Converting rear straight axle to independent rear suspension

[DatDime1972]

Hello fellow ratsun friends,

 

I am fairly new to this datsun world. Just last year I picked up a 1972 datsun 510 sedan (4 door). My plans for the car are to do a complete resto mod. I will be installing an sr20det which I have came to find out it has been done plenty times. I wanted to reach out in hopes that I can get help/advice from the professionals on something that came up. After purchasing the car I began my search on different options for engine, suspension, wheels/tires etc. Well I came to find out that I bought a mexican imported 510. It has a straight axle in the rear with leaf springs. I am now trying to convert it to an IRS setup. The obstacles that need to be addressed seem to be cutting the wheel well and making strut housings for the new coilovers being installed. Also,  it looks like I dont have frame rails that run all the way to the back for the mounting of the new differential. My question is; if there is anyway to get measurements for these things to be fabricated? Has anybody else done something like this? I appreciate your guys help in advance. I am excited to become part of this community. 

 

Thank you,

 

DatDime1972  

[datzenmike]

For an SR20 I would keep it solid axle and swap the H-190 from a 510 wagon in. The H-190 is much larger and stronger than the R-165 in the IRS. By the time you add enough spring and shock stiffness you might as well have a solid axle anyway. IRS is over rated and has it's own drawbacks.

 

 

 

[DatDime1972]

Thanks for the information and the speedy response. I was thinking instead of running the r165 I would run a wrx/sti diff with an lsd. I would need to see what kind of suspension set up to run with a solid axle. I am not a big fan of the leaf spring set up. But, if it works then it works. I will definitely keep that in mind. I appreciate the feedback. 

[datzenmike]

Better check, I think all the Subaru were R-165 made by Fuji Heavy Industries and a common easy and direct swap into the 510.  165 is the ring gear diameter and an indication of strength. 165mm is 6.5" and 190 is almost 7.5" allowing the gear teeth to be larger and stronger.

 

Fuji Heavy Industries grew into what today is Subaru. I believe Mazda, Nissan and probably Toyota at one time owned shares in the company and certainly used it's products and why some Toyota / Datsun and Subaru parts will swap perfectly.

 

 

[fiveoneO]

I'm not a big fan of solid axles and leaf springs either, but the IRS set up in the 510 isn't that good of a design. If you're going through the trouble of ditching the leaf springs, maybe do some kind of 4 link set up or do an IRS swap from something else. If you do go with the 510 IRS, the stock R-160 diff is the same as the Subaru R-160. I'd look for an R-180. 

[carterb]

For the amount of time/money you might be into the project converting your straight axle 510 into an IRS 510, have you considered finding a different car to start with?  It sounds like you are at the beginning of your project here.

[DatDime1972]

I am actually at the beginning of this project. But after some research and taking your guys comments into consideration. It might be less expensive for me to do a ford 8.8 straight axle with a 4 link suspension. Although, I am not sure of all the details on how the 4 link set up will mount up. By different car, do you mean like a completely different project? If so, not really, im interested in making things happen with this 510. 

[carterb]

I meant a different 510 to start with, yes.  If you have already fallen in love with the one you have, then there's no turning back now!  : )

 

It will be cool to see you come up with something a little different.

 

Can you share some pictures?  I'd love to see your car.  There are very few Mexican 510's shared over the internet.  I'd love to see all the different details that makes them unique.

 

--carter

[DatDime1972]

Yeah i did kinda got attached to the car. Not to mention, its not easy to find dimes now a days. So that was also kind of my thought, it would be different to see a 510 sedan with a straight axle and a 4 link set up. Ill definitely try and post as many pictures possible throughout the process. Right now Im just trying to plan as much as possible before I start purchasing parts. My plan is to first get all the fabricating done. Then send the car out to be all straightened out and painted. I will hopefully have the body shop pull and roll the fenders a little bit. After paint ill hopefully have some suspension and drive parts to be installed, along with the engine. And chip away little by little.  

[Lockleaf]

I would agree as well with what has been said.  If you are not dedicated to keeping to "original" suspension technology, pick something that improves on the 1960s tech.

 

With 4 link, if you plan to go low at all, that often drives the upper link up in to the bottom of the rear seat.  Unless you do short upper arms and triangulate, but that just gets more and more technical.

 

You could also look at something like a narrowed Miata subframe.  Miata is 6 inches or so wider than the 510 rear end.  However, Miata subframes are not terribly difficult to narrow.  Then you shorten the CV shafts and you are done, except for lug pattern.  Miata is 4x100 as opposed to 510 4x114.  If you are at all interested, I've found multiple threads over on Grassroots motorsports about narrowed miata subframes.  Nice thing about miatas is that all the suspension links bolt to the subframe.  The only suspension mounting point you would have to add is the strut top.

[DatDime1972]

That sounds like a pretty decent option as well. Only thing there is that my Mexican 510 sub frame is not the same as 510s that came with irs. I noticed that i dont have frame rails that run to the back of the car. Which were used to support the rear diff. So those links might not mount to my sub frame. 

[DatDime1972]

Im thinking something like this might work

 

 

http://www.cardomain.com/ridepost/1666988/1972-datsun-510/

 

[carterb]

I would love to see what the rear of your uni-body looks like.   You are saying there are no shock towers on either side of the fuel tank in the trunk?  The IRS 510 sedans don't really have "frame rails" so-to-speak anyway.  Bury us in pictures!

[bananahamuck]

What engine came in that 510 j15 ? 
   
 

 

.

[Str8jacket]

23 minutes ago, DatDime1972 said:

Im thinking something like this might work

 

 

http://www.cardomain.com/ridepost/1666988/1972-datsun-510/

 

That would be good until you want to turn corners at speed. Then it would end up in the opposite lane, or in a ditch upside down. Straight four links are good for drag racing. 

 

Look into a 3 link and watts, which will cut into your floor, or a torque arm like mm motorsports it think do for the mustangs. Watts link will be better than pan hard as the car is narrow and the arc will be more pronounced than a wider vehicle. 

 

Work out what sort of driving you want to do and design around that, not what is cheapest. That said a good set of monoleafs and a watts link will perform quite well too. 

[datzenmike]

LSDs are over rated. If too tight it will increase over steer, wheels will hop and chirp turning in town, tires will wear out, you may as well just weld up the open differential. Great for straight ahead acceleration where you have gobs of (excessive) power but they must be capable of some slipping. If on poor traction surfaces and you get out of control, almost impossible to recover.  Ever watch those idiots in Mustangs/Camaro/'Vettes leaving a car show and they light the tires and quickly get sideways and are barely moving but end up over the median or sidewalk? And you say WTF? I could have steered out of that. So could they if they had an open diff.

[Str8jacket]

7 minutes ago, datzenmike said:

LSDs are over rated. If too tight it will increase over steer, wheels will hop and chirp turning in town, tires will wear out, you may as well just weld up the open differential. Great for straight ahead acceleration where you have gobs of (excessive) power but they must be capable of some slipping. If on poor traction surfaces and you get out of control, almost impossible to recover.  Ever watch those idiots in Mustangs/Camaro/'Vettes leaving a car show and they light the tires and quickly get sideways and are barely moving but end up over the median or sidewalk? And you say WTF? I could have steered out of that. So could they if they had an open diff.

Combine this with the roll overseer issue from fancy looking 4 link set ups they all run, not very forgiving. 

[datzenmike]

Anything like  lift off oversteer?

[Str8jacket]

Straight 4 link (view from above) for the street needs to have the top and bottom links parallel on the side view to stop the diff "steering" the rear end when the body rolls as in going around a corner. 

The issue with this is the arse end of the car sags under acceleration, you see this on some rear drive cars, late 80s era. 

To stop this you angle the top links slightly down at the front, this introduces "antisquat" and allows for a better launch, the side effect is this designed in bind which causes antisquat also causes roll steer. 

 

29 minutes ago, datzenmike said:

Anything like  lift off oversteer?

 

I "think" this is more caused by a vehicle having compliant bushings, say a late 80s sedan with a 4 link arrangement and a panhard bar, the compliant bushings are to deal with the rollsteer issue, which was caused by the antisquat introduced which was there to fix the saggy rear end. 

 

All the suspension links come under compression and tension under load, distortion happens in the bushes and every thing loads up, when you lift off the gas everything sort of unravels in a rapid and uncontrolled manner, the driver shits themselves and over steers to correct, introducing more body roll, which then causes more roll steer in the opposite direction, ie spectacular out of control fiahtails as you leave the car show. 

[DatDime1972]

Thanks everybody for the information. Sounds like I need to continue doing some research. I definitely want the car to be able to handle around corners. Ill be driving the car most days out of the week. And also some circuit from time to time. So I definitely need it to handle corners well. I will do some more research on on the 3link suspension with the watts link. If you guys can provide me with some links or photos to look at. That would be great!

[Icehouse]

On 2/16/2021 at 12:23 PM, datzenmike said:

For an SR20 I would keep it solid axle and swap the H-190 from a 510 wagon in. The H-190 is much larger and stronger than the R-165 in the IRS. By the time you add enough spring and shock stiffness you might as well have a solid axle anyway. IRS is over rated and has it's own drawbacks.

 

 

 

 

The ring gear is bigger on the H-190 but the axles are garbage, they will brake if you weld the diff.  We swapped a R165 into Sam's car and with I would estimate 300HP (comparing how bad he leaves me in the dust in my stock SR with the boost turned up 510).  He has yet to snap an axle.  He did bust the LSD we found so he put in a welded center, eventually the welds broke haha. The LSD was out of a SCCA racecar so it may have been on it's way out.  The ears off the clutch plate sheared off.  Luckily I had a busted R160 subi diff, the internal clutch plates fit perfect.  The R165 axles are strong, I've know guys to brake the H190 axles with a welded diff just turning around in a parking lot.  All I'm saying is I wouldn't toss the H165 in the bushes just yet.  The 1200 guys found a way to use the AE86 LSD in the H165.  I would look into that before doing a bunch of fab work.  Maybe get the SR swap done and driving on the H165 with LSD before I made any crazy decisions.  The sedan IRS sucks for launching.  

 

 

On 2/16/2021 at 1:23 PM, DatDime1972 said:

Thanks for the information and the speedy response. I was thinking instead of running the r165 I would run a wrx/sti diff with an lsd. I would need to see what kind of suspension set up to run with a solid axle. I am not a big fan of the leaf spring set up. But, if it works then it works. I will definitely keep that in mind. I appreciate the feedback. 

 

The 1200 guys use the AE86 LSD in the H165 axle.  Look into that.  Depending on your HP goals it may not be the end all diff but it should hold up for a bit.  

 

 

[DatDime1972]

Thanks everybody for the input. I decided I will be running a ford 8.8 diff that I will be getting cut to size. For the suspension I referenced the 2jz wagon that im sure some people have seen. He has a 3link set up with a panhard. I will be running a 3 link using the same ae86 links that he used with the techno toy tuning ford 8.8 weld on brackets. Instead of the panhard I will be installing a watts link. I will have to fab some stuff up for the 3rd link mount. Looks like i will need to relocate my fuel tank, so ill just run a fuel cell that i will be cutting into the trunk. Some cutting will be necessary under my rear back seat as well for the 3rd link. Ill take some pictures when i get started with the process 

[banzai510(hainz)]

you must be Rich$$$$

[DatDime1972]

@bananahamuckYes it does have a j15. Car was bought in modesto. Do you know about this car? Any information I should know would definitely be helpful. Ive been lagging on the project due to life and getting all my ducks in a row. Thanks in advance. 

[datzenmike]

Must be from Mexico. Leaf spring?