1999 tahoe rear disc brake conversion, developed issue

[contor]

hey guys. I recently installed a summit racing rear disc conversion, the vehicle now has a firm pedal, but takes A LOT of pressure on the pedal to stop the vehicle. all the brakes have been bled ect.

after researching I found many issues with rear disc conversions, just haven't been able to find a similar issue. and to answer the generic questions ive seen repeatedly pop up with a disc conversion, yes it will be used for towing (hence the conversion.) yes everything is hooked up properly, no leaks, cut lines ect.

but was just curious if any one has had a similar issue, or knows of simple checks that I could possibly be over looking.

any info would help, thanks in advance. :happy160:

 

[MarkD51]

I'm no expert on such, but you should probably go over to the Tahoe-Z71 Forum, and the boys there will tell you why such is most likely occurring.

I'm thinking the reason you now see actual losses instead of gains, is because the Disc Calipers have much more brake fluid volume compared to the smaller volume wheel cylinders. And all with a Master Cylinder (with the wrong size bores), and Proportioning Valve which wasn't designed or intended for such.

The boys there may be able to help you initiate a fix, in which a different MC, and some other mods might be in order to get such to properly work.

If you really want killer brakes, then it seems the PowerBoost option is the best way to go.

 

[lesterl]

I have the Hydroboost on my 2012 work van and they are killer....

 

[MarkD51]

I have the Hydroboost on my 2012 work van and they are killer....

Sorry all, what I meant to say was "Hydroboost".

Again, like I said, the OBS Master Cylinder was not designed for Rear Disc Brakes. And I believe an NBS (New Body Style) Master Cylinder will not button up to the Booster without some machining modification due to a difference in the flange-collar diameter.

I do know that on the 11" drums, the wheel cylinders are actually smaller in size than the wheel cylinders are for the 10".

I believe the NBS MC has a larger internal Bore for the rears, thus it can move more fluid through the lines to supply the larger volume of fluid in the rear Disc Calipers. Again though, I'm pretty certain that it will not button up correctly cause of the different flange size on the MC.

As I previously said, the boys over on the other Tahoe-Z71 forum toy with stuff like this, there's quite a few there that will know what needs to be done as far as parts to make this modified rear disc conversion setup properly work.

It is possible Summit Racing themselves might have some answers also.

I assume nothing was done to the front brakes when this swap was done, correct?

In any case, and for sure, don't live with poor brakes, and such issues, a vehicle that doesn't properly stop is a dangerous one.

This could be a possible cause, because in effect, the rear calipers are barely applying any pressure to the rotors, in other words, you only now have just front brakes.

The other possible causes are a possible vacuum leak at the Booster, or a bad Booster.