IRS - Shock Absorbers - Plan B ?

[pinza]

Hello all,
I am doing a complete rebuild on my ‘64 FHC 3.8 and need 6 new shock absorbers. I can get hold of 4 rear Boges, but am struggling to find front ones. Apparently Boge have stopped making them for the E Type.
So the question is : can I mix Boges on the rear and something else on the front ? Or what is the plan B option if I don’t use Boge - happy to get Gaz if that’s my next choice. If I get Gaz, do I need to get new springs too? I don’t need to transform the car, but want something that’s going to let me enjoy touring into the future.
While talking about IRS, is there an explanation why my car had different size springs on the rear shockers (279mm plus 19mm spacer) compared to the front (284mm plus 4mm spacer) ?- see photo
Thanks in advance,
Glenn

[MarekH]

There is no reason why you can't have two different makes of damper front and rear.

The springs (torsion bars = front; concentric coils = rears) control the ride height and how far the car moves up and down when going over bumps.

The dampers (separate ones mounted to the picture frame = front; mounted inside the coils = rears) control the rate of decay of movement and how long you keep bouncing).

Using different springs and spacers on the rear is unconventional but interesting. The stronger spring will always be progressively harder to compress, so mixing them does nothing for compression and two springs are always taking more compressive load than the other two. Conversely, when "airborne", the stronger spring resists stretching more and will max out in length but the weaker spring will then presumably allow the continuing pulling of the wheels down to the ground. What you have achieved is a differential performance in compression and extension. Whether that is a good idea or not - I have no idea. It is certainly needlessly confusing.

When not going over bumps, the default position is that the four rear springs take equal loading and that is why different strength and length springs are mated with different spacers. Think of as a straight line graph with two lines of different slopes. The crossover point (where spring+spacer lengths are the same) is the weight of the car when the suspension is not moving.

You need to replace dampers when they no longer dampen out movement.
You need to replace (or maybe shim) springs when the ride height is no longer correct and replace if they allow excessive travel when load changes.

kind regards
Marek

[Mich7920]

Hi Glenn
I'm not agree with Marek this time. The dampers front/rear are normaly built to work together on a specific car.
If you are in race it's different, you could want a specificity on your rear or on your front with different dampers but for a n " everyone car" there is not any interest. Apart having a car with reactions a little bid odd sometimes.
Your 55-year-old springs deserve their retirement so rebuilt your dampers with new springs and exact spacers.
The gain in geometry, stability and confort will be really great.
Mich

[MarekH]

Dear Michel,

I would image (and hope that) front and rear dampers made by the same manufacturer are designed to work together.

I can also see plenty of people fitting only Gaz adjustable rear dampers simply because they want to alter the rear ride height. They may or may not have thought about the amount of damping effect of one manufacturer's product vis-a-vis another's but it would be unsurprising if the range of settings made available by one manufacturer didn't overlap with those offered by another.

I'd be more worried by the use of dissimilar springs and spacers mixed up in the rear cage.

kind regards
Marek

[mgcjag]

Hi Glenn.....There should no be a problem useing different manufacturers shocks front and rear......so long as they are specified for your model car.....I know quite a few useing boge rear and Gaz adjustable (for damping only not height) on the front...as supplied by SNGB https://www.sngbarratt.com/uk/#!/Englis ... 47077872d2 look at the list of suitable models this shock is suitable for at the bottom of the page.......just check if you go for gaz(adjustable for height) on the rear.....as some models require a specific spring.....standard springs are too long........the boge would be ideal for the rear if you have them......also consider useing your original springs...assumeing they are all the same size etc as replacement springs have caused ride height issues on some cars....as for you different spacers who knows whats been done to the car in 50 years...maybee just left out by someone.....all the best....Steve

[christopher storey]

In relation to the front dampers , make absolutely sure that whatever you get will not extend to a length between centres of more than about 405 - 410mm. There are various threads on here which deal with this - the consequences can be serious, as I had a track rod fatigue fracture as a result of the dampers extending to 430mm and thus allowing the track rod to act as the stop for downwards movement of the wishbone

This is the original link to the 2009 thread

http://forum.etypeuk.com/viewtopic.php? ... ">Steering

[Mich7920]

Sorry but I'm not agree to change the balance of a car, E Type or other.
Mix the dampers change the way the car is going to react.
Not really when you drive quitly on our small French roads that you like so much but for sure when you'll need to brake hard under a thunderstorm. That's why I don't advise to mix the dampers, the brakes and of course the tires.
Ok you can do everything you want, the car Tuning is here to show us that all is possible but it's not my "cup of tea"...

[abowie]

And another, different, opinion.

There is absolutely no problem with mixing different manufacturers or specifications of dampers front and rear. Or indeed fitting adjustable dampers. On various of my cars I have fitted Boge, Gaz and Koni front shocks without trouble. I have always used Boge rears in the past simply because they are the cheapest and do the job.

I would have some trepidation about having differently adjusted springs on the IRS however. If, for example, the rear spring is stronger or longer than the front one this might tend to make the IRS tilt front down under load, which might be bad. Now I suppose that it is possible that your rear springs have been tested for spring rate and length, then shimmed to ensure all 4 are identical, but if it were my car I would want to confirm that before reinstalling the shims.

So my advice, for what it's worth is use whatever shocks take your fancy at the front and use your Boges on the rear, but get the springs checked first so you know that all 4 have the same compression rate.

[pinza]

Thank you all so much for your prompt responses.
I have never been comfortable once I discovered that I had different springs, so I am happy to take the advice to either get them tested as they are or to replace them. We feel my car was raced a bit based on the panel damage and hasty repairs so the springs may have been a victim of “get it ready by the weekend”. Replacing them seems a sensible option as has been advised. I have a bit more reading to do of older threads to find my best option to source springs ??
Thanks for all of your guidance.
Regards,
Glenn