Thread: 53 Is back from the Body Shop

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Originally Posted by 53 Chevy5

I got a brake question for you guys. I cannot get Rita's back brakes to grab as much as they should, It's really noticeable when pulling a trailer that it is almost entirely reliant on the front brakes. The master cylinder is an 1/16 bore off of a 1990 F-150 , The rears are disc brakes off of a 2000 Explorer, The fronts are GM metrics that came with the m2 kit, not really sure exactly what the vehicle they're off of. I have a willwood adjustable proportioning valve, and with max pressure to the rear brakes, I still can't get them to slide on a gravel road, and smashed hard to the floor, you can power brake like there's almost no brakes there. I've double and triple checked the line routing to the proportioning valve, and swapped the front and rear lines around on the valve, absolutely nothing I do makes a noticeable difference. The only thing I'm starting to think is that I maybe need a smaller bore master cylinder to increase caliper pressure, a 2000 Explorer with four wheel disc brakes does use a 1 in master cylinder vs my 1/16. Any suggestions?

After reading your description my first thought is that you are not using a master cylinder for Disc / Disc front & rear. To me it sounds like you are not getting enough fluid into the rear. Or maybe the master you are using doesn't have the capacity needed for your rear brakes. My other thought is that perhaps the calipers have pushed all the fluid back into the master, then when you hit the pedal there isn't enough volume from the master to build psi.....

I'm starting to wonder if that's the case. I did some more research, a 2000 Ford Explorer also uses a 1 1 /16 bore master cylinder (not a 1-in bore like I thought), which would be the master cylinder that was used with rear end and brakes I'm using. A 1990 F-150 also uses a 1 1/16 master cylinder, but it of course has drum brakes in the rear which don't need as much fluid. I wonder if the Explorer master cylinder has a longer stroke so it is able to fill the rear calipers. I might grab an Explorer master cylinder from our local salvage yard and see if that fixes it.

There is a brake line valve called a hold off valve. It goes in the line to the front brakes and prevents them from operating until the line pressure reaches 100 psi or so. It is intended to allow rear drum brakes to catch up with front discs, since the drums have farther to move. Most distribution blocks for disc/drums have one built in.

I had an issue on my T bucket with the rear brakes not doing much, but they were drums front and rear. I installed stand alone hold off valve and it seemed to help. I know you have discs front and rear, but it sounds like you are having a similar problem. It may be worth a try if nothing else works.

It could also be a pad material issue. The brakes may actually be working as far as hydraulics, but the pads in the rear are harder and never getting up to operating temp.

I remember reading that on the S10 rears, GM was having an issue with rear brake lock up. This was in the days before anti-lock. Their solution was to use metallic shoes and very small wheel cylinders. This effectively prevented the rear brakes from doing much until the line pressure was very high and there was a lot of heat in them, like when hauling or towing heavy loads. This came from another forum, supposedly from a brake engineer familiar with the story. I do know that the S10 rear wheel cylinders were only 3/4" bore! Ford may have done a similar trick with the Explorer rear brakes. FWIW - I have Explorer rear brakes on my 46 and have never been completely satisfied with them either, but they worked well enough that I never got around to working out the reason why.

Going to a softer, higher friction pad material, may solve your problem. Seems like I remember that you are using an Explorer rear. I'm sure someone like EBC probably makes replacement pads in various known compounds. Going to something like EBC Yellow Stuff pads front and rear may make a difference. You could also look for full organic rear pads from the local parts store if they are available. Look at their cheapest line of parts. They should be softer and have a higher friction.

This is a typical hot rod issue. We take parts from different manufactures or different vehicles by the same manufacturer and hope that they will play nice together. Sometimes they don't. That's when you just have to give it some thought and start making changes.

Also, the Expedition calipers will fit on the Explorer brackets or at least they look like they should. They have a larger piston than the Explorer calipers. This would increase the clamping force a little. I have never made the swap, but plan to in the future on my 46 coupe. I suggested this to 40FordDeluxe and I think he either did it or at least tried it. He should have the details.

Thanks Mike, I did not know they made something like that, that could be exactly what I need! Tonight I'm going to eliminate the proportioning valve to see how it acts and see what my next step is from there.

Finally had time to mess around with Rita's brakes again. I bypassed the willwood adjustable proportioning valve to the back brakes and they work perfect. Just sitting there applying the brakes you can hear stuff crunching in the back when you push on the pedal hard, and on the gravel road they almost lock up before the fronts but not quite. I think we're going to call it a win, I don't know why they work perfect without a proportioning valve but I'm fine with it.

Nice! Always good when you can leave something out and fix a problem!

Originally Posted by 53 Chevy5

Finally had time to mess around with Rita's brakes again. I bypassed the willwood adjustable proportioning valve to the back brakes and they work perfect. Just sitting there applying the brakes you can hear stuff crunching in the back when you push on the pedal hard, and on the gravel road they almost lock up before the fronts but not quite. I think we're going to call it a win, I don't know why they work perfect without a proportioning valve but I'm fine with it.

On my coupe with the same valve, I have the adjustment all the way backed off. I don't need it at all. Glad to hear you made a big difference and scored a win!

Need some wiring help here. I've been messing around making a latching relay so if my door is opened a horn will turn on, but I want it to stay on till I hit the kill switch. I can make a latching one easy if I use a power wire to turn it on but my dome light switch runs on a ground and for the life of me I can't get it to latch. Anybody done this sort of setup before ?

Use to standard automotive relays as drawn

Thanks a bunch, I was messing around with two relays trying to get something like that figured out and nothing quite worked. I was Google searching quite a while too and could find nothing. I really appreciate the help, did you draw that up yourself?

Glad I could help!
It doesn't take me long to draw em. I have lots of symbols in store and cut / paste em together, the rest is just connecting lines.

Correct me if I'm wrong, but in order for this to work the switch has to be on at all times since it supplies 12v to the horn. Wouldn't it be simpler to eliminate the second relay and use the first to interrupt the ground leaving the horn supplied with 12v at all times as it was designed?

Ken, you are correct it can be done with a single relay switching the ground. I may have misread his post thinking he wanted to switch positive via a negative input, thus the second relay.
Thank you

Originally Posted by 36 sedan

Ken, you are correct it can be done with a single relay switching the ground. I may have misread his post thinking he wanted to switch positive via a negative input, thus the second relay.
Thank you

I printed your diagram out a couple of times trying to figure out how it worked and it just dawned on me that only one relay was needed, at least the way I understood it. Glad to help and FWIW, the only "latching" relays I've seen were on DC-10s and they were big and used in the generator power system.
I wish there were more questions of this nature as it helps me keep my brain active

The only caveat with single negative latch relay is the horn needs to be switched through the vehicle's horn relay, otherwise the horn's initial current load will be through the door jam switch until the relay latches. The door jam switch may not tolerate the initial current demand of the horn's coil.

I'll revise my original drawing to remove the horn's ground source from the door jam switch and place directly to ground when I get back to my office.