In Thread:

https://www.f150online.com/forums/wh...ml#post4588616


I describe my problem. As I say there, maybe my brake booster is worn and moving so that my pedal goes lower than it should.

I wonder if anybody out there has a similar E or F series van or truck and can help me. If there is, could you have someone watch the end of the master cylinder while you press the brake pedal with the engine running. I'm hoping yours does not move at all.

My MC moves. Not much, an average of three measurements with the engine running gave 0.0128 inches. Not much but looking at the mechanical advantage of the brake pedal, I'm hoping this is too much and I need to replace the booster.

An image of the area I am talking about is at:

http://www.f150forum.com/attachments...r-cylinder.jpg

Thanks In Advance,

Pete

 

I am having this SAME problem...You ever fix it?

 

Yes I did by building a bypass. But first I would suggest you make sure your rear brake self adjusters are working. One of mine was broken and I am sure that contributed to the problem.

Anyway, I started a thread on another forum. I don't know if it is a violation of "netiquette" to post a link to another forum but here goes:

http://www.fordforum.com/forum/gener...s-floor-24307/

There is also a spreadsheet at:
http://home.roadrunner.com/~pjcalins...asurements.xls
where I posted a picture of what I built. I was also making readings about how far the Master Cylinder might be moving. They are shown but it was a red herring.

The spreadsheet has a second worksheet showing what it cost me. The column "Dan" is what I had to reimburse my son.

Hope this helps,

Pete

 

Thanks !!! So it was inside the ABS unit that caused you to be able to build no pressure?

 

I guess I'll never know. I believe the first replacement MC was bad. I couldn't get pressure. After installing the bypass I still couldn't bleed the system. I must have run three quarts of fluid through the system before I finally got pressure. With the first replacement MC being faulty, by the time I got that replaced I had so much air in the system it took many bleed cycles to get the air out. By then I had installed the bypass. I believe that if the ABS was still in there I would have filled it with air and it is really impossible (I believe) to properly bleed an ABS without the computer.

That is why I started by saying make sure your rear brakes are adjusted properly. You need to be an old coot like me to remember before self adjusters and adjusting brakes everytime you changed the oil.

 

Yep i snugged the rear drums up adjusters before all the bleeding. Everything is brand new and working tho. Calipers rotors pads drums shoes slave cylinder whole new drum kits in the rear with new adjusters and break lines master cylinder and brake booster. So im basically on my hands and knees hoping this works lol.

What did you use to tie the 2 front brake lines together? Just a T? Wondering how to go about it since they are two different sizes.

 

It wont let me access the pictures of your bypass pictures. Any way you can post them here?

 

All the fittings are different so they can't be crossed up. I bit the bullet and cut them off. I got a flaring tool (double flare) and new fittings that match the Tees. Flaring the steel lines is really tough. Crank the tool as hard as you can. I actually made a jig that fit my compressor to test the fittings between the tees. 100 PSI air is a pretty good test for lines that carry fluid. That gave me the feel for how hard to turn the tool so the fittings on the lines in the van were made correctly.

Here is a link to the spreadsheet with some explanations:

http://petecal.co.nf/VanABSBypass/PedalMeasurements.xls

Here is a larger picture:

http://petecal.co.nf/VanABSBypass/vanbrakes11Crop.jpg

And one with the ABS side by side:

http://petecal.co.nf/VanABSBypass/vanbrakes12CROP.jpg

Finally, I decided I wanted to fix up the wiring so the ABS light wasn't on so:

http://petecal.co.nf/VanABSBypass/ABSCircuit001.jpg


Hope this helps.

Pete

 

Thanks! And just curious, does the line coming out of the mc more toward the front, for the front breaks, and the line closer to the brake booster for the rear?

 

I don't remember anymore. But the rear line is connected to the MC using (I forget the name) a device that lowers the pressure to the rear brakes. It looks like a long nut (like 3/4" wrench, 1-1/2" long) and is screwed into the MC. Then the rear line is screwed into it.

 

no
The line that is closer to the booster is the Primary Circuit... it feeds your front brakes (on a truck, cars are usually diagonal split systems)
The line at the "front of the cylinder" is the secondary circuit... it feeds your rear brakes.

the "long nut" on the secondary circuit is a Proportioning Valve (AKA Prop Valve) and it does indeed reduce the pressure to the rear brakes. Not all vehicles have one... some have the prop valve on the rear axle and it controls the pressure based on the weight in the truck. Newer vehicles just use ABS/ESP/Traction Control to keep the rear brakes from locking up.

 

"Proportioning Valve", right, I just couldn't get that to pop into my head last night.

On my 1999 150 Van the line on the MC for the rear brakes (including the Prop Valve) is near the boaster and the line on the MC for the front brakes is near the front of the MC.

I just took a look.

Pete

 

Just another thought. Someone said they knew of a case where the booster could move when the pedal was pressed. Something like the firewall was flexing or something. I made a lot of measurements but couldn't detect that with mine.

 

I won't argue with you as I don't know for sure... but I design MCs for a living and I've never yet seen one where the front brakes are fed off the secondary circuit.

... but maybe it is from a different supplier so anything is possible...

 

I guess I don't know what defines a primary verses secondary. I just know that the line for the rear brakes comes from nearer the firewall on my van