88emjay Posted September 29, 2005 Share Posted September 29, 2005 Hi all, I'm new to the forum. I just swapped a ford 8.8 into my 88 MJ and the brakes are not what they were with the dana35 in the rear. The pedal goes down pretty far before doing anything. The truck stops fine, but the pedal has excessive travel. I replaced the rubber hoses in the rear and bled the system. If I pump the pedal it does not get harder, like it would if there was air in the lines. It gets a little harder if I pump it with the engine off, but as soon as I start the truck the brakes go down near the floor again. The rear pads are a little past 1/2 way and the master cylinder and booster aren't new. I have a new M/C + booster sitting in the shop but before I go swapping those in, I was wondering if the disc brakes require more pressure than drums, and maybe my solution is to get an adjustable combination valve. I already bypassed the proportioning valve in the rear. Have any of you guys with 8.8 disc swaps had to get an adjustable combo valve? Any of you having a similar problem? Thanks a bunch fellas 88Emjay Link to comment Share on other sites More sharing options...
mj_lover Posted September 29, 2005 Share Posted September 29, 2005 kinda sounds like there is not enough fluid in the lines, or you have a small leak somewhere. did you check all the steel lines? they tend to rust and die. other then that, i'ma clueless Link to comment Share on other sites More sharing options...
88emjay Posted September 29, 2005 Author Share Posted September 29, 2005 Yeah, I replaced the bad metal lines with new ones. Just did a bunch of searching on other forums and it seems there is some kind of o-ring mod for the combo valve that sends more fluid to the rear.... anyone know more about this? I have an XJ combo valve on there now, and I read that the MJ combo valve is just a junction block.... so should I just bypass it? Thanks! Link to comment Share on other sites More sharing options...
Pete M Posted September 29, 2005 Share Posted September 29, 2005 As I understand it, dead travel at the top of the pedal means either air in the lines, or excess travels of the pistons. I would fix the pedal problem first and then see if the rear needs more or less pressure. Jeep on! --Pete Link to comment Share on other sites More sharing options...
88emjay Posted September 30, 2005 Author Share Posted September 30, 2005 As I understand it, dead travel at the top of the pedal means either air in the lines, or excess travels of the pistons. I would fix the pedal problem first and then see if the rear needs more or less pressure.Jeep on! --Pete I was under the impression that if there is air in the lines the pedal would get harder as you pump it up (with engine running). I also thought that the rears would work better if the pedal had more "useful" travel. I adjusted the piston at the M/C, and the rears have slight drag, as they should. I also bled the crap out of the system, but I'm not excluding that as the problem. So you think I should bleed it more? Also, the parking brake isn't hooked up yet, but I don't think that affects the performance on discs like on drum brakes. 88Emjay Link to comment Share on other sites More sharing options...
Bounty Hunter Posted September 30, 2005 Share Posted September 30, 2005 Did you plug one of the rear ports out of the MJ proportioning valve? How did you bypass the valve over the rear axle? Having rear disc, I've heard it's benefecial to remove the check ball coming out of the master cylinder. There's a check ball for drum brakes, it's not needed for discs. I've heard you remove the rear line from the master cylinder, pull the metal seat with a self-tapping metal screw, remove the check ball, and reinstall the seat. Link to comment Share on other sites More sharing options...
88emjay Posted September 30, 2005 Author Share Posted September 30, 2005 Did you plug one of the rear ports out of the MJ proportioning valve? How did you bypass the valve over the rear axle? Having rear disc, I've heard it's benefecial to remove the check ball coming out of the master cylinder. There's a check ball for drum brakes, it's not needed for discs. I've heard you remove the rear line from the master cylinder, pull the metal seat with a self-tapping metal screw, remove the check ball, and reinstall the seat. I'm using an XJ combo valve at the M/C so there isn;t a need to block the line going to the proportioning valve over the rear axle. I bypassed that one by cutting the line to it and continuing it to the axle. I'm sure I did it right because brakes were great with the d35 back there, only thing I changed was the axle and brake hose at the time of the swap. I'll bleed it again in the morning just to make sure. Link to comment Share on other sites More sharing options...
attaboybob Posted September 30, 2005 Share Posted September 30, 2005 I am NOT the guy to answer brake questions. However, toggle down at this site until you see brakes. there is trouble-shooting for 8.8 brakes. Good Luck! ...BOB http://www.therangerstation.com/tech_library/index.htm Link to comment Share on other sites More sharing options...
Pete M Posted October 1, 2005 Share Posted October 1, 2005 I found a site where a guy used a ZJ prop valve to accomodate rear disks: http://gojeep.willyshotrod.com/HowtoZJvalve.htm Jeep on! --Pete Link to comment Share on other sites More sharing options...
Bounty Hunter Posted October 1, 2005 Share Posted October 1, 2005 It could be that your master cylinder doesn't push enough volume for the larger capacity of the rear calipers. Just a hunch. Link to comment Share on other sites More sharing options...
88emjay Posted October 2, 2005 Author Share Posted October 2, 2005 That's what I think too. Could I test it without buying a ZJ combo valve though? Could I take the rear brake line straight from the MC to the axle, bypassing the combo valve by blocking the rear in/out ports on the valve? Not intending this as a permanent setup but just wondering if its possible for a test. Or would I have to swap the MC for one with a larger piston? 88Emjay Link to comment Share on other sites More sharing options...
88emjay Posted October 2, 2005 Author Share Posted October 2, 2005 Perhaps this is the solution? http://store.summitracing.com/default.a ... toview=sku Does anyone know what the front/rear ratio is from the MC without the combo valve installed? 50/50? 70/30? 88Emjay Link to comment Share on other sites More sharing options...
Bounty Hunter Posted October 2, 2005 Share Posted October 2, 2005 What you describe is not a common problem with 8.8 swaps into jeeps, I'd recommend installing that new master cylinder you have and see if that doesn't fix it. If you want to upgrade, consider a corvette or E350 master cylinder. Not sure what years make the best donors, but they're both pretty common swaps. Link to comment Share on other sites More sharing options...
88emjay Posted October 3, 2005 Author Share Posted October 3, 2005 Ok, so here's an update guys. I went again and bled the crap out of the brakes. All 4 of them. Still low pedal. I was about to swap in the new M/C but I really had it set aside for my XJ, so I decided to bleed the brakes again the old fashioned way.... without speed bleeders. I replaced the speed bleeders with regular ones and had the Mrs pump the pedal as I cracked the bleeders. Low and behold.... I have good brakes now! I don't know if the speed bleeders were sucking in air or what but the old 2 person bleeding did the job. Strange thing is I never saw any air come out when I bled them. Thanks for all your help guys! 88Emjay Link to comment Share on other sites More sharing options...
barnygeroell Posted October 9, 2005 Share Posted October 9, 2005 if you get this problem again this probably helps too: http://www.bigoffroad.com/bigpages/bigt ... _valve.htm Link to comment Share on other sites More sharing options...
88emjay Posted October 10, 2005 Author Share Posted October 10, 2005 if you get this problem again this probably helps too: http://www.bigoffroad.com/bigpages/bigt ... _valve.htm Thank you! That's the oring mod I was looking for. :D 88Emjay Link to comment Share on other sites More sharing options...
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