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Braking performance

C

Chancer

NAXJA Forum User
Location
Bonnie Scotland
I've just swapped in a double diaphragm booster and ZJ disks on the back into my stock 93 Sport, and wanted to get a bit of feedback...

I can lock the tyres up well, and do 60-0 in about 5 seconds on 215's, but the pedal seems to sink really easily, and whilst it doesn't appear to be affecting the performance, I did expect it to be a firmer pedal feel. I'm assuming that more bleeding is in order.

To pre-empt the questions, I bench-bled the master, then gravity bled the whole system, finally finishing off using my Eezi-bleed to double-check that there were no bubbles in the pipes.

What do you all think? Is the performance about right for the upgrade, and is the pedal feel just a matter of getting used to something new, or do I need to do more bleeding?
 
did you swap the combination (porportioning) valve?

the rear disks require more fluid then the drums did. that may be reason for the pedal travel
 
Did you check the Booster rod adjustment when you installed the master cylinder?? This is a critical adjustment that is overlooked... I am not saying this is your cure, but just a sugestion..
 
I used the 95-96 booster (Part number 52008647) for the swap, which is supposed to have the same length rod, and be a bolt-in. In fact, it was a straight swap, and the easiest thing of the whole conversion to carry out - even teh actuator rod hole is the same diameter.
 
I used the 95-96 booster (Part number 52008647) for the swap, which is supposed to have the same length rod, and be a bolt-in. In fact, it was a straight swap, and the easiest thing of the whole conversion to carry out - even the actuator rod hole is the same diameter. I retained the aluminium spacer too.

Sorry for the double post- firefox isn't showing the delete button.
 
one other thing to consider is the length of any added brake lines. If you use exended rubber lines, I think they can give you a longer travel. I believe one of the benefits of the stainless Braided lines is the smaller diameter of the hose, in addition to the braided hose not giving/stretching at all under pressure. Just a thought.
 
Thanks for the ideas. I think that maybe it's a case of a few small bubbles in there and the greater volume of the rear calipers over the old cylinders. I don't see how any increase in the length of lines would make a difference, since it's the amount of volume required to push the pistons out by to make contact with the discs that defines the travel, rather than the total volume witihn the system. Extra volume/ travel generated in a closed hydraulic system during braking and which wouldn't go directly to the pistons would only occur if the soft lines or something else was deforming under pressure, and at the amount I paid for the OEM lines, I definitely hope that that's not the case! :dunno:
 
My guess is the larger volume causing the long travel. If you can lock up the brakes you are OK; most XJ's can't with the stock brakes.
I have the 95 booster on my 89 with 10" drums on the D44 and the pedal has very little travel; but you can adj the drums to need little expansion of the wheel cylinder.

a big improvement in early xj's is to replace the front rubber lines (especially if they show bubling or cracking) as they weaken and will expand under pedal pressure - lessening stopping power. Replacing mine resulted in 40' shorter stopping distance (greatest improvement of all the mods)
 
prob stupid question but is the master cylinder a must when doing the booster swap ?

why not just use original master cylinder and just swap out the booster ?
 
I did'nt swap anything but the drums for calipers and mine worked fine. When I took out the O ring the rear locked up better. The only problem I ever had was from not bleeding enough after taking out the O ring.
 
With this swap I'm assuming that you continue to use the existing master cylinder (mine is a 1994).

Does anyone have a part number or a year model for the proportioning valve? I'm assuming that this is out of a ZJ with 4 wheel disc brakes.

Robert
 
Thanks for the info on the install, great write-up!

But I didn't find anything in there about what prop valve to use. I've got disc brakes on the rear. Does anyone have the part number or the year of the ZJ prop valve that they used?

Robert
 
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