TXjeepTJ

iTrader: (8)

i noticed that its extremely hard to make my jeep come to a complete stop.. then i realized that its because my rear brakes arnt working. it slows down fine from high speeds, then when your about to come to a complete stop, the front tires lock up and it skids about a foot until it stops


i dont see how it is possible for an engine swap to effect brakes... or could it? my jeep has been sitting in the garage for 6months while doing the install- could that be the problem?

LS1MCSS

iTrader: (18)

Sounds like proportional valve problems. My car did that when I had the rear out of it. If it works like mine does, there is a small plunger that you can see move when you apply the brakes. Get someone to grab it with pliers and pull on it while you mash the brake pedal.

ghettocruiser

iTrader: (17)

What rear do you have in that jeep??? What brakes are you running in the rear? Stock drums?

If they are drums, its quite possible that something in the drums is frozen or the wheel cylinders are stuck. Ide be surprised that happened in such a short time, but its still possible.

So you didnt do anything at all to the brakes during the engine swap? Didnt open the system or change any components???

If you still have the stock rear and brakes now is a great time to do the D44 swap and use discs in the rear.... or even the 8.8 with discs already installed! You'll be able to stop like a sports car then.

J.

TXjeepTJ

iTrader: (8)

wheres the plunger?

once you grab it with pliers then what do you do?

Bubbapoppie

A fairly common problem is that the brake switch is improperly adjusted. If the switch doesn't allow the peddle to return completely u won't get much brake action.

TXjeepTJ

iTrader: (8)

well all the brake switch in my jeep does it turn the brake lights on, i dont see how it would cause the brakes to not work at full strength

LS1MCSS

iTrader: (18)

Here is a decent picture of a proportional valve. Have someone grab the plunger and pull out a little and then you mash the brakes. That should make certain the plunger is centered. If your back brakes are still not working correctly, make sure the automatic adjusters on the rear are working correctly. They may not be adjusting the back shoes out enough.
http://board.moparts.org/ubbthreads/...28Small%29.jpg

TXjeepTJ

iTrader: (8)

i want to try this, where is the plunger like thing located?

ghettocruiser

iTrader: (17)

The plunger he is referring to is in the front of the prop valve. Its covered by a cap that you probably have to pry off to gain acess.

Removing the spring or modifying the spring that is in there is a common mod to jeepers when swapping to rear disc brakes. It will allow more pressure to the rear brakes. I believe the valve will "bleed" off pressure to the rears under braking. Keeping them from having more pressure than the fronts and locking up.

Honestly, and no offense to the person that suggested it, but I wouldnt even mess with the plunger at this point. If the brakes worked fine before the swap, and you didnt open or touch the braking system during the swap, then I would try to track down the issue before messing with the prop valve. Make sure you didnt pinch a line, or kink that soft line at the rear axle...simple stuff like that. Its really easy when lowering an engine in or messing around like that to pinch a brake line. Just bumping a line with the block or something can put a good kink in it.

Just a suggestion though. And I still think if you arent running discs in the back, now is the perfect time to swap to discs, ditch the prop valve, get an adjustable wilwood valve, and REALLY give that thing some stopping power. Now that you've more than doubled your horsepower, it would be nice to double your braking power to match.

Justin

LS1MCSS

iTrader: (18)

The picture in the link shows where it is. They are calling it a valve stem, though.

'JustDreamin'

It'd be real nice if converting to rear discs actually did that, but it doesn't. Rear brakes on pretty much every vehicle only account for about 20% to 25% of braking force. Why? It's not because of the rears being drum, it's because of weight transfer and vehicle stability.

Basically, it all boils down to the fronts do most of the work. If you're going to spend money upgrading brakes, spend it where it matters, which IMO is on the fronts.


However, I would suggest that you check the simple mechanical stuff first.
1.) Verify you don't have any kinked or pinched lines.
2.) Verify you've got fluid in both sections of the master cylinder reservoir (I know it's a duh, but....)
3.) Bleed the brakes on the rear, make sure you're getting fluid and don't have any bubbles.
4.) Make sure the rear drums are adjusted close to but not grabbing the drum (you may have to pull the drums and disassemble the adjusters, since often times they'll try to rust solid).
5.) Make sure that the front discs don't have oil / grease on the rotor or pad surface, since that makes them grab / lockup. Might want to spray them down with Brakekleen just for insurance.

If that doesn't fix it, I'd start looking at hard mechanical parts. For example the combination valve (proportioning and residual pressure valve) or the master cylinder (might have lost something in the rear circuit).

'JustDreamin'

bczee

iTrader: (12)

You can also check that you are getting pressure to all four corners buy putting a brake pressure gauge on each to check pressure as you step on and engage the brakes.

But if it is locking up just as you come to a stop. Is it both sides or just one ?.
I think you might have a bad caliper.. (piston is not moving smoothly or getting stuck. I have had that happen on my VAN before and swapped out the Caliper and that fixed it)

ghettocruiser

iTrader: (17)

Not sure I made my post too clear... I know the rears only account for about 1/4 of the braking. BUT... and this is especially with lifted jeeps, you WILL notice a nice improvement just from switching from stock drums to discs. The most popular swaps are brakes from a grand cherokee (dana 35 axle) or swapping in a ford 8.8 with discs. Either one will give you a better feel in the brakes. However...since the system was set up for disc/drum, it wont be optimal. I cant remember the exact procedure, but I think you remove, or cut some coils out of the spring in the combo valve. It will improve how the rear discs work.

In my opinion, if you are doing that, the best way to go is do like I said. Ditch the stock valve, run front brakes right off teh caliper, and run the rears through an adjustable prop valve. I have my lifted cherokee set up like this with the rear grand cherokee discs, and stopping even with my 33's and steel wheels is TONS better than when it was bone stock. I also have my trans am set up this way. LS1 fronts and LS1 rears with an adjustable valve for the rears.

Weight transfer in a jeep like TXjeepTJ has and like I have will be more than in an f-body car... But, I wouldnt go back to stock drums on my cherokee for anything. One of the best mods Ive done to both vehicles.

Not tryin to start a brake set up argument, just wanted to make sure I was clear in what I was saying.

J.

'JustDreamin'

Not trying to start an argument either. Just alot of folks think that rear discs are inheritantly better than drums, which isn't necessarily the case. They both have some advantages and some disadvantages. But the biggest problem is often times the rear brakes are contributing so little to overall performance that swapping from drums to normal sized discs to 15" discs you'll see little performance advantage. Especially because you need to make sure the brake system is balanced such that you lock the fronts just prior to locking the rears (because that scenario is stable but locking the rears first leads to the rearend passing you). Basically, it boils down to you can't fully utilize the power of big brakes on the rear because there usually isn't enough traction to allow it. Wow, that was a book. Sorry.

Completely off topic, I still find it interesting that semi's still run drum brakes. Wonder if or when they'll change....


Basically, the original poster needs to figure out what happened to his current system, and fix whatever the problem is. Then think seriously about upgrading. Rear discs would be nice, budget allowing, but I would think very seriously about the front brakes first and foremost (after getting whatever mechanical problem exists currently fixed). Its where all the work is done.

'JustDreamin'

TXjeepTJ

iTrader: (8)

ok, well i lowered my idle down to 600rpm and not it seems to brake a little better. i jacked up the rear end and put it into drive and the brakes will stop the rear, it just does a really bad job at doing it. there is no kink or anything in the lines, the brakes worked perfect before the swap- now they just seem to have a little less stopping ability

sooo proportioning valve?

i do plan on swapping to disc brakes when i get a new rear end, but that prob wont be anytime soon

ghettocruiser

iTrader: (17)

Just a thought... Would the idle/vacuum properties be different enough between the 4.0 and LS1 to cause a difference in brake feel? Maybe the power assist isnt working the same way and you notice a different in pedal feel? Thats probably not it, but I was just brainstorming.

You'll love a rear disc conversion on that thing. I really noticed a huge difference when I did mine. And that was after I went from the smaller stock (8.25 rear) drums to the larger dana 44 drums.

Good luck! i hope ya figure it out.

Justin

TXjeepTJ

iTrader: (8)

i lowered the idle of the engine down to 600rpm. the jeep stops fine now lol im guessing all that little extra power at 900rpm wasnt allowing the brakes too grip (my brakes suck)

im putting in a ford 8.8'' this week, w/ disc brakes - cant wait

thanks guys!

ghettocruiser

iTrader: (17)

Good stuff man. If you need any help with the 8.8 swap or setting up those brakes...shoot me a PM.

J.

Rhino

iTrader: (6)

That's strange. I did the rear disk swap (the tera kit) and hardly noticed any gain. I had the D44 from the factory, I wonder if there are any differences in the braking system.

ghettocruiser

iTrader: (17)

What vehicle rhino?? My cherokee was stock with a corp. 8.25. Before it was lifted, the brakes worked fine. Lifted it, put 33 and steelies on it, and the brakes sucked. Re-geared with a dana 44 with the larger drums, and brakes were still crappy. So I used dana 35 discs off of a grand cherokee and right after install I could feel them.

I read of plenty of folks messing with that plunger, but I didnt feel like going through that. I just ditched everthing and started over with new lines. Ran the fronts right off the master, and the rears through an adjustable brake valve. Put the valve at roughly 50% and was locking the rears up under hard braking. Backed it down so that the front tires were squawking and the rear tires were just barely starting to make noise. Seatbelt hurts you now if you jamb on the brakes too hard. haha

J.