Given these cars are 30+ years old, the seals in the steering rack tend to go bad. And/or the plastic boots crumble, leading to contamination of the rack and fluid, destroying the seals. Based on that, you're likely going to have to deal with some steering rack issues, regardless. You may also want to change the rack, or how it works, depending on your situation. For example, there are options for powering the rack hydraulics, such as Electrohydraulic Power Steering (EHPS) pumps from several manufacturers. I'm putting together another post for the known options there.
The XR4Ti came with two steering racks as standard, the TRW early on, and switching to the ZF for most of the production timeline of the car. Given these cars are 30+ years old, power steering rack seals and boots tend to fail, so knowing the rack is probably a good idea.
TRW
Model years: 1985 - mid-1986
Lock-to-lock (L2L): 2.7 turns (According to what I assume is specs released early in the production of the XR4Ti, the rack was 3.6 turns, https://www.carfolio.com/merkur-xr4ti-99077?car=99077).
Suitability: average driving, cruising
Note: Identifiable by a smooth surface on the rack housing.
Note: Interchangeable with the ZF rack.
ZF
Model years: mid-1986 - 1989
Lock-to-lock (L2L) : 2.7 turns
Suitability: average driving, cruising, racing
Note: Identifiable by the waffle pattern on the rack housing.
Note: Interchangeable with the TRW rack.
Manual Steering Rack Conversion
Manual racks are desirable for road racing and drifting since you're aggressively turning the wheel and working the rack. These racks were never designed to take the abuse a rack will receive on a race track, especially drifting.
Manual racks aren't desirable for a daily driver because you're having to do all the work yourself at slow speeds. Makes you realize just how heavy a car can be.
A manual rack does simplify the engine bay by removing a pump and the belt(s) that run it. Looks great!
If you're going to run a manual rack, beef up the rag joint and steering shaft mounts, since they weren't designed to take the abuse of non-power steering forces on them.
Manual racks are not recommended if you're rally racing.
How to Order a New ZF rack at AutoZone (as of 2008):
AutoZone was $139.00, Advance Auto was $350.
"For example, the way to get the ZF rack from Autozone is to have the sales person phone ATSCO at the time you place the order. I had no problem getting them to do this. The Autozone sales person should tell ATSCO they want the Type 2 ZF rack. ATSCO will then link the order and the rack type to the PO# which Autozone also supplies.
ZF Rack: ATSCO p/n 6441 Type 2 $139.99 + $90 core
TRW Rack: ATSCO p/n 6441 Type 1 $139.99 + $90 core"
Note: Oreilly brand is A1 CARDONE part no 26-1921
Steering Rack Bushings
Stock, the XR4Ti comes with rubber bushings in the rack. You might be able to get poly or solid aluminum bushings, depending on timing and vendors:
MC2 Racing, a site by avid autocrosser Chris Grayson, has had poly and aluminum steering rack bushings available from time to time, but now recommends nylon steering rack bushings, available here.
Steering Rack Fluid Cooling
You can use power steering coolers, akin to automatic transmission fluid coolers, purchased from many places, but Summit Racing as them for $25 (Item DER-13200).
Steering Rack Rebuilds
You can get XR4Ti steering rack rebuild kits from: Power Steering Rebuild Kits, XR4Ti TRW Rack Kit, XR4Ti ZF Rack Kit
The size of the rack end seals (2 required) for the TRW rack are: 24-33-7 referring to the inner diameter, outer diameter, and thickness, respectively, in millimeters. Most industrial/pneumatic supply houses can provide these if you're inclined to just replace the end seals on the existing, early rack.
Other options
Ford Sierra (European) Manual Rack:
Model years: unknown, all Ford Sierra's with non-power steering
Lock-to-lock (L2L) : 3.75+ Turns
Suitability: average driving, cruising
Where to buy: http://www.kellybraysteering.co.uk/pages/manual_steering_racks_12938.cfm
Requires manual steering shaft, European part: https://www.motomobil.com/en/products/steering-idler-shaft-not-for-power-steering-not-4wd-lhd-60959030-1
Aftermarket Ford Sierra (European) Manual "Quick" Rack:
Model years: aftermarket only.
Lock-to-lock (L2L) : 2.7 Turns
Suitability: racing, right hand drive (RHD) only.
Where to buy: http://www.kellybraysteering.co.uk/pages/manual_steering_racks_12938.cfm
Requires manual steering shaft, European part: https://www.motomobil.com/en/products/steering-idler-shaft-not-for-power-steering-not-4wd-lhd-60959030-1
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