TA22 + rack and pinion

[stidnam]

I have cut up a AE71/KE70 inner rack end to work out some measurements also.







Giving the total effective length of the AE71/KE70 rack as per below

[stidnam]

Okay more details. Taking an oxy torch to the aluminium housing and whacking it in a vice I managed to get it apart as I suspected could be done .



The tube in its glory


The tube only goes in a certain depth in the aluminium housing as there is a lip to stop it




now the tube end is a bit smaller diameter than the tube.



So now to shorten this housing I wont have to weld it after all . What will have to be done is to chop the required amount off and then recreate the smaller diameter section on the end and the beveled end edge.

Lucky I have access to the lathe at work to do this. Then to fit it back together heat up the aluminium housing and freeze the tube and whack together.

The bottom pinion bearing came out while I was torching the housing and here is the markings on it for reference if you want to replace it.

[Radar]

(just getting off topic for a moment) but Jaffa using the 32GTR subframe which by the looks of it fits pretty nice, has R+P so my question is, would just the normal 32GTS with R+P fit up and work?

[LeeRoy]

Youll probably find that since hes using so much other skyline stuff using the skyline rack was the easiest option. If your not doing anything like what Jaffa is doing then i dare say the skyline rack will be a worse rack than anything mentioned in this thread so far.

Also think about how much wider an r32 is than a ta22.

[stidnam]

Slight update time.

I have finished measuring the variables. I will be using AE86 struts so I obviously will be using AE86 steering arms. The TA22 steering arms are similar in dimension by the eye when I compared them a while ago but you will need to measure them yourself if you are going to use TA22 steering arms. Note FYI all my measurements less than 10cm are made with either callipers or a height gauge so should be fairly accurate.

AE86 steering arm


TA22 crossmember
The bolts are 12mm diam so the distance between the centre of the crossmember pivot points is 560mm - 12mm = 548mm.


So this brings me these calcs.

Crossmember pivot point distance - steering arm offset distance x 2 = overall length that shortened rack needs to be between pivot points.
or 548 - (16.2 x 2) = 515.6mm

Now as the crush washer and the inner rack ends wont change the rack is the only thing that can be shortened so 598mm - 515.6mm = 82.4mm that needs to be removed from the rack. I have rounded this to 82.5mm as I can measure acurately down to 0.1mm with calipers but can't mark it that finely as to where to cut.

Now the housing needs to be shortened too and this will be as follows to keep the ratio of the rack to the housing the same.

Uncut ratio 545:400 = 0.73394
Cut ratio 462.5:339.5 = 0.73405

So the housing needs to be shortened by 60.5mm so that it is 339.5mm in length when the two pieces are reassembled.

Cutting the end off the rack




I also measured the notches that are machined in the end of the rack so that I can machine these back in the cut off end.

Top view. There is the same duplicated on the underside of the rack


Side view


Next step is to measure the thread size and pitch of the hole in the end of the rack that the inner rack end screws into so I can drill a hole and tap a new thread into the cut off end of the rack. Then machine the above notches back in the rack and onto the housing.

[mynameisrodney]

this is awesome work you've been doing on this mate. keep it up.

[Rob KE25]

I haven't read this thread for a good year or so. Brilliant! My rego'ed KE25 corolla has a
3sge, and it's weak spot would be the steering too. I have the steering bits and pieces of a KE70 and a complete AE86 steering setup (rack and pinion, crossmember, steering arms etc) at home, constantly measuring and and thinking about them.

In studying this thread, my thoughts have been confirmed: shorten the available KE70 rack. I have borrowed some of "the flea's" ideas, such as purchasing the split lock collars, as there is very little room in my car for the standard rack mounts.
Well done !!

[Rob KE25]

Got some dimensions of the AE71 / KE70 rack.


Now I'm thinking of cutting up the housing to see if the tube is press fitted into the alloy housing because it could mean that no welding is needed to shorten the housing if it can be removed and refitted together after shortening the tube.


For the actual shortening here is what I am thinking, I have to shorten the rack by say 70mm (not exact so don't use this figure) so if I shorten the inner by 70mm and then shorten the rack housing by 51.4mm which still keeps the ratio of the rack inner to the housing length the same as an uncut inner and housing. Calcs below

uncut 545:400 = 1:0.73394495
Cut 475:348.6 = 1:0.73389474

This should still give relatively the same amount of rack travel as the ae71/ke70 before the inner rack ends hit the housing from lock to lock. Might not be explaining this quite well as its clear in my mind but hard to describe in words. Ideally the rack would be mounted on the cross member and then the steering turned fully each way and see where the rack inners are just before the tires rub on the control arms and this is where the rack housing length should be so that the rack housing stops the rack travel and not the tires on the control arms.

Any flaws with any of my logic so far?

Great work, buddy.
I think what you've posted, pics, measurements etc are great.
You ask if there are any flaws so far. Possibly one flaw, and one thing to think about.

Possible flaw regarding how much to cut off the rack: To get roughly the same amount of 'turn' (or exactly the same amount of steering angle) from a shortened ke70 rack, you need to shorten the rack housing and the rack itself by the same amount. It isn't a ratio thing, it is how much TRAVEL the rack has, that pulls (or pushes) the steering knuckle. So if you cut the rack say 86mm, shorten the housing by 86mm. A very long rack, with the same amount of 'travel' will turn steering knuckles the same angles, if all other things remain the same, eg pivot points, LCA lengths etc.




Now about the steering knuckle offset, 16.2mm

Something to think about (I wouldn't discard this): you said this about how much the rack needs to be shortend considering the ackerman of the steering arms:

Crossmember pivot point distance - steering arm offset distance x 2 = overall length that shortened rack needs to be between pivot points.
or 548 - (16.2 x 2) = 515.6mm

Whereas the offset of the knuckles is 16.2mm, the thing we are REALLY after is the actual ackerman offset BETWEEN THE LCA BALL JOINT AND THE TIEROD BALL JOINT. Think about that for a minute: the two tapered holes of the steering knuckle are not parallel, in a vertial plane. The tierod taper is on an angle in such a way that the tierod balljoint will actually sit further inward (towards the centre of the car) than the LCA balljoint. This is one of the reasons that shims can address bumpsteer here, the other being that the tierod is effectively lenghthened or shortened, and not on the same horizontal plane as the LCA balljoint.

So, it should be:

Crossmember pivot point distance - LCA balljoint to tierod balljoint offset distance x 2 = overall length that shortened rack needs to be between pivot points.
or

548 - (16.2 x 2(plus I'm assuming a good few mm more) = less than 515.6mm.

I do think the amount of difference of the ackerman offset is quite important. If you didn't allow for this, and thought you had zero bump steer, you would end up with toe-in on bump, which is not good. If you were to have some bump steer, just a little toeout on bump would be preferred.

Wow, having reread that, there is a fair bit in it. Hope somebody understands what I'm trying to write. Let me know if you need clarification.

Robj.

[stidnam]

I understand what you have said and I agree.

I considered the angle of the hole in the end of the steering arm and what impact it would have on the measurement of the offset while I was measuring the steering knuckle but decided that it was too hard to work out how to measure it at that point in time. Now I have given it some thought and have worked out how to measure this change. Lucky I can correct this by cutting an additional bit off the rack.

Regarding the housing again you are correct. I had mistakenly thought that by shortening the rack the effect on the teeth of the rack would be greater. In reality this will not change as it will still take for arguments sake 2 turns to extend the rack 10cm out of the housing. Shortening the housing by the same amount as that was cut off the rack will keep the lock and rack travel amount the same as the uncut rack.

+ rep for you for pointing this out before I got too far.

[jeffro ra28]

Errrr, major fuck up. sorry.

[jeffro ra28]

stuffed up............

[o_man_ra23]

So the easy to get ST162 power steering rack is useable in this conversion?? SCORE!!

[jeffro ra28]

sorry oman, i had a major fuck up with my epc. so that is wrong ........

[stidnam]

Ok worked out the angle of the hole in the end of the steering arm



by using good old logic and maths



Now that the angle is known this can be drawn out in an enlarged scale on paper to work out the needed measurement.

I still have to dissect the tie rod end that I will be using to see where the centre of it is to determine just how far down the orange line I will need to be to take the measurement back to the first blue line which should then give the correct offset for the AE86 steering arm and whatever tie rod end that I use.

[oldcorollas]

I do think the amount of difference of the ackerman offset is quite important. If you didn't allow for this, and thought you had zero bump steer, you would end up with toe-in on bump, which is not good. If you were to have some bump steer, just a little toeout on bump would be preferred..

heya Rob,
i had thought a little toe in on bump steer is better?

ie, if you are mid corner and hit a bump, adn get toe out, then the front of car turns toward outside of corner...
if it is toe in, then the tyre temporarily increases understeer, but keeps going same direction?

or am i missing somehting vital?