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Thread: Straightening a TR4A IRS chassis

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    Jedi Knight Brinkerhoff's Avatar
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    Straightening a TR4A IRS chassis

    I'm working on a TR4A IRS chassis but only have a Robert Bentley manual for a TR250 / TR6 . I wonder are the specs the same for the TR4A ?

    Kevin

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    Obi Wan M_Pied_Lourd's Avatar
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    Re: Straightening a TR4A IRS chassis

    Good question...I'm no TR4A expert but I would think it would be close with some possible differences in the differential carrier area and engine mounts/Trans mount area but dimensionally, it's got to be pretty close.

    I'm sure someone will know for sure.

    Cheers
    Tush
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    Re: Straightening a TR4A IRS chassis

    Hopefully someone with better information will chime in here for you, but like M_Pied_Lourd said they should be fairly similar since they both use the same basic central tub structure. The lower front suspension pick up points are different (single stud mount vs dual stud mount) than the later cars but as far as I know are in the same position. Engine mount stuff is different but that shouldn't impact the basic frame dimensions. I do know that the rear trailing arms are slightly different on the TR4A vs the later cars but I don't know if that translates into a different set of measurements in that area of the frame or not.

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    Great Pumpkin TR3driver's Avatar
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    Re: Straightening a TR4A IRS chassis

    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

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    Jedi Warrior
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    Re: Straightening a TR4A IRS chassis

    There are TR4 frame dimensions however on what page are the TR4A frame dimensions?

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    Great Pumpkin TR3driver's Avatar
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    Re: Straightening a TR4A IRS chassis

    Quote Originally Posted by JerryVV View Post
    There are TR4 frame dimensions however on what page are the TR4A frame dimensions?
    5-104 (256 of 331)

    If you download it and open the bookmarks panel (I have mine set to open by default), expand the "Frame" bookmark and it has "TR4A" under it. I should probably write a proper "Contents" page, but the original manual didn't have one and ...
    Randall
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    71 Stag LE1473L waiting engine rebuild
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    Re: Straightening a TR4A IRS chassis

    Quote Originally Posted by TR3driver View Post
    5-104 (256 of 331)

    If you download it and open the bookmarks panel (I have mine set to open by default), expand the "Frame" bookmark and it has "TR4A" under it. I should probably write a proper "Contents" page, but the original manual didn't have one and ...
    Thanks,

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    Re: Straightening a TR4A IRS chassis

    I tried to download the manual to do the work myself, but it didn't take (probably a problem on my end). But I am very curious, convential wisdom says the 4a begat the TR250, which was a 4a with the TR6 motor and racing stripes. The TR250 begat the TR6, which was a TR250 with a new body. You'd think the frames would be the same with the exception of some mounting points, but curious if the same dimensions are published for both.

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    Yoda Marvin Gruber's Avatar
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    Re: Straightening a TR4A IRS chassis

    I am putting a TR6 frame under a TR250 now. Don't see any issues or mods needed. I thought about going the other way and using a solid axle 4A frame to get rid of the IRS axles.
    Marv

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    Re: Straightening a TR4A IRS chassis

    Quote Originally Posted by glemon View Post
    I tried to download the manual to do the work myself, but it didn't take (probably a problem on my end). But I am very curious, convential wisdom says the 4a begat the TR250, which was a 4a with the TR6 motor and racing stripes. The TR250 begat the TR6, which was a TR250 with a new body. You'd think the frames would be the same with the exception of some mounting points, but curious if the same dimensions are published for both.
    I am curious about that dimensional thing myself between the TR4A and the TR250/TR6 frames since the TR4A trailing arms are different. It won't be able to dig into it this week but maybe next I'll get a chance to sit down and compare the two sets of dimensions.

    Quote Originally Posted by Marvin Gruber View Post
    I am putting a TR6 frame under a TR250 now. Don't see any issues or mods needed. I thought about going the other way and using a solid axle 4A frame to get rid of the IRS axles.
    Marv
    I know that the TR250, TR5 and the "CC" and the "CP" series TR6s used the same frame. The frame was changed with the "CF" and "CR" series TR6s. This also coincided with a change to the rear transmission mounts but as long as you use a rear mount set up compatible with the transmission w/ or w/o OD fitted to the car, I'm not aware of anything off hand that would keep anyone from fitting any TR6 frame under a TR250/TR5.

    As for going with a solid axle TR4 frame, I don't see that being worth while. First off you would need to redo all the engine mounting stuff, then you would probably want to change out the lower front suspension pivot bracket mounts to the later two stud style. The real kicker though is that you would still have what I consider to be the overriding weak point of the TR IRS frame and that is the narrow waisted section at the rear of the cockpit that makes the TR6 a bit of a Flexible Flyer. The solid axle TR4A was something that they cobbled together to shut up dealers in the NA market and to reduce the amount of the price increase of the 4A over the 4. The IRS cars carried a premium of about $150 over the solid axle 4A IIRC (hey, I was a kid then and it's been a loooooong time ago). They essentially hung a bracket off where the outer trailing arm pivot bracket mounts and used that as the front spring mount and used the existing bracket toward the rear of the frame for the other end. If you could round up all the rear parts from a solid axle 4A I can't think of any real show stoppers off hand that you would keep you from building solid axle variant using a TR6 frame.

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    Great Pumpkin TR3driver's Avatar
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    Re: Straightening a TR4A IRS chassis

    Whoops! Turns out the "Optimize scanned document" function was not kind to the frame dimensions diagram. I'll rescan it, fix the PDF and also post here, sometime this evening.
    Sorry bout that, I'm still learning how to drive the tools I have.
    Randall
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    Re: Straightening a TR4A IRS chassis

    I'm not quite sure I understand the question. Do you have a bent frame and need dimensional info to straighten it, or do you just need to check it for straightness?

    If the latter, that should be pretty simple. Even if you don't have the dimensions, you can check it for symmetry, and that might be enough. Not much chance that features on opposite sides would be bent identically. In any case, here's what I did: http://www.nonlintec.com/tr4a/frame/#dims.
    Steve Maas
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    Great Pumpkin TR3driver's Avatar
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    Re: Straightening a TR4A IRS chassis

    Ok, let's see how this works. If I'm lucky, you should be able to click on the thumbnail and get a nice large scale image
    5-104 combined (don't reduce) 300.jpg
    Randall
    56 TR3 TS13571L once and future daily driver
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    Great Pumpkin TR3driver's Avatar
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    Re: Straightening a TR4A IRS chassis

    Here's a link to the TR4A frame drawing (in high res, click in the image for even higher)
    https://i.imgur.com/C22Fk5a.jpg
    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

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    Re: Straightening a TR4A IRS chassis

    Quote Originally Posted by Sarastro View Post
    I'm not quite sure I understand the question. Do you have a bent frame and need dimensional info to straighten it, or do you just need to check it for straightness?

    If the latter, that should be pretty simple. Even if you don't have the dimensions, you can check it for symmetry, and that might be enough. Not much chance that features on opposite sides would be bent identically. In any case, here's what I did: http://www.nonlintec.com/tr4a/frame/#dims.
    I should have really done this double check of my frame after I got it back from the shop. I never got the warm and fuzzy that the frame was REALLY straightened correctly. Too late now I guess unless there is a way to do it with everything on. Probably the reason my passenger side as really bad camber.
    Gary
    1962 (Nov Build) Triumph TR4 CT/16836L Restoration in process

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    Jedi Knight Brinkerhoff's Avatar
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    Re: Straightening a TR4A IRS chassis

    Thanks for the help guys ! Thanks Randall for the better quality image. The Bentley manual for the 250/ TR6 gives setup dimensions to check for a twist that the TR4 manual does not. Mine has suffered a hit to the rh front causing a slight twist. There is no rust on it fortunately. I have a friend with a frame rack that will set it up and straighten it for me , I want to give him all the measurements before I take it in. I'll update.

    Kevin

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