Hydroboost

[70 Steed]

Keep us posted on how the residual pressure valve works. My understanding is with no valve the rear brake shoes retract all of the way. With a pressure valve it maintains 10 pounds of pressure to the rear brakes which doesn’t allow the shoes to retract all of the way. That means the shoes contact the drums sooner when you step on the brakes. If my understanding is correct I don’t think the pressure valve will solve your problem.

[CityHick]

I am having difficulty with this idea as well. I can see that the residual pressure valve will help with pedal feel, but I do not know that it will address the lack of front braking performance. While I enjoy time out in the garage turning wrenches, this project has gotten a bit ridiculous.

As I look back on how my Bronco braking worked before, it was never good and I am wondering if my front brakes were always weak. Perhaps the extra boost is making the rear brakes respond better than they ever have before, and that's exacerbating the weakness with the fronts. I don't know... just thinking out loud here.

I do know that the front brake calipers are grabbing, I can see the wheel stop rotating when I hit the pedal with the front end off the ground. They're just not grabbing enough when driving.

[71BRONCO71]

Do you have Ford brakes upfront or the Chevy conversion?

[CityHick]

Chevy conversion

[CityHick]

I am getting there.

One thing this project has taught me is that increasing the amount of pedal boost will expose the problems in a brake system.

First piece of followup: the 10lb residual pressure valve on the rear brakes helped with pedal feel - and in fact, buried in the Wilwood documentation for my master cylinder, it is stated that this is required for rear drum applications. Lesson learned.

Things are improving but I am not out of the woods yet. I still have the issue of not stopping totally straight.

After beating my head against the wall a while, I pulled the front wheels off and noticed that the o-ring inside of one of the right front caliper bolt hole was sticking out the end. I pulled the caliper off and after an hour of cussing and frustration I got it back into it's groove and re-assembled. I believe this was a small part of the problem - the o-ring being out of place wasn't allowing the caliper to slide in the manner it is intended to (at least not as freely as it should). Again.. minor but after addressing this I did notice that my bronco is at least stopping a little bit straighter.

A guy around the block saw me roll by today and followed me back to my house, introduced himself and we talked for a half an hour. Turns out he's a retired Ford mechanic. We talked about my problems and he said that a lot of Ford cars with drum rear brakes are known to lock up the rears first when the brakes are cold, cited several models of vehicle and TSBs that he addressed while he was still working. So... I took his advice and drove around for a while. I do think this is a part of the issue as the braking performance is improved after the brakes are warmed up. I am now not sure if the rears are locking first or not, but it is better.

As stated, my remaining issue is that when I come to the end of a skidding stop, the bronco pulls to the left - though what seems to be happening is that the rear is actually sliding out to the right. Having put it into a skid about 20 times by now, I have learned that a very slight correction on the steering wheel straitens it out, though I don't feel that this should be necessary. I've been screwing around with adjusting the rear brakes trying to get them to equalize and haven't been able to get it there yet. I can see from the skid marks that the left is locking sooner than the right. Perhaps I just need to continue tinkering with it. While this is manageable on dry pavement and sub-40mph speeds, I am imagining this thing being a handful in slippery conditions.

As stated I can't really tell what's happening now. I don't know for sure whether or not the rears lock first, all I know is they do lock. I may need to rig up the GoPro pointed down the side of the bronco to record what's happening when slamming on the brakes.

Also, I question if my front brake pads are somehow compromised. I rebuilt everything from the knuckles out back in 2018 after my wheel bearing "incident" and have not put a ton of miles on since then. I did pull it all apart a couple of months ago to re-pack the front bearings and at that time I do remember getting some bearing grease on the rotors (which I removed with brake cleaner spray) but I don't remember if I'd rotated the rotors with the grease on the surfaces at that time. That's about the only way I could see the pads having been compromised, and I do hear what sounds like a little bit of chatter as I come to a stop. No pedal feedback so not likely warped rotors, but if the pads are somehow compromised then perhaps that's what I am hearing.

Pads are cheap... I may experiment there next. Though I should have the rotors turned if I go down that road, and I don't really want to go there...

Long story short - the bronco definitely has more braking power than it ever did before. I do not remember being able to lock the wheels up from 10-20mph before. It is not the "head into the windshield" experience described by most, but it is locking up the tires without trying very hard.

I am pretty tired of this project and I need a break. I'll return to it in the coming days.

[904Bronco]

Take a break Tony, let the wounds on your head heal from beating it against the wall...

[71BRONCO71]

Can you post a couple photos of your install?

[CityHick]

Here's one photo. It looks cool...
As mentioned I'm taking a little break from this. On top of my frustrations with this, I've now got some personal stuff going on and my mind is not in this game at the moment. I'll get back to this, but my focus is elsewhere. I need to chill out and wrenching is not doing that for me as of late. lol.

[GloNDark2]

Have you put a pressure gauge on there? Maybe the bypass valve in the pump is stuck open? I had a Wildhorse dual return canned ham pump and it would steer "OK" but my brakes were spongy. I put a gauge on it and turns out the pressure relief valve was stuck open on a brand new pump. Sent it back, got a new one and holy crap do the brakes stop now. I finally needed the proportioning valve to adjust the rear down.

[CityHick]

Well I've been ignoring my bronco since November. Today I went out and fired it up just to hear it run; the good news is that it runs.

In answer to the last question, no I have not put a pressure gauge onto my hydraulic lines; I suppose I could do that to try to get more answers. In the mean time, I decided that I don't want to deal with drum brakes anymore, so I ordered the rear disc conversion from Wild Horses last week. The kit is backordered for 2-3 weeks.

This will either solve the problem, or compound the issue further. In any case, I should end up with better brakes after all is said and done. I've got a few more wild ideas in mind, but I hope to get past the brake problems and just enjoy it a while before I start any more projects. I'll update again in a few weeks I guess...

[904Bronco]

Keep at it Tony... You will get through this.

[71BRONCO71]

Do you have the bronco prop valve on the frame?

[CityHick]

Do you have the bronco prop valve on the frame?

I do not. I have the Wilwood adjustable prop valve that's supplied by WH as part of their "MOAB" hydroboost kit. I suppose I could try to put the other prop valve back into the system but I've already replumbed and that's not a simple change to make anymore.

Someday when the supply chain gods smile upon me and my disc brake kit shows up, I will revisit all of this. Until then, my Bronco will continue it's winter hibernation.

[ba123]

I'm a little late to this convo...just noticed this thread but interested in how its going and the troubles.

Just an added note on the brackets from the first page of comments that Tom's is now selling a kit with that bracket that shifts the master over. I'm interested in the WH kit and will most likely go this way as I like how it looks and the convenience (if it works). I'm planning on doing something similar to what JB did and shift the pedal controls behind the firewall due to my own clearance issues so I hope I can figure that out--I have some ideas.

CityHick, have you tried pressure bleeding? Not really the easiest thing to do with those master cylinders, but I've always done this on all my cars and it's the best thing ever. I have a Motive kit that I've used for a while and works great. They make an adapter that is needed for this type of MC.
Motive Bleeder Adapter: https://www.summitracing.com/parts/mvp-1105

They might make a kit with both together. If you were closer to me I'd offer to bring mine over and try.

Ben

[CityHick]

I've spent some time this weekend trying to better understand what's going on with my brakes. Starting with the good: stopping performance is definitely improved from the old vacuum booster. I am totally convinced that the hydroboost unit is doing what it is supposed to do: provide lots of boost.

I installed the rear disc conversion last weekend. Installation was easy and straightforward. People warned me that I won't have a good parking brake anymore - I beg to differ. I will say without a doubt that the parking brake holds better than my drums ever did.

This being said, I still have the same problem with the rears locking before the fronts. I now have the adjustable proportioning valve set to the least amount of pressure going to the rear, and during "normal" stopping I can tell the fronts are engaging first and I come to a nice, controlled stop. However, when I slam on the brakes, the rears lock first and the bronco starts to go sideways. Initially I thought this was due to imbalanced pressure to the front brakes. I thought I was seeing evidence of this in the skid patterns but now I am not so sure about that. What seems to be happening is when I slam on the brakes, once the weight transfers forward the rear brakes lock up and that's what's sending me sideways. I am not certain to what extent the fronts are locking up, but I can see the rears are locking without a doubt.

I have bled and re-bled the brakes and I'm certain I've chased the air out of the system. I have confirmed with Wild Horses that the master cylinder they sold me is what they use with my exact configuration - GM front brakes and their rear discs. It is a 1 1/8" cylinder bore Wilwood master cylinder, the one that came with their "MOAB" kit.

It was suggested that I confirm that my caliper slide pins are greased. I pulled it apart today and confirmed - they were greased but I added more grease and re-assembled. There's no appreciable difference in braking performance before and after. The panic braking situation persists.

I've done some reading online to find other ways to address rear brakes locking before the fronts. While I don't like to throw money at problems before I can confirm a solution, I did find an interesting device, designed for racing applications to delay the application of rear brakes when applied suddenly. I feel that this is a band-aid for this problem, but it's interesting to me: https://www.larsenracingproducts.com...ystem-lbs.html

At $134, if it solves this problem for me (or masks it so that my rig is safer to drive) then I'm willing to give it a shot. I believe that BC Broncos used to sell something similar. It is not intended to reduce pressure to the rear, but it acts as a shock absorber.. allows the fronts more time to do their thing before the rears are applied. I feel like this should not be needed, but clearly what I currently have is not working as intended so perhaps this device can help.

I really used to enjoy tinkering more, solving problems. I've got a lot less patience and tolerance for this kind of thing now - this is something that I feel should just work and lately these projects have really not been enjoyable. I just want to drive and enjoy the dang thing again... Maybe a part of that is I've got basically no time to screw around during the weekdays anymore, and on weekends when the weather is nice I'd rather take a day trip and relax... ugh. Perhaps old vehicles are not such a good fit for me anymore...