IRS in a gmt400

[Pinger]

I am looking at these knuckles and there is plenty of meat on them to redrill the tie rod hole about an inch further back.

Remembering it is a tapered hole....

This would give me the angle/ratio I want BUT at the expense of slight anti Ackerman. Is it worth it? I will leave it as is for now so I can drive it for a bit and decide later.

The benefit would only be at full lock. The anti-Ackerman effect would be present before that and thus more often.
A Nissan I ran had anti-Ackerman and it chewed up any surface less than tarmac when turning tightly.

What is the state of play currently? Is the truck up and running, been driven at all since the modifications began, not on the road yet? If you've been driving it, anything to say on how the steering feels? I tripped over an article discussing electric power steering and it remarked on the inherent friction in electric systems being greater than in other systems to the point where the steering geometry sometimes has to be modified to compensate. Are you seeing anything of that?

 

[Alteca]

Remembering it is a tapered hole....



The benefit would only be at full lock. The anti-Ackerman effect would be present before that and thus more often.
A Nissan I ran had anti-Ackerman and it chewed up any surface less than tarmac when turning tightly.

What is the state of play currently? Is the truck up and running, been driven at all since the modifications began, not on the road yet? If you've been driving it, anything to say on how the steering feels? I tripped over an article discussing electric power steering and it remarked on the inherent friction in electric systems being greater than in other systems to the point where the steering geometry sometimes has to be modified to compensate. Are you seeing anything of that?

I have the tapered reamer matching the taper so that wouldn’t be an issue but yeah I really don’t want anti Ackerman. Truck has not been driven since I started the front end so I can’t speak for how the steering currently feels. The rack has a bit of friction unpowered but not anything ridiculous. You would still be able to steer if it stopped working while driving. There is a guy on tiktok that has one of these trucks, same rack, bolted to stock knuckles and he loves how it steers.

 

[Pinger]

I have the tapered reamer matching the taper so that wouldn’t be an issue but yeah I really don’t want anti Ackerman. Truck has not been driven since I started the front end so I can’t speak for how the steering currently feels. The rack has a bit of friction unpowered but not anything ridiculous. You would still be able to steer if it stopped working while driving. There is a guy on tiktok that has one of these trucks, same rack, bolted to stock knuckles and he loves how it steers.

I'm quite relieved to see that. The stuff about friction I've been sat on for a while - didn't want to be the bearer of bad news! But seems concern on that front is/was misplaced.
Incidentally, where I came across it was in an interview with the head of chassis tuning at GM Europe (back in 2015/6). Maybe the issue is more acute with cars that weigh in at around 2640lbs. Front wheel drive too.

 

[Alteca]

I'm quite relieved to see that. The stuff about friction I've been sat on for a while - didn't want to be the bearer of bad news! But seems concern on that front is/was misplaced.
Incidentally, where I came across it was in an interview with the head of chassis tuning at GM Europe (back in 2015/6). Maybe the issue is more acute with cars that weigh in at around 2640lbs. Front wheel drive too.

Interesting, I’ve driven multiple vehicles with electric racks, one of which was an f150 with a very similar rack to the one I have and was happy with how it felt. Some of them don’t have much road feedback but the newer mustangs don’t have that issue imo. I’ve never driven one while it was unpowered/failed so I can’t speak for that side of things but I’m certain ford took that into account when designing it.

 

[Pinger]

My only experience with electric steering was with a second gen Mercedes A-Class. Soulless doesn't begin to describe its steering. That was an early iteration of electric assistance though and I suspect they've improved since (maybe with more attention to steering geometry) and when 'feel' is super critical (sportscars) the tendency seems to be for an electric motor driving a hydraulic pump with a more familiar hydraulic system downstream.

 

[GrimsterGMC]

Or, by trigonometry (not difficult) if a suitable protractor isn't at hand.

Good point, I always use trigonometry everyday for measuring angles, it's the only accurate way for marking out sheet metal developments.

 

[Pinger]

Good point, I always use trigonometry everyday for measuring angles, it's the only accurate way for marking out sheet metal developments.

Yep. Accurate and guaranteed easier than finding a suitable protractor. I used it last week to obtain a linear dimension from the 'sum toe angle' to set my steering alignment. Dammit, where's that 1/4 degree protractor when you need it?...

 

[fancyTBI]

Alteca, I couldn’t get the measurement. I was turning against the steering stops, turned the truck off, then the wheel wanted to return to center some. The PS pump really didn’t like it either (original pump and box, both showing their age), so I couldn’t seat it fully for a good measurement. I also didn’t have my GF around to hold the wheel for me so I could lay down some tape.

I’m sorry man. She will be around tomorrow. I was thinking if I had it jacked up some I could easily turn the wheels and get the measurement.

 

[Alteca]

Alteca, I couldn’t get the measurement. I was turning against the steering stops, turned the truck off, then the wheel wanted to return to center some. The PS pump really didn’t like it either (original pump and box, both showing their age), so I couldn’t seat it fully for a good measurement. I also didn’t have my GF around to hold the wheel for me so I could lay down some tape.

I’m sorry man. She will be around tomorrow. I was thinking if I had it jacked up some I could easily turn the wheels and get the measurement.

No worries bud, it’s not crucial that I get the information. It would be nice to know if I gained or lost some angle. I would hope I didn’t lose any.

I think it would help if the front was jacked up some so the caster isn’t trying to push the wheels back to center, as well as being easier to turn.

 

[fancyTBI]

No worries bud, it’s not crucial that I get the information. It would be nice to know if I gained or lost some angle. I would hope I didn’t lose any.

I think it would help if the front was jacked up some so the caster isn’t trying to push the wheels back to center, as well as being easier to turn.

Yeah definitely going to put it on stands. I need to change the oil in it soon so that would be a good time.