IRS Rear spring length and ride height

[grimboh]

Hi everyone,

 

I have a 4a that had lowered suspension - too low for the bumpy Kent lanes.

So I bought a 'standard' set of springs from Moss.

Part 216275PR rear, free length 11.6" 350 lbs

Part 213165PR front, 10.3", 310lbs

 

The fronts seem perfect. Ride height now up to around 5.5" to the chassis rail by the front suspension.

Height to top of wheel arch 27.5"

 

Rears at first sight seem OK, ride height around 6.5" at the chassis elbow just ahead of the rear wheel.

Height to top of wheel arch 28.5"

 

So in my view a nice 'downward' tilt to the front.

 

Problem is the damper link arm - I have the original type of damper, no conversion of any sort.

If I bolt up the link arm to the rear of the trailing arm, with the rubbers of course (which are new), it is effectively too short and trying to compress the spring more than the free weight of the car does.

So this will mean the wheel would compress on a bump but not droop at all when unloaded.

 

Clearly this isn't right, but stuff I've read from various sources does seem to suggest the springs are the right length, and an increase from the factory 280lbs to 350lbs seems to now be regarded as standard.

But I don't see how anyone can have fitted these successfully without having a longer link arm, which does not seem to be an option.

 

It's possible that the springs are not to spec I guess, and are a much higher poundage - that's not easy to check without specialist equipment. Moss confirm the part number is definitely to spec.

 

Has anyone else had similar issues?

Any help/advice/comments greatly appreciated!
Graham

[Rob Salisbury]

Hi Graham, Have you got the correct damper links (Moss Pt No. 141464A)? .... if you are using the old ones they may have been shortened for use with the lowered springs. With the car off the ground the arm of the shock should rest on the lower bump stop and the link keep the spring firmly in place but only lightly under compression.

Cheers Rob

[grimboh]

Thanks Rob, Yes they are correct, in fact they are new from Moss when I recently replaced exchange dampers. I also double checked with the old ones and they are exactly the same length.

Cheers,

Graham

[grimboh]

Rob, sorry should also have said I agree with your statement on the damper/link keeping the spring under some compression.

As it is now it keeps the spring more or less in the same compression as when fully loaded with the car - ie the wheel hardly drops at all when the car is jacked up.

Graham

[stuart]

Have you run the car since changing the springs?

Stuart.

[grimboh]

No not run it Stuart as to me it seems clearly wrong - the suspension is surely designed to go down to some extent, as well as up!

 

I guess what I'm hoping for is some metrics from others on the forum, eg how much droop is appropriate, what ride height, etc. And especially if anyone has the same Moss springs. Nominally the spec for Rimmer's equivalent springs are the same as Moss's.

 

Regards

Graham

[Bulatovic]

so the issue is that shock absorber links, in order to be installed to the radius arm, need to compress the spring more than the weight of the car itself? - how much lower would it sit then?

a 350lbs spring should be fairly easy to compress, so i guess they need to be longer not to bottom out - so perhaps they need some time to settle under the car's weight

[stuart]

No not run it Stuart as to me it seems clearly wrong - the suspension is surely designed to go down to some extent, as well as up!

 

I guess what I'm hoping for is some metrics from others on the forum, eg how much droop is appropriate, what ride height, etc. And especially if anyone has the same Moss springs. Nominally the spec for Rimmer's equivalent springs are the same as Moss's.

 

Regards

Graham

If you havent run it then the suspension wont have settled at all, take it round the block a few times and then see what it looks like.

Stuart.

[lynchpin]

Hi all

I am sure I read somewhere that tr's handle better with the rear slightly lower than the front??

 

Phil..

[Peter Cobbold]

Could the previous owner have moved the shocker lever arm on the splined shaft, to allow for lowering?

[peejay4A]

Hi all

I am sure I read somewhere that tr's handle better with the rear slightly lower than the front??

 

Phil..

That was Jef Savouret's assertion as I recall.

[grimboh]

Peter - the damper lever arm has the range of movement - its the rebound rubber stop that is limiting the movement because of the longer/stronger spring. A longer link to the arm would be the perfect solution I would think.

 

Stuart, yes OK will do that, I guess it might well settle down 1/2" or so. Still would not allow much droop. If it does settle that much that would give 6" height at the rear and 5.5" at the front - so nearly flat. Surprised that its thought that upward tilt is best, certainly on my race kit car I look for 1" or so difference down to the front.

 

Anyway, I'll see how it drives and report back. Of course I'm also fully expecting camber issues, especially at the rear - but at least that is fairly easily modified by mixing and matching the swing arm chassis brackets.

 

Seems to me that the accepted stronger springs might always have been the same length as the original 280lbs and so always increase the ride height and limit the droop more.

The workshop manual specifies a free length for the front springs but, frustratingly, not for the rears.

 

Thanks to all,

Regards

Graham

[TR4A1965]

Hi Graham.

 

As I remember, the ride height should be around 41ch at the rear and 42cm at the front.

 

I can't locate my reference material on this so it is from memory.

 

It is on my website somewhere but I can;t locate it.

 

Stuart is right. My TR4A looked high. I drove it to the MOT station and when I got back the ride height was perfect.

 

My new bushes need to settle in.

 

Have faith and take it for a spin.

 

Best

 

Paul.

[stuart]

Also FWIW if you dont have the camber set correctly that will also alter the ride height slightly too.

Stuart

[TR4A1965]

I found my notes. This is what I worked to.

 

Best

 

Paul.

 

 

TR4A Ride Height

Exactly 40cm from wheel center to underside of wheel arch. That is 15.75". And....... the most important: car rear should be lower than front by 1.25 +/- 0.25 cm, i.e. 1/2". This relates to the distance from ground to underside of wheel arch.

NOTE: During the rebuild the car looked proud and the ride height all wrong. After a drive and back to the MOT Station (18 miles round trip) it came back perfect. The new poly bushes had settled in - new springs and bushes as well as suspension will sit the car proud and it will need a drive to settle before you start taking it apart again to get the ride height right:-) Have faith!!!!!

 

 

www.tr4a.weebly.com

[grimboh]

OK, so took it for a drive yesterday as a fairly dry day. Did around 20 miles.

Measuring ride height by your method Paul, before was 42.5cm at rear, after driving 41cm - that's without me in it.

When I measure now with me in it drops 2cm to 39cm, and that's close to the front measurement of 38.5.

 

The good part is that it rode the bumps way better, the whole car is higher and the springs soak the bumps up rather than crashing into them all the time.

So its not quite in line with being lower at the rear - for general road driving I doubt that most drivers would notice much difference either way. On the track would be a different matter of course.

 

More work is required though as the handling is not good at the rear - it already had misplaced packing (by the previous owner) on both inner swing arm brackets causing way too much toe in, and the RHS much more that LHS. So still need to sort that, should be easy enough.

Also swing arm bushes are knackered. Have new poly bushes on the way - that will also affect ride height a little as well.

And as expected, rear camber is way positive. But using this really useful doc:

http://www.buckeyetriumphs.org/technical/Suspension/AdjRS/AdjRS.htm

I have enough options to sort that using my existing 1 and 2 notch brackets in another config.

 

I'd prefer the rear springs another 1/2" or so shorter, but I think I'll stick with them as they are - they may also settle down a bit more with more miles.

And the 'standard' front springs don't seem to have raised the front of the car quite as much as expected, but prob only 1/2" lower so again I'll live that. The LH front camber as way negative, so another job there as well. The fronts have poly bushes already.

 

So once all that is sorted out (over the Winter) it should be driving and handling pretty well.

 

And the guy that restored it worked for Moss - that doesn't mean that he knew how to set the car up properly it seems!

 

I'll report back in the spring after it's all sorted.

Thanks everyone.

Regards

Graham

 

BTW - Paul we live pretty near to each other, would be good to meet up at some point....

[TR4A1965]

PM Sent

[RogerH]

Hi Graham,

the spring insulators #18 http://www.moss-europe.co.uk/shop-by-model/triumph/tr2-4a/steering-suspension/rear-suspension/rear-suspension-tr4a-with-irs-axle.html are available in different thicknesses.

 

What are yours?

 

Roger

[grimboh]

Hi Roger,

 

I didn't get the poly ones, which are available in 2 thicknesses, just the standard rubber ones. They probably account for a lot of the settling in. Didn't see the need for poly ones TBH.

Its the swing arm bushes that are on the way that are poly.

Cheers

Graham

[ctc77965o]

My car has stiffer/shorter springs...420lb/in (?) i recall....was running too low and scraped its arse on most speedbumps..Today I fitted 3/4 inch spacers from goodparts...camber angle looks good, speedbumps are hardly noticed and the magic number is 15.75inch.

https://www.goodparts.com/shop/index.php?productID=283

 

 

TR4A Ride Height

Exactly 40cm from wheel center to underside of wheel arch. That is 15.75".

[ChrisR-4A]

Guys, don't read too much into measurements to the wheelarch. As part of the body the WA dimension can vary depending how the body is mounted to the chassis which can vary depending the condition of the chassis and how it has been repaired/ restored.

A more valid comparison from car to car would be from the underside of the diff to the ground, as the springs, swinging arms and diff are all mounted to the chassis.

My 4A. Rear wheel centre to arch is nearer 14.5 ins with Moss springs no TT4212 (no spacers).

Chris

[meesonia]

Hi all

 

I'm so glad this post came along, I'm in the middle of my body off restoration, and I'm in a quandary about Springs. The PO had started to replace the mechanicals from the Rear forward and had fitted a Shock conversion kit and new springs, but hadn't touched the front. Before I started the strip the Front was miles higher than the Rear, I did put a post about it sometime ago but can't find it. So having stripped everything off I have the following, new Rear as fitted by previous PO free length 10 inches, and from the bundle of invoices I got they were bought from David Manners with part number TT4212.

 

The Fronts, the old crusty ones untouched are 10.25 free length. In the boxes of parts I got were a new set of Springs which I presume were intended for the Front, these measure 9.75 inches free length. I can't find an invoice to support the purchase of these.

 

Should I stick with the Rears as they are, but what about the Fronts? Incidentally all appeared to have standard packers / spacers fitted top & bottom. Thanks,

 

Ian

[ChrisR-4A]

Hi Ian, the front springs from Moss which match the rear TT4212 420lbs are the TT4102. 420lbs.

I have these with 5mm poly bushes below, camber and ride height is fine for me.

Regards Chris

[qkingston]

Having driven the car for 700 miles now, the ride height at the rear still seems rather high. I have TT4006 springs at the front and TT4211 at the rear, tyres are 195/65/15. I believe the springs are matched at 390lb and seemed to be recommended as a combination; however the measurements are 38cm front,42cm rear (wheel centre to lower lip of wheelarch), so the rear gap looks high, and there is a nose down angle rather than the other way round. I fitted poly spring insulators (but I didn't record what thickness). Should I change the rear springs for std height, I understand the 4211s are slightly lengthened?

Many thanks

David

[Waldi]

To get 40 mm lower you would have to reduce the insulators by some 25 mm (top and bottom together), seems a lot, unless you have additional spacers as well. So likely lower springs are better.

On my tr6 I have TT4212PR springs, and with a couple of superpro thicker insulators where needed, I have 385 mm rear height. Not sure if this is entirely comparable.

Waldi