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View Full Version : Measuring Lift Height -- The Official "Dirty" Method


Eagle
May 23rd, 2004, 18:17
The question arises periodically, how to measure lift height if the flares are gone and the fenders trimmed. A long, long time ago someone had a personal web site with a compilation of height measurements, both "clean" (hub to flares, no need to get dirty), and "dirty" (measured under the vehicle, from the axles to the frame. That link seems to have gone away.

Poking around in the back of the '85 Factory Service Manual the other day, I was surprised to find a section on suspensions that gives the factory's OFFICIAL measurements by the "dirty" method. For the benefit of anyone who is interested, here they are:

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Checking Front Ride Height

Measure front ride height with the vehicle unloaded (no luggage or passengers) and with the fuel tank full.

Place the vehicle on a level surface and measure the veryical distance between the top of the axle tube (A) and the underside of the frame sill (B). Refer to Figure 1 for driver's side measurement and Figure 2 for passenger side measurement. Be sure each measurement is taken from the top of the tube and not from the axle or shift motor housings.

With Standard or Soft Ride Suspension, vertical distance should be 17 cm (6-3/4 inches) plus or minus 13 mm (1/2 inch). With Heavy Duty Suspension, vertical distance should be 20 cm (7-3/4 inches) plus or minus 13 mm (1/2 inch).

Checking Rear Ride Height

Measure rear ride height with the vehicle unloaded (no luggage or passengers) and with the fuel tank full.

Place the vehicle on a level surface and measure the vertical distance between the top of the axle tube (C) and the underside of the frame sill (D) inboard of the jounce bumper (E).

With Standard or Soft Ride Suspension, vertical distance should be 15 cm (6 inches) plus or minus 13 mm (1/2 inch). With Heavy Duty Suspension, vertical distance should be 18 cm (7 inches) plus or minus 13 mm (1/2 inch).

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The letters in each paragraph refer to diagrams, which I have no way of reproducing. Once you get underneath and look, though, the measurement points should be fairly obvious.

This section of the FSM also provides a listing of stock springs and spring codes, but it doesn't provide any specifications regarding spring rate for the various springs.

The springs are coded with a 2-letter code. In general, moving up one letter increases ride height by 1/2 inch. For example, stock (standard) front coils are coded FC through FP. If the right front has a spring coded FH and rides 1/2" too low, replacing that coil with one coded FJ would raise it 1/2". Typically, the factory used front coils with one letter code higher on the driver's side, to compensate for the weight of the driver.

Ed A. Stevens
May 24th, 2004, 13:00
Eagle,

You have a good memory, of my old web page content. The FSM method matches up well for the rear axle, but the front is a different method (and the FSM seems to be a better, not so dirty, method).

XJ Help 3 (http://members.aol.com/Stvns/XJhelp3.html)

"The best and easiest measurements are the simple axle centerline to flare height (stock non-Upcountry/Chief Front -- about 17 1/2 inches, stock Rear about 17 inches). These are the approximate stock heights obtained with the measurement help of Chris Pigeon <pigeon@smtp-gw.gdls.com> & David Windle <windle@flash.net> on the XJ-list. I have found no better quick method to settle lift height comparisons. My 88' currently (Jan 1999) sits at 21 7/8 and 21 3/8 inch, front/rear respectively.

You can get more accurate (if not dirtier) by measuring the front lower axle bumpstop pad to the top of the spring tower seat, above the isolator & spacers at the frame. This stock measurement up front is about 11 1/4 inches. A tape can be fished down inside the spring to make this easy to measure.

The more accurate rear measurement is from the axle tube top surface to the frame above the bumpstop, about 6 1/4 inches. Larger diameter tubes (D-44) will measure 1/4 inch less, about 6 inches. Again, a tape makes this measurement easy and quick."

WrenchMonkey
May 24th, 2004, 13:53
The letters in each paragraph refer to diagrams, which I have no way of reproducing

How about these (http://www.mike-g.net/jeep/yinyang/tech/rideheight/)?

http://www.mike-g.net/jeep/yinyang/tech/rideheight/front_driver.jpghttp://www.mike-g.net/jeep/yinyang/tech/rideheight/front_pass.jpg http://www.mike-g.net/jeep/yinyang/tech/rideheight/rear.jpg

Robert

Eagle
May 24th, 2004, 14:17
How about these (http://www.mike-g.net/jeep/yinyang/tech/rideheight/)?

http://www.mike-g.net/jeep/yinyang/tech/rideheight/front_driver.jpghttp://www.mike-g.net/jeep/yinyang/tech/rideheight/front_pass.jpg http://www.mike-g.net/jeep/yinyang/tech/rideheight/rear.jpg

Robert

Them's the very ones. Thank you, kind sir.

Lawn Cher'
May 24th, 2004, 14:40
Take note, figure 3 shows a MJ rear axle/suspension, and will look different in a XJ.

JCSXJ
May 24th, 2004, 15:13
On XJ's, the factory short arms are parallel to the ground. So all I did was measure from the ground to the center line of the control arm bolts. Then find out the difference. So if the axle mount bolt was 11" to the center line and the body mount bolt was 16 1/4", I know I have roughly 5 1/4" of lift. Don't know if it's the proper way but it worked for me.

Weasel
May 24th, 2004, 15:14
whats wrong with measuring from the ground to the bottom of the spring box on the rear and from the ground to the bottom of the point right behind the lower control arm mount on the front?

Lawn Cher'
May 24th, 2004, 15:18
JCSXJ's method sounds good for measuring the front suspension height, it negates any change in tire size. Weasel, if you are measuring both the front and rear with respect to the ground, it will change based on tire size, pressure, etc. so how do you accurately take that into account?

Weasel
July 21st, 2004, 18:54
Weasel, if you are measuring both the front and rear with respect to the ground, it will change based on tire size, pressure, etc. so how do you accurately take that into account?

Yeah it would but I thought it would be easy enough to measure your tires sizes and adjust accordinly. As for psi of the tires, thats getting pretty exact measurments. I was just thinking for a pretty close guesstimate and for me it works, since I havn't changed tire size for awhile.