Author Topic: Rear spring dimensions and rates  (Read 717 times)

AcemanToo

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Rear spring dimensions and rates
« on: October 04, 2021, 18:00:36 »
Does anyone have information on the rear coil springs on the Ace Brooklands please? I'm looking to get some uprated ones to try and stiffen up the suspension and get rid of the well-known 'thump' at the rear end. Trouble is, I don't quite know where to start! If anyone has any information no matter how trivial, please help with some answers!
Many thanks!

paho

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Re: Rear spring dimensions and rates
« Reply #1 on: October 05, 2021, 09:11:54 »
Hi,
I looked at topic "Spring rates", https://www.acownersclub.co.uk/forum/index.php?topic=2752.0 ,
when replacing my coil-overs. I had to translated the spring rate figures given to metric
measurements and assumed the weight of the car to be 1720 kg without spare wheel.
(its actually 1668,5 kg with me in the driving seat and half a tank of petrol, 1590Kg without.
Weight distribution is 50,13%/49,99% respectively).

The old shocks and springs were checked by SDV in Dalarna Sweden and the results were close to the figures in the topic.
So the coil-overs were made up to these specs. The origonal Koni coil-over kit is not manufactured any more.

The origonal coil-overs on my 1995 model looked pretty tired after twenty odd years of service,
rusty with the bumpstops disintegrating and one front shock absorber leaking slightly.
I found the car sat unevenly after I fitted the new coil-overs, so I wish I had measured the ground clearance
before fitting (could'nt use the old springs as we reused parts of the old Koni shocks). The handbook states 15cm,
but I have not managed to match that so the clearance is 13,5 passenger side, 14cm drivers side without driver.
I'm happy with the result, the ride is firm but not bumpy, and seems to clear sleeping-policemen better, which it didn't before!

Br /Paho




Max Allan

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Re: Rear spring dimensions and rates
« Reply #2 on: October 11, 2021, 09:58:58 »
Hi AcemanToo

When I tackled the suspension probs many years ago I found the rear shock absorber travel was not equal distance above and below ride height (I decided on three fingers gap between tyre and wheel arch which equates to about 4 inches) – there was less travel from ride height to bump stops compared with suspension fully extended. To obtain equal travel I relocated bottom shock mountings closer to wheels ( I welded the brackets directly above the tube linking the two wishbone arms). I retained the original Konis and springs, but had several different thickness spring packings machined to bring the car up to desired ride height.

Did the same with front suspension – relocated the shock lower mountings further out to achieve equal travel above and below ride height and fitted longer Konis to suit increased distance between upper and lower mountings and to increase suspension travel. Finally had new springs made to achieve 1) correct ride height 2) accommodate extended travel 3) eliminate coil binding issues.

Not had issues with grounding or hitting bump stops on normal roads since.

Hope that helps.   

Nev

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Re: Rear spring dimensions and rates
« Reply #3 on: October 12, 2021, 08:30:26 »
The previous owner of my car did a lot of work re springs etc (calculations etc etc) , he was an engineer and seems to have been a bit of an expert on this topic. I can have a look through the file and share info. I had a leaking shock, so went for the set up that Redline have specc’d and had made, I now a couple of other members have the same set up , seems good, I have never experienced the thumping, but I don’t think  this one has never done it since George put on the revised coils and springs he had made up.

AcemanToo

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Re: Rear spring dimensions and rates
« Reply #4 on: October 15, 2021, 16:31:46 »
Hi Paho,
Many thanks for your reply and links to past answers! Apologies also for the lateness of my reply - simply forgot which is really no excuse at all when you've taken the trouble to help me.
It was very interesting to read that the spring coils are too close together on the rear springs - it certainly helps explain why the back end makes so many thumping noises when the road isn't as smooth as glass!
Do you know if the springs were tailored to the Ace or were they just picked off the shelf somewhere, maybe XJS or similar?
Once again, grateful thanks!

Max Allan

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Re: Rear spring dimensions and rates
« Reply #5 on: October 15, 2021, 19:47:18 »
From my experience there isn't a problem with the rear springs becoming coil bound - only the front springs have that problem! The rear springs are much lighter than XJS.

The thumping is a result of the shock absorbers hitting the bump stops because there is insufficient travel available between ride height to maximum deflection. I first experienced it going over a repair in the road. The shock was sufficient to trigger the fuel cutoff valve causing car to grind to a halt. Although I had only had car a short while at the time I had spotted the valve in the boot so knew what had happened. 

paho

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Re: Rear spring dimensions and rates
« Reply #6 on: October 16, 2021, 17:22:52 »
Hi AcemanToo/Max,
I have'nt experienced the coil binding problem that others have reported, but my supplier took that fact into consideration for the front coil-overs. From the outset I have tried to keep to the origonal specs for the car, and not change the "base line". I made a miss by not measuring the origonal ground clearance figures for the car. But the tyre/wheel arch clearance figures were never has much as 4", mine are 2" at a pinch. (4 fingers for me is 3")

I sent complete examples of the front and back coil-overs with the calculations I had made based on the figures given in the topic and calculations I had made. The figures corresponded roughly with the tests made on the examples I sent to SDV so we went with those figures.

I knew the car had experienced a broken front spring, off-side front if I understand the service invoice correctly, which was replaced in 2011 (both sides) this could have been caused by the coil binding problem reported by other owners. I think the replacements came from Redline. I have checked through the other invoices I have and believe the rears were replaced in 1999 and the fronts replaced in 2001, the invoices refer to shock absorbers so I assume the origonal springs were retained.

To be quite honest the rears looked terrible, with totally "decomposed" bumpstops, very rusty springs and shocks. The springs on the front were in better condition. I now have a completely new set which were built up by SDV "in-house" using H&R sport springs mounted on SDV's own shock absorbers with adjustable lower spring perch and locking collars; they re-cycled the upper-mounts from the Koni shocks I had. They look similar to Dgoose's coil-overs illustrated in "Reply #9 on: June 12, 2014, 13:06:51".

I'll send you (AcemanToo) a copy of the specs I derived from the origonal post sent to my supplier.

As a footnote I also triggered the inertia switch on my Ace last week. took two days to work it out too! I dropped the rear of the car abruptly when releasing the hydraulic jack. So I've also updated the " Non-starting" thread.

BR /Paho

Max Allan

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Re: Rear spring dimensions and rates
« Reply #7 on: October 17, 2021, 14:10:39 »
To clarify I went for wheel arch clearance of 2 inches (3 fingers for convenience) which equates to 5.25 inch ground clearance measured at sill lower lip.


paho

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Re: Rear spring dimensions and rates
« Reply #8 on: October 17, 2021, 17:41:41 »
Hi Max,
that's about the same as mine (whew!) Mine's about 13,5 cm both sides when I'm sat in the driving seat with weight distribution 50-50 front/rear measured transversly.
I forgot to measure before I changed the coil-overs so its quite a relief to know I'm not far off!
BR /Paho

Max Allan

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Re: Rear spring dimensions and rates
« Reply #9 on: October 17, 2021, 23:46:01 »
Hi Paho

I can't claim to have used any more technical approuch than to copy the same gap as my Daimler Double Six which looked about right and proved okay in reality.

Regards Max

paho

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Re: Rear spring dimensions and rates
« Reply #10 on: October 18, 2021, 09:24:00 »
Hi Max,
if its good enough for your Daimler, then its good enough for me!
BR/Paho