TJ Dual Diaphram Brake Booster Swap.

[ThisGuyUKnow]

Yep you read that right, TJ. Come on you guy should expect this from me by now.

A fellow jeeper and I (I will not name names just incase he doesnt want to be named in the addition of wrangler parts to a CJ) took apart a rusted out TJ the other week in order to sell of the good parts left over. During the process I got to take a good look at the inner workings and designs of many tj internals that I had not really seen up close for a general lack of interest in TJs since I got into jeeps years ago.

A while back I put a Hydraboost in my CJ7 . And I want to say it is a very cool and very good upgrade;however, I run 30s currently and plan to go no larger than 31s in the future of my 7. That HB can lock up the brakes in an emergency stop with my set up on a dry day at any speed. This is great when its DRY. If the roads are any bit slick any sudden stop locks up my brakes and sends me sliding down the road if I am not very conscious about how much pressure I put on it. I think that the HB is just too much for 30s and would be better paired with 33+ tires.

Well we all know that the YJ booster is supposedly a better braking booster than the CJ power booster. AND it is common internet lore that the dual diaphragm brake booster from the 1995 YJ (only certain 95s) is dual diaphragm and more powerful than the single diaphram booster of the previous years.

It appears that the knowledge of the fact that the dual diaphragm booster is a desired part and the fact that they truly are pretty rare has driven prices up to above AMC 150 bucks for one if you can find it.

Back to the point. When I removed the booster from this TJ (which is a dual diaphragm for all years)i took a long look at it and thought too myself, I wonder what the differences are between this and the YJ dual Diaphragm set up.

The first thing I did was measure the bolt pattern and check it against the YJ brake booster bracket. To elaborate, the TJ BB mounts directly through the fire wall but the YJ booster (all years though the DD ones are slightly different brackets) have a brakect that mounts directly to the BB and to the firewall/pedal assembly. What I found that the TJ booster is close enough in bolt patter that it can be mounted in place of the the YJ booster if you take a larger drill bit and widen the holes.

SO it mounts to the same bracket.

Next I did some parts crossreferencing and I found that, surprisingly, The MC for the brakes is actually the same PN between the 95 and TJ brake boosters

HMMM interesting.....

Then I took a look at the rods (now keep in mind no super exact measurements were taken) side by side the push rods that connect the pedal to the booster look to be almost identical with the exception being that the TJ rod is shorter than YJ booster because it is mounted directly to the fire wall. (for anyone wondering, I am 99.9 percent sure the YJ BB has the bracket to space it off the firewall in order to clear the Hydraulic Clutch MC, this is why the push rods have to be different lengths) by the same I also mean that they have the same contour at the end of the pedal that allows the rod to stay relatively center and swoops down to mount to the brake pedal stud.

OK so with a little fabbing we can extend the length of the input push rod. Looked into rod removal and its not worth the time.

Finally, not having direct access to good information or a 95 yj booster I googled as many images of a 95 booster and a 97 plus booster and you know what, I have been wrong before but I would say judging by the body of the boosters they are the same part.

So the conclusion I was left with was that, if using a YJ booster bracket (which has the correct bolt pattern for the CJ firewall/pedal assembly) I should be able extend the pushrod and use what ever adapter (cant find them in any searches) people are using to adapt the 95 YJ dual diaphragm BB to their CJ7 brake lines. IN THEORY mind you, I should be able to get the desired Dual diaphragm BB for free in this case, but had I not had access to a free TJ booster, they go for around 25 bucks on fleabay vs AMC 150 for an authentic 95 one. And if my theory holds true next week when I put it into practice, the only compromise Ill have to make is cutting the pushrod and extending it to the YJ length.

I will definitely include pics as I intend to tear into this monday when I return home.

Will it all work and brake right? I don't know, I will let yall know next week!

 

[caveman]

 

[ThisGuyUKnow]

teaser

 

[caveman]

Nice. How did every thing line up? I've still got the single diaphragm booster and 35 inch tires. I could use a little more boost.

 

[ThisGuyUKnow]

Nice. How did every thing line up? I've still got the single diaphragm booster and 35 inch tires. I could use a little more boost.

I think a hydra boost would be appropriate for 35s. If your interested in the one I just pulled

 

[tarry99]

Dual Boosters do not increase the braking force. They merely have more stored vacuum volume that would perhaps give you one more complete push / cycle on the brake system if in fact everything else failed.

Single & dual boosters require a minimum of about 18 inches of Vacuum coming off the motor.........more is better. Most like to see 20-22 inches.

A dual Booster also is better at altitude where the air is thinner.

Any Booster can be adapted to any firewall or vehicle as long as you maintain the correct centered position of the push rod and Ratio coming from the pedal set. The main difference in Boosters is the physical size and how they fit under the hood........that is why some are spaced away from the firewall while others use a Linkage adapter that moves it away and also changes the pedal Ratio at the same time.

The correct Pedal ratio for a Power Brake system is about 5:1 vs near 7:1 for non power.......anything greater than that will make your brakes seem overly aggressive.

 

[caveman]

I think a hydra boost would be appropriate for 35s. If your interested in the one I just pulled

Thanks for the offer but I'm afraid that I'm going to have to pass for now. Other upgrades have just about bled the jeep fund dry.

 

[ThisGuyUKnow]

Dual Boosters do not increase the braking force. They merely have more stored vacuum volume that would perhaps give you one more complete push / cycle on the brake system if in fact everything else failed.

Single & dual boosters require a minimum of about 18 inches of Vacuum coming off the motor.........more is better. Most like to see 20-22 inches.

A dual Booster also is better at altitude where the air is thinner.

Any Booster can be adapted to any firewall or vehicle as long as you maintain the correct centered position of the push rod and Ratio coming from the pedal set. The main difference in Boosters is the physical size and how they fit under the hood........that is why some are spaced away from the firewall while others use a Linkage adapter that moves it away and also changes the pedal Ratio at the same time.

The correct Pedal ratio for a Power Brake system is about 5:1 vs near 7:1 for non power.......anything greater than that will make your brakes seem overly aggressive.

Never claimed it did. but people go apey over the yj dual diaphragm none the less. The rod will be correct. I'll post up a lot of detailed info once I get done fixing the brake lines and get it back in the road.

 

[ThisGuyUKnow]

Sorry for the long wait. When we got everything together it turned out the brake line on the frame to the rear was completely clogged and had to replace it and it became a thing. It is all fixed now.

My friend who I left nameless said he wanted his credit in this, he is another forum member: ONLYINAJEEPCJ

So here are the parts:
TJ Brake booster(dual diaphragm)
TJ Brake master (same part number as a YJ dual diaphragm booster)
TJ Master fittings (removed from the TJ brake lines)
YJ Brake pedal
YJ Brake Booster Bracket (from a single Diaphragm booster)
YJ Brake Booster Push Rod boot.
Half inch bolt(this will make sense later)
The first three parts were free and the last three I already had in my CJ. Some sort of Brake booster bracket will be needed as the bolt pattern on the booster is not the same as the bolt pattern on the CJ Firewall, this is actually true for both style of YJ brake booster too BTW neither style can be mounted directly to the firewall. The TJ booster fit the YJ bracket which also fit the Hydrabooster, and I know that you can but adapter brackets for HBs on ebay that are the correct pattern for the CJ firewall so that could be an alternative bracket if acquiring a YJ bracket is not possible or feasible. What I did originally was buy a single diaphragm

The bulk of the modification was the push rod. The TJ booster mounts to the fire wall and the YJ boosters mount on brackets so the push rods are longer. We started by comparing the booster rods to a YJ single that we had laying around. What we found was the rods were fairly identical with the exception of one being longer than the other. TO clarify both have the same angled end at the brake pedal as well as the eye center location.



We then looked at the TJ pedal assembly vs the YJ one to compare the geometry. I forgot to take pictures so sorry in advance but basically the rod stud on the TJ pedal is located a little further closer to the driver than the YJ pedal and is slightly lower. If you look at the mating surface of the booster you will see that the booster rod is actually angled down so this keeps the booster on close to the same angle. The TJ pedal is shaped and contoured so that although to rod stud is further inside the jeep but the pedal footpad is actually in a very similar location to where the YJ footpad is located giving the two assemblies very similar throw distance when depressed. THIS IS EXTREMELY IMPORTANT because it would be a total waste and possibly dangerous if the articulation of the pedal bottomed out before the push rod could move far enough to push the brake master cylinder to its max extent or if the booster puts the wheels at full lock within the first 2 inches of travel.

We then measured the length of the pushrods on the YJ and the TJ boosters (keep in mind that we did not have the YJ Dual Diaphragm booster to compare to) and found that the YJ rod was 2 inches longer. This makes sense due to the bracket. I looked into removing the push rod and it looked to be too much work and time so the only option was to cut the rod and extend it 2 inches. We decided to fully commit to our measurements and weld in an extension but an alternative would be to cut and thread the rod and get a threaded sleeve like people do with hydraboost conversions.

Giving credit where it is due, ONLYINAJEEPCJ did all the welding.

Cut the rod


Grind and bevel the ends


Cut the Half inch bolt to 2 inches and bevel the edges as well


Once everything was cut Ed welded it all up being careful to quench the shaft to avoid heat damage to the booster. I seem to have forgotten to take a picture of the completed extension but when he was done you could not even tell that it was an extended and welded up rod. I guess ill leave that to the imagination.

The only other issue was the brake master fittings. On the single diaphragm installs the fittings are on the opposite side as our CJ ones and people use an adapter fitting to screw into the CJ fitting. Also the CJ and early YJ fittings are inverted flares and the late YJ/TJ master fittings are bubble flares. Oh and the TJ/late YJ master has metric threaded fittings to further be complicated. To put it simply I could not find a dang adapter fitting to go from standard inverted to metric bubble so I gave up and cut the ends of the CJ hoses and removed the fittings and replaced them with the ones I got on the TJ master. The only issue was that the line for the rear port one the CJ is a larger diameter than that of the TJ so we drilled out the center of the fitting and slid it over the line then used a flaring tool to make something resembling a bubble flare which seemed to work very well.


After all the work above, it was kinda just bolt on. I had to finagle the sleeve to seal the firewall because it was for the single diaphragm booster which isn't angled at the mating surface.




[/quote]

On the road:
The results were great. The pedal feels just like i'd expect a factory pedal. Coming from that hydraboost that was able to lock the tires with a big toe I feel better driving this on wet roads. I can still lock up the tires if I stomp the pedal good in the neighborhood. I didnt try to lock the brakes at highway speeds do to obvious safety concerns but I tried some mock emergency stops when I was sure no one was behind me and it felt like i was in good control of the vehicle.

Ed (ONLYINAJEEPCJ) drove it and agreed with my assessment of the pedal feel and function.

That is about all I got. Overall the project was free minus supplies.

 

[caveman]

Nice write up. Thanks.

 

[ThisGuyUKnow]

Nice write up. Thanks.

I am pretty convinced after looking into all this that the TJ booster is actually the same model booster as the one used in the late YJS just the YJ one had a longer push rod for the added length. The MCs are the same and externally the cases are the same when comparing the only difference I can find is that push rod.

 

[ThisGuyUKnow]

A few weeks into this mod and so far so good. Been through several storms and didn't go sliding down the road which had become common.

 

[gert]

Are you running drums on the back still? Im not sure where they put it on CJ/YJ brake systems (should be in the Master cylinder brake line port) But master clyinders for a disc/disc set up will not have a residual pressure valve. To my understanding drum brakes require residual brake pressure in order to function correctly. I am going 4 wheel disc on my CJ and was planning to either find a 4 wheel disc Master cylinder that fits my booster or remove the check ball out of my master cylinder. great work on the write up

 

[IOPort51]

Looks like a good job to me.

for those reading this with AMC 258 i6 / 4.2l l6 motors, this may not (I am pretty sure) not clear the carburetor.