Rebuilding a 69 IRS and am looking for info on best shock and springs to use. I’m looking for performance!
Tom IMO fully adjustable Spax are the best shocks I’ve used on the cars I’ve hillclimbed and autocrossed with. As to springs I don’t know what you are asking - “best”? Springs are typically springs. Are you looking for a higher spring rate?
Terry, i was looking at a spring and shock package. XKs has Spax & Gaz shock and spring sets. They don’t have any info on the specs at all. They don’t appear to be adjustable. Any thoughts?
Hi Tom There have been issues over the last few years about rear spring replacement, and you can look at the archives for past threads on this topic. In a nutshell the issues center around springs that are too strong resulting in the rear sitting too high. I’ve got a set of new springs sitting in my garage, that I’ve abandoned, that have this problem - this is so even though the springs appear to match the old ones perfectly. The only solution is to make an extended lower perch (I’ve done that years ago when I was racing - easy if you have a lath), or cut or torch the springs like a hot rodder (unacceptable). Adjustable for height shocks don’t help as the perch is no lower than stock, and in the Spax shock may actually be higher. The adjustable shock is good if you plan on using your old springs as you can raise ride height with them, just not lower it. I use my original springs with Gaz shocks in one of my cars. The springs are somewhat exhausted, but work with the adjusters, and I can set the height where I want it.
I believe that XK’s sell adjustable Gaz and Spax shocks with the spring package - you may just have to call. I believe both shocks. adjustable or otherwise are readily available at other sources.
Over the years I’ve used the following shocks: stock Girlings, Koni, both orange and the black “Classic”, Leda’s ( a bespoke racing shock built to order in England), Gaz, Spax, Boge, and one other whose name escapes me (or is repressed - they were awful).
I believe (from some research) that the bigger the body a shock has the better it is - bigger piston is better. The Gaz front shock is a real wuss, the rear are very big - so I use Spax up front and Gaz in the back on the car I occasionally compete with. All are adjustable for hardness and the rears for ride height. You probably don’t need ride hardness adjustment, but it comes on Spax and Gaz if the shock is height adjustable. If you tour with your car it’s nice to be able to harden the shock and raise rear ride height to compensate for full loads. IMO the shocks can be mixed back and front.
All the shocks I’ve used are perfectly acceptable. The Spax are the best for competition - that is they seem to me to be so, but if you don’t the rest are good. The Koni’s are adjustable for hardness, but not for height. Adjustment is difficult - particularly the rear as the spring has to be removed. The adjustment for Koni’s is primarily for wear - that is when they get old and flabby you can make then harder and “new” again.
Does any of this help?
Terry, thanks for the feedback! I am interested in going with Spax or Gaz adjustable in the rear! The ride height is a concern. I want to be able to lower the height if necessary. I don’t have my old springs and would like to buy a set with the springs on! What do you think?
If you buy new springs you take the chance that they will sit too high. Gaz are better because they have a lower perch. On both, the lower perch consists of two aluminum rings per shock that screw up and down the lower body of the shock to raise or lower the perch. The rings are designed to lock together into position like two nuts used for taking out a stud, but you don’t have to use two. That is so, in particular if you find the car sitting two high. The rings don’t screw off the bottom of the shock so under these circumstance you don’t need to lock them together. You will need a special wrench to turn these rings under load - it’s a piece of stamped steel - cheap - if your supplier doesn’t have one Summit Racing does.
Terry, Thanks again for your help. Do you do any competitive events with your Jag?
I was wondering what’s the difference between the black and orange Koni??
Black and orange Koni. The black Koni is sold by them as a Koni “Classic”, complete with a fancy decal. It adjusts like the orange one. I had a set in the front of my coupe put there by the p.o. They provided an excellent ride etc. Can’t tell you if there is any internal differences with the orange one.
Hi Tom I do autocross with my '68 ots. I was more involved with it a few years ago, and seem to have drifted away (pardon the pun) from it - don’t do it more than a couple of times a year now. I hold the record in the SPL class in the JCNA slalom event. That’s a class for mildly modified street cars running on street tires.
Terry, where do you live? Are you in the north east?
Victoria BC Canada - hard to be farther away!
Tom, I don’t have the same experience as others, but as a data point I can tell you that I have adjustable GAZ dampers with adjustable perch. The picture shows mine adjusted to the height as per the manual and as you can see, there is enough to lower the car a bit. Maybe 1.5".
Thanks for the info! That’s exactly what i was looking for! What is the little “L” bracket at the bottom of the damper? Also, looks like you went with the original rear disc brake set up. Do you have any thoughts on that?
As far as the rear brakes go, I have no complaints. Apart from the well known gradual locking up of the brakes that was MC related and now cured, the brakes works fine. Mind you, I have not been tracking the car or even had it on a long drive in the Shenandoah valley. Yet !
The “L” bracket is as far as I know original to the car and used as an anchoring point when shipping the cars. I believe it was introduced with the S3 and maybe only for US export models. It has a single center mounted one at the front as well.
Thanks again, would love to see more pics of the Jag!
Hi Tom, there are more pictures here:
If you have any specific area in mind, I’m very likely to have a picture of it, so just ask.
Would love to see the engine and front suspension!
I’ll send you some pictures when I get home today.