TR4A vs TR4AIRS chassis, is there any differences ?

[Tr4aJim]

40 minutes ago, stuart said:

Ive abused the life out of mine in the 30 yrs I`ve had it plus it was a New Jersey car from new and you know what their roads are like and my axle is fine, so I wouldnt worry that much.

Stuart, the fact that your car survived both our potholes and our, shall I say “spirited” drivers, is a testament to the design!

Jim

[Chris59]

3 hours ago, stuart said:

TBH  would find a TR4 chassis and use the IRS shell, The rear main floor mounts need a bit of altering and you`d need to cut a hole in the floor for the handbrake and remove the IRS handbrake mount on the tunnel but thats it and its bound to be easier that way round I would have thought especially if you have all the TR4 running gear.

Stuart.

 

Many thanks to all contributors, especially to Stuart : I'll follow your recommendations, ie buy a good TR4 chassis and use the IRS shell.

Lady Anne will help me in finding where to cut the floor.

Cheers !

[Malbaby]

IMHO....I would buy a IRS chassis [more plentiful, and probably in better condition] and modify it to suit the live axle [if that is your preference].

The IRS chassis that was used for a factory live axle install is a poor design, and the rear will flex and twist even more than the factory IRS fixed diff due to extra load placed on the rear ends of the chassis rails.

For the IRS chassis with a live axle, I would weld in an additional outer chassis rail to bridge the space left by the deleted IRS swing arm....Similar to the original TR4 chassis design which has continuous outer chassis rails...[plus other strengthening modifications]

[Andy303]

20 hours ago, Malbaby said:

IMHO....I would buy a IRS chassis [more plentiful, and probably in better condition] and modify it to suit the live axle [if that is your preference].

The IRS chassis that was used for a factory live axle install is a poor design, and the rear will flex and twist even more than the factory IRS fixed diff due to extra load placed on the rear ends of the chassis rails.

For the IRS chassis with a live axle, I would weld in an additional outer chassis rail to bridge the space left by the deleted IRS swing arm....Similar to the original TR4 chassis design which has continuous outer chassis rails...[plus other strengthening modifications]

While I agree some reinforcement may be good idea for either the IRS or the SRA chassis in the "tee shirt" area, I think the coil spring bridge likely indues more twist in that area than the rear leaf spring shackles do as the IRS load taken by the coil springs is transmitted through a cantilevered structure above the plane of the main frame. That said, I have no analysis to back to up my claim, but only the "seat of the pants" experience to say I can't notice any twisting in real world driving, at least not within my comfort zone which may well be lower than some folk. The SRA is still a blast to drive.

Edited November 19, 2023 by Andy303

[Efuentes]

I have read that the TR4 chassis is more rigid and has not the problem of the TR4A chassis by which the front and rear ends bend downwards, causing funny door gaps where the gap opens up at the upper part of the door

[John Morrison]

On 11/18/2023 at 7:13 PM, Chris59 said:

 

Many thanks to all contributors, especially to Stuart : I'll follow your recommendations, ie buy a good TR4 chassis and use the IRS shell.

Lady Anne will help me in finding where to cut the floor.

Cheers !

Following on from what others have said, especially the advice on using a TR4 chassis, with your bodyshell.

 

It is possible to use the TR4A type handbrake, with a tr4. We had an aged member who because of a weak wrist struggled with the TR4 set up, and I made him a kit of everything needed to use the 4A system, it should really boil down to what you are most comfortable with - what are used too.

 

John.

[SuzanneH]

On 11/18/2023 at 7:13 PM, Chris59 said:

 

 

Lady Anne will help me in finding where to cut the floor.

 

Remembering our dearly departed Badfrog, very very fond memories 

[Chris59]

4 hours ago, John Morrison said:

Following on from what others have said, especially the advice on using a TR4 chassis, with your bodyshell.

 

It is possible to use the TR4A type handbrake, with a tr4. We had an aged member who because of a weak wrist struggled with the TR4 set up, and I made him a kit of everything needed to use the 4A system, it should really boil down to what you are most comfortable with - what are used too.

 

John.

Interesting point, John, thanks, this solution is certainly a + for the confort of the passenger (in a LHD car).

On this IRS bodyshell, the handbrake lever' box as already been removed from the tunnel, so I'll keep the Tr4 fly off system.

[Chris59]

58 minutes ago, SuzanneH said:

Remembering our dearly departed Badfrog, very very fond memories 

I'll never forget my soul mate, dear Suzanne 

[Tr4aJim]

Chris, just wanted to mention that though the 4 and 4A are both “fly-off”designs, the TR4 handbrake system has a better “leverage” design than the TR4a system. In other words, more upward force is required on the 4A handbrake lever to achieve the same braking effect.

That said, the handbrake on my 4A once saved my wife and I after a hydraulic brake failure at speed.

Jim

[Chris59]

15 hours ago, Tr4aJim said:

That said, the handbrake on my 4A once saved my wife 

Did you disconnect it for the next try ? I'm far, tin hat on 

Edited November 22, 2023 by Chris59

[Tr4aJim]

Well it could have been the other way around! I did see her in the garage before we left!!!

Jim

[Paul Lovell]

Yes, the TR4A rigid axle chassis does not have the cross-piece for the coil springs. As has been said before, the front mounting for the leaf spring is a bracket bolted to the outrigger, which is the same location as the outer semi-trailing arm mounting. The rear leaf spring mounting is on the rear cross-tube outboard of the rear chassis legs. However, the TR4A chassis differs from the TR5 and 6 chassis in that there is a sort-of trapezoidal pressing welded to the inboard ends of the rear chassis legs, in front of which is a ribbed arch which goes over the propshaft. Judging by the shape of it, it was probably intended to provide some torsional stiffness to the TR4A rigid axle chassis as the coil spring crosspiece was missing.  The TR5/6 chassis does not have this, as the live axle was not an option. The other difference is that the studs used for the rear diff. mounting were not needed so were omitted from the cross-member used to mount the rear dampers. There's a good photo' of the rigid axle chassis in Graham Robson's 'The Triumph TRs A Collector's Guide'.

The bodyshell of the TR4A differs from that of the TR4 in that the rear, inner wheelarches are different. This could be to avoid the IRS coil spring cross piece but I don't know for certain. However, John Hill states on his website that the rear trim is different (and you can see this if you study side-by-side photo's), and the TR4A parts list shows that the part number for the rear, inner wheelarches is not the same as for the TR4, whereas all the other parts around it, such as the rear, inner wings, boot floor, etc, were carried over.

Paul

[stuart]

4 hours ago, Paul Lovell said:

Yes, the TR4A rigid axle chassis does not have the cross-piece for the coil springs. As has been said before, the front mounting for the leaf spring is a bracket bolted to the outrigger, which is the same location as the outer semi-trailing arm mounting. The rear leaf spring mounting is on the rear cross-tube outboard of the rear chassis legs. However, the TR4A chassis differs from the TR5 and 6 chassis in that there is a sort-of trapezoidal pressing welded to the inboard ends of the rear chassis legs, in front of which is a ribbed arch which goes over the propshaft. Judging by the shape of it, it was probably intended to provide some torsional stiffness to the TR4A rigid axle chassis as the coil spring crosspiece was missing.  The TR5/6 chassis does not have this, as the live axle was not an option. The other difference is that the studs used for the rear diff. mounting were not needed so were omitted from the cross-member used to mount the rear dampers. There's a good photo' of the rigid axle chassis in Graham Robson's 'The Triumph TRs A Collector's Guide'.

The bodyshell of the TR4A differs from that of the TR4 in that the rear, inner wheelarches are different. This could be to avoid the IRS coil spring cross piece but I don't know for certain. However, John Hill states on his website that the rear trim is different (and you can see this if you study side-by-side photo's), and the TR4A parts list shows that the part number for the rear, inner wheelarches is not the same as for the TR4, whereas all the other parts around it, such as the rear, inner wings, boot floor, etc, were carried over.

Paul

The arch on the chassis is also on the IRS cars as they only have the lower T shirt. The only difference in the rear wheel arches are the addition of the bump stop brackets

Stuart.

[KiwiDave]

I went the opposite way (leaf spring to IRS) with a 4A chassis - see my blog on the main website - https://www.tr-register.co.uk/rebuilders-diary/2022/01/0196/19667-TR4A-Restoration-Part-3

The only other minor detail is the IRS chassis has a small bracket for the brake hose on the RHS just behind the strengthening bridge, which you can cut off, or leave it unused.

The rear inner wheelarches are different as the bumpstop brackets have a captive nut for the rubber to screw into.  Later cars has the rubber on the trailing arm and the bracket was plain.