Brake pedal goes to the floor, couple of questions

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silvermerk
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Brake pedal goes to the floor, couple of questions

Post by silvermerk » Thu Jul 12, 2007 11:18 am

I just recently bought my 2nd XR4Ti. It wasn't running, I ended up replacing the head gasket and had to get another cylinder head because the original one was cracked. That part is done. The previous owner told me the brake pedal went pretty far down to the floor and he was right. When I opened the reservoir I could see no fluid so I figured let's start by adding fluid and bleeding the brakes. I probably went 6 rounds of doing this and the pedal seemed to firm up, that is until I started the car and then it became mush again. I may still have some air in the system but it should have improved some. I did a search and it appears I might have a master cylinder/booster issue. Mine is a 86 so I'm thinking about upgrading to the 88 setup. It appears this is a bolt in deal, am I correct? Also, it's hard to tell if I have any leaks around the wheel cylinders but I don't think so. I am also going to replace the pads/shoes. Any suggestions or thoughts on the matter would be appreciated. I will also post up some pics of the car soon, it's bright yellow with a cosworth wing and cosworth grill and some aftermarket wheels. :)

Thanks.
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Post by Ed Lijewski » Thu Jul 12, 2007 2:48 pm

First I'd check each wheel cylinder for signs of leaks and also the lines and hoses; also check the carpet/firewall under the dash. Then I'd go for more rounds of two-man brake bleeding (one pushing the pedal). the pedal going closer to the floor with engine vacuum sounds normal.

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Post by thesameguy » Thu Jul 12, 2007 2:50 pm

Sounds like the MC may be leaking into the booster...

I don't know that's specifically necessary to upgrade to the later setup versus replace/rebuild the MC, but yeah, it's bolt-in.

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Post by Mike McCreight » Thu Jul 12, 2007 2:53 pm

Check for leaks, then replace the MC/Booster. Good cheap upgrade. You'll be glad you did it. :D
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John R. Rowlands
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Post by John R. Rowlands » Fri Jul 13, 2007 9:43 am

silvermerk,

Like "Ed" said. In addition run your finger under where the Master Cylinder connects to the brake booster. If its wet with brake fluid you know you have a leak!

John
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Post by Reno3133 » Fri Jul 13, 2007 9:52 am

I had a similar issue, i found out the cylinder to my passenger side drum brake was gone. Check the wheel cylinders, replace if need be. Make sure you bleed the whole system properly. Check for leak. Then if your still squishy (lol) and stumped, check your master cylinder.

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Post by John Brennan » Fri Jul 13, 2007 11:17 am

On that note (slave cylinders), be sure that you have the right ones for your car-- some were SAE, and some were metric.
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Baldy_54
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Post by Baldy_54 » Fri Jul 13, 2007 1:25 pm

What's the difference between the MC on a 86 XR and 88 XR? You say interchangeable and cheap? Is 86 SAE or Metric?

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Post by thesameguy » Fri Jul 13, 2007 3:03 pm

The '88+ cars (maybe '87+, but I don't think so) have a substantially larger booster and a bigger MC than the earlier cars. The booster+MC will bolt up to the firewall on an earlier car, but you must keep the booster+MC together - a later MC will not bolt up to an earlier booster, for example.

Not sure about the metric vs. SAE thing - my '86 was metric. I used a Thunderbird MC when I switched to the later booster so I can't comment on a later MC threads...

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Post by silvermerk » Sat Jul 14, 2007 9:51 am

Thanks for all the responses. The car has been sitting for the past week in the driveway and when I came out to investigate there was about a 2 foot diameter puddle of brake fluid in the area around the MC/booster and/or driver's side wheel. Doesn't look like it's a rear cylinder problem. The interesting thing is when I opened the cap to the reservoir it didn't look like the fluid level had dropped. Hmmm. I will check out the areas that you guys suggested and get back with you this morning on what I found.

On a side note, after I got the car running after the head gasket change it idled pretty well even without the timing pointer (ordered from OPMD) but after I bled the brakes on the subsequent drive I noticed it was not idling as well and was missing under steady state cruising. I didn't notice it under acceleration. I know the booster pulls vacuum from the the intake. Could this be related? Oh yeah the idle was pretty low, around 500-600rpm. I'm assuming the previous owner didn't mess with the idle screw or TPS.

Thanks,

Steve
86 XR, all stock for now.

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Post by DPDISXR4Ti » Sat Jul 14, 2007 10:51 am

thesameguy wrote:The '88+ cars (maybe '87+, but I don't think so) have a substantially larger booster and a bigger MC than the earlier cars.
The change-over date was actually during the '86 model year - ball-park date of 3/86 or so. Ya know, for all that the "1987.5 model year" gets talked about, there really should be a "1986.5 model year" designation too, as all the following changes occurred mid-'86...

1) Wide tunnel floor pan
2) E6 Exhaust manifold
3) ZF Steering rack
4) Larger Booster and MC

But I digress... :roll:

The hardware on either brake setup is all metric.

The brake booster will have nearly zero effect on how the motor is running, so get that thought out of your mind. You really need to get the motor timed properly - at least in the right ballpark - before you blow the head gasket.

As for the leak, I'd get the car up on ramps and find out the highest point that is wet with brake fluid. That will tell you where your leak is.
Brad

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Post by Baldy_54 » Sat Jul 14, 2007 11:25 am

The Sticker on my XR says Manuf. in 7-86. Can I tell if they made the changes you say were upgrades, just from looking?

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Post by DPDISXR4Ti » Sat Jul 14, 2007 11:38 am

Baldy_54 wrote:The Sticker on my XR says Manuf. in 7-86. Can I tell if they made the changes you say were upgrades, just from looking?
Of course! That said, July is the typical final month of model year production, so unless something has been back-dated, you would have all of the above.
Brad

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Post by silvermerk » Sat Jul 14, 2007 12:06 pm

Update. The leak is from a hard line up in front of the driver's side splash guard related to the power steering, add that one to the list. I checked under and all around the MC/booster and wheel cylinders for leaks and have found none. I'm going to go ahead and do the pads and shoes today to knock that off the list and try rebleeding again.

I have the timing set up for 0 initial using the TDC/rotor line up the cam sprocket with the auxiliary pulley method so if anything the timing is pretty retarded plus I haven't been driving or running the car since the head gasket swap. As far as the vacuum line being related I just wanted to cover all the bases.

I'll have to check when my build date was to see if it falls in the realm of the changes you mentioned above.

Any other thoughts or suggestions are appreciated.

Steve
86 XR, all stock for now.

silvermerk
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Post by silvermerk » Sat Jul 14, 2007 2:28 pm

I guess I'll be waiting on the pad/shoe replacement until Monday, didn't have them in stock anywhere I called. The front pads were pretty shot. As soon as I get that done than I'll rebleed and then pursue the master cylinder.
86 XR, all stock for now.

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