Spring and damper lengths to suit lowered mk1 imps - advice sought.

[Yoeddynz]

As per title..

I'm starting this thread and asking for advice here because I don't want to deal with dozens of peoples facebook advice when they have no experience. This keeps it simple and concise.

My Imp is a mk1. From what I know, most imps in NZ are mk1/mk2 with the high pivots. So I will make do with what I have.

Its currently running quite low (not Ash Cull low, but low enough) and I am happy with it. Here's a pic with the Datsun engine installed and one standard size Hannah installed ...


I have now installed the goldwing engine/subaru Leone 5speed box and added about 20-25 kgs (I will be borrowing some corner weight scales to confirm this in the future). It possibly sits a bit lower in the back now. Can barely spot it though...



Anyway. I want to sort some issues out. I lowered the front back in 2018 by creating some front monte carlos springs (read:'Makita one ways'). These measure up at 9.5" long. Here they are next to standard mk1 springs..






I then lowered my bottom spring perch by machining up a new seat and welding it to the bottom of the shock. Easily done if you're a careful accurate welder.



So now the spring perch sits lower. and there are no collets to fall out...



The bottom of the spring is about 50mm from the centre line of the shock mount bolt..



Understandably my shock length is too long to retain the springs when the imp is on the hoist so I added the standard spec straps..



Now this setup has worked fine and my wof (mot) man has had no issues with it. I have measured the camber at around 1 to 1.5 degrees, at a static height with no one inside but an almost full tank of fuel. The rear springs are less a half coil and seem well suited to the weight. I do intend to raise it 15mm at the back with a spacer due to the extra weight the rear now has.

The imp rides beautifully and handles really well imo. I have no other imp experience to judge it against other than the stock stand mk3 Hannah had in the UK but I'm very happy with how it rides and handles. Its not raced. Its just a fast road car.

I would prefer less front camber , as per what Mike Dent suggests. But I have not yet set out to adjust it because of the following......

Here in NZ our modified cars have to go through a certification process when you do things such as fitting a more powerful/different engine etc etc. My car is already certified for the Datsun engine, fitted waaaaaay back in 1990 or something. But I'll have to re-cert it for the new engine. I dont think the retaining straps are going to please the certification engineer and for non- certified cars they are not allowed anyway. Here is a bit from NZTA technical information sheet which states..

'replacement springs are self-retaining in their seats at full extension, without the use of non-standard devices such as wire-ties, straps, or external spring locators'

So I have to change my front shock absorbers to have no hassles when it comes to the certification and I would like to maintain a similar ride height.

These are my questions..

My springs are effectively Monte carlos with a 1" shorter free length. I have been offered some as new Gaz coilovers for 150 squid - the ones specified for lowered imps. From the pics I have seen on the Gaz website (which I must say is quite lacking in information...) it looks like with the collars wound right down the spring will sit around 20-25mm higher than my own setup. With the collars so low I then wonder if the spring will remain captive at full droop? If not then I will have to set the car even higher because I cant use straps. Otherwise I will have to get shorter springs.

Does anyone here have experience with Gaz shocks/monte combos?

Are the Gaz 'lowered/short' shocks the same length as the Spax lowered/shorter units?

If I go up an extra 1" in height I expect my resting camber will be close to zero, if not a positive figure? I can adjust that out once I have confirmed my ride height etc (again - taking mikes advice on how to go about this before de-cambering)

Are the extra low monte springs just less one more coil or are they set at a more compressed state so giving the same rate as standard montes ?

I like the rating my current springs have. I will measure them next time they are out but I figure they are around 200-210 ib/in if the stock ones were 195. I'm not really keen on going much stiffer.

Btw - as part of my engineering apprenticeship I spent 6 months in the blacksmith shop and I helped set many coils and leaf springs via the furnace and larger press etc. Very interesting (hot dirty) work. I have a decent enough bit of knowledge on springs but I'm here because you cant beat experience, of what I have on Imps is little.

I have owned both Spax and Gaz shocks for my Viva HB I had here in NZ and my UK based Mazda rx3. My only issue with the Gaz ones were corrosion from UK road salt. We don't use salt in NZ so not an issue. I am not sure who builds the best shocks. I have seen one video on youtube showing a Gaz unit being assembled and I was none to impressed when I saw they just use little plastic air bags to allow for the oil displacement from the shaft insertion on compression. I dont know if they have any extra gas filling to help stop cavitation? As I said earlier - the website is devoid of info on such things. Spax is not much better in this regards but at least they are gas filled. I know nothing of protec but they do look nice!

Lol @ wall of text. Hopefully I can get some advice. I will get the Gaz shocks offered anyway because I can at least try them out. I will have no problem selling them on if I decide to try out something else like protech etc.


Alex

[moose549]

Hi Alex. Monte springs are just 2 1/4 dia 9.5 inch long 195lb springs. On the rally car I run 250lb 10 inch long. This is because the rallying I do it is on every surface so the set up is a compromise. For your fast road car a 210lb will be fine. For the dampers you need shorter bodied items to retain the spring and to ensure you still have travel. If you remove the dust guard from your dampers and sit the car back on he floor have a look at how much damper rod is exposed. Make sure you either drive the car a bit or bounce on the front end and rock the steering from lock to lock whilst rolling back and forth. This will then be the ride height to start wtih. Add the weight of two people whilst rolling the car around and see where it settles and what the difference is between people in the car and not. Then measure the amunt of exposed damper rod. You may find that you are almost on the bump stop and certainly when braking and the nose dips you will reduce the gap further. If you then imagine hitting a bump in the road you will be on the bump stop and have no damping. If a 1 inch shorter damper regains the amount of damper travel you need and the springs can still fall out at full droop fit some helper springs. https://www.race-parts.com/racetech-...-2-inch-length if you go for a low poundage spring you will not notive the difference on the road. You will need a collar to fit on top of the helper to locate it on your main spring. A 4lb spring will be crushed flat at normal ride and expand enough at full droop to prevent the main springs from being loose. When you have the Gaz dampers and the set up you have now you will be able to fit to one side and compare. https://www.compbrake.com/product/2-...-adapter-pair/ The springs and spacers should be readily available all over the world as they are common fitment on race and rally cars. You could even make the spacers yourself. If you decide to go the protech route and what their damper rating talk to them direct. If you want my motorsport spec or a variation of my spec and Protech road spec please get in touch. I would reccommend my motorsport spec for the front as they are set to cope with 195 to 250lb springs so on the lower end of the clicks it will be smooth enough on the road especially as I have specified a different rebound rate when developing them. If you need any more help or advice I am happy to help regardless of whether you buy anything from me. impcompetitnparts@gmail.com Regards Mike

[Yoeddynz]

Thanks for that Mike. I was just about to pop up a picture of tumbleweed because there had been no response at all.

Frank has sent me over his Gaz dampers (the shorter ones) plus some super low montes springs, also sourced from Gaz although I dont know who makes them for Gaz. They measure up at 8.6" and he said they are 195lb so I presume they must have the same coil count as standard montes but are set shorter. I'll find out when I bench test them against my standard ones and my Monte replicas.

I dont mind if it has to sit a tad higher at the front but I'll have to raise the back as well.

One of my rear dampers is low on oil. Under compression it sinks quick but the rebound circuit is fine. I have just picked up a mint set of Code9 dampers off a Nissan Navara at the wreckers to try out. They are almost identical in measurements to Imp units however I'll need to machine up some spacers and a new nut to suit the top.

Now you expect that Navara dampers would be stiff in compression considering they have to manage the weight of the front of a ute with a big hefty diesel engine. But they are actually lighter in compression damping than my one good Imp rear damper and about the same in rebound. It could just be that the Imp dampers are quite basic in their valving and share the same port for both bump and rebound whereas the Navara items have a more refined damping circuit.

I'll try the Navara items out and see whether I find the rear feels wallowey under compression. I might have to investigate uprated items or just bite the bullet and get some adjustable dampers.

I'm actually a fan of soft, well damped suspension on road cars - given how rough some roads can be with the lack of council spending. My last trip to Oxfordshire and also Wales showed me that the roads there are even worse. I'd not be keen on super stiff suspension on those roads!

[moose549]

What you have to remeber about imp rear shocks they are mounted on the arm behind the spring so you have to take into account the leverage from the pivot point. As an example the impr rear springs are 550lbs. If you move the damper to where the spring sits and convert to coil overs like davrian did.Then you halve the spring rate approx. A nissan navarra spring is rated at 500lb and is a coilover fitment i.e. directly around the damper. Add the 50lb of an imp spring and the damper moved further away from pivot point and the spring they will feel softer and maybe more so if they are old from a breakers.

[Yoeddynz]

The Navaras these shocks come from are torsion bar springs. But I totally get what you mean. Anyway- I have removed the navara shocks and will take them back. I've refitted my Imp shocks, after having refilled the unit that was down on oil. I've got another OE pair on their way but so far from testing my old ones are good now. Much better control!!!

There's a big update on my thread if you're interested..

https://oldschool.co.nz/index.php?/topic/58204-yoeddynzs-1965-hillman-imp-911-thinking-inside-the-box/page/6/#comment-2664459

[moose549]

Hi Alex. Just seen your post on FB. Do not like putting too much on there, too many idiotic comments. I am assuming you do not have floating floor pads for set up? Drive the car down the road to setle all the suspension and then drive it into workshop on a flat surface. Take 4 axle stands and place them equal distance at the four corners of the car lay a long straight bar on stands accross the front and back of the car make sure the bars cannot move G clamp? Set the height of the bar so the strings will run throug hthe centre line of the wheels, drive shaft and stub axle height Then use fishing line or some fine string 1-2 mm tie one end in a loose loop around one bar and hang a weight off the other end of the bar to keep sting tight. The car is now in a box with the string running down either side of the car. Measure from the driveshaft ends to the string wit ha steel rule and set distance equally say 100mm from driveshaft end to string. With the front dust caps removed do the same at the front and get equal measurements from end of stub axle threads to string. It takes a few goes to get the string lines parrallel down either side of the car. The car is now in an accurate square box. Using the steel rule measure the front edge of the wheel to string and do same on rear edge of wheel. This will give you toe measurements for example 100mm on front edge and 100mm rear edge you are parrallel on that wheel if the front edge is 103 mm and rear 97 mm you hve 3mm toe in on that wheel. You want 1.5mm toe in on each wheel giving a total toe of 3mm. You can check the rear wheel alignment as well but to adjust this is difficult involving shims behind rear crossmember. Now check the camber you want 1/2 deg neg max with the car at driving weight. If you have too much raise the car and vice versa. This is the pain if you do not have floating floor pads. You need to now settle the supension again by rolling the car backwards and forwards bouncing the supension up and down or go for a drive and park back in the box and put the long bar you removed back in place and re-set the string lines and check toe again. To do this and get accurate results make sure all suspension bushes are in good order with little to no movement including the rack bushes in the steering arms. All wheel bearings must be in good condition and fronts adjusted correctly, tyre pressures set equal all round. At the rear you want 1mm toe in. When the car is all set up use it for a good few miles and check front tyres if showing slight signs of scrubbing re-set toe to 2mm or 1mm in never set toe out some people have used parrallel but a bit of in is better. Rear toe in helps the car stay in a straight line at higher speeds same for the front. toe out makes the car feel wandery and unstable when turning into corners and on straights the slightest steering input moves the car too much. If you have excessive toe out at the front the car will feel horibble, scrub tyres and generally be awful. If when pressing down on the suspension the car does not rise back up to nearly the same height it can be tyre presures too low so the sidewalls compress and the tread moves on the floor and does not return to position creating a bit of drag. Or the rebound damping is set to firm not allowing the spring to rise or the springs are too soft for the damper setting. When you have checked all bushes and set up the track and ride height the alteration in camber from rolling forwards or backwards should be minimal and is only due to tyre rubbing on the floor. I noticed one person posted about using string to set up the car so may not have been done accurately. Well string under tension does not curve and does not need to be calibrated! So it is the most accurate way of setting the car up if you take time and care, do not move the string etc. Let us know how you get on.

Here is a pic of my professional kit for doing alignment. With this and the car sat on floating pads there is no need to settle the suspension/tyres when altering angles so removes the need to roll car and bounce suspension or drive between each setting and re-set the box.