Bias spring for new master cyl?
Thread Starter
Racer
Joined: Nov 2003
Posts: 377
Likes: 0
From: Tucson Ariz
Bias spring for new master cyl?
Replaced the master cylinder on my 94 with a new GM unit and when I attemted to swap over my aftermarket bias spring I discovered the proportioning valve assembly on the new unit is a different design. The bias spring is almost twice as long as the old design. Anyone have experience with this issue and maybe know where to get a replacement spring for the new design that improves rear braking?
Le Mans Master
Joined: Oct 2000
Posts: 6,204
Likes: 9
From: St. louis, MO
Someone could have replaced it with one from DRM. They have one that will give the braking even braking from front to back. Makes the car stop loevel, less nose dive. Here is a thread where Jim changed his out:
http://forums.corvetteforum.com/show...25&forum_id=23
Its called a bias spring: http://www.dougrippie.com/
http://forums.corvetteforum.com/show...25&forum_id=23
Its called a bias spring: http://www.dougrippie.com/
Thread Starter
Racer
Joined: Nov 2003
Posts: 377
Likes: 0
From: Tucson Ariz
Finally got to taking and uploading some pictures.
The top assemblies are from the original master cylinder which had a DRM bias spring installed by the previous owner. The bottom pieces are from the new GM master cylinder. The length of the spring is significantly different but the bodies are very similar in size. I'm really stumped. Any light that anyone can shed on the issue will be greatly appreciated.
The top assemblies are from the original master cylinder which had a DRM bias spring installed by the previous owner. The bottom pieces are from the new GM master cylinder. The length of the spring is significantly different but the bodies are very similar in size. I'm really stumped. Any light that anyone can shed on the issue will be greatly appreciated.
Large Impressive Member
Joined: Jul 2003
Posts: 65,811
Likes: 71
From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
I don't think you'll have any problem. I believe my DRM spring was longer than stock too but it works fine. It can be a bee-otch to get back together. I drilled an appropriate sized hole in a block of word to hold the valve while compressing and clipping it. Be ready to chase flying parts! 
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
The principal problem I see is how to reassemble the new PV without
damaging the disk and plastic mechanism which I assume from your
positioning of them, fit between the spring and the c-clip retainer.
I considered suggesting installation of the old PV but at least one orfice
in the new design is decidedly larger in dia.
Looks like the new PV has a coating applied to the barrel segments
between the o-rings. Anti-corrosion? It is a non-contact region.
.
damaging the disk and plastic mechanism which I assume from your
positioning of them, fit between the spring and the c-clip retainer.
I considered suggesting installation of the old PV but at least one orfice
in the new design is decidedly larger in dia.
Looks like the new PV has a coating applied to the barrel segments
between the o-rings. Anti-corrosion? It is a non-contact region.
.
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Race Director
Joined: Apr 2000
Posts: 15,344
Likes: 4,009
From: Texas
Originally Posted by leadfoot2
The top assemblies are from the original master cylinder which had a DRM bias spring installed by the previous owner. The bottom pieces are from the new GM master cylinder. The length of the spring is significantly different but the bodies are very similar in size. I'm really stumped. Any light that anyone can shed on the issue will be greatly appreciated.
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
Originally Posted by 96GS#007
Here's how I compressed the spring
forward end of the PV? (I did not disassemble the components in the
nose of my valve so I am not familiar with what they look like. My
'89 did not have parts like these at the rearward end.)
If not, how does he apply pressure with the hex drive? Your technique
would work on my PV because the hex drive would bottom against the
inside end of the valve.
.
Thread Starter
Racer
Joined: Nov 2003
Posts: 377
Likes: 0
From: Tucson Ariz
96GS#007
Knowing the assy out of your 96 looked the same as the one from my new master cyl makes me feel a little better - I suspected a design change. My concern though is that the DRM spring is not going to provide the desired change in brake bias if I put it in the new PV given the shorter length and consequent decrease in spring pressure.
Slalom4me
Yes, the disc w/ 4 holes and the plastic piece (looks like a valve) came from the forward end of the PV, in the same sequence as shown. I had also thought about putting the old PV in the new master cyl since they are the same diameter and length. Also noticed the difference in the orfice dia. Part of my quandary.
Knowing the assy out of your 96 looked the same as the one from my new master cyl makes me feel a little better - I suspected a design change. My concern though is that the DRM spring is not going to provide the desired change in brake bias if I put it in the new PV given the shorter length and consequent decrease in spring pressure.
Slalom4me
Yes, the disc w/ 4 holes and the plastic piece (looks like a valve) came from the forward end of the PV, in the same sequence as shown. I had also thought about putting the old PV in the new master cyl since they are the same diameter and length. Also noticed the difference in the orfice dia. Part of my quandary.
Melting Slicks
Joined: Feb 2005
Posts: 2,592
Likes: 13
From: USA
I would not use the new spring until checking with DRM. (I presume you got it from them). I just ordered one for my '85 two weeks ago and was told that there are two styles; a long one and a shorter one, and the DRM spring could not be used if I had the longer style. Unlike yours, my original was very close to the size of the DRM spring.
Racer
Joined: Jan 2005
Posts: 476
Likes: 0
From: Tucson, AZ. L98-85 AUTO COUPE: 120k MILES: daily driver. SOUND OFF IF YOU'VE BEEN THERE. Ex-Jumpin' Junky-82nd Airborne-2/505 PIR: 1st ID-1/16th Inf: Recon Marine Retread. GOD BLESS GRUNTS.
Originally Posted by Slalom4me
The principal problem I see is how to reassemble the new PV without
damaging the disk and plastic mechanism which I assume from your
positioning of them, fit between the spring and the c-clip retainer.
I considered suggesting installation of the old PV but at least one orfice
in the new design is decidedly larger in dia.
Looks like the new PV has a coating applied to the barrel segments
between the o-rings. Anti-corrosion? It is a non-contact region.
.
damaging the disk and plastic mechanism which I assume from your
positioning of them, fit between the spring and the c-clip retainer.
I considered suggesting installation of the old PV but at least one orfice
in the new design is decidedly larger in dia.
Looks like the new PV has a coating applied to the barrel segments
between the o-rings. Anti-corrosion? It is a non-contact region.
.
the shorter spring looks like it is a larger (heavier) diameter than the longer spring. they may both have the same pressure rating, and they may also be using a shorter thicker spring to increase longevity and consistency.
frog.
Last edited by parafrog; Feb 8, 2006 at 01:25 AM.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
This is a combination valve.
The DRM spring is shorter and stiffer, but should take about the same amount of force to compress to the installed length of ~0.9"
The preload of the spring 20-25 lbs, I believe determines the 'crack point' where it begins reducing pressure to the rear brakes.
The DRM spring is stiffer, but with about the same crack point, so it doesn't reduce rear brake pressure as much. Should be about 50% stiffer.
The spring I used is even shorter than the DRM spring and stiffer, but with the same preload.
In short... just stick the DRM spring in there and you're done.
The DRM spring is shorter and stiffer, but should take about the same amount of force to compress to the installed length of ~0.9"
The preload of the spring 20-25 lbs, I believe determines the 'crack point' where it begins reducing pressure to the rear brakes.
The DRM spring is stiffer, but with about the same crack point, so it doesn't reduce rear brake pressure as much. Should be about 50% stiffer.
The spring I used is even shorter than the DRM spring and stiffer, but with the same preload.
In short... just stick the DRM spring in there and you're done.
Last edited by CentralCoaster; Feb 8, 2006 at 03:30 AM.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Originally Posted by leadfoot2
Some good info - seems like doing a stiffness test on both springs at the .9 in. compressed height would be smart. I'll try to get that done.
If you're done with the stock spring, can you send it to me? I think GM changed the bias a bunch of times through the years, I'm trying to compile all that info.
Former Vendor
Joined: Feb 2004
Posts: 9,615
Likes: 13
From: Burlington NC
You guys are on the right path. I don't know anything about that long spring. You and one other guy are fighting it. My other customer just put it in and said it worked great. But I can't advise that it will work, because I don't think he is the best driver in the world. But he said there was a better change.
I could measure the springs too, if you guys need me to,
Randy
I could measure the springs too, if you guys need me to,
Randy
Thread Starter
Racer
Joined: Nov 2003
Posts: 377
Likes: 0
From: Tucson Ariz
Randy
Glad to see you in the conversation. Any data you could provide would be a great help - especially on the original GM spring (short version) since I don't have one. Don't want to get into anything that might be of proprietary nature though.
CentralCoaster
I can give you the GM spring when this gets sorted out.
Glad to see you in the conversation. Any data you could provide would be a great help - especially on the original GM spring (short version) since I don't have one. Don't want to get into anything that might be of proprietary nature though.
CentralCoaster
I can give you the GM spring when this gets sorted out.