XR4Ti Archived Tech Articles

    Rear Shock Tower Brace Install - based on Allan Slocum's $5 angle-iron shock brace design, this is nearly all you need to know to install a brace in your XR4Ti.


Post Date:    Fri, 17 Apr 1998
Subject:      $5 rear shock tower brace - XR4Ti

Unbraced list members,

I have an experience to share.  One that I know others have talked about, but
I thought I'd add my two pennies on the subject...

This last Monday, Jeff Jackson (spyker@juno.com) drove up to Dayton from Cincy
for a work related training event.  He let me know about it and we got
together.

His XR is a late 89, with a T-5, lowered with Eibach's and RS adjustables,
cossie front bumper and grille, all OEM Ford pieces, mono-red, looks nice.  He
also had the Slocum design rear brace for the shocks.

Anyway we went tooling around in it (I drove it) so I could see how the
suspension felt lowered.  He put the fronts on full hard and I loved it!  This
is where it gets interesting...

I am pretty familiar with how my 87 XR4 feels when pushed to the limits.  I
have autocrossed it, done illegal things in it (insert standard disclaimer
here), and basically darn near discovered the cars handling *limits*.  I have
good tires, too.  Yoko AVS's, nice and shaved.  The car sticks good, and I
know how the shell of the car responds during corners...  I *know* my car...

Jeff let me push his XR a bit in some local parking lots (he didn't flip out
the way I was tossing his car around, great guy!).  Well, having NOT driven
his car before the shock tower brace was installed, I can say that I CAN tell
the difference between the way his behaved and mine behaved, beyond the level
of the springs and dampers.

To describe:

Jeff's XR4Ti - the rear suspension had a one-ness to it (great for you Zen-
masters...), no feeling of independent movement, just connected movement.

My XR4Ti - I didn't notice until I drove Jeff's XR4Ti how truely our cars have
an *independent rear suspension*, it feels as though there are two separate
units in the rear.


The truth is, you never can experience what I am describing without putting
the brace in.

Quotes from the XR4Ti suspension masters:

"The front brace was noticable, but adding the rear brace made a night and day
difference".
- From a discussion at the Carlisle 97 M-O banquet

"Just by moving one end of the brace with two fingers, there was 3/16th's of
an inch of play visible at the shock tower that the brace was attached to".
- From a list member/autocrosser

(note: quotes were paraphased, qualifying them as non-quotes...)

My advice:

Grab a cup of Java or ActiveX and point your browser here:

http://home.pacbell.net/aslocum/

Look for the link to the Merkur Encyclopedia, and seek info on the shock tower
brace...

Am I getting reimbursed for my endorsement?  Sure, I can make a brace too!!!
(insert standard disclaimer here)

----------

Post Date:    Sun, 19 Apr 1998
Subject:      $5 rear shock tower brace INSTALLATION - XR4Ti

Unbraced list members,

This is part two of my rear shock tower brace adventure.  As I mentioned a few
days ago, I drove Jeff Jackson's lowered and rear shock tower brace equipped
XR4Ti.  I was very impressed with how it handled.

On to present info:

Yesterday I purchased an angle iron that measured 1/8" x 1 1/4"x 1 1/4" x 48"
for $6.05 from my local Furrow.  It is plain, untreated steel.  Sears Hardware
has galvanzied angle iron for about $0.75 more for the same size.  I would
have gotten that, but they were out of stock, the next useable size being 60"
and costing twice as much.  Not worth it.

Parts, tools, and equipment:

- angle iron, 1/8" x 1 1/4"x 1 1/4" x 48" - $6.05
- dremel tool (cutting, sanding, grinding bits)
- 1/2 chuck drill (variable speed)
- 25/64 drill bit (13/32 is the correct size, but Sears didn't have it in
stock) - $4.36
- phillips screw driver
- 17mm socket wrench
- 17mm box end wrench
- *clicker* torque wrench
- dark primer and black paint - about $7.00 and plenty left on both cans
- two slightly smaller and much shorter bolts used to center shocks
- small pocket knife
- some scotch tape
- the Dead Sea Scrolls

I followed Allan Slocums dimensions from the Merkur Encyclopedia to build the
bar.

http://home.pacbell.net/aslocum/ - Click the link to the Merkur Encyclopedia

I gave the bar a nice wire brushing, sanding, and paint job to prevent surface
rust (since it isn't galvanized).  Since I didn't buy the correct size drill
bit I had to slightly enlarge the holes to the required 0.400" (from the
0.390625" hole I made)

I found a few areas where the rough edges of the design can be smoothed over.
These aren't required but help improve the appearance (not that you see it
once in the car) and fit and finish of the bar.  These will come later on.

How to install the rear shock tower brace:

- Remove the rear parcel shelf from the car.  I found it easier to fold the
seats forward, too.

- Remove the plastic trim covering the shock tower bolts (two phillips screws
per side).

- Remove the Nylock nuts from the bolts, being careful not to drop them behind
the trim panel (it's a pain to take it out to recover a dropped nut or bolt).
Get out of the trunk if you climbed in.  You want the shocks to remain as much
as possible in the original position.

- Jeff noted that installing his brace with the Koni RS adjustables became
difficult when he compressed the shocks by getting in the car.  The rebound
damping kept them from extending when he got out of the trunk.  My stock
shocks didn't have that problem.  More in the next bullet point.

- Remove the bolt from the shock.  My stock shocks wanted to extend.  No
biggie.  I just stuck a phillips screw driver in the hole (from the front side
of the tower) to realign the shock with the hole.

- With the screw driver holding the shock into position, I stuck a smaller
bolt in the shock from the rear of the tower to keep it generally aligned for
later.

- Next I installed the bolts in the brace, holding them in position with the
scotch tape.

- I laid the bar in it's approximate position so I could trim the carpet panel
to allow the brace to be in place.

- I used the pocket knife (a utility knife would have been better) to make two
vertical cuts in the carpeted trim piece.  I didn't cut any lower than the
impression made by the plastic panel in the carpet.  Am I clear on this?

- I didn't cut a notch out, rather I separated the carpet from it's backing,
folded the carpet in towards the trunk space and the backing toward the tower.
This way I can return it close to stock if need be.

- Next I put the bolts into the shock tower holes and the shock.  I did one
end at a time.  The smaller bolt held the shock generally in place and I
jounced the car with my body weight until (I was in the car) the alignment was
perfect just long enough for the bolt to slide it.  Unfortunately, the bolt
jumped in so quickly that the smaller bolt jumped out the back and down behind
the panel.  DOH!!!

- Repeat this step for both ends.

- Install the Nylock nuts on the ends of the bolts and turn it.

- Torque the bolt to 30-37 lb-ft.

You have to trim the shock tower plastic cover panel to get it to fit over the
brace.  I am not *down with that* as I don't have decent replacements now, so
I left them off for the present time.

For my improvements on the design:

- I'd round off the ends on the surface that bolts to the tower.  It seems
like it would conform to the shape a bit better.  My dremel isn't up to the
task and I have no bench grinder.

- Install a washer between the bolt head and the brace.  The OEM bolt may not
be long enough to reach the Nylock part of the nut with a washer in there.
But replacement bolts are cheap and they are a standard cad plating.  My
supplier just isn't in on Saturdays.

- The reason for adding the washer?  The surface that the bolt head meets up
with is different with the brace than with the tower itself.  This might have
an effect on the torque when you apply it.  You may be wasting torque on the
friction between the bolt head and the brace.

The results:

Not only does the car feel more solid and UNITIZED in the rear, but some of
the creaks are gone!  This isn't all that odd considering the body is now
stiffer preventing flex therefore less movement of the plastic components.

Just coming down off a curb you can tell the body doesn't move as much in the
back.

A list member said that he could tell the difference in handling on a SNOW
COVERED road.  That's incredible.

I was concerned about reduced storage capacity in my trunk.  I don't haul
much, but I normally have a 10" bass tube in the trunk.  It clears just fine.
As for it being an eyesore, it isn't even visable when I open the trunk.  I
have to bend down just a bit to see it (I'm 5'11").  It is close to the seat
backs and the parcel shelf so space isn't reduced by much.

I'll be posting pictures of the installation on my Picture Page sometime
Sunday:

http://members.aol.com/mc2racing/pictures/

Until then, just email me and ask any questions you have.  I really like how
easy it was to install and the results are great for the capital outlay.  How
many other components could you build and install so beautifully for $17.00
complete?

If you haven't done it and plan on autocrossing at Carlisle (or in Akron,
Josh...) you haven't gone as fast as you can!

----------

Post Date:    Tue, 26 May 1998
Subject:      Re: rear shock brace difficulties

A list member, concerning the installation of their shock tower brace, wrote:

>When I went to instal it it didn't fit, the holes for
>the bolts were too close together.  I had to wreck
>the finished product by enlarging the holes so
>that they were 1/4" wider at the ends
>:-(

Maybe my theory is wrong, but I understand that the whole idea of the brace is
to prevent movement of the shock towers toward each other.  What these slots
now allow is movement in the slots.  Tightening the bolts more would help to a
point, but keep in mind that bolts are designed to hold in tension (along the
axis of the bolt) not in shear (perpendicular to the bolt, like the brace).
So, technically, you'll have to get a new section of angle iron and cut the
holes again.

Here is the method I used to ensure the holes lined up.  First, I drilled one
hole.  I slid it onto the threaded section of the bolt while it was in the
car.  Then, I scribed an arc (using the threaded end of the opposite bolt as
the scribe) onto the section of angle iron, indicating the exact line that the
hole should be drilled on.  It fit like it had been machined not just drilled
out by hand.

----------

Post Date:    Mon, 2 Aug 1999
Subject:      Re: Rear strut brace effective?

List Members,

Bill Williams has brought up this question before.  It seems as though there
is almost no way to test this other than using racer-testing methods of
torsional rigidity.  That would be pretty involved, requiring one side of the
shell to be bolted to something solid and applying a known weight to a
lever-arm bolted to the other side.  Few are equipped to do this sort of
testing.

Allan Slocum wrote:

> This is consistant with the reduction of
>  noises when I added the brace. I also think I feel the rear is stiffer.

Speaking for another list member as well as myself, it has been said that the
difference was noticed while driving on snow covered roads.  As for my
experience, I noticed that the rear end was stiffer when I backed down the
driveway and the first rear wheel went off the curb.

Here is a testing method suggestion.  With creative use of a yardstick and
some wooden dowels (or other cheap stock), I am sure some sort of measuring
device can be installed between the shock towers to measure total relative
movement in a braced and unbraced car.

Back to the Tech Articles main page

Published by Chris Anglin.