JPD Posted September 1, 2014 Report Share Posted September 1, 2014 Can anyone tell me if there are 2 standards of rear bump stops for a 4A? (the large bracket under the wheel arch). The ones from my 67 4A that I'm rebuilding have a hexagonal 35mm spacer between the bracket and the rubber, that screws into a captive nut on the inside of the bracket. The rubber is also about 35mm. These need replacement/repair and I've found some replacements, but although the bracket itself is the same overall dimension, it doesn't have the spacer, just a longer rubber. On the replacements, the bottom tip of the rubber is positioned about 30/40mm higher than my originals, so the trailing arm will travel further before hitting the bump stop. Not sure if the replacements are from a 4A, 5 or 6. This is probably difficult to visualise from my description and I'll try to post some pics later. Jeff Quote Link to post Share on other sites
stuart Posted September 1, 2014 Report Share Posted September 1, 2014 (edited) Sounds like you may have TR5/6 ones which screw onto a plinth on top of the trailing arms. They are wrong for your application so send them back and get the correct ones. You need part number 140290. Stuart. Edited September 1, 2014 by stuart Quote Link to post Share on other sites
JPD Posted September 1, 2014 Author Report Share Posted September 1, 2014 Stuart It's the whole bracket assy I need to replace as it's badly corroded. The attached photo of my old one (on the left) and the replacement on the right shows the differences. Quote Link to post Share on other sites
stuart Posted September 1, 2014 Report Share Posted September 1, 2014 Bit difficult to see from the picture but I would say that neither is correct, I think you should have something like this. Stuart. Quote Link to post Share on other sites
RogerH Posted September 1, 2014 Report Share Posted September 1, 2014 Interesting. My 67 4A had the stops with the hexagonal base. I think the rubber may unscrew from this. I think I have the later shorter variety fitted now. Roger Quote Link to post Share on other sites
JPD Posted September 1, 2014 Author Report Share Posted September 1, 2014 Hopefully this pic is a bit easier to see what the differences are. Roger - Have you had any problems with the shorter stop? There seems to be about 1.5 inch difference between the position of the rubber on my old one than the replacements. I think what I'm going to have to do is rebuild the bracket and then attach a new rubber to it - but is the rubber stop position critical? Jeff Quote Link to post Share on other sites
RogerH Posted September 1, 2014 Report Share Posted September 1, 2014 Hi Jeff, I have Koni struts on the back and these have their own built in stops. I've not experienced a problem. However it is possible to snap the attachment of the back of the 'trailing arm' if it all goes awry. Roger Quote Link to post Share on other sites
stuart Posted September 1, 2014 Report Share Posted September 1, 2014 What you would need to do to check criticality is remove the road spring and push the trailing arm up until it contacts the rubber stop. If the shock absorber bottoms out first before the trailing arm hits the rubber then it is possible to snap the rear section of the trailing arm. Stuart. Quote Link to post Share on other sites
LGFromage Posted September 1, 2014 Report Share Posted September 1, 2014 Your original bump stop seems fine to me so it would make sense to refurbish/make new at the same time as maintaining the height. It is not a good idea to over compress a spring. Tim Quote Link to post Share on other sites
AlanT Posted September 2, 2014 Report Share Posted September 2, 2014 My 65 4A IRS is as per Stuart's picture. Quote Link to post Share on other sites
LGFromage Posted September 2, 2014 Report Share Posted September 2, 2014 My 67 4A is as per Jeff's picture! What a difference a couple of years make. Tim Quote Link to post Share on other sites
stuart Posted September 2, 2014 Report Share Posted September 2, 2014 (edited) Its possible that the factory decided on the change as the circular base doesnt spread the load that well as I have seen some where the stop has been punched up into the box. The squarer base would spread the load better. The factory changed the spring rate when they went to the later style of bump stop on the TR5 as well. Stuart. Edited September 2, 2014 by stuart Quote Link to post Share on other sites
Peter Cobbold Posted September 2, 2014 Report Share Posted September 2, 2014 Bottoming the rear suspension on an over-long bumpstop can give alarmingly fast over-steer. Quote Link to post Share on other sites
Geko Posted September 2, 2014 Report Share Posted September 2, 2014 when you end up with this you're probably better off having an hexagonal spacer to work with. Possible why they changed it. Mine is 66 reg w com# 65808 Quote Link to post Share on other sites
JPD Posted September 2, 2014 Author Report Share Posted September 2, 2014 Thanks for the info and advice, it seems there is a variety of standards on these cars!! I haven't yet decided what rear suspension set up I will be using. It will either be lever arms or the Revington telescopic set up. Once I've bottomed that out and have the dampers fitted I'll do Stuarts test before I weld refurbished brackets and bump stop in place at the appropriate height. Jeff Quote Link to post Share on other sites
stuart Posted September 2, 2014 Report Share Posted September 2, 2014 when you end up with this you're probably better off having an hexagonal spacer to work with. Possible why they changed it. Mine is 66 reg w com# 65808 The square shaped one is just as susceptible to the bump rubber breaking off as its the usual steel to ally reaction problem. Stuart. Quote Link to post Share on other sites
Geko Posted September 2, 2014 Report Share Posted September 2, 2014 (edited) The square shaped one is just as susceptible to the bump rubber breaking off as its the usual steel to ally reaction problem. Stuart. I mean it's probably easier to remove the bump stop assembled with the hexagonal spacer which you can handily undo with a spanner unlike the circular one. Edited September 3, 2014 by Geko Quote Link to post Share on other sites
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