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Old 12-14-2013, 10:28 PM   #1
Midnight 85
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Default Brake bias spring

I put the bias spring from DRM in my '85 and I have never really been happy with the front brakes since. I thought it may be a lack of pressure from the master cylinder so I put a reman master on which made it worse. Since then I have also replaced the booster trying to figure out how to get the car to stop right.
Now I am getting ready to do the C5 upgrade on the front so this leads to my question. I have read that the bias spring is a necessity when doing this upgrade so is the bias spring the reason the stock front brakes are not quite adequate? I'm just about ready to order another master cylinder, thinking that maybe I just got a defective one. One other thing, I also installed a vacuum canister just in case the vacuum was not enough, it did no good either.
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Old 12-14-2013, 11:02 PM   #2
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Originally Posted by Midnight 85 View Post
I put the bias spring from DRM in my '85 and I have never really been happy with the front brakes since. I thought it may be a lack of pressure from the master cylinder so I put a reman master on which made it worse. Since then I have also replaced the booster trying to figure out how to get the car to stop right.
Now I am getting ready to do the C5 upgrade on the front so this leads to my question. I have read that the bias spring is a necessity when doing this upgrade so is the bias spring the reason the stock front brakes are not quite adequate? I'm just about ready to order another master cylinder, thinking that maybe I just got a defective one. One other thing, I also installed a vacuum canister just in case the vacuum was not enough, it did no good either.
Do you know that you have the correct bias spring? There's an ABS and a non ABS. Do you know that you were sent the correct one even if you ordered the correct one? Several years ago there was some debate as to short or long and DRM responded to the thread with a comment like we'll check and I don't remember them returning back to the post. Check with VBP and see what they have to say regarding the length or maybe number of coils or the value of maybe loaded/unloaded.

This is one of the "better" reads regarding C5 on early C4 conversions. There's nothing that seems to be overlooked and if your interested in "better" braking it's a very good read. Your car seems ideal for maybe a complete hydraulic change. Maybe? Maybe not?

http://members.shaw.ca/corvette.84/C5brakes.html
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Old 12-15-2013, 12:06 AM   #3
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Do you know that you have the correct bias spring? There's an ABS and a non ABS. Do you know that you were sent the correct one even if you ordered the correct one? Several years ago there was some debate as to short or long and DRM responded to the thread with a comment like we'll check and I don't remember them returning back to the post. Check with VBP and see what they have to say regarding the length or maybe number of coils or the value of maybe loaded/unloaded.

This is one of the "better" reads regarding C5 on early C4 conversions. There's nothing that seems to be overlooked and if your interested in "better" braking it's a very good read. Your car seems ideal for maybe a complete hydraulic change. Maybe? Maybe not?

http://members.shaw.ca/corvette.84/C5brakes.html
I never heard of the possibility of having the wrong spring, thanks, I'll check in to that and I will read the article too, I've got the new engine going and it sounds real strong so I want to be sure my "whoa" is good enough to handle the "go".
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Old 12-15-2013, 09:06 AM   #4
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I just ordered the VB&P spring and there is different springs so I hope this takes care of the problem. The car will stop, even in a close call situation but it just doesn't feel right and since it does not have abs it should lock the fronts up easily, it will not do that.
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Old 12-15-2013, 09:23 AM   #5
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I just ordered the VB&P spring and there is different springs so I hope this takes care of the problem. The car will stop, even in a close call situation but it just doesn't feel right and since it does not have abs it should lock the fronts up easily, it will not do that.
If you had access to a '92+ brake pedal and an "off the car" '85 pedal to compare the "leverage" and pivot positions it looks like it would maybe be possible to increase the leverage also. That would seem to me to be a great advantage. If the pivot and pedal profile is the same or very similar I'd think it would require very little effort. I used to understand the leverages etc but haven't been in an environment for many years where it's been of any value.
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Old 12-15-2013, 01:01 PM   #6
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Quote:
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I just ordered the VB&P spring and there is different springs so I hope this takes care of the problem. The car will stop, even in a close call situation but it just doesn't feel right and since it does not have abs it should lock the fronts up easily, it will not do that.
It may be the current pads on your car that are not doing the job you expect. Another thing may be weak flex hoses on the front. When the hose lining starts to get weak, the line pressure will cause the hose lining to expand which reduces not only the amount of fluid volume, but lowers pressure at the caliper.

I did a C5 front brake conversion about 5 years ago on my '87 and it was a huge improvement in braking performance. I didn't have that link at the time, but it does have the same information about what I had to do.

Right now, I have stock C5 Z06 front pads and Hawk HP+ in back. I also used Earl's stainless lines to replace the original rubber lines. As mentioned, there are different bias springs for ABS and non-ABS cars. I did not change the MC.

When you do the C5 upgrade, know that there is no difference between the Z06 caliper and the standard caliper except for the red paint on the Z06 caliper. Also I use standard C5 front rotors; my '87 is for autocross and track days so rotors are just a maintenance item. I don't use the drilled/slotted rotors.
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Old 12-15-2013, 02:25 PM   #7
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Hey midnight. I don't know If this would help you but earlier this year I replaced my stock corvette rear calipers with strange dual calipers, 4 pistons each, on each rear wheel. That's a total of 16 pistons in the rear compared to the stock 2. Combined with soft pads this setup could probably hold a freight train at the line. I installed a brake proportioning valve in the rear line to dial in the front rear brake bias.


Last edited by 383vett; 12-15-2013 at 02:45 PM.
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Old 12-15-2013, 02:41 PM   #8
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For reference, I installed the VBP spring in my 89 and it help with nose dive during hard braking situations. Good luck with your application.
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Old 12-15-2013, 03:31 PM   #9
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I noticed a little difference on the track. I actually liked it. Then my m/c went out and I haven't taken the time to put the DRM spring into the new m/c. Installation is no fun.

On a street car I'm not sure what good it is. Ok, it's always fun to work on the Corvette.

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Old 12-15-2013, 03:38 PM   #10
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Installation is no fun.
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Old 12-15-2013, 11:03 PM   #11
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Hey midnight. I don't know If this would help you but earlier this year I replaced my stock corvette rear calipers with strange dual calipers, 4 pistons each, on each rear wheel. That's a total of 16 pistons in the rear compared to the stock 2. Combined with soft pads this setup could probably hold a freight train at the line. I installed a brake proportioning valve in the rear line to dial in the front rear brake bias.

Now those are some serious binders.
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Old 12-15-2013, 11:09 PM   #12
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It may be the current pads on your car that are not doing the job you expect. Another thing may be weak flex hoses on the front.
Good suggestions but I have Hawk pads all the way around and braided stainless hoses w/Teflon liners, also on all 4 corners. I really think all it is is a defective master cylinder but I am not going to change it until I get the new bias spring and the C5 brakes installed. If it isn't right then I will get the master.
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Old 12-16-2013, 12:25 AM   #13
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How's the booster? Vettes seem to be famous for eating them I went through 3 in 5 years on my 90 & yes I had the replacements wrapped in insulation.

Easy check: Park on an incline, engine off let it sit for 5 minutes. Without starting the engine or stepping on the brake put the car in neutral. When it starts rolling apply the brakes. If you have to jam the pedal hard to stop the car the booster is not holding vacuum, its dying.
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Old 12-16-2013, 06:13 AM   #14
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The booster is new too but I also have my doubts about it. I put a vacuum canister on to see if low vacuum, (cam) was a problem, it has a gauge on it and I notice the vacuum drops to zero within a short time after shutting the engine off. Also when I put this booster on I had to extend the rod a lot, the pedal was real low with the new booster. The old booster had failed internally. I seriously hope I don't have to do that job again.
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Old 12-16-2013, 09:56 AM   #15
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The booster is new too but I also have my doubts about it. I put a vacuum canister on to see if low vacuum, (cam) was a problem, it has a gauge on it and I notice the vacuum drops to zero within a short time after shutting the engine off. Also when I put this booster on I had to extend the rod a lot, the pedal was real low with the new booster. The old booster had failed internally. I seriously hope I don't have to do that job again.
Perhaps you might try a new vacuum check valve at the booster. They (the Corvette spec) sure come at a price these days though. Did the booster come with a new valve or less the valve and grommet?
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Old 12-16-2013, 10:13 AM   #16
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The install is no fun like everyone else has mentioned. I dont track my car very often but I did notice a difference before and after the spring...I'd say for a street car you could skip it.

disclaimer: Mine is a 93, not sure how the 85's may be different.
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Old 12-16-2013, 11:48 AM   #17
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Our Bias spring should not affect front line pressure (front brakes)

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Old 12-16-2013, 05:23 PM   #18
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It looks like my "new" booster is defective. I started the car & let it build vacuum on the gauge on the canister. I then clamped the line to the booster so the vacuum would stay in the booster. I then shut the car off and watched the gauge, after several minutes it had only dropped a very slight amount. I then unclamped the line to the booster and the gauge dropped to zero immediately. Naturally, it has been too long now to go back on the seller of the booster but that does not bother me as much as having to do the miserable damn job again. I have a steel booster coming.
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Old 12-16-2013, 06:57 PM   #19
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It looks like my "new" booster is defective. I started the car & let it build vacuum on the gauge on the canister. I then clamped the line to the booster so the vacuum would stay in the booster. I then shut the car off and watched the gauge, after several minutes it had only dropped a very slight amount. I then unclamped the line to the booster and the gauge dropped to zero immediately. Naturally, it has been too long now to go back on the seller of the booster but that does not bother me as much as having to do the miserable damn job again. I have a steel booster coming.
That should make a big difference.
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Old 12-16-2013, 07:18 PM   #20
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It looks like my "new" booster is defective. I started the car & let it build vacuum on the gauge on the canister. I then clamped the line to the booster so the vacuum would stay in the booster. I then shut the car off and watched the gauge, after several minutes it had only dropped a very slight amount. I then unclamped the line to the booster and the gauge dropped to zero immediately. Naturally, it has been too long now to go back on the seller of the booster but that does not bother me as much as having to do the miserable damn job again. I have a steel booster coming.
If it held vacuum until you unclamped the line, isn't it possible it is just the check valve? ( i may have misunderstood - which side of the clamp is the gauge on?)
Edit - I think I understand now - with equal vacuum in the canister and the booster, the guage will only drop if the booster leaked while the hose was clamped. Duh. I am interested in this thread because it seems to take too much pedal pressure on my car as well. I have swapped the booster and m/c, but they were not new, supposed to be "known good units".

Last edited by nobodycls; 12-16-2013 at 07:29 PM.
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Old 12-16-2013, 07:18 PM
 
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