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Paul J

Trailing Arm Chassis

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Hello all

Thought I would share this repair discovery with you.

 

Having recently bought a 73 CR home market TR6 project that only required cosmetic attention I have been looking at what I feel is actually needed to put the car in a good roadworthy condition.

 

It appeared that the chassis had never been parted from the tub so I decided to remove all the chassis mountings to re align the panels etc, having gone so far it would have been foolhardy not to part the tub and give the chassis a thorough inspection paint and clean.

 

It was then I discovered the replacement of the trailing arm sections of the chassis which had obviously been replaced with the body and chassis intact, in my view this is not a practice to be encouraged, the chassis section was only welded in place bottoms and sides, no attachment to the top rail of the chassis at all, the top T shirt plate had no structural duty at all having been cut to remove the old chassis members. Have now replaced the top T shirt plate and welded all tops of the trailing arm chassis, hopefully the chassis has not lost a great deal of its original shape.

 

Not having driven the car the way it was I cannot comment on the effect this repair may of had on the handling but can only assume how much flexibility the chassis would have had without a top T shirt plate functioning.

This type of repair to the trailing arm chassis has been regarded as a cheap quick fix repair but surely not one I would advise.

 

Paul

 

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If you’ve gone that far I would get the kit and box in the diffpins and the front suspension lower wishbone gussets!

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That was last weeks project Dave, I removed the rear bridge as it had cracking on the upright where it meets the chassis, repaired it and boxed it. Also boxed the front bridge mounts and plated the top which was also badly fractured.

Paul

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Hi Paul,

Obviously you know what you are doing, but since very important, I still mention it:

Also carefully check the front suspension brackets welded to the chassis, there may be hair-line cracks, not easily deteced when painted or dirty.

Mine only showed up after grit blasting, when oil that had penetrated over the years in the narrow cracks bleeded out.

Regards,

Waldi

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Hi Paul,

Obviously you know what you are doing, but since very important, I still mention it:

Also carefully check the front suspension brackets welded to the chassis, there may be hair-line cracks, not easily deteced when painted or dirty.

Mine only showed up after grit blasting, when oil that had penetrated over the years in the narrow cracks bleeded out.

Regards,

Waldi

Thanks Waldi I will give them a good looking at. Going to strip the front suspension to replace all bushings with Poly. Thankfully under all the paint the chassis is not so bad, pleased I made the effort to remove it though as it was rather fatigued in the usual places.

Regards

Paul

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Not welding the top of the trailing arm sections is very bad, in the past there have been a couple of dealers who will replace these sections with the body in place but their method, not for the purist, was to cut and bend up a section of the rear floor thus gaining access to the top of the chassis. The floorpan was then bent back the cuts welded up and cleaned up and barely visible. If there is no other reason to take the body off then seems like a reasonable solution.

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Waldo, out of interest when you removed the chassis what were the top faces like of all the box sections, were some better than others?

Chris

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Gaining access through the floor to weld the tops would be quite acceptable Chris but to leave them un-welded both ends was not good.

Paul

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Waldo, out of interest when you removed the chassis what were the top faces like of all the box sections, were some better than others?

Chris

Hi Chris,

My chassis had limited corrosion, to my surprise (EU TR6).

The top of the entire chassis had no corrosion, despite having only one layer of black paint to the bare metal.

The upper T-shirt however had bubbles on a couple of places, which looked pretty harmless, until I removed the corroded parts.... the chassis below had rotten away (upper part only). I welded in new plates and then a new T-shirt, ensuring there was a proper connection to the TA chassis sections.

Waldi

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Not welding the top of the trailing arm sections is very bad, in the past there have been a couple of dealers who will replace these sections with the body in place but their method, not for the purist, was to cut and bend up a section of the rear floor thus gaining access to the top of the chassis. The floorpan was then bent back the cuts welded up and cleaned up and barely visible. If there is no other reason to take the body off then seems like a reasonable solution.

 

 

Done this very thing - just last week on 4A,

simple, safe and tidy.

 

No - probs.

 

John.

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Had the same issues on my chassis when I removed the body.

http://72tr6.blogspot.com/2014/

It handled OK, and scarily we even took it around Spa Grand Prix circuit in this condition..

Cheers

Tim

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