1940 Chev Rear End Options

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leocar
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1940 Chev Rear End Options

Post by leocar »

Hi Everyone,

I am looking to start the suspension for my 1940 4 door Chev. I have decided on a Rod Tech front end (even though it will be a long wait), what I haven’t decided on is the rear end. The motor and box will be a 6lt LS2 and 6 speed from a VE Calais. I was hoping to use the rear end as well but the track looks to be too wide. The track on the Chev is about 1500 with about 1530 face to face on the axle mounting face. The Calais is about 1630 track and about 1715 face to face on the axle face. Although the wheels are much wider on the Calais and I could get offset wheels, I think around 115mm each side is a bit too much to compensate and hence would need to flare the guards which I don't want to do, happy to be corrected or get suggestions from others. Currently there is about 50mm clearance from the tyres to the guards on the Chev.

From what I can see I have 2 main options:
1. Buy a solid axle diff and shorten it. Currently looking at a VY Commodore Ute diff for about $400(needs to be shortened) or custom 9” from rod tech (will end up about $5000 with centre)
2. Buy a Jag rear. They seem to be quite narrow and should fit. Can get a XJS with 2.88 gears for around $1200 and will need a rebuild/tidy up

I am drawn to the Jag diff. Although the Jag diff will be more work than the 9” with leaf springs I think the ride will be better. Question is what wheels do the Jag’s run, are the stud patterns the same as other common wheels i.e. Commodore, Old Holden, Falcon, European etc.?

Any other suggestions and or comments would be appreciated.

Cheers
Twin Spinner
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Re: 1940 Chev Rear End Options

Post by Twin Spinner »

Try and find an early tank Fairlane 9 inch diff, they are just right for most early yank cars.
If it has tits or wheels, you can expect trouble.
36Phaeton
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Re: 1940 Chev Rear End Options

Post by 36Phaeton »

From memory the Jag rears from Series 1 and 2 XJ6 is 5 x 4.75, the same as HQ/HZ Holden
I’m bilingual, I speak both imperial and metric.
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jeffa
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Re: 1940 Chev Rear End Options

Post by jeffa »

Try searching on this very forum. Loads of responses from people that have put Jag rear ends under chevs.
I am not familiar with the 1940 Chev chassis or guard dimensions specifically. A quick Google show it to be the usual top hat design Chev used from 1936.
I have put a Jag rear end under a 1936 Chev, using the jags original "cage" mounted on the jag rubber mounts.
Its a good fit. Engineer liked it too!
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thatold.chevy
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Re: 1940 Chev Rear End Options

Post by thatold.chevy »

If you use a live axle and the car isn't too low, do what I did with my Valiant.

I took a (Ford Falcon) live axle rear and used two short axles - only had to reduce the one axle tube and have it rewelded from disassembly.

The pumpkin is central but the input shaft was a few degrees off centre - had no problems of vibrations with a remanufactured tailshaft and new unis needed anyway.
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thatold.chevy
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Re: 1940 Chev Rear End Options

Post by thatold.chevy »

jeffa wrote: Wed Jan 25, 2023 10:34 am Try searching on this very forum. Loads of responses from people that have put Jag rear ends under chevs.
I am not familiar with the 1940 Chev chassis or guard dimensions specifically. A quick Google show it to be the usual top hat design Chev used from 1936.
I have put a Jag rear end under a 1936 Chev, using the jags original "cage" mounted on the jag rubber mounts.
Its a good fit. Engineer liked it too!
yeah 36-40 chevs and 36-40 fords all take a jag cage at the stock chassis width which is "mildly" convenient....!
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toprodz
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Re: 1940 Chev Rear End Options

Post by toprodz »

leocar wrote: Wed Jan 25, 2023 8:31 am
2. Buy a Jag rear. They seem to be quite narrow and should fit. Can get a XJS with 2.88 gears for around $1200 and will need a rebuild/tidy up

I am drawn to the Jag diff. Although the Jag diff will be more work than the 9” with leaf springs I think the ride will be better. Question is what wheels do the Jag’s run, are the stud patterns the same as other common wheels i.e. Commodore, Old Holden, Falcon, European etc.?

Any other suggestions and or comments would be appreciated.

Cheers
You would be wanting to get a jag diff with around a 4.11 ratio if you are using a 6 speed auto, my one is running 3.77 ratio with the 4L60E4 speed trans and is doing about 1870 revs at 100 kph with 29.5" tall tyres, the jag stud pattern is chev with 1/2" studs but I found that using steel wheels the tapered wheel nut didn't fully engage in the taper of the wheel as Chevs use smaller 7/16" studs so I had the hubs redrilled to ford pattern, also the jag studs are very short.
I hope that helps a little
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leocar
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Re: 1940 Chev Rear End Options

Post by leocar »

Thanks for the info. I have been trawling through previous posts but when you search Jag and get 491 pages of hits, it takes a while to go through them. I noticed that someone mentioned that there should be a specific section for Jag IFS and IRS considering how many people use them and ask questions, I think they may have a good point!

I have done some calc's and for a 15” 205/75 wheel, if I go with a 2.77 diff ratio the motor will be at about 1430 RPM which I think is way too low. Using a diff ratio of around 3.54 should get around 1830 RPM at 100km/h which I think is much better.

From what I have read so far the Jag diff’s are really good but you need to set them up right which can be tricky, I just can’t seem to find the information on what the tricky part is. They look to come in a frame (the XJS I’m looking at has in board brakes) with 2 transvers arms. I’m obviously missing something but not sure what. It does seem that a 9” leaf sprung will be easier to install just may not look and ride as nice.
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steve the ford guy
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Re: 1940 Chev Rear End Options

Post by steve the ford guy »

I have several pictures scanned from Street Rodder magazines from 1995 about the Jag rearend, they ran a series of articles written by Jerry Slattery in March, April, May, June of 1995 it has a DIY how-to guide on full assembly using a hydraulic press.
There's also information on swapping the Jag rearend in a British hot rod magazine from back then. It might be "Custom Car" magazine
I have screenshots of the article and it was written by a Richard Nicholls, Eddie Wimble, Mike Key and a Patrick Hook. The article has a full DIY how-to guide on cutting and shortening the axles.
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Sudsy
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Re: 1940 Chev Rear End Options

Post by Sudsy »

If you are going solid axle and want a cheaper option but still good for about 600hp go for a Hi-lux or Hi-ace diff. They are Fraud pattern, and good ratios are available. Soarer centres will fit and can be found in LSD. Have had one in my 37 for about15 years and no problems. Good solid axles and big diameter bearings so can handle good offset rims. I've fitted a few jag rears but never with the cage. Always solid mounted to the chassis as it's much tidier and easier to get it lower
Regards Bob
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steve the ford guy
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Re: 1940 Chev Rear End Options

Post by steve the ford guy »

From memory I think the Toyota uses a 28 spline axle compatible with a 28 spline Ford 9 inch center, so later on you could upgrade it by splicing in a 9 inch housing center section to upgrade it using your existing Toyota brakes and axles
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Re: 1940 Chev Rear End Options

Post by Gojeep »

Don't forget the mounting guide in the Government Street Rod Manual.

https://www.infrastructure.gov.au/sites ... _App_3.pdf
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Sudsy
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Re: 1940 Chev Rear End Options

Post by Sudsy »

steve the ford guy wrote: Sat Jan 28, 2023 4:30 pm From memory I think the Toyota uses a 28 spline axle compatible with a 28 spline Ford 9 inch center, so later on you could upgrade it by splicing in a 9 inch housing center section to upgrade it using your existing Toyota brakes and axles
The Hi Ace axles are 31 spline and much beefier than a 9 inch with larger wheel bearings. From memory bearings are 40mm id
Regards Bob
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steve the ford guy
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Re: 1940 Chev Rear End Options

Post by steve the ford guy »

steve the ford guy wrote: Sat Jan 28, 2023 4:30 pm From memory I think the Toyota uses a 28 spline axle compatible with a 28 spline Ford 9 inch center, so later on you could upgrade it by splicing in a 9 inch housing center section to upgrade it using your existing Toyota brakes and axles
I've done this swap and at the time I knew the Hi Ace had better rearend highway ratios than my 4wd V8 87 Hilux and I know we are all passionate here about our preferences of engines, transmissions, rearends etc.
I agree basically with what's been said, that the Toyota axles are superior, I wasn't advocating my preference for 31 spline Ford axles, just the centres. the Fords axle bearings are still a healthy 39.675 mm ID, to the Toyotas 40mm and to me that's not much to worry about. I did this swap years ago, I had a transmission place weld on the Hilux housing ends to the Ford housing, and set up the spring mounts and I installed the Ford 9 inch Galaxy centre section with end gears fitted to suit my Hilux 4wd axles, I ground and detailed, primed and painted it in black gloss 2 Pak and bolted it in place in my back yard, on the highway with a 3.5 gear it flew past other Hilux pickups, I couldnt honestly confirm if the axle spline count was 28 spline on the Toyota axles after all this time, the early galaxy 9 inch housing certainly looked more cool than my toyota hilux housing ever could.
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FRANK BASILE
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Re: 1940 Chev Rear End Options

Post by FRANK BASILE »

I did find the S1.2.3 Jag rear to be a fit under the Chev 38 frame. Used the Jag "floor hats" at the time. They still are or were a rust repair item available. Also, if using a live axle keep in mind that those Chev torque tube rear ends have an offset locating center bolt on the springs. Shoving a replacement diff with conventional locating bolt holes in the pads will leave your wheels not central in the wheel arch. Forget which way now, forward or aft.
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