. It was replaced with a reproduction unit from MSA not long ago. If the cable is leaking where it attaches to the speedo can the lubricant enter the guage and cause damage?

What's the best way to bleed the master on the car? The shop that did the work said that they bench bled the master.

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I believe that the speedo cable is causing the interior leak. It was replaced with a reproduction unit from MSA not long ago. If the cable is leaking where it attaches to the speedo can the lubricant enter the guage and cause damage?

What's the best way to bleed the master on the car? The shop that did the work said that they bench bled the master.

I doubt that oil from the speedo cable will get into the meter. It will run out at the joint were the cable attaches to the meter. Keep in mind, the oil leak is actually at the transmission. The oil seal in the speedo drive pinion is bad.

The master cylinder should have bleeder valves on it. Look on the drivers side of the master just above where the brake lines attach. If there are no bleeders just bleed at the fittings where the lines attach.

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More than likely it is the rear brakes that will give excessive brake travel. Recheck your adjustment. You might have thought you had the shoes seated properly, but once engaged they seated and caused extra brake pedal travel. Usually pumping will regain this travel-so revisit your rear brakes

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Is the oil seal in the speedo drive pinion part of the new cable that I bought from MSA? Could you explain further?

Thanks

Peter

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Is the oil seal in the speedo drive pinion part of the new cable that I bought from MSA? Could you explain further?

Thanks

Peter

No, it is not part of the cable. The seal is in the side of the transmission where the cable attaches. To replace the seal you must remove the pinion gear from the transmission.

To remove the pinion gear you remove the cable from the transmission. Next remove a small hex-head screw from the side of the transmission just below where speedo cable attaches. This screw holds on a little plate which retains the pinion gear assembly. Now you can pull the pinion assembly out. It might be tight due to having been there a long time. You can use pliers if neccessary to grab the end but be carefull so you don't damage the threads. Wrapping the threads with a rag helps.

There are 2 seals on the pinion assembly. One is an o-ring in a groove around the assembly. This one will allow oil to leak onto the ground if bad. The other is pressed into a bore at the end of the pinion assembly and will allow oil to leak into the cable. Both are still available from your Nissan dealer for a few dollars.

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