8.8 disc brake help

jscrayto

Well-Known Member
Joined
Aug 18, 2006
Location
kannapolis
Just swapped an 8.8 with disc brakes into a 2004 TJ. Since the install, the brake pedal has little pressure and the brake light stays on. Brakes have been bleed 3 times already. Is there anything else that needs to be done? checked? Seems like the brake pressure is too low.
 
You can pull the o ring off the tube in the proportioning valve and gain a little. On something that had drum brakes before, there isn't enough volume going to the rear to operate the caliper like it should.
 
I am about to do the same swap on my ZJ, and it came stock with rear drums. What can you swap out to make it work better?
 
Just did the swap on my XJ. I put the calipers on the wrong sides. Check your calipers and make sure you have the bleeder screw above the brake hose. Take out the o-ring in your proportioning valve. Bleed the prop valve first and then bleed the brakes as you normally would. If none of that works you can forgo the prop valve all together or look into upgrading to a larger master cylinder/power booster combo. I believe a E350 master cylinder will bolt into a TJ with very little modification.

See my thread on this very subject in Gen tech.
 
Before you spend $$$ on new master cylinder/power booster get a proportioning valve from a 4wheel disk Grand Cherokee. I too put an 8.8 under my TJ many years ago and did not realize any improvement from the "new to me" rear disks. I did the whole O ring thing but it really did not help. A ZJ proportional valve, however, did.
 
My 93 ZJ has(d) drums in the rear. I think by 1995 or so all ZJs had discs in the rear
 
I did an 8.8 swap on my 89 YJ. Had disc brakes on the 8.8 and drum on the D35 I took off. Brake lines matched up on the 8.8. Hooked them up and everything worked fine. I didn't have to change anything. Not sure about the TJ's though. I did have to work a little magic on the E-brake.
 
Got my brake problem solved. I had the calipers on the wrong sides.

See my thread for more details.

Key points to remember:
  • Make sure your bleeder screw is above your hose. This means your calipers are on the correct sides. It DOES matter.
  • Remove the o-ring in the proportioning valve (Don't lose it in case your brakes are worse) Should give you more rear pressure.
  • Run quite a bit of fluid through your lines as your bleeding to make sure you have no air. Pedal should go to the floor each time you open a bleeder valve.
  • If you still aren't satisfied with stopping power, upgrade to dual diaphragm power booster and matching master cylinder. For pre 95 XJs, a 96 will bolt right in. I believe TJs already have a dual diaphragm, at which point you can upgrade to a larger MC or a hydraulic style system.
 
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