rear bias plugs?

[iselltonsofthings]

I'm familiar with what the bias plugs do, but I have another question.

Rather than using a plug to hold a valve open to permit full flow, can I just delete the valve, and install a coupler to connect the lines together. That seems like it would be much cheaper and just as effective. Is this possible, and has anyone done it.

I am unfamiliar with how the brake fluid is routed through the metering block.

If someone could explain? I've never tore into one of these. Thanks much. Scott

 

[Yamaha V6]

Well, let's re-familiarize you with the plugs' function...

The plug REPLACES the valves completely, and are shorter than the valve assemblies, which means they're OPEN all the time, not sometimes or partially closed.

You replace the valves with plugs, and you have 100% rear braking all the time. That's what the plugs do.

 

[fricker66]

Yamaha V6:
Well, let's re-familiarize you with the plugs' function...

The plug REPLACES the valves completely, and are shorter than the valve assemblies, which means they're OPEN all the time, not sometimes or partially closed.

You replace the valves with plugs, and you have 100% rear braking all the time. That's what the plugs do.

Fred, isn't the main benefit from this found on the racetrack? Also, I'd tend to think that on a non-abs car such as my 89, this modification would result in rear lockup under heavy braking situations.

 

[Dr. Tweak]

That's correct, which is why you don't do it on a car that doesn't have ABS. Also it's not really recomended for a daily driven SHO.

At least what I've read. shrug

 

[iselltonsofthings]

Thanks for the replies.

I'm still confused thumb

I thought the valve is open/closed by the suspension arms. As the suspension moves up/down the linkage arm actuates the valve. When removing that linkage arm, you just install the plug. That plug just holds the valve in the open position.

How does the plug, "replace" the valve.

Can I remove the whole metering block and just install a standard coupler. Just couple the lines coming from the front of the car, with the lines running to the L&R rear brakes.

Thanks in advance. Scott

 

[K-Dawg]

The valves are like a button that are pressed (open) when the suspension is compressed. They simply screw into the "proportioning" block. When they are removed, the remaining holes have to be plugged. Hence the "bias valve plugs".

When installing, you remove all the mechanical stuff (valves, linkage, etc) and screw in the plugs.

As far as the plugs not being appropriate for the street, I like mine very much on my ABS-equipped street car.

 

[Shoaz]

I'll opine that whether the bias plugs are appropriate at the track depends on the rest of your braking system, your suspension, and your driving style. Having too much rear brake at the track can be a detriment and result in overall loss of braking performance.

Personally I think this is a better street mod than track mod. It's usually not too big of a deal if the ABS kicks in while driving on the street.

 

[luigisho]

I think the other part of his question was would there be any difference in coupling the lines vs plugging the mechanism?

 

[Shoaz]

Making a coupler would presumably do the same thing, but you might have to rework the lines to fit a coupler, or make a custom coupler. The bias plugs are probably the easiest way to bypass the proportioning valve.

 

[iselltonsofthings]

Not to be rude, but I'm trying to focus on the idea of cost savings with just a standard brake line coupler.

Here are some simple drawings that illustrate the line couplers.

Will this system work correctly by eliminating the proportioning valve entirely!

I assume that the couplers could be found at any auto parts store for under $15 for the two.

Yes/No ??

Thanks. Scott

 

[gmorrell]

iselltonsofthings:
Not to be rude, but I'm trying to focus on the idea of cost savings with just a standard brake line coupler.

Here are some simple drawings that illustrate the line couplers.

Will this system work correctly by eliminating the proportioning valve entirely!

I assume that the couplers could be found at any auto parts store for under $15 for the two.

Yes/No ??

Thanks. Scott

Scott,
if you don't mind cutting, bending, and splicing brake hard-line, what you've proposed will work just fine. Have fun and just be damn meticulous, your safety and the safety of others is at stake.

The flare connectors on the four lines to the bias valve body are all different thread pitches and sizes to prevent cross-connects at the factory, so unless you want to build a forest of Metric ISO flare adapters, the best way is to cut off the OEM flare connections and make some new splices with standard flare connectors.

Please consider this advise from someone who has re-plumbed the brake systems on several track cars:
1. Don't use brass fittings in your brake system, use only steel. Brass fittings are soft and are subject to rupture at brake system pressures.
2. When flaring brake tubing, use only ISO double flares. Single flares can develop cracks around the cut edge of the tubing where its been stretched, allowing the fitting to leak and/or fail catastrophically. Buy a good double flaring tool if you don't have one.
3. Be aware that the steel brake line in your 10 year old car may be a bit brittle from age, so you want to avoid introducing new bends into it. If you have to do some serious re-routing of OEM tubing, cut out the old section and use new tubing that hasn't work-hardened. Buy a proper bending tool for the size tubing you're using.

I'm not gonna' go into the pluses and minuses of defeating the rear bias valve, its been discussed here and on other SHO lists, ad-nauseum. Use the search function if you're so inclined.

Edited for speeling and clarity...

<small>[ December 28, 2003, 12:46 PM: Message edited by: Gary M. ]</small>

 

[Todd TCE]

If cost effective is part of the plan then the plugs are certainly the better way to do. Either pull the old ones, and have them welded up or go to the junk yard and get some to weld the hole in, then simply replace them. The second method would be the easiest of all given you don't leave the lines dripping....But man, that idea of what you propose is waaayyy too much work.

And NO, I don't suggest this for a nonABS car without a proportioning valve fitted. My experience has shown this is a better street mod than a track one in 'most' cases (other changes being considered) as the track ususally nose dives the car.

 

[iselltonsofthings]

Thanks guys for the straight forward posts.

I'm not full throttle ahead with this thought. I proposed the idea, just to see how much work is envolved.

I did not know that the flanges are all different thread pitch. This would make it very difficult to purchase a standard brake line connector.

I'm not looking to spend a whole weekend, designing the setup to save a few dollars. I was just seeing if there was a simple, cheap, yet 100% safe & effective way to bypass the proportioning valve without the plugs.

Too much work for this home-made setup. Bias plugs are well worth the money. Again, thanks everyone for not jumping down my throat. Sincerely, Scott

 

[MyBlue92SHO]

Hello!

I'm not a guru on this stuff, but I can say from experience MAKE SURE YOUR FRONT BRAKES ARE 100% FUNCTIONAL!!! I had a scare last night when I had to panic stop and spun on the highway a few times, WAY too close for comfort. Turns out my front caliper brackets got a notch in them so the pads weren't fully engaging the rotor. Yikes! You definitely don't want the rears doing more work than the fronts!!!

 

[Todd TCE]

We've tried to warn you guys of some of this foolishness a few times....the bias plugs should only be done if:

1. You have made changes to the front brakes with the fit of a larger system. (thus returning some 'normal' bias to the car with the mod)

2. Your car has ABS

3. You really understand what brake bias is all about and what it can and cannot do to the car.

Be glad you didn't hit anyone.

 

[gmorrell]

Todd TCE:
We've tried to warn you guys of some of this foolishness a few times....the bias plugs should only be done if:

3. You really understand what brake bias is all about and what it can and cannot do to the car.

Ding ding ding ding ding...

I'll heartily second Todd's comments.

My '89 track SHO has a defeated rear bias valve, and because it has no ABS, I replumbed the whole brake system to be split front-rear, instead of diagonally. I have a single hydraulic circuit going to the rear brakes with a Wilwood cockpit adjustable proportioning valve for the rear circuit. With Porterfield R4 pads front and rear, the system is sensitive enough that I have to dial out rear bias on the track as the fuel load decreases. Keep in mind that running a big track like Road America (~4 miles/lap) can use 10 gallons of fuel in 20 minutes.

One time on a road trip a few years back, I inadvertently had too much rear bias dialed in, and encountered a panic stop situation on the highway. On I-70 through Glenwood Canyon in the Colorado Mountains, concrete barrier on both sides of the road, due to rear lockup, I ended up backwards facing oncoming traffic. This is the definition of one of those situations where you hope you have some clean underwear stashed in the car. I flatspotted two Bridgestone RE-71's in the process.

If you don't fully understand, or are prepared for the implications of this mod in all of your daily driving, and how your car will react to it with different axle loads and road conditions, just don't do it. It caught me off-guard, it can do the same to you.

<small>[ December 29, 2003, 02:42 PM: Message edited by: Gary M. ]</small>

 

[Mike Kopstain]

Todd TCE:
We've tried to warn you guys of some of this foolishness a few times....the bias plugs should only be done if:

1. You have made changes to the front brakes with the fit of a larger system. (thus returning some 'normal' bias to the car with the mod)

2. Your car has ABS

3. You really understand what brake bias is all about and what it can and cannot do to the car.

Be glad you didn't hit anyone.

These points can't be stressed enough!

1. I wouldn't stick these on anything with less than a 96' brake upgrade upfront.

2. If you are putting these on a car with no ABS, get full coverage insurance. On my old 95 (No ABS), the rear end used to break to the side during heavy braking. Plugs on a non abs car = trouble.

This is not a mod you want to buy just so you can add it to the list. This is something you want to think out and determine where you usually use your car and what you're looking to get out of it, and then decide whether you think the plugs will benefit you or not.

 

[Shoaz]

Mikeys_Taurus:
This is not a mod you want to buy just so you can add it to the list. This is something you want to think out and determine where you usually use your car and what you're looking to get out of it, and then decide whether you think the plugs will benefit you or not.

I'll second this well-worded sentiment and also Todd's and Gary's inputs. Anything having to do with brakes should be done with a lot of thought and care, and this one is included. Just because it's inexpensive doesn't make it a good idea.

I think it's pretty durn cool that we have a cheap, reliable, automatic bias controller in our cars, and I've gone to pains to make sure mine still works after installing the aftermarket control arms. They're reasonably well adjustable, too, so if you want a bit more rear bias, it's possible to do that while retaining the proportioning valve. Mine seems to be about right for me where it is now, because the ABS just barely starts to kick in sometimes under trail braking in RH corners. Anyone (with ABS) could do some simple adjustments on the valve until it behaves the way you want it to. If you go too far the ABS will be kicking in at the rears under hard braking. IMHO the system should be backed off with some safety margin from that point. The ability to maintain control is much more important than squeezing maximum braking capacity out of the rears, which don't have a hope of contributing much in these cars, anyway.

BTW, the current issue of Grassroots Motorsports (GRM, Feb. 04) has a nice article on brake bias and does a good job of conveying that this isn't something that's very straightforward to manage. Might be helpful for those so inclined to get some more info on the topic.

 

[DeaconBlue]

Todd and Gary have stated some great points here and everyone should listen to them.

I had a 13" Cobra/PBR front brake upgrade and stock rear non vented setup on my '95 MTX when I first installed the plugs. This mod shiffed enough load to the rear brakes that I warpped a set of new stock rear non vented '93-99 rotors during normal to agressive street driving and no, the slidder pin were not stuck. I have since done a vented rear brake upgrade. The car is still too rear biased and I have to run a more agressive front pad when I take the car out on the track. Hopefully a front caliper upgrade with larger pads this Winter will help shift the brake bias back more to the front.

The last thing anyone needs is a car with rear brake bias on a slick surface without a properly functioning ABS system. There is a great article on brake bias in the latest issue of Grassroots MotorSport.

 

[Todd TCE]

Pads work, so too do larger rotors, but the best value is larger piston area. There's more return on torque value with this, followed by pad Cf, then rotor diameter last. Sorry all you would be 14"ers...lol

Played around too much with the bias program the other day. Learned a few tricks though. Try this one: .02 Cf change is equal to 1% bias shift. Yup, nearly constant.