cutting and re-welding the chassis

[PedroFJ45]

i'm doing some research on shortening my LWB 1976 fj45 by cutting the chassis in order to improve departure angle at the rear. i'm planing on doing a triangulated 4 link so wont need the extra length for spring perches.
i've asked a few ppl about cutting and welding the chassis and have been told to bolt the chassis ends back together as welding will crack over time. but after reading some build threads i've notice some ppl seem to have stitch welded their chassis along the boxed section.
does this allow you to then weld up the chassis ends without worry or does this crack over time too??
a lot of ppl box the rest of the chassis as well, do both these things need to be done for this to work or can u do one without the other?
btw i've searched multiple times for this and am yet to find a definative answer, but i may have missed something, if so point me in the right direction please.

 

[Bret]

I would start with a weld area at least twice the vertical distance of the frame where you cut it and use fish plates to help strengthen it. You may try searching for companies that refit commercial trucks (esp agriculture), they should have a process to do just what you are planning. Expect the official answer to include preheating and post heating.

Or just weld it up and keep an eye on it

 

[4rnr]

First off....this is the rear of your frame after the axle and you are now a 4 link?.... You dont need to worry about much, that frame see's very little stress anymore.

But dont make a verticle weld on the frame either in the joining or the scabbing... I suggest notching the frame, then welding it. Then bridging the joint with a scab plate (again with out a verticle weld) and maybe a few rosette (sp) welds.... That should be the strongest part of the frame after that point....even though now that you are 4-linked, it see's less stress than any other part of the frame.

Oh and preheat/postheat isnt necessary...only for cast iron.

 

[Bret]

Here is some stuff that may help.

Tips on truck frames

Cutting Truck Frame - WeldingWeb™ - Welding forum for pros and enthusiasts

 

[PedroFJ45]

as yet not a 4 link, but i'm trying to do my research b4 jumping in and screwing it up, again its the rear i'm worried about. because its a rivoted chassis the chassis flexes doesnt it? therefor there'd be stresses due to the contortion of the chassis. would notching and staying away from vertical welds help with this issue?? i've been told u can get chassis bolts which will allow flex, but would they be as strong??

thanks for the replys

 

[4rnr]

as yet not a 4 link, but i'm trying to do my research b4 jumping in and screwing it up, again its the rear i'm worried about. because its a rivoted chassis the chassis flexes doesnt it? therefor there'd be stresses due to the contortion of the chassis. would notching and staying away from vertical welds help with this issue?? i've been told u can get chassis bolts which will allow flex, but would they be as strong??

thanks for the replys

A non-verticle weld is to avoid breaking the frame...due to metalurgy/the grain of the steel, i guess....a vericle weld is likely to cause the frame to crack at the weld.

*I no nothing of/about a "riveted frame"* But I still dont think there should be a problem, lots of people stiffen up a 40 frame either on purpose or by simply adding x-members for t-cases, links, anti-wrap bars, shock mounts, etc...

as far an flexy chassis bolts....are sure you arent crossing over in the world of heavy/towing equipment (IE semi's etc...) where the chassis' ability to twist ALOT is what keeps it from breaking?

 

[rusty_tlc]

If I read your post correctly you are planning to bob the rear and replace the rear cross member. Then you want to do a 4-link rear suspension. I assume you will triangulate off a new cross member located mid frame some place.

IMHO with a 4 link rear suspension you will eliminate a lot of the stress on the rear section of the frame and it really won't matter if you bolt or weld the new rear cross member in place.

 

[PedroFJ45]

thank everyone ofr ur help , it seems the general consensus is that it should be fine to weld the chassis so long as i dont do vertical welds and do the four link conversion.

thanks again for people's input appreciate it.