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 Posted: 01-15-2017 09:54 am
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NigelK
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Dear All

My GT still leans to one side, about 2cm lower on the right-hand (driver's) side at both the front and rear wheel arches. I've already done all the usually recommended fixes - replaced suspension bushings, tightened bolts with load on the suspension, replaced front and rear coil springs and shock absorbers. When the LSD axle was fitted a few months back, LotusBits reported that the rear lower trailing arm metalastik bushings on the right-hand side were toast, despite being less than 2 years old. There is a noticeable twist in the right-hand side lower trailing arm relative to the axle flanges, which is resulting in the bushing crush tube tearing out of the surrounding rubber. This is shown in the picture below.



The twist of the lower trailing arm seems to be caused by misalignment of the trailing arm mounting holes in the chassis rail, which are at least 1 cm out of alignment inboard to outboard. The picture below shows there has been some fairly significant welding repair to this part of the chassis rail. Incidentally, this is the same chassis rail to which attention was required to the front sub-frame mounting holes, which were also out of alignment inboard to outboard, and incorrectly positioned in the chassis rail itself. This is making me think that a PO did a lot of welding on this chassis rail, but did not re-drill the suspension mounting holes correctly.



It is possible, therefore, that the lean is also attributable to incorrect positioning of the lower trailing arm mounting holes, which are not only misaligned inboard to outboard in the chassis rail but also incorrectly positioned in the chassis rail itself (i.e. just like the mounting holes for the front sub-frame). Remedying the inboard-outboard misalignment should be relatively straightforward. But given the substantial amount of welding all along the chassis rail, how best to reposition the mounting holes relative to the chassis rail? I have drawn a schematic below, which is hopefully clear.



The question is, which direction should the lower trailing arm mounting holes move in the chassis rail, in order to increase the dimension B-B' (and therefore raise the chassis/body on the driver's side, correcting the lean)? The dimension A-A' should be fixed, as it is set by the axle flanges which are fixed relative to the wheel and therefore the ground (assuming constant tyre pressure). My current thinking is that moving the mounting holes down relative to the chassis rail will allow the rear coil spring to expand, lengthening the dimension C-C', and raising the chassis/body. Conversely, moving the mounting holes up relative to the chassis rail will compress the rear coil spring, shortening the dimension C-C', and lowering the chassis/body. Does this sound right?

Many thanks in advance for any thoughts / advice.

Best wishes,
Nigel

Last edited on 08-15-2017 07:44 pm by NigelK

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 Posted: 01-15-2017 01:08 pm
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gmgiltd
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Hi Nigel,
Obvious question I suppose, but have you had the wheel alignment checked front to rear. Things can get twisted when replacing things like sills and floor panels if not done properly. If you take the car to a body shop that specialises in repairs they can check the alignment front to rear and diagonally and also measure the corner weights when the car is level.
It should give you a better idea on what the problem is and if required they should be able to true the datum points. Alignment info is I believe at the back of the workshop manual.
Gordon

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 Posted: 01-15-2017 04:00 pm
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NigelK
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Thanks Gordon, I haven't had the chassis/wheel alignment accurately checked. I've seen places online that offer laser wheel alignment, but don't I also need laser measurement of the chassis as well? I'm not sure what this service is called? Any further suggestions gratefully received. Best wishes, Nigel

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 Posted: 01-16-2017 08:52 am
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NigelK
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I remeasured wheel arch heights this morning, as I've not used the car for several months and wanted to see whether the suspension had leveled off at all. Ground to wheel arch heights are ±5mm at the o/s front, n/s front and n/s rear, which is within the WSM specs. The o/s rear measurement is about 15mm lower than the other wheel arches.

I am wondering whether the o/s rear could be sitting low because of the damage to the o/s rear lower trailing arm bushing caused by misaligned lower trailing arm / chassis mounting holes and/or a twisted lower trailing arm. So I'll replace all the trailing arms and all the bushings (with Superflex PU this time, as it seems the metalastik bushings currently available are not up to the job) and then see where things sit.

Note that newly manufactured suspension components, including upper and lower trailing arms, rose-jointed control arms, and front upper wishbone arms adjustable for camber, are available from Adrian Foreman in the UK (turboade820 on eBay). I bought Adrian's lower trailing arms, and they are solid rectangular section steel and look much stronger than the Vauxhall-sourced originals.

Best wishes,
Nigel

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