Stuwindsurf 4 Posted July 3 Ok, so to anyone wishing to fit power steering to their Mk3 Cortina, I have learned some info along the way which I thought I could share with others so they don't have to go through the head scratching I did. So I fitted a Mk4 Cortina power steering rack which apart from a bit of grinding on the cross member rib and bit of nibbling around the drivers side engine mount it will bolt in place using the original mounts. Now the issues I had once swapping out the racks and setting up the tracking was I ended up with excessive toe in with the suspension drooped, ie dangling with car raised on lift (bump steer). About 17mm overall in fact. Now apparently this is due to not just the rack swap but also because I have fitted 1" lowering springs all round. The combination of both of these I am being told is what is causing the issue. I know I am not the first person to have done this mod but just wanted to make others aware that is does upset the steering geometry. I'm guessing most have just not checked to see what sort of bump steer they are getting. But remember the 17mm toe in I am getting is with the suspension at full drop, where as I am told bump steer is usually measured between the car is sitting on the ground and under full compression. I have yet to measure between these points as it requires removing one for the springs to be able to raise the suspension up to the bump stops and they're not the easiest of springs to keep taking on and off. But I will get round to it at some point. Well I hope that helps anyone wishing to do the same. Stu Quote Share this post Link to post Share on other sites
John Mack 338 Posted July 3 2 hours ago, Stuwindsurf said: ...........I am told bump steer is usually measured between the car is sitting on the ground and under full compression. I have yet to measure between these points as it requires removing one for the springs to be able to raise the suspension up to the bump stops and they're not the easiest of springs to keep taking on and off. But I will get round to it at some point. In an ideal world the steering arms should be "straight" from the rack to the hub, if the suspension is standard then this should be the case. If the springs are not standard then this will affect the tracking under compression more than the standard set-up. The rack swap ( I think ) will not affect bump steer....... but your springs will. Quote Share this post Link to post Share on other sites
Stuwindsurf 4 Posted July 3 24 minutes ago, John Mack said: In an ideal world the steering arms should be "straight" from the rack to the hub, if the suspension is standard then this should be the case. If the springs are not standard then this will affect the tracking under compression more than the standard set-up. The rack swap ( I think ) will not affect bump steer....... but your springs will. The problem I have found with the power steering rack is the main body length is shorter than the standard rack, which means the track rods are longer in length, which in turn means the track rods move in a slightly different arc. So normally you would think after lowering the front by 1", to compensate you would need to either raise the steering rack to bring the track rods back to level or space the track rod ends with a rose joint spacer kit. But this isn't the case with this set up, in fact the opposite appears to be happening, ie when the suspension droops the wheels are being pulled inwards at the front by the track rods. Which would suggest in theory the rack is too high or the track rod ends need raising, neither of which I can see would be possible. The route I am currently thinking about is either modifying or making custom stub axles with a higher mount for the track rod ends. I will however first check the bump steer with a spring removed and moving the suspension up and down within the normal operating range. If it's not too extreme I may run with it and see what happens. I can't be the only person to have both fitted the mk4 power steering rack and lowered the suspension 1". Quote Share this post Link to post Share on other sites
sheffieldcortinacentre 759 Posted July 3 Never had this with any Pas swap I've done ( prefacelift need the minor mods to cradle) but never had bumpsteer problems the V8 is an inchish lower. Due to weight reduction the racer needed circa 3in shorter springs to drop the ride height back down (it looked like it didn't have an eng in it). I've only ever had front end problems with one mk3 a 74 fitted with a Mk5 2.3 cradle complete with pas & 3.0 springs & eng. But like I've mentioned a few times the problem this had 3* of negative camber otherwise was ok ( handled great but killed tyres ) could never find any physical problems except the camber, cured in the same way that race proved did with savages by redrilling cross member lower arm mounting hole. Quote Share this post Link to post Share on other sites
Stuwindsurf 4 Posted July 3 17 minutes ago, sheffieldcortinacentre said: Never had this with any Pas swap I've done ( prefacelift need the minor mods to cradle) but never had bumpsteer problems the V8 is an inchish lower. Due to weight reduction the racer needed circa 3in shorter springs to drop the ride height back down (it looked like it didn't have an eng in it). I've only ever had front end problems with one mk3 a 74 fitted with a Mk5 2.3 cradle complete with pas & 3.0 springs & eng. But like I've mentioned a few times the problem this had 3* of negative camber otherwise was ok ( handled great but killed tyres ) could never find any physical problems except the camber, cured in the same way that race proved did with savages by redrilling cross member lower arm mounting hole. Have you ever checked the bump steer with the suspension at full drop Craig? My track rods look to be parallel to the lower wishbones and pointing downwards rather than upwards which is usually what happens when lowering springs are fitted to most cars! Quote Share this post Link to post Share on other sites
sheffieldcortinacentre 759 Posted July 3 (edited) Nope as they've drove ok but I'll be able to check 4 that are on ground tomorrow & possibly my mk5 crayford. There's a stock 4dr GT,,my 302 V8 2dr GT,the light weight racer twin cam 2dr GT, & my twin cam GT EST all 72s Looking at above pic have the front tie bars been apart at all? Also the track rod ends look very long. Edited July 3 by sheffieldcortinacentre Quote Share this post Link to post Share on other sites
Stuwindsurf 4 Posted July 4 (edited) 5 hours ago, sheffieldcortinacentre said: Nope as they've drove ok but I'll be able to check 4 that are on ground tomorrow & possibly my mk5 crayford. There's a stock 4dr GT,,my 302 V8 2dr GT,the light weight racer twin cam 2dr GT, & my twin cam GT EST all 72s Looking at above pic have the front tie bars been apart at all? Also the track rod ends look very long. That would be a great reference if you do get time to check! Especially if any of them have the power steering rack fitted? Yes the whole front suspension has been apart when I rebuilt it all. I have set the tie bar length each side so the front/back wheel centre to centre is 101.5". The track rod ends are Mk3 Cortina ones and the tracking set up ok with the car on the ground which suggests they are the correct length. Edited July 4 by Stuwindsurf Quote Share this post Link to post Share on other sites
sheffieldcortinacentre 759 Posted July 4 Yep all got pas. Quote Share this post Link to post Share on other sites
Stuwindsurf 4 Posted July 4 1 hour ago, sheffieldcortinacentre said: Yep all got pas. 👍🏻 Quote Share this post Link to post Share on other sites
sheffieldcortinacentre 759 Posted July 4 All are either parallel or pointing slightly down when sat on ground ,track rod ends are 90mm overall length. All are roughly an inch lower ride height Quote Share this post Link to post Share on other sites
TimB 102 Posted July 4 Tracking, wheel alignment, Toe or whatever term is used, should only be checked with the car on the floor. Measuring it with the car in the air and the wheels not touching the ground will give unreliable results. 17mm Toe-in is massively excessive and suggests the rack, tie rods and ball joints combined are too narrow if it cannot be adjusted to correct. Even the slightest misaligned of wheel tracking will make the steering operation, suspension movement and braking dangerous and will knock tyres out like there is no tomorrow. Suspension movement should not affect wheel alignment (Toe), camber will alter as bump and rebound happens but this is natural and accounted for in the suspension design. I cannot comment on the mod you have made as I am not familiar with MK3 steering or Mk4 racks. But please make sure whatever you do is safe. Hearing making mods to the stub axles is quite worrying. Hope you get it sorted, good luck. Quote Share this post Link to post Share on other sites
sheffieldcortinacentre 759 Posted July 4 MK3/4/5 are all the same, must admit I don't understand why you keep wanting measurements with the car in air ( except to check if one is showing same results) as said don't know of any vehicle set up in that way, it's always done & quoted at normal ride height. Quote Share this post Link to post Share on other sites
Stuwindsurf 4 Posted July 5 12 hours ago, sheffieldcortinacentre said: MK3/4/5 are all the same, must admit I don't understand why you keep wanting measurements with the car in air ( except to check if one is showing same results) as said don't know of any vehicle set up in that way, it's always done & quoted at normal ride height. It is exactly for that reason, to see if you get the same results. I don't know how else I can check! Quote Share this post Link to post Share on other sites
Stuwindsurf 4 Posted July 5 (edited) 18 hours ago, TimB said: Tracking, wheel alignment, Toe or whatever term is used, should only be checked with the car on the floor. Measuring it with the car in the air and the wheels not touching the ground will give unreliable results. 17mm Toe-in is massively excessive and suggests the rack, tie rods and ball joints combined are too narrow if it cannot be adjusted to correct. Even the slightest misaligned of wheel tracking will make the steering operation, suspension movement and braking dangerous and will knock tyres out like there is no tomorrow. Suspension movement should not affect wheel alignment (Toe), camber will alter as bump and rebound happens but this is natural and accounted for in the suspension design. I cannot comment on the mod you have made as I am not familiar with MK3 steering or Mk4 racks. But please make sure whatever you do is safe. Hearing making mods to the stub axles is quite worrying. Hope you get it sorted, good luck. Thanks. Yes I understand that wheel alignment is done with the car on the floor. I'm not trying to set anything up with the car in the air. But when you can visibly see the wheels pointing inwards when the car is raised on the lift you can't ignore it. As you mention it above all needs to be safe to drive hence me asking the questions. So I have copied others who have done exactly the same, fitted a Mk4 power steering rack to a Mk3 and I'm just trying to find out why I now have these issues. It is very frustrating!! Edited July 5 by Stuwindsurf 1 Quote Share this post Link to post Share on other sites
sheffieldcortinacentre 759 Posted July 5 Did you text me recently about this? As with my numb fingers ( bloody carpol tunnel) accidentally deleted it so couldn't reply. Quote Share this post Link to post Share on other sites
