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axle & brake question

Micha

NAXJA Forum User
Location
Vancouver
hi guys,

my 87 xj has a bigger drum brake on the rear axle then my 91 xj - how hard would it be to take the 87's and swap them to the 91?

i believe the 87 is a d44 and the 91 probably a d35 (it's got abs as well)

any ideas?
thanks,
michael
 
10x2.5'' brakes on a 44- how about you disable the ABS, and throw that beefy 44 axle under the 91. considering same gear ratios.
 
Is it worth the effort? The rear brakes provide very little braking force. I doubt you'll see any improvement, and more likely a degradation, since the existing master cylinder and proprotioning/combination valve are setup for the smaller drum, not the bigger one your swapping too.

I'd think your effort would be better spent in just keeping the existing brakes in tip-top shape and maybe throw in a set of good aftermarket performance pads/shoes to improve braking. Front hi-performance pads is what will really give you better performance.

If you doing a lot of towing, then I can see the desire for bigger rear drums. But no towing, put your effort in the front brakes before the rear.

Just remember, rear drums have to be working properly and adjusted properly for the Front Brakes to Work well also, so don't ignore the rear brakes as you upgrade the fronts.
 
91 xj: 'new' ride, got it just one week ago...
87 xj: was my dd till about a month ago when it got rearended and damaged beyond the current replacement value

i checked the front brakes on the newer one and they seem to be in very good shape. i notice a considerable difference in braking from the 87 to the 91 though. apart from the brakes themself, what could decrease the breaking power? i figure that it comes down to less pressure in the braking system. is the master cylinder bad? i'd like to keep the abs. but could the fault be in the abs components as well?

thanks for your insights,
all you help me a lot
 
Re-Read the Last Line of my last post.

The rear drums have to working properly and properly adjusted for the front brakes to work well.

The front disc pads always ride on the rotor, they are self-adjusting by nature, as they wear, they just move closer to the rotor as they ride on the rotor.

The rear drums, the shoes wedge themselves into the drum (thats why they take realatively less force to activate the drums, than discs), the shoes have to pulled back from the drum by springs. So as the drum and shoes wear, the distance between them increases. You have to adjust the rear drums to remove that slack that comes from the wear.

When you stomp on the brake, the master cylinder creates pressure to push the slave cylinders out and activate the brakes. None of the brakes activate until the pressure is built up in all the brakes. So any slack in one brake, will be felt in all the brakes. So, if there is lots of space between the drum and shoes in the rear brakes, your pushing in the brake pedal doesn't do anything until the rear shoes extend enough to actually contact the rear drums, then pressure starts to build on all the brakes, but by this time you've got the brake pedal pushed half way to the floor and it will get to the floor before you've built enough pressure to give you a really hard stop.

Adjust the rear drums, that will remove the slack in the brakes, you will get more of a bite from the brakes much sooner as you press the pedal down. That give you more pedal to push even farther and get even more braking force.

Your rear drums should have "SELF-ADJUSTERS". They are designed to "MAINTAIN" the adjustment of the rear drums. If your rear drums are in good shape, working properly and are close to proper adjustment, the "SELF-ADJUSTERS" will help keep them that way. Usually you just have to slam on the brakes with the car moving in reverse to activate them, and it will adjust the rear drums. You may need to do it several times if they are more out of adjustment.

BUT, THE REAR DRUMS HAVE TO WORKING PROPERLY, IN GOOD SHAPE AND CLOSE TO PROPER ADJUSTMENT. The vehicle is 15 years old, and judging from the brake performance you describe, the previous owner never did that. I'd pull the rear drums, inspect them, clean them, correct any problems and then lube them up. Then adjust them manually. There are lots of little linkages, springs and sliding parts, that rust, sieze up, drag, etc that mess up the rear drums. The front brakes often suffer until the rear drums are working right. You should see much better brake performance after you get the rear drums working right and adjusted properly.
 
A dead give away for improperly adjusted/worn rear drums is a low but firm pedal. It takes most of the master cylinder stroke to get the rear shoes in contact with the drums, then the pedal firms up as pressure build properly.
 
87manche said:
A dead give away for improperly adjusted/worn rear drums is a low but firm pedal. It takes most of the master cylinder stroke to get the rear shoes in contact with the drums, then the pedal firms up as pressure build properly.
Thanks, that sums up a rather long post real well.

Yep, its called "PEDAL HEIGHT", the height at which the pedal actuall firms up and makes a real bite of braking force. Adjusting the rear drums raises the pedal height.

If pedal height is really bad, by the time you get a firm pedal, there isn't much stroke left to get even greater braking force, so the brakes give a pretty good stop, but the pedal hits the floor before you can really brake the car as hard as possible.

One note: I've had a siezed rear brake cylinder, it decreased brake force and made the pedal feel really wierd. So there could be other problems with those rear drums messing up the brakes in total.

Another way to sum it up: If I just got a 15 year vehicle and the brakes didn't feel right, I'd take the rear drums off and inspect everything, clean and lube up all the rear drum parts and make sure they are operating smoothly and correctly.
 
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