Problem with manual brakes?

[NY Twin Turbo]

I've read through the manual brake conversion thread. The summer before last, I also did a manual brake conversion. I'm not sure I'm happy with it. I was hopeing you guys can help.

I called willwood and went with their tech rep's recomondations. I used a willwood 1" bore master cylinder. Willwood proportioning valve kit. Factory powermaster mounting pad. Factory stock Turbo Buick brake pedal. Generic adjustable length pushrod from Jeg's. All braided stainless tubing for flex hoses. 10 psi residual check valve on the line going to the rear wheels. Custom bent by myself and changed all the hard lines to 3/16" stainless tubing to the front and rear. Factory stock calipers with EBC 7000 series pads that grip crossdrilled and slotted Powerstop replacement rotors. In the back are factory drums with the standard S-10 cylinder and big pad mod (I think).

The problem is this. There seems to be too much travel on the pedal before anything happens. After that, the pedal is firm but not hard. I'm kind of used to it now, but I wish I wasn't. I jacked the front end up after the install and rotated my front tires by hand. When someone depresses the brake pedal, it goes down about 2 inches before I can no longer easily spin it. I have full pressure to the front and rear. (4.5 inch tire on the front so the back needs to do a lot of the work)

I was almost considering extending the pushrod to lift the pedal 2" and then installing a stop so it may only return to my desired height. Effectively "pre-loading" the brake pedal. But this don't seem right. And I don't wan't to cheat if I can make it right.

Workmanship is top notch. There is no air in the system. There are no leaks.

Willwood also said this set-up would lend itself to a "big brake 4 wheel disk conversion" in the future. The residual valve would be removed and brake pressure bias would have to be re-tuned.

To this day, I have never driven a manual brake car before. I have nothing to compare it to. Does anyone see a problem with this?

 

[pacecarta]

http://www.markwilliams.com/braketech.aspx

 

[Nick Micale]

Do a search as this subject had lots of good info about manual brake conversion on a GN.

A popular and inexpensive conversion was using the early S-10 truck manual master cylinder using a modified push rod from the Powermaster.

My race car has front and rear Baer disk brakes with a manual MC and no prop valve. It stops in 1/2 the distance from 150 MPH over the stock set up!

 

[NY Twin Turbo]

http://www.markwilliams.com/braketech.aspx

Paul,

It seems as if a little travel to "take up the slack" is normal. Still, there doesn't seem to be as much travel on a power brake system. Maybe because it's done easier due to power assist?

I may put a gauge on it to see the pressure rise in relation to travel. I't looks like 1/3 travel before a firm pedal is normal according to the link you sent me. I don't think I have that much.

 

[NY Twin Turbo]

Do a search as this subject had lots of good info about manual brake conversion on a GN.

A popular and inexpensive conversion was using the early S-10 truck manual master cylinder using a modified push rod from the Powermaster.

My race car has front and rear Baer disk brakes with a manual MC and no prop valve. It stops in 1/2 the distance from 150 MPH over the stock set up!

Nick,

I have the Willwood now so I'm going to try to work with what I have.
I may be going with Baer disks on all corners in the future. Last time it was at the track, I didn't drive it. Brian C. did. He said he had no problems stopping it from 145MPH. It's more of a feel thing. I thought it should feel firm from the second you begin applying pressure.

 

[malibudave1978]

With a 1.0" bore master cylinder, you should have a pretty firm pedal right when you press on the pedal. With a lot of pedal travel, it seems if you have low drag calipers on the front. This would cause your pedal travel you explained then the firmness at the bottom of the pedal stroke.

You need to change out your front calipers with NON low drag units and reduce the size of your master cylinder to a 7/8" bore. The 7/8" bore master cylinder will supply more pressure to your front calipers, requiring less leg effort from the driver. You should not have to "stand" on the pedal to stop the car.

 

[Nick Micale]

Nick,................ It's more of a feel thing. I thought it should feel firm from the second you begin applying pressure.

My brake pedal only has about 1/2" of movement when applying it, and it is very firm there which will lock up the brakes.

Just be positive that there is NO air in the MC, and also check that the push rod does not have any slack or play in its travel.

 

[87geeinn]

I'm going to second what Dave just mentioned regarding the calipers. Simply put, you are using a straight bore master cylinder with low drag stock calipers. What this means is the seal in the stock calipers is cut with an angled bevel which allows the piston to pull farther away from the rotor when you release the brakes. This type of seal requires more fluid volume to operate properly and that is achieved with a step bore master cylinder. That initial pedal sink you are feeling is the calipers taking up a large quantity of fluid that the straight bore master cylinder cannot provide since it does not have the large primary bore to supply the needed volume.

Search Google "step bore master cylinder" and "straight bore master cylinder" to educate yourself on the difference. Also, search this site for the same topics, including "manual brakes." Dave's posts (malibudave1978) have covered this in much detail. Search his posts, mine, and several others to get a good warm and fuzzy and I'm sure it will all make sense to you. In summary, what you need is to swap your calipers to NON low drag units. Your choices are limited in this area. AFCO and Wilwood are really your only sure bets. Again, malibudave1978 recently posted a disassembly of the much cheaper AFCO units (as compared with the Wilwood units that I used) which confirmed they do indeed utilize square cut seals (i.e., NON low drag seals) despite the marketing description.

Here's some good reading to get you started:

http://www.turbobuick.com/forums/threads/manual-brake-conversion.368183/
http://www.turbobuick.com/forums/threads/manual-brakes-brake-pad-selection.419704/

 

[NY Twin Turbo]

Thanks guys. You all have been a big help. My car does triple duty work as a street/show/race car. Every time I have to go near brake fluid, I get so nauseous I come close to passing out. If I can solve this issue at the calipers it would be a hell of a lot easier on my nerves.

I have some time before I can do the work. I'm going to follow through on the research tips you guys provided me with. I'll probably opt for the Willwood replacement calipers if it turns out I need them. If I'm not mistaken, they are usually black aluminum with "Willwood" engraved across the front?

And Nick, I will certainly double check and make certain there is no air in the system first.

 

[87geeinn]

If I'm not mistaken, they are usually black aluminum with "Willwood" engraved across the front?

Yep, part number 40-12097-BK is for the black calipers, pads and hardware. Replace the "BK" with "P" if you want polished (more $) or replace it with "R" for red. The link is for the kit since the calipers alone, without pads and hardware (p/n 120-11870-BK) is only like $20 cheaper...but Amazon doesn't seem to carry them anymore. See post #35 in that second link I posted above ^.

 

[NY Twin Turbo]

OK, I've done a little reading now. So I have another question.

Would you guys still believe it could be the low drag calipers that are giving me my trouble even considering I have 1" bore MC and 3/16" brake lines to the rear?

You guys are using 7/8" and 15/16" MCs. So, basically I'm thinking I'm displacing more fluid into less cavity with the 1" bore and the smaller brake line. The volume should fill faster. No?

If air isn't present, then this should provide a hard pedal right away. No?

If I still should get the non-low drag calipers from Willwood, should I get single or dual piston?

 

[87geeinn]

I understand your reasoning and I suppose that is possible. You've done quite a number of mods and this only goes to show how just piecing a brake system together with random parts is not as simple as it seems. Small changes = large differences. May also want to consider the bias in the combination valve as well since you replaced that also.

The large primary bore tends to be rather large, as in well over 1" so that must be taken into account. As such, it's hard to really come to a solid conclusion IMO and this is one of those instances where you might have to resort to swapping parts out to make things work.

The Wilwood single piston units have more surface area vs. the two/three piston units. Stick with what works.

 

[NY Twin Turbo]

I understand your reasoning and I suppose that is possible. You've done quite a number of mods and this only goes to show how just piecing a brake system together with random parts is not as simple as it seems. Small changes = large differences. May also want to consider the bias in the combination valve as well since you replaced that also.

The large primary bore tends to be rather large, as in well over 1" so that must be taken into account. As such, it's hard to really come to a solid conclusion IMO and this is one of those instances where you might have to resort to swapping parts out to make things work.

The Wilwood single piston units have more surface area vs. the two/three piston units. Stick with what works.

Gotch-ya. I'll stick with the single piston caliper. So, I don't see why I shouldn't be able to get this set-up to work a little better. I'll work with what I have.

Next time I'll find someone who has the set up first and ask them how it works and leave Willwood to just supply me with the parts.

I hope later if I convert to 4 wheel disc brakes my plumbing and one inch bore MC will be what is needed.

 

[malibudave1978]

Brake line size makes no difference. See link below.

http://www.pro-touring.com/threads/34180-Brake-line-size

Single Piston/Dual Piston doesn't matter either. As long as you match the caliper's piston area to the size of the master cylinder bore. Dual Piston does not always equate to more piston area.

 

[RmvBfrFlght]

There are a bunch of things that can cause too much pedal travel before engaging the brakes. The use of return spring(s) on the pedal to get it fully back up against the switches helps. Then adjust the distance between the pushrod and M/C piston to about 1/32" of an inch.

Drum brakes will pull the shoes back, so need to adjust them as far out as possible. This way they don't need to be pushed back out as far before they start to operate. As this will also affect the front brakes.

Last but not least, the M/C's compensation ports may be machined too far down the bore. These ports need to be covered by the seal before the M/C will build pressure. This distance is multiplied by the pedal ratio. With a ratio of 6:1 an 1/8" of M/C travel becomes 3/4" of pedal travel. In a case such as this Wilwood recommends preloading the M/C.

Need to be careful if this is done, as going too far into the preload will cause the brakes to lock up once then get hot. With the brake pedal at rest the compensation port must be uncovered (hot and cold). Otherwise the M/C won't release the pressure.

RemoveBeforeFlight

 

[NY Twin Turbo]

There are a bunch of things that can cause too much pedal travel before engaging the brakes. The use of return spring(s) on the pedal to get it fully back up against the switches helps. Then adjust the distance between the pushrod and M/C piston to about 1/32" of an inch.

Drum brakes will pull the shoes back, so need to adjust them as far out as possible. This way they don't need to be pushed back out as far before they start to operate. As this will also affect the front brakes.

Last but not least, the M/C's compensation ports may be machined too far down the bore. These ports need to be covered by the seal before the M/C will build pressure. This distance is multiplied by the pedal ratio. With a ratio of 6:1 an 1/8" of M/C travel becomes 3/4" of pedal travel. In a case such as this Wilwood recommends preloading the M/C.

Need to be careful if this is done, as going too far into the preload will cause the brakes to lock up once then get hot. With the brake pedal at rest the compensation port must be uncovered (hot and cold). Otherwise the M/C won't release the pressure.

RemoveBeforeFlight

I mentioned my thoughts of pre-loading the MC in my first post. I didn't realize that under specific situations that this was acceptable. I will only do this if it's my very last resort. I imagine I would make a stop at the switch bracket where the pedal rests at standard height. Lengthen the push-rod a little at a time. Then test drive till the brakes are hot. A return spring isn't needed now, and I'm sure it won't be needed after a pre-load.

I have a 10psi residual valve on the rear brake line. I think the rear brakes are adjusted properly as well. I will recheck.

First thing is the calipers and a good re-bleed. This sucks because my front seat has more air time then JetBlue. Damned cage!

I've driven this thing everywhere like this. Too cold for this stuff right now. When I get it right I'll be sure to post my recipe for success. I said in another thread "everything is complicated until you know it. Then after you know it.....it's easy"

 

[RmvBfrFlght]

I mentioned my thoughts of pre-loading the MC in my first post. I didn't realize that under specific situations that this was acceptable. I will only do this if it's my very last resort. I imagine I would make a stop at the switch bracket where the pedal rests at standard height. Lengthen the push-rod a little at a time. Then test drive till the brakes are hot. A return spring isn't needed now, and I'm sure it won't be needed after a pre-load.

I don't like preloading either, a race car yes, but not a street car. IIRC, it was Wilwood M/C's that had too much travel before the compensation ports were covered. If it were me I'd make a shim that went between the rear c-clip and the piston. This way no preload is required.

87geeinn installed a stop on his set up, has a picture on his thread:

http://www.turbobuick.com/forums/th...rake-pad-selection.419704/page-2#post-3487032

Lots of good info in his thread.

I have a 10psi residual valve on the rear brake line. I think the rear brakes are adjusted properly as well. I will recheck.

The residual valve won't prevent the springs from pulling the shoes all of the way back against the stops. The purpose of the valve is to keep the wheel cylinder seals pressed against the bores. This prevents fluid from weeping out (ruins the shoes), and prevents air from getting in on a pedal lift.

RemoveBeforeFlight

 

[NY Twin Turbo]

I don't like preloading either, a race car yes, but not a street car. IIRC, it was Wilwood M/C's that had too much travel before the compensation ports were covered. If it were me I'd make a shim that went between the rear c-clip and the piston. This way no preload is required.

87geeinn installed a stop on his set up, has a picture on his thread:

http://www.turbobuick.com/forums/th...rake-pad-selection.419704/page-2#post-3487032

Lots of good info in his thread.



The residual valve won't prevent the springs from pulling the shoes all of the way back against the stops. The purpose of the valve is to keep the wheel cylinder seals pressed against the bores. This prevents fluid from weeping out (ruins the shoes), and prevents air from getting in on a pedal lift.

RemoveBeforeFlight

Yes, it's the Willwood I'm using. I got the idea on how to make the stop for the brake pedal idea from that thread. I like she shim idea too.

I'm banking all my new found knoledge.

 

[NY Twin Turbo]

I finally bled the new calipers yesterday. And guess what? They seemed to work successfully at taking a lot of slack out of the brake pedal travel. I have not driven the car yet and wont for a few more weeks. But I can tell you now, that I definitely get brake engagement with much less distance on the pedal. I'm very optimistic! I may still take another 1/4 inch of travel out by adjusting the push-rod length longer and providing a return stop. Not sure yet. But this is a big improvement!!!!!

I've posted this in my other threads as well to help others who may do a search for help. It seems as if I complained about this a few times. And now I'm finally getting it resolved.