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DIY T44/urS Vac Assist Conversion

PostPosted: Sun Aug 25, 2013 9:41 pm
by loxxrider
DIY T44/urS(?) Vac Assist Conversion

Why Convert?

You may want to convert your T44 (and I think this will work on S-cars too) to vac assist for various reasons. Maybe you don't want to deal with the bomb anymore, don't like the pedal feel of hydro, or your ps pump doesn't fit because of your monster intake manifold ;) Whatever the reason, this thread will guide you through the process. I really didn't run into any hiccups along the way, the process is relatively easy, but here is the basic information needed to get the job done.

What parts do you need?A

You will need the following items from either an 80, 90, 4k, original coupe, b3 coupe quattro, quantum, or C4 100 CS (if you can find them in vac assist... not all of the above came this way in North America):

-Vacuum booster
-Check valve for the booster
-Clevis pin for the connection between the brake pedal and the booster pushrod

Here are the parts laid out on my garage floor along with the master cylinder from my 200 20v and the master from the 80q I got the vac booster from.



1. Remove the master cylinder.

Unscrew the two 13 mm bolts holding it to the hydraulic booster and the two 11 mm brake lines from the driver's side of the master. Also, disconnect the line to the brake reservoir and pull the master cylinder off of the hydro booster.

^^^ stupid zip-tie!

2. Remove the hydraulic booster (this is the hard part).

Unscrew the two 11 mm brake lines on the hydraulic booster. Then move into the car where you will remove the four 13 mm nuts holding the booster in along with the clevis pin.

The first thing you want to do here is remove kick panel. This process may vary depending on vehicles. It should be easy enough that I don't have to explain it. Next, remove the clevis pin clip by pushing on it with a screw driver or something. Once it is removed, you should be able to remove the clevis pin freeing the brake pedal from the hydraulic booster's push rod.

Now comes the hard part. Remove the four 13 mm nuts holding the hydro booster into the firewall. You'll have to pull back the carpet and a lot of sound deadening material to get a good view of the bolts. Three of the four bolts should be visible immediately. I found that it made things easier if I removed the foot vent as well as the panel where the hood latch mounts for easier access and to pull the carpet back further respectively.

Once all of the crap is out of the way the first three nuts should go by relatively easily with some good 3/8" extensions and a ratchet. The fourth one is the real bitch. You can try various combinations of u-joints, misalignment extensions, etc. to get at this one. I found that I could only get at it with a certain combination of extensions and such and I had to wedge my hand up between the clutch and the brake pedals to get a ratchet in there. Once in position I could only get about one click out of the wrench at a time, so I decided to try one of those snake things connected with a screw driver at one end and a short 13 mm socket at the other end. This worked very well. **There is a small access hole between the clutch and brake pedal that you can use to help you see the nut you are trying to get the socket on. I tried getting to the nut through the hole, but I just couldn't get it right. It was very useful for spotting my snake thing while attempting to get it on the nut though.

I don't have any pics of the hydro booster removed, but it should come right out at this point.

3. Prepare/swap parts

In order to get the vacuum booster to fit into a large chassis car, there are a few things that need to happen. First, you need to un-bolt the adapter/spacer used on the vacuum booster from a small chassis car. It converts from four to three bolts. Then, you need to compare the push rod length between your hydro booster and your vacuum booster. Make sure both are fully extended when you do this. There is a threaded rod with a stop nut on the vacuum booster's push rod which needs to be adjusted (shortened) to the same length as your fully extended hydraulic booster's push rod. Finally, there is a spacer on the master cylinder which needs to be removed before installation onto the vacuum booster.

4. Install the vacuum booster

Once you have made these adjustments, you can try to finagle the vacuum booster into place where your old hydraulic booster used to sit. I had to remove my ps fluid reservoir to do this (lots of hose clamps) and I had to take my fuel lines off of their bracket and bend them a bit along with bending some random brake lines a little to get it back in its little area. I also had to remove the ps reservoir bracket and hood closing sensor to get it in there as well. Once everything is out of the way, you should be able to just push it right in. Make sure you get the clevis (on the end of the push rod) lined up with the brake pedal before you drive the whole assembly home. You can get to it after the booster is installed, but it makes things a little harder sometimes. From here, just do the reverse of the removal for this part.


5. Install the original master cylinder

Pretty much the reverse of step one, but you'll have to bend the brake lines a little because the master will sit a bit further back in the engine bay now. You can do it by hand with no problems.


6. Install check valve and connect to a vacuum source

Pretty much self-explanatory. Any vac source will do.

7. Bleed the brakes (and maybe clutch)

You'll need to bleed the hydraulic system after this installation.

That's it! Let me know if you have any questions or comments.

Re: DIY T44/urS Vac Assist Conversion

PostPosted: Sun Aug 25, 2013 10:48 pm
by gtn116
About time you posted this up here. ;-) I have all of the stuff to do it, and I'm actually doing an ABS delete too, which is just short of a nightmare. It never worked anyway though, so I don't see too much of an issue.

Re: DIY T44/urS Vac Assist Conversion

PostPosted: Sun Aug 25, 2013 10:52 pm
by loxxrider
Your post reminded me about it actually! Thanks :) ABS delete is definitely not a terrible idea if it doesn't work anyway and you are used to not having it. You should make a DIY if you do it :)

Re: DIY T44/urS Vac Assist Conversion

PostPosted: Mon Aug 26, 2013 9:15 pm
by gtn116
Planning on it. I just have to figure out how I'm going to run a prop valve and all that stuff.