96 MC/booster swapped into a 90 XJ and now no brake lights?

I followed the different write-ups to the letter but to no avail, something had to go wrong.

I drilled the 96 push rod to same diameter as the 90 push rod then ground the "flat" onto the end with a cut-off piece of the 90 push rod as a guide and I'm sure I got it perfect. The switch and bushings went back on smoothly as did the rest of the swap but now no brake lights? I can push up or down on the switch and the lights will work so why won't they work when the brake pedal is depressed?

I also had exact same problem tried everythinf, even welding material back on and re grinding to no avail. hooked up a toggle switch to get home with. Final fix was installing an inline pressure switch in the front brakeline and extending the wires to the underhood. works great and permanent

it was a high pressure switch screwed into a 3 way junction block. had to cut and flare the in and out lines, so effectively an inline. was like 15 bucks and some brakeline fittings

I don't understand why it won't work as it is. Actually I do not really understand how this switch works to begin with. The switch swivels on the bolt so there is no way the flat can apply pressure to the switch with the movement of the pedal. Or am I missing something?

I thought about a micro switch mounted to a bracket of some sort

Is the bolt in the correct way ? My manual shows that the bolt is to be installed different ways, auto vs stick. HTH

Wayne

I had a similar issue when I did the swap on my 88. For me the trouble ended up being that I had accidentally hooked the connectors back up to the switch backwards. Might be worth trying to swap them around and see if it does the trick. Good luck.

xjtrailrider!
I am about to undertake same mod. I have a 1990 XJ. Yesterday I picked up a complete 1995 XJ dual diaphram booster/MC/Pro valve lines etc...
I have looked at that switch on my 90 XJ over and over and have researched this mod on and other sites to n-th degree but cannot find a good photo of the switch installed and how it functions, let alone the secret to making work properly. That is probably why Jeep went to a simpler design in later models.

Does your XJ have cruise control? When you compare the hole in the 90 push rod to the one you bored out in the 95 push rod, is there a bit of elongation in the original oem 90 hole or is it perfectly round?

I recall a written description of an installation where the author did a littel extra grind of the 95 rod hole. I apologize for not having the author's name for citation and do not take credit for his advice but here is the quote i cut and saved to my research file:
-best, Vinnie

Yes mine does have cruise. Both circuits run off the same switch. I do have some slop in the pedal to rod connection just like it had when I started but I may have ground a little too much and the rod is not pushing the switch enough to actuate it. I may have to insert a shim between the end of the rod and the switch to remedy the problem. I also will check the connections but it really should not matter as the switch just completes the circuit. I could have the switch in "upside down" also.

Could some one look at their switch and tell me if connector that comes off of the side of the switch is towards the kick panel or the center of the Jeep. That could be part of my problem as well.

Wayne, I'm 100% sure I put the bolt back in the same way, that thing is a bugger to get to as I have remote start and an alarm system as well as a separate fuse panel for accessories under there. I had as much trouble getting it in and tight as I did getting it out.

Thanks for the replies.

I had the issue when I did this mod to my '91.

The pedal is going to sit at a different height.

Take out the switch and pull the plunger out with pliers. It feels like it's going to break, but it won't. You should hear a ratcheting sound when you pull it out. Then install the switch while holding the break down. Once the switch is in, release and press the brake pedal. It will automatically adjust to the correct spot.

I hope this helps.

There are actually two switches on the 1990 XJ brake pedal. The upper is a plastic plunger with two wires...the other is a switch mounted to the same bolt which connects the booster rod with the brake pedal. This lower switch has a two connectors (four wires) coming from it which activate the brake lights and interupt the cruise control. I do not have any idea what the upper plunger type switch does.

I believe the problem XJtrailrider is having is attributed to the lower switch. I looked very closely at how the switch operates this afternoon. When the brake pedal is depressed the pedal moves forward pushing the bolt which puts pressure into the booster rod and at the same time very slight bolt movement in the hole of the pedal allows the spring switch to make its connections...when pedal pressure is released, the pedal moves aft and any pressure that was on the switch is released and teh contacts open. Total movement is very small and barely perceptible; by eyeball I would say about 1/32" to 1/16".

Don't think the strech the switch hint will be helpful. If the lower switch is damaged, it is a fairly cheap autozone replacement...

I did look at the pair of connectors attached to the lower switch. On my XJ both of the brown plastic connectors come straight back toward the driver's shins.

grimah1w said:

There are actually two switches on the 1990 XJ brake pedal. The upper is a plastic plunger with two wires...the other is a switch mounted to the same bolt which connects the booster rod with the brake pedal. This lower switch has a two connectors (four wires) coming from it which activate the brake lights and interupt the cruise control. I do not have any idea what the upper plunger type switch does.

I believe the problem XJtrailrider is having is attributed to the lower switch. I looked very closely at how the switch operates this afternoon. When the brake pedal is depressed the pedal moves forward pushing the bolt which puts pressure into the booster rod and at the same time very slight bolt movement in the hole of the pedal allows the spring switch to make its connections...when pedal pressure is released, the pedal moves aft and any pressure that was on the switch is released and teh contacts open. Total movement is very small and barely perceptible; by eyeball I would say about 1/32" to 1/16".

Click to expand...

Yes this is the issue I'm having. Two things that I did wrong;

1) I did not bore the hole in the 96 booster rod large enough, the bushing fits but it needs to be loose in order to depress the switch. The switch plate needs to fit snug to the end of the rod but not so snug that it is depressing the switch. This is a delicate balance to achieve. Make sure you get it right before putting the booster back in.

2) I ground too much off the end of the rod. The thickness at the thinnest spot on the 90 rod is 0.15, I ground the 96 rod to 0.10, I need to build the thickness back up with weld then grind it to the proper thickness.

As far as I know the upper plunger switch is either for TC unlock or for the shift unlock (foot must be on the brake before the tranny can be shifted into R or D.

I have it all back apart now and will MAKE SURE I have it right this time before I put it back in this time.:twak:

Also another note, the brake light switch is "normally open" or "NO" and the contacts close as the switch is depressed.

Appreciate your update!
What was your technique for boring the hole on the '96 rod? (Step drill or normal drill bit...what diameter did you shoot for?)

I have dug through some wiring diagrams and in the 1988 MJ diagram I found the upper two wire switch is also associated with the cruise control. Connector C251 - Cruise control clutch switch --- supposed to be a jumper in automatics -- which looks just like the 1990 XJ.

PM me with e-mail address and I will shoot the diagram I made and or the wire diagram.

Did you keep your windshield washer reservoir installed? mod to the isntallation???

grimah1w said:

Appreciate your update!
What was your technique for boring the hole on the '96 rod? (Step drill or normal drill bit...what diameter did you shoot for?)

I have dug through some wiring diagrams and in the 1988 MJ diagram I found the upper two wire switch is also associated with the cruise control. Connector C251 - Cruise control clutch switch --- supposed to be a jumper in automatics -- which looks just like the 1990 XJ.

PM me with e-mail address and I will shoot the diagram I made and or the wire diagram.

Did you keep your windshield washer reservoir installed? mod to the isntallation???

Click to expand...

I got the switch working, there is a trick to it of course. The thin part of the rod between the hole and the flat has to be .013 in order for it to work. I bored my hole on my drill press with a 5/8" (.625)(the hole is actually slightly larger than .625 but you can use a round file to open it up slightly) drill bit and then elongated the hole slightly with a round file(towards the booster side of the hole). The bushing has to be able to move back and forth some for the switch to actuate.

I have everything done with the exception of;

I had to move the wire harness above the booster(the one that goes to the wiper motor and has the washer hose and washer pump leads in it) it just did not want to fit under the booster.

So....
I need to extend the pigtail for the brake pressure switch
I need to extend both washer pump pigtails and washer hoses

Then I will bleed the system and try it out.

A couple of notes specific to the 90 model year;

I used the 90 proportioning valve and just pulled it forward so it would clear the new booster. I literally did this by hand, there was plenty of slack in the 3 brake lines to achieve this. This made it so I would only have to adapt 2 lines instead of 3.

Also, I used 19/32 brake booster hose as a patch for the purge line to the charcoal canister. I used this hose between the firewall and the booster as the hose will give without cracking, the plastic pipe was being squeezed too much. I used weather strip adhesive at both ends and glued the hose onto the pipe at the elbow and just below the MAP sensor.

The washer reservoir will fit in the stock location albeit moved forward about an inch. It clears fine. I used the 96 brake lines that wrap over the top of the MC and over to the proportioning valve.

Here are some pics of the switch;

This is the distance you need to achieve in order for the switch to operate properly.


Make sure you elongate the hole towards the booster so the bushing can slide slightly



The switch is "NO", or "normally open". Make sure before you put the booster back in that the switch is open when no pressure is applied to the bushing towards the booster and that the switch closes when the pressure is applied to the bushing.





This is what the switch should look like installed on the rod, the "open" end of the switch frame goes towards the drivers kick panel.


This is the side towards the center of the Jeep


I hope this helps answer any questions anyone might have about the stop switch and getting it to work.

Jon

Awesome!
Thanks very much Jon. The photos, narrative, and advice are very helpful!
Vince

ill be using this thread when i do my swap. i have the booster, MC, and prop valve waiting to go in

I'll post more pics of the swap as I get them. My garage is cold and I'm out of propane for the heater.

We are supposed to get above freezing later this week for the first time in a month so I will definetly finish the swap then.

A few more pics and explanations from the swap.

I re-used the 96 brake lines that were routed over the top of the MC. This got the lines away from the washer bottle. I re-used the 90 proportional valve by moving it forward to clear the booster. I did not have to re-plumb the PV, there was enogh slack in the stock lines to allow it to move forward 2" or so. This made it so that I only had to adapt 2 lines with unions.




I used 19/32" pcv hose to run behind the the booster in place of the hard plastic line(charcoal canister purge line). My stock plastic line had been crushed and cracked by the stock booster and just wouldn't fit behind the new booster very well. I cut the plastic line under the MAP sensor and at the elbow above the bulkhead connector, I then used weather strip adhesive and glued the 19/32" hose to the each end of the pipe to complete the connection. The rubber hose will colapse and fit into the tight spot behind the booster without cracking.


The stock washer bottle fits just fine but I will move it a inch or so further farther forward to clear the booster. I have a new bottle and sensor on order, this one is ugly and cracked.


Since I had to run the wiper motor wire harness above the booster and the brake pressure switch pigtail, front and rear washer pump pigtails and washer hose are located in this harness, I will have to extend these 3 pigtails and hose then clean up all of the wiring harnesses.



This should answer any of those questions that you may have and that I know I had, about this swap.

i just did this swap today. Instead of trying to grind everything down and drill holes i just cut the end off my 87 booster and then welded it to the 98 booster. took about 30 min and i didnt have to worry about tolerances and over grinding. Switch worked on the first try. I would recommend this method. No headaches here

-Mike

mnaemark said:

i just did this swap today. Instead of trying to grind everything down and drill holes i just cut the end off my 87 booster and then welded it to the 98 booster. took about 30 min and i didnt have to worry about tolerances and over grinding. Switch worked on the first try. I would recommend this method. No headaches here

-Mike

Click to expand...

I thought about this as well. I originally did not want to break out the welder for this job but ended up having to anyway since I had to build the end of the rod up where I over-ground it.

Here it is all back together. I will bleed the brakes and drive it tomorrow.