pfenlon Posted February 9 Report Share Posted February 9 I suppose the subject has been debated many times , but the last mention of it in Traction, made me just check the studs in my trailing arms, which were fortunately as spec @14 ft lbs. Watching Elin Yakovs answer to the stud problem, was a simple way of repair for the DIY TR men. (on you tube, rusty beauties TR6 trailing arm stud repair) basically he removes the 1/4" studs, drills the trailing arm a little deeper and fits 5/16" studs, turned down and the outer part of the stud tapped at 1//4" A lathe is required to make up the studs from a 3/8" bolt. Its worth a look or how did you do it? Quote Link to post Share on other sites
Motorsport Mickey Posted February 9 Report Share Posted February 9 (edited) Nearly Peter, The studs are not 1/4" they are 5/16".UNF thread both ends. The repair back to standard is to use 5/16UNF Helicoils, this means drilling the holes out to the tapping size for a 5/16th UNF Helicoil which is 0.328 thou tapping size. Now these studs are drilled and tapped into alloy blocks which abut the trailing arm central hole dia, unfortunately these blocks were made by the apprentice (a YTS probably) who set the position in the mould for the blocks to be formed. He had only had the job 3 weeks, and he was drunk when he came back from lunch so the block positions can be variable, and I've seen numerous trailing arms where the hub studs have broken through the side wall of the trailing arm hole. Now when the studs strip out of the trailing arm, the 5/16th thread pulling out leaves the hole as 5/16th Dia,...that's handy ! .312 thou Dia is the tapping dia for a 3/8th UNC tap, so just tap the hole 3/8th UNC. So my suggestion is keep more material in the trailing arm (I know it's only 16 thou on the dia, but every little helps prevent the stud breaking through) and either buy 3/8" UNC - 5/16" UNF staggered studs and use standard 5/16" UNF nuts, or use 3/8" UNC cap head bolts with the hubs drilled out from 5/16th to 3/8th (my choice). It's what the racing lads do. Mick Richards Edited February 9 by Motorsport Mickey Quote Link to post Share on other sites
pfenlon Posted February 9 Author Report Share Posted February 9 I stand corrected Mick, the original studs are 5/16" as you say, and Elin replaces with a 3/8" to 5/16"stud. The 3/8 UNC to 5/16 staggered studs is for me the answer. Where can you buy the above studs please. Quote Link to post Share on other sites
Dave McDonald Posted February 9 Report Share Posted February 9 Pete, Classic Car Developments (CDD) sell a stepped stud for this, one end oversize 3/8” unf to fit into the trailing arm and other end 5/16” unf to carry the hub as standard. My reticence would be that, as Mick mentions eloquently above, some of the localised “blocks” incorporated around the rim of the trailing arm are very marginal for drilling oversize. This has the potential for the drill/tap to break through the outside. My own solution as a “racing lad” has been to replace the 5/16” unf tappings with 5/16”unc helicoils and use unc cap head screws rather than studs and nuts. Many years of satisfactory use on race TR6 with wide sticky tyres and high corner side loads. Use standard torque, 16 lb ft, though I do check them every 2 or 3 race’s just to be sure. Dave McD Quote Link to post Share on other sites
Motorsport Mickey Posted February 9 Report Share Posted February 9 Dave, Slight correction to your prose..."one end oversize 3/8” unf to fit into the trailing arm and other end 5/16” unf ". The trailing arm thread end is actually 3/8"UNC which fits in the 5/16th dia stripped or drilled to that dia holes. Mick Richards Quote Link to post Share on other sites
Dave McDonald Posted February 9 Report Share Posted February 9 Hi Mick, I bow to your superior knowledge. How’s the TR4 restoration going? Dave Quote Link to post Share on other sites
Motorsport Mickey Posted February 9 Report Share Posted February 9 Hi Dave, Very slowly at present, we were due to go on a Panama holiday early December but we had injections for Covid, Flu and the Pneumonia jab within a week in November and Margaret has been very unwell with reactions. So the cruise went down the pan with her very dizzy and her blood tests showed up a few abnormal readings which we think are the results of the cocktail of of injections. Currently I'm head cook and bottle washer, so time is stretched and we are on weekly doctor/hospital./Scan visits, I'm sure hope that all will shortly settle and I can progress a little further. Your rebuild seems to be coming on well again. regards Mick Richards Quote Link to post Share on other sites
Lebro Posted February 9 Report Share Posted February 9 1 hour ago, Dave McDonald said: My reticence would be that, as Mick mentions eloquently above, some of the localised “blocks” incorporated around the rim of the trailing arm are very marginal for drilling oversize. This has the potential for the drill/tap to break through the outside. My own solution as a “racing lad” has been to replace the 5/16” unf tappings with 5/16”unc helicoils and use unc cap head screws rather than studs and nuts Dave McD Surely by the time you have tapped the thread for the 5/16" helicoil, you end up removing about the same amount of metal as if you just went for the 3/8" tap. My preference would be go for the stronger 3/8" UNC stud. Bob Quote Link to post Share on other sites
Dave McDonald Posted February 9 Report Share Posted February 9 Put like that, you could be right Bob. I’ll stick with what I’ve got now. Dave McD Quote Link to post Share on other sites
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