Two Measurements Required on Steering Rack for TR4A Please

[Malbaby]

1...Accurate overall length between the steering rack ball/pivots...centre to centre...[not the outer tie rod ends]....approx 26.75 " ?
2... Angle of the rack pinion shaft relative to the horizontal line of the chassis.....approx 25 deg?
And a further question to help a dummy....theoretically, if one was to draw a line between the top and bottom inner control arm pivot points, where should that line intersect the centre of the steering rack, at the rack ball pivots?
 

[Malbaby]

Anyone?

[peter clarke]

5 hours ago, Malbaby said:

Anyone?

1.  27.94     source Haynes Manual

 

[Ralph Whitaker]

Question2, Yes in an ideal world the suspension pivots and the steering pivots should be the same centres to eliminate bump steer.

Ralph

[Malbaby]

18 hours ago, peter clarke said:

1.  27.94     source Haynes Manual

 

Thanks Peter....Haynes Manual should be correct ...Not convinced as yet.

Edited February 13, 2022 by Malbaby

[james christie]

Hum…I wouldn’t be too sure - except if they have lifted it from the original Workshop Manual!

james

[Z320]

3 hours ago, Ralph Whitaker said:

Question2, Yes in an ideal world the suspension pivots and the steering pivots should be the same centres to eliminate bump steer.

Ralph

+1 for the same y-position / height above the street,

for the x-position „behind“ each other a closer look on the steering geometry is needed 

What makes the inside wheel angled more than outside wheel?

Edited February 13, 2022 by Z320

[Malbaby]

9 hours ago, Z320 said:

+1 for the same y-position / height above the street,

for the x-position „behind“ each other a closer look on the steering geometry is needed 

What makes the inside wheel angled more than outside wheel?

Thanks Marco.....not sure on your X and Y?

[Z320]

x =to the rear and front

y = up and down

I wanted to make photos for you today but everything is very close 

[Z320]

The length of the old one from my LHD TR4A is 707 mm from on top of the nut to on top of the nut, the tie rods bolted on.

From center tie rod ball to center tie rod ball could be 20 mm less (the about d=1“ balls reach out the nut about 2-3 mm)

I hope this answers your question.

[Malbaby]

Thanks Marco....

Can you assist with the pinion angle question please, plus, what angle is your lower steering column shaft to the horizontal line of the chassis....25deg??

Also, I have two old racks where the rib/flange is cut at a different angle, see pic...I presume this is not factory??

[peter clarke]

Apology     dimension is 26.78 according to Haynes Manual

[Z320]

With the right green line on your photo based on my horizontal workbench the pinion is 25 deg. up

[Z320]

The lower steering shaft in angled 23-24 degrees, measured with a digital gauge in the car with the car on in parking position.

[Malbaby]

21 hours ago, peter clarke said:

Apology     dimension is 26.78 according to Haynes Manual

That sounds better 

[Malbaby]

20 hours ago, Z320 said:

The lower steering shaft in angled 23-24 degrees, measured with a digital gauge in the car with the car on in parking position.

Thanks Marco....so the base mount brackets that are welded to the chassis should have been horizontal from the factory. [although on my 4A project car the base plates are about 5deg]

But now the extra approx 4 deg must be taken up by the uni joints

Or in theory the mount base plates should angle down 4deg towards the rear of the car [ but that cannot be correct] to achieve the steering column shaft angle of 24deg.  

Edited February 15, 2022 by Malbaby

[Z320]

You have in mind my complete assembled car parking in the garage perhaps gives some different measurements to your project in the workshop?

[Malbaby]

Thinking I should weld in the new base plates at zero deg.

Just have to work out the optimum theoretical height now.

[Z320]

You could post some photos how it looks like at the moment?

[Malbaby]

Pics as requested.

This is a TR4A IRS chassis that will have a 6cyl TR6 engine fitted.

Pic 1...I have welded in 40mm rhs.

Pic 2& 3...Shows position of the temporary brackets with the rack in position with tie rods straight.

Pic 4...Bracket in what I believe is the factory position. Tie rods angle towards the rear of the car with approx 13mm offset.

Pic 5...Bracket moved to the rear approx 13mm.

Pic 6...Distance between the rear face of the rack and the front face of the main cross member is approx 95mm.

Pic 7...centre of bracket and therefore rack is 30mm above the base line.

My engine is dismantled ATM, so I cannot place it in situ to check clearances.

Please note that I will be delating the engine fan.

One aspect that bothers me is if there is enough clearance between the front engine components and the rack if it is moved back about 13mm.

 

[Z320]

Hi Malcom,

the crossmember in front of the oil sump is lovely to relate measurements to,

I will do some on my 4A in about 10 hours (now at my office). Two thinks I can tell you now already:

With your DIY steeling rack crossmenber it will be a bit finger braking to bolt the steering rack in position, special later when the car is assembled.

And you still want to use the original TR4A "one bolt"-brackets to hold the wishbones? It will rip off one day, guess why I sadly know....

You better drill the frame suitable to use the later TR6 "two bolts"-brackets.

Ciao, Marco

 

[Z320]

Hi Malcom,

back from my TR4A I realise I can not help you with measurements and photos from my assambled car.

Ciao, Marco

Edited February 16, 2022 by Z320

[Z320]

Hi Malcom,

I have to tell you the truth: of cause I can measure and make photos,

but comparing your photos with my TR4A I have been shocked what I realised and did not want to be involved more in your project.

But - knowing this I can't stay silent and let you go on your way. So I did some sketches with my old and simpe CAD.

I told you at another post the position of the rack and the angled tie rods are the steering geometry and you should not change it.

The tie rods are moving sidewards and in circles and turn the wheels in circles, triangles and angles are in- and degreasing.

The next sketch is "approx. about" in in dimensions of our TRs, but it#s only for the principle.

Green the steering rack, moving it XY mm to the left turns the inner wheel more than the outer wheel, that's like it should be

Next I move the rack  35 mm back and see what happens with the same turns on the steering wheel.

The inner wheel turns more, the outer less, that's also OK, I guess this car steers more with the same turns on the steering wheel.

Please compare

Next I move the rack forward in line to the tie rods, this is what you want to do.....

The outside wheel turns more than the inside wheel!

With this construction you can only slide the car through a curve!

The center line of the wheels will never cross, the lines are expanding.

My post may be unpolite, I could have sent you a PM.

But sorry me, all this work makes no sence for only one person.

My advice to all of you: change nothing on the steering geometry if you don't know what you are doing!

For more information browse the web for "Ackermann steering"

Ciao, Marco

Edited February 17, 2022 by Z320

[Malbaby]

Thanks Marco, as always, you are excellent with technical information.

Plus I love diagrams as an explanation.

[Malbaby]

Dumb me trying to understand the following difference in steering geometry, and how it works, not why it was done.

TR4A IRS chassis with 4 cyl engine, rack is mounted to the rear of the lower control arm brackets with the tie rods angled out of the rack towards the front of the car.

TR6 has the rack mounted to the front of the LCA's, with the tie rods angled slightly to the rear of the car.

Edited February 18, 2022 by Malbaby