Brake Booster Question

[Heavy_Metal_Thunder_81]

Will a dual diaphragm brake booster from a 86+ GW bolt up in place of a single diaphragm booster in a '79 Cherokee? The reason I ask is because I was going to use a dual diaphragm booster from a '77-'79 J-20 but the part literally does not exist anymore. All the parts places require you to send your old dual diaphragm booster in and have it rebuilt then sent back, and, well, I don't have a dual diaphragm booster to send in. I did notice however that you can still get dual diaphragm boosters for the Grand Wagoneers but it is a different part number than the ones for a J-20. I know they used different master cylinders in the 80's FSJs but can the boosters still be swapped? If it is a direct bolt on swap that would be primo.

And NO. Hydroboost is NOT an option.

Sorry for the long thread

[babywag]

Yes same firewall bolt pattern.

You'll want to check pedal travel though.
Might need to modify your pedal or swap in a matching one.

Can't speak for a '79 vs. late model, but on my '73 I used the matching pedal from the donor due to the differences.

[elskeptico]

I put a dual-diaphram booster in my 79 Cherokee no problem

[Heavy_Metal_Thunder_81]

I put a dual-diaphram booster in my 79 Cherokee no problem

Out of what though? They changed some time in the 80's

[elskeptico]

Here's what BJ's says: "OEM correct for 1983-1991 FSJ's, but will fit earlier years. Note that the dual diaphragm boosters use the later model plastic-reservoir master cylinders."

I guess you'd have to also use the later master cylinder.

http://www.bjsoffroad.com/prod-17.htm

[Heavy_Metal_Thunder_81]

Would my brake line fittings work with the later style master cylinder? Or did they go metric then?

[The Anti-Chrysler]

You're thinking of the power steering lines. The brake lines are all SAE for all years, so no problem there. Upgrade to the newer master like the others said and you'll be good.

Would my brake line fittings work with the later style master cylinder? Or did they go metric then?

[Heavy_Metal_Thunder_81]

You're thinking of the power steering lines. The brake lines are all SAE for all years, so no problem there. Upgrade to the newer master like the others said and you'll be good.

Perfect! Exactly the answers I was looking for. Thanks a load guys

[ScottsMojo]

Your original master cylinder will work with the dual diaphragm booster. I put one on my 74 last year and it will affect your brake pedal height. The newer booster made my pedal stick up about another 1/2" which doesn't seem like much till you need your brakes in an emergency. I solved this by building an aluminum spacer out of 1/4" stock that mounts between the bracket and the firewall. This brought the geometry almost back to original. When you finish don't forget to check your brake light switch adjustment, it will probably need some tuning.

[Heavy_Metal_Thunder_81]

Well I just ordered an 84 J-20 dual diaphragm booster and master cylinder. I'll return the '79 master I have already. Hopefully this should be a bolt in deal with no spacers or mods needed.

[Heavy_Metal_Thunder_81]

Your original master cylinder will work with the dual diaphragm booster. I put one on my 74 last year and it will affect your brake pedal height. The newer booster made my pedal stick up about another 1/2" which doesn't seem like much till you need your brakes in an emergency. I solved this by building an aluminum spacer out of 1/4" stock that mounts between the bracket and the firewall. This brought the geometry almost back to original. When you finish don't forget to check your brake light switch adjustment, it will probably need some tuning.

Wait, did you need to make the spacer because of the booster or because you used the old style master with the newer booster? Will I need to fabricate a spacer when using an 84 master/booster combo on my '79???

[ScottsMojo]

Wait, did you need to make the spacer because of the booster or because you used the old style master with the newer booster? Will I need to fabricate a spacer when using an 84 master/booster combo on my '79???

I don't know if the new style mc will correct the geometry, it might. I have one, just haven't got to putting it in yet. It will work as is. I have really long legs and I am cramped up to begin with when in the drivers seat so I am a little finicky when it comes to ergos. You may not notice it at all, it boils down to personal preference. Best I can suggest is to put it together and see what you think.

One thing to know about the new mc - the ports are opposite from the old mc. The line that is in the front on the old mc will need to be hooked to the rear port on the new mc, and vice versa...

[Heavy_Metal_Thunder_81]

Alright, good to know. I'm pretty short for a guy at just under 6 foot. Thanks for the info.

[flatbackdragon]

replaced single with dual at Ouray one year. Can use old master on it with no problems (on my 79) You don't need the newer version.

[Heavy_Metal_Thunder_81]

Ok, so here's another question. Which master cylinder is better? I have both styles sitting at home now, which one should I use? I have had to replace a few of the older style ones due to leaking out by the booster (same reason my booster needs to be replaced now). Are the newer aluminum/plastic master cylinders more reliable? Do they improve the braking system at all? Or should I just stick with the old cast iron master cylinder?