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Search is down, Need help on Disc Conversion on 90 w/Antilock

GRINCH

GRINCH

1/2 ton status
Joined
Jan 30, 2001
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Location
Helena, MT
I just installed TSM's disc conversion on my 14b SF. Skip @ TSM said I would not need any proportioning valves or residual valves since my 90 K5 has Rear anti lock brakes. The brakes work great as long as I'm in 2 wheel drive. No issues at all and I can stop great even runing 35's.

The problem is when I shift into 4 Low or High I lose just about all of the rear brake. I do know that the Antil lock system is disengaged in 4 wheel. You would think I would have more brakes in the back with it disengaged.

I thought about removing the antilock system but it ties into the VSS (Speedometer) and computer.

Any advice?????
 
If I do pull the fuse then I may have to add a proporting valve or a residual for the rear.
 
I like the idea of pulling the fuse. What about replacing the whole damn vacuum boosted ABS unit with a hydroboost? Will that affect the truck's puter? I really wanna go hydroboost and ditch the ABS once I get the 1 tons. All I know is that the ABS sucks!
 
??? Why? The ABS should have nothing to do with the proportioning. The proportioning valve is a mechanical device. I'm confused. /forums/images/graemlins/confused.gif
After my rear disc conversion, I didn't have to do a single thing with the ABS (4 wheel) or even add an adjustable proporting valve or anything. Hmm...
 
My thoughts exactly!!!! So why is it I have good brakes in 2 wheel and harldy any in 4 wheel. Going to be putting it up on stands this weekend and see whats happening. I thought for sure I would get lucky and someone else would have experienced the same problem
 
[ QUOTE ]
The problem is when I shift into 4 Low or High I lose just about all of the rear brake.

[/ QUOTE ]

<font color="blue">Why do you feel that you lose rear brakes in 4WD, because the rear wheels don't lock up under hard braking like they did in 2WD? Think about this for a minute; when your locked in 4WD the front and rear brakes are all tied together through the drivetrain. The front brakes are also slowing the rear wheels through the drivetrain and the rear brakes are also slowing the front wheels through the drivetrain. The front and rear wheels should slow at the same rate except for some side to side differentiation, depending what style differentials you have in your axles. Does that help?</font>
 
I am running a 10b open diff in front and a 14 B SF with an eaton E-locker in the rear.

When in 4WD I can hear the brakes barely grabbing. It is like the caliper is not getting enough pressure to grab the rotor. I agree with your theory on them all working together through the drive train. But when I was on a slight hill the brakes would barely hold me. The rear was making noise like it was slipping.

Going on jack stands today to measure rear pressure in 2wd and 4wd to see if there really is a difference in pressure to the rear.
 
I'm not 100% sure, but I don't think the ABS is affected by what position the transfer case is in (on these models at least). If it was, I still don't know why the ABS would be defeated in 4 high??

In any case, I think that the person talking about the brakes feeling different because of the front and rear being locked together may be on the right track.

Also, did you make sure the lines were completely bled after doing the rear disks?
 
The ABS is disengaged when the shifer is selected to 4wd. The lines were bled again after I noticed the difference in 4wd, still same problem. I do agree about the drivetrain theory somewhat. The only problem is the pressure on the calipers is lower in 4wd. Didn't get a chance to measure the actual pressure yet.
 
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