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Converted Rear Shocks - size?


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Hi all,

I have searched on here but no luck, poss my poor skills though....

My car has Protech Coil-overs fitted to the front, on the rear, it has Gaz adjustable shocks and springs, which I imagine are standard - the car sits as standard.

It feels sensible to be to match up the springs and shocks on the rear to the front, Protech seem able to do this.

The missing information is, what are the sizes of the shocks and springs - as measured when not fitted?

Any thoughts and advice would be appreciated.

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Not entirely convinced the make of the shocks on the front have to be the same as the rears.

Naturally not all shocks are the same in terms of quality but what are you hoping to achieve by changing your rears. The spring ratings and damping are about balancing comfort and handling and you won't necessarily make it better by changing them.

Given that the gaz shockers are adjustable you could try adjusting them and see which way you prefer.  Do you know what the spring ratings are for the fronts, standard or higher? If higher than you might want to even things up by swapping the rears to a set of similarly increase rate to balance things out if you feel the rear needs to be firmer. Again you have the option to retain the existing shocks and adjust or not depending on how you like it set up.  Car manufacturers employ test drivers to help them do this with less trial and error but it takes us mortals a lot more trial because we make more errors before we get the adjustable dampers set right.

Unless it's a track car don't go to heavy on the spring rates or too low for that matter (tracks don't have speed bumps). Adjustable dampers give you ample choice for tinkering.

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Andy,

Thanks for a thoughtful reply.

I guess I am hoping for improvements in handling. Comfort is ok, car not too rattly on reasonable roads. It is kind of difficult to know whether my car handles as it should or is behind par.

It also struck me, that if you were designing from the start, you wouldn't choose to have different suppliers for front to rear - although that is an assumption.

Totally agree with you about not going heavy on springs, my Landrover has had that done and shakes you about something rotten!

Maybe what I should do is understand a process for adjusting what I have!

Thanks again.

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Best way to check is pick a route locally that doesnt have too much traffic and not in a built up area. Then drive it once with the car as is then try adjusting the shocks only doing either front or rear at a time and making a note of what youve done then go and drive it again and see how it handles and then keep doing that until you have the best that you can get and then do the same with differing tyre pressures. It will take a while but thats the sensible way to approach it, only try one thing at a time or you wont know which way to go to improve.

I have a local "Test track" that has all sorts including wrong camber bends rough/smooth surfaces and steep uphill and downhill sections and as I know it really well its easy for me to judge what needs to be done.

Stuart.

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Stuart is as ever spot on!

I have a "test track" locally that includes a nice range of road surfaces including a couple of pot holes (no trouble finding these!). My experience was that softer damping rather than harder was best. I did have spax on the rear before I rebuilt the car and these (Even full soft) were too firm, I now have Konis and they feel great. And remember you have a chunky ARB on the front which keeps things from rolling too much on corners

It is also correct to say you do not need to match makes front to back.. side to side, yes... 

Interestingly the thing that made the most difference to the ride in my 6 was swapping in CV jointed axles for the sliding splines. My wife noticed imediately and it seems to make the car much more fun to drive (the sliding splines I replaced were pretty new so it wasn't wear, I actualy swapped to CVs because the supercharger setup was wearing out UJs too quickly)

Tim

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17 hours ago, Tim D. said:

Stuart is as ever spot on!

I have a "test track" locally that includes a nice range of road surfaces including a couple of pot holes (no trouble finding these!). My experience was that softer damping rather than harder was best. I did have spax on the rear before I rebuilt the car and these (Even full soft) were too firm, I now have Konis and they feel great. And remember you have a chunky ARB on the front which keeps things from rolling too much on corners

It is also correct to say you do not need to match makes front to back.. side to side, yes... 

Interestingly the thing that made the most difference to the ride in my 6 was swapping in CV jointed axles for the sliding splines. My wife noticed imediately and it seems to make the car much more fun to drive (the sliding splines I replaced were pretty new so it wasn't wear, I actualy swapped to CVs because the supercharger setup was wearing out UJs too quickly)

Tim

The CV's get rid of the spring whine up which all TR.s suffered from new. I noticed that when I changed mine and also gets rid of spine lock up when cornering.

Bruce.

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1 hour ago, astontr6 said:

The CV's get rid of the spring whine up which all TR.s suffered from new. I noticed that when I changed mine and also gets rid of spine lock up when cornering.

Bruce.

I can that CV joints have advantages, but wouldn't have thought it would make any difference to spring wind up. That would be dependant upon the suspension set up wouldn't it?

Mike.

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5 hours ago, michaelfinnis said:

I can that CV joints have advantages, but wouldn't have thought it would make any difference to spring wind up. That would be dependant upon the suspension set up wouldn't it?

Mike.

The original TR6's had TR4 spring rates! then there were complaints about the softness and the front end of the car rising up for take off under hard acceleration as can be seen in the early PR Photos because of spring whine up. BL went through a whole load of attempts to cure this problem by fitting 4 different spring rates rear springs by increasing the poundage. If you have  a BL spares book or Moss, you will see what I mean.

Bruce.

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Spline lock is more relevant on cornering under load. Affects worn/dry splines the most. The CV jointed shafts are not subject to this although the coated splined shafts have also provided an effective solution for along time before the CV shafts came onto the market.

Soft rear springs do give a fairly characteristic rear end squat under load.

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Thank you all.

As I am one for taking advice, matching up rear and front project is shelved!

I think I will see if i can improve one thing at a time and see where that gets me.

First thing is the front being a bit skippy - moderate speed into right turn at roundabouts or higher speed sharp corners.

I fitted the higher spec drop links, really because TRGB had run out of standard… so I wonder if they might be working against me and maybe, get some standard ones before doing anything else.

Interesting dialogue on the CV rear drive shafts, I thought these were the answer to a maidens prayer? Are the sliding splines mentioned the standard beasts?

Cheers

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1 hour ago, RobRennie said:

First thing is the front being a bit skippy - moderate speed into right turn at roundabouts or higher speed sharp corners.

The front is probably a lot stiffer in roll than the rear giving you excessive understeer. I’d start by equalising the tyre pressures to 28 to 30 psi all round and follow that up by taking the arb out of the equation by removing one drop link. If that sorts it you can either bin the arb or fit a rear arb to balance things up. 

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Cars are generally set up to be neutral to slight understeer to give handling that is pervceived to be"safer" for the average driver.

Excessive oversteer is certainly on the dangerous side of things and escpecially id it is without much warning as the 911s are a famous for alledgedly famous for.

On the 6 I have both front and rear anti-roll bars and am happy with the balance and grip

The 4A has a front ARB fitted by the previous owner and does feel different in spite of similar spring and damper set up.  Opted to leave it that way for now.  My wife asked me if I really wanted to turn it into a car that drove exactly like the 6, and she probably was right. Both corner and handle well but differently.

 

 

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1 minute ago, Andy Moltu said:

Cars are generally set up to be neutral to slight understeer to give handling that is pervceived to be"safer" for the average driver.

 

 

 

True but the OPs car is far from as factory especially in the front suspension so all bets are off as far as that is concerned.

Stuart.

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  • 2 weeks later...

Hi All,

Thought I would give you a bit of a rolling update.

Changed the drop links for standard one and the roundabout cornering is much improved and generally steering feels better.

My mechanic thinks that I am confusing two problems into one. His view is that the front springs are too hard and harder than the rear, also, to have the car made level on all corners the springs were wound up - which also has the effect of compressing the springs, again adding 'firmness' - so this creates a kind of porpoising.

I plan to soften up the rebound settings on the front - they are at 50% now, and maybe then try firming up settings on rear - that may help, but I am not convinced.

So I think what I need to do is find a Protech partner, or someone with coil over expertise and see if they can calculate the correct stiffness of spring and correct length of spring - Protech can supply pretty much whatever I ask.

Hope this is interesting or useful :)  I will update further!

Thank you all for your nudges and ideas

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