Steering rack mount

[rsk289]

Can anyone tell me how the steering rack was mounted on a leafspring car?
I have a Kirkham frame and the rack installation calls for four aluminium spaces under the rack mounts to raise the rack by about 1/2 - 3/4". Is this likely to be a mod to improve geometry, or was it original?
Main reason for asking is that the rack is too high to allow the cast coolant tube to pass through the frame on that side. To lower the rack would require some metal grinding for clearance.
Thanks
Roger

[Dan Case]

Roger,
I’ll see if I have a picture that shows what you ask. In the mean time, on an original car, the housing can't sit directly on the brackets welded to the front of the front road spring tower because of the details of the pinion housing. To get the pinion housing above and clear there are round section plain carbon steel distance pieces between the brackets and rack on both sides. I would imagine that the steering mechanism location was decided, distance pieces length decided, and then chassis mount location picked last.

After our last discussion on the thermal switch housing subject, I hand held in position a switch housing over the rack and pinion assembly over the pinion side to simulate your right hand drive application. It appears that if the boss had not been cut off by SAI that the housing could be bolted in as AC Cars did for chassis shipping and work fine for the inlet (radiator side). I don’t have the radiator back in yet so I couldn’t verify hose bib alignments. The person that had his own new castings made including the chassis mounting boss has been seriously ill a lot lately so I have not asked him if he has any more of them.
Dan

[rsk289]

Thanks Dan, ever helpful as always. From what you say my rack may well be in the correct position, as I would expect. Something, somewhere, must be different as there is no room above the rack to pass a 1 3/4" tube through the frame. It shouldn't make any difference which side the steering pinion is as everything is mirrored from the other side. I wonder if Kirkham have beefed up the spring tower a little and thereby restricted the size of the triangular hole in this part of the frame.

Jim Cowles is going to send a repro tube with my trans, but it's possible his source is the same chap so I won't press him.

Roger

[Dan Case]

The fit is close so any deviation that reduced pass height would make fit worse, i.e. the pipe closer to everything in the vertical plane.

[Dominik]

If one drops the front (suspension) of a car, you have to raise the steering rack to bring your geometry back. Check if your tie rods are pointing up. The spacers might exactly raise the rack that the tie rods are back to level.

[strictlypersonl]

Originally Posted by Dominik

If one drops the front (suspension) of a car, you have to raise the steering rack to bring your geometry back. Check if your tie rods are pointing up. The spacers might exactly raise the rack that the tie rods are back to level.

No! If the relative lengths of the control arms and the steering tie rod are correct (and the bump steer is correct at one ride height), shifting the rack height will only ruin a bump steer curve. If it is a poor original design, with incorrect relative lengths, it might be necessary to raise or lower the rack a little, but nowhere near the change in ride height.

[Mark IV]

I have a 289 on the rack and will take and post a picture ASAP.

[Dominik]

Thanks Bob, but why could you buy such spacers for thr old 911 and the 427 (5/8")

[strictlypersonl]

The McPherson Strut of the 911 creates an extremely long (theoretical) upper control arm radius. Consequently, the intersection of the horizontal plane of the rack and the line between the lower and "upper" control arm pivots moves around quite a bit. Unless the rack is mounted at the height of the lower control arm, it can get ugly with suspension movement. Note that FWD cars with a high-mounted rack have inner tie-rod pivots close to the centerline of the car.

As far as the 427's spacer, I suspect that they designed it with some adjustability built in, the rack length was less than ideal, or they wanted to build in more roll-understeer for high-speed stability.

[Dominik]

Thanks Bob, feels like being back at school :-)

[Mark IV]

Here is a 289 setup as built now by Superformance (new Shelby's will be the same)

[Mark IV]

More....

[mickmate]

Nice shots Rick, the first one shows the problem Dan mentions where the pinion spring has that boss on the underside of the input housing which requires the spacers under it to clear the mount. The other reason for the spacers is to correct bump steer by putting the rack at the correct height. That's a great set up with adjustable control arms, double shear plates and even some tie down loops discreetly slid in there. I would mention that increasing the heim joint size on the control arms from 5/8 to 3/4" doubles the strength of them.

[rsk289]

Thanks, some very helpful photos there that show the same setup as mine. I think it's going to need some careful alignment as Dan has indicated for the hose. For practical purposes with the RHD it may make sense to make up a lower hose that comes in through the large triangular hole in the spring platform, but I'll work on getting the right part and getting it to fit.

[mickmate]

On some right hooks we have been making parts for we have mirror imaged a few parts and just swapped radiator fittings or moved them or changed their angle to clear. Whatever it takes that still looks factory.