TR4A1965 Posted June 3, 2015 Report Share Posted June 3, 2015 Thought you might like to see this unusual chassis strengthening mod by John Gardner in Australia. Best wishes. Paul. Quote Link to post Share on other sites
stuart Posted June 3, 2015 Report Share Posted June 3, 2015 Not entirely unusual though normally fitted straight front to back as it gives more strength between the 4 mounts. Stuart. Quote Link to post Share on other sites
TR4A1965 Posted June 3, 2015 Author Report Share Posted June 3, 2015 I still have time to make it as the body is not on. I was wondering if it would add real value in strength terms. I think the front to back mod as oppose to the angle would make more sense as Stuart says? Thoughts? Best Paul. Quote Link to post Share on other sites
Tr4Tony Posted June 3, 2015 Report Share Posted June 3, 2015 Hi If you think about what's happening in the rear of the IRS cars, the sort of strengthening that's advantageous becomes a bit clearer. I've been through this with my own 4a and a TR5. In the first instance, the chassis tends to 'rotate' about the narrowest point, ie just behind the breast plate, so if you are putting considerable extra power into the engine and / or running a higher CW&P ratio (say greater than 4.1:1 for arguments sake) then it's worth reinforcing the chassis here by adding horizontal fillets top and bottom connecting the inside of the outriggers to the breast plate. Do this above and below. You need to be careful of clearances up and down of the Propshaft and IRS castings but this is very effective. Some also all additional side to side circular cross tubes but this probably isn't necessary unless you're racing or rallying. Secondly, the 'diff mounting bridge' does two main jobs in mounting the DAS10 type lever arm shock absorbers and holding the diff assembly in place. The main source of twisting load is in transmitting power from the prop to the diff and driveshafts, usually at varying rates to each of the three attachment points depending on the wide variety angles caused by cornering, accelerating and braking. Anything you can do to keep this 'bridge' straight and true will help reduce twisting loads and consequentially movement and cracking enormously. I've made attached a stiffener front and aft on an IRS chassis and in that order they are beneficial. The shock mountings tend to be adequate in themselves, however the welding which attaches the base of the 'bridge' to the chassis is sometimes a bit weak, so here again it's a question of adding small 'filleting' pieces along the line of the chassis rail and re welding the joints does that job. If you're adding telecscopic shocks yiu need to think carefully in how they attach and associated 'punching' loads where they bottom out / exceed the bump length. Lastly the common modification of 'boxing in' the diff mounting pins and adding 3 inch or so discs of steel round the tops of the pins to spread the punching load is proven to stop them either bending, dropping out or being punched up. By adding about 3 kgs of steel in the right places you can make a substantial improvement to the rear of an IRS car, all of which shows in the handling of the car and also in the amount of wear experienced over time. Hope this is useful. Regards Tony Quote Link to post Share on other sites
TR4A1965 Posted June 3, 2015 Author Report Share Posted June 3, 2015 Amazing response Tony. Many thanks. I have fitted the CTM chassis strengthening kit and it has many of the additions you highlight. The work we did can be seen here: http://tr4a.weebly.com/chassis-strengthening-kit-welding.html And, you can see the strengthening kit as supplied by CTM here: http://tr4a.weebly.com/ctm-chassis-strengthening-kit.html What I have not done is go for the diff bridge to to spring bridge that sits above the prop (Breast plate?) Looks like it is well worth doing? Best Paul. Quote Link to post Share on other sites
Tr4Tony Posted June 3, 2015 Report Share Posted June 3, 2015 Hi Paul Yes indeed - I hadn't realised that CTM had manufactured a kit but this is all worth doing. The front kit goes without saying as this is mainly as the factory recalled / reissued. Worth also noting that I've seen an u modified 4a with the front suspension torn off the chassis after a couple of hours on an airfield based rally, so this modification as I've done myself works too. Regards Tony Quote Link to post Share on other sites
TR4A1965 Posted June 22, 2015 Author Report Share Posted June 22, 2015 (edited) After seeing John's mod on the chassis early this month I thought I would do the same. Although I took up Stuart's advice and positioned them so they were straight. There is a video on my home page here http://tr4a.weebly.com. And there should be a picture below comparing the two. Click the thumbnail for a bigger picture. Best wishes. Paul. Edited June 22, 2015 by TR4A1965 Quote Link to post Share on other sites
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