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Discussion Starter · #1 ·
I know this topic has been spoken on over and over. It seems that most people tat are building/swapping their GTs have also gone with a rear end swap as well. Other than the obvious power gains and the rear end not holding up..... does nobody make a hardened set of rear axles..? Ultimately it seems like the 2 most viable options are the Volvo 240 swap and a Chevy 10 bolt swap. looking to see if anyone has any diagrams or drawings from when they did the swaps. Maybe even just photos with some measures that can be taken? We will be putting down about 260hp/220tq out of my little Blitz. This is not an estimation. it is what the tires will put to pavement. Just looking to put all of my potential options in one place. If Links are easier, by all means, let's see em!

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Other than the obvious power gains and the rear end not holding up..... does nobody make a hardened set of rear axles..?
The axles aren’t the weak point. The differential is, as the spider gears are very hard and tend to fracture. A proper clutch-type limited slip costs about $1300. A new set of installation bearings costs around $400.

The next weak link is the torque tube inner shaft, but that can be reinforced and balanced too.

If you decide to change gears ratios, a ring and pinion set from Europe is $700 to $1000, dependent on ratio.
By the time labor is figured in, it’s probably $2000-$2500 to build an Opel axle strong enough for 250 hp.

So it’s just economically more feasible to change the rear axle for something stronger in the US. Those parts exist in Europe because of motor vehicle rules and motorsports (historic) regulations which require the OEM differential housing.
 

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Not to mention Opel's parts bin policy of taking parts from different models to create new ones, like stuffing a Rekord engine in the Kadett to come up with the 1,9 liter Rallye. The reason there is so many rear end ratios is not so much racing, but a wide spread in engine sizes for some models like for example the Manta/Ascona B, with 4,30:1, 4,22:1, 4,11:1, 3,89:1, 3,67:1 or 3,44:1 available depending of engine.
I would add the Dana 44 to the list, as a UK built copy of it was a popular upgrade for the Vauxhall Chevette HS and HSR and original equipment in different Jaguars and in the Reliant Scimitars and Jensen Interceptors among others.
 

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Discussion Starter · #4 ·
The axles aren’t the weak point. The differential is, as the spider gears are very hard and tend to fracture. A proper clutch-type limited slip costs about $1300. A new set of installation bearings costs around $400.

The next weak link is the torque tube inner shaft, but that can be reinforced and balanced too.

If you decide to change gears ratios, a ring and pinion set from Europe is $700 to $1000, dependent on ratio.
By the time labor is figured in, it’s probably $2000-$2500 to build an Opel axle strong enough for 250 hp.

So it’s just economically more feasible to change the rear axle for something stronger in the US. Those parts exist in Europe because of motor vehicle rules and motorsports (historic) regulations which require the OEM differential housing.

Perfect, Thank you RB for the info. I'll have to keep digging. Really hoping someone has some drawings or schematics of what they did just to make it a little easier. I've seen all different styles of setups. Mine will likely be a combination of sorts.
 

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Discussion Starter · #5 ·
The axles aren’t the weak point. The differential is, as the spider gears are very hard and tend to fracture. A proper clutch-type limited slip costs about $1300. A new set of installation bearings costs around $400.

The next weak link is the torque tube inner shaft, but that can be reinforced and balanced too.

If you decide to change gears ratios, a ring and pinion set from Europe is $700 to $1000, dependent on ratio.
By the time labor is figured in, it’s probably $2000-$2500 to build an Opel axle strong enough for 250 hp.

So it’s just economically more feasible to change the rear axle for something stronger in the US. Those parts exist in Europe because of motor vehicle rules and motorsports (historic) regulations which require the OEM differential housing.
Getting close to putting this thing to full power and likely going to have to dyno/tune it with the stock rear end. we're aiming to be around 260hp 220tq. The goal is not to thrash the car just yet. The dyno will be the heaviest stress we're putting on the car for a bit. Need it to have the highest chance for survival. Will be driving it fairly gently in an effort to extend the life until I can finish setting up the beefier rear end.

Knowing this is substantially higher than the "tolerance" for the rear gear assembly, would it be "safer" to leave the diff open for dyno or weld the rear end? Leaving it open will likely leave power on the table, welding will make it less enjoyable for basic driving.

Thoughts?
 

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Getting close to putting this thing to full power and likely going to have to dyno/tune it with the stock rear end. we're aiming to be around 260hp 220tq. The goal is not to thrash the car just yet. The dyno will be the heaviest stress we're putting on the car for a bit. Need it to have the highest chance for survival. Will be driving it fairly gently in an effort to extend the life until I can finish setting up the beefier rear end.

Knowing this is substantially higher than the "tolerance" for the rear gear assembly, would it be "safer" to leave the diff open for dyno or weld the rear end? Leaving it open will likely leave power on the table, welding will make it less enjoyable for basic driving.

Thoughts?
Personally I could handle driving a car like yours with a welded rear end. However it will be really bad if you choose to do autocross. A welded diff in autocross would make it impossible to run most courses without purposefully drifting. Your times would be horrible.

I would recommend the Quaife or Quaife copy like this one OPEL GT ASCONA MANTA 400 RA18 AXLE LSD DIFFERENTIAL LIMITED SLIP DIFF BRQ | eBay. I would imagine it’s plenty strong and it’s cheaper than the ZF like I have (although I got mine for $800).
The ZF is better for a couple reasons but not enough better for the extra hassle of dealing with finding one in Germany.

It will require a 3.67 or higher ring gear and a later style axle 1971+. I got a axle housing and a 3.67 ring gear from OU for $500. I would only bother going in person to pick out a ring gear or axle. I believe he still has a 4.11 rear with welded spider gears that would make a decent axle for a LSD swap.

Pinion bearings and carrier bearings are probably fine on most used rear ends. But if they aren’t you are looking at a small fortune. The axle bearings are also a fortune ($110+ ea).

It cost me a total of $2000 for my LSD upgrade.

Roll onto the power lightly on the dyno and you’ll probably be fine with stock gears. There are people running V8s on the stock gears on this forum. You’ll eventually break the rear end with sticky tires and harsh throttle application with stock power. As long as your wheels slip before the teeth you will be good:)
 
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Since you are already heavily modded, why stop now? I've only got a touch over $400 including new Moser axles in my narrowed 4.10 posi Ford 7.5" rear end.
 
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Getting close to putting this thing to full power and likely going to have to dyno/tune it with the stock rear end. we're aiming to be around 260hp 220tq. The goal is not to thrash the car just yet. The dyno will be the heaviest stress we're putting on the car for a bit. Need it to have the highest chance for survival. Will be driving it fairly gently in an effort to extend the life until I can finish setting up the beefier rear end.

Knowing this is substantially higher than the "tolerance" for the rear gear assembly, would it be "safer" to leave the diff open for dyno or weld the rear end? Leaving it open will likely leave power on the table, welding will make it less enjoyable for basic driving.

Thoughts?
If you weld the diff and then lash the car down tightly on the chassis dyno to avoid slippage, any small diameter difference in the tires, even a fraction of a % (which IMHO is likely going to be the case), is gonna require that something slips somewhere. So either loosen one strap a bit so it can slip a bit on that side to relieve any torque build-up across the rear axle, or the welded rear may break somewhere. With it open, you can torque down both straps. Seriously how much power do you think will be 'left on the table' if the open diff rotates slowly? Chasing a HP or 2 on the dyno is not a good use of time and resources.... you gonna have the HP vary more in real use just with temp and humidity changes, and the dyno accuracy is NOT in the <1% range anyway. (Regardless of what the operator may say...)

The only concern is for breaking a spider gear as noted. But the dyno should not present a shock load to the rear.

But I am making some assumptions on the dyno you will be using? Do you happen to know the dyno type?
 

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Discussion Starter · #9 ·
If you weld the diff and then lash the car down tightly on the chassis dyno to avoid slippage, any small diameter difference in the tires, even a fraction of a % (which IMHO is likely going to be the case), is gonna require that something slips somewhere. So either loosen one strap a bit so it can slip a bit on that side to relieve any torque build-up across the rear axle, or the welded rear may break somewhere. With it open, you can torque down both straps. Seriously how much power do you think will be 'left on the table' if the open diff rotates slowly? Chasing a HP or 2 on the dyno is not a good use of time and resources.... you gonna have the HP vary more in real use just with temp and humidity changes, and the dyno accuracy is NOT in the <1% range anyway. (Regardless of what the operator may say...)

The only concern is for breaking a spider gear as noted. But the dyno should not present a shock load to the rear.

But I am making some assumptions on the dyno you will be using? Do you happen to know the dyno type?
Pretty sure he's running a dynojet, so you'd be correct. Agreed on the shock load. definitely not looking to chase a couple horsepower as he's about $150/hr. Always willing to listen to an informed opinion! honestly, another person talking through their thoughts on the issue was what i was looking for, Thanks!
 

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Discussion Starter · #10 ·
Since you are already heavily modded, why stop now? I've only got a touch over $400 including new Moser axles in my narrowed 4.10 posi Ford 7.5" rear end.
Already planning on it, but want o get the car driving so I can work out any mechanical bugs while I get the rear end put together outside of the car. I am using half of a buddy's garage so I don't want to leave this thing undrivable for too much longer. I was looking at 8.8's or chevy 7.5's. what did you pull your rear end out of?
 

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Discussion Starter · #11 ·
Personally I could handle driving a car like yours with a welded rear end. However it will be really bad if you choose to do autocross. A welded diff in autocross would make it impossible to run most courses without purposefully drifting. Your times would be horrible.

I would recommend the Quaife or Quaife copy like this one OPEL GT ASCONA MANTA 400 RA18 AXLE LSD DIFFERENTIAL LIMITED SLIP DIFF BRQ | eBay. I would imagine it’s plenty strong and it’s cheaper than the ZF like I have (although I got mine for $800).
The ZF is better for a couple reasons but not enough better for the extra hassle of dealing with finding one in Germany.

It will require a 3.67 or higher ring gear and a later style axle 1971+. I got a axle housing and a 3.67 ring gear from OU for $500. I would only bother going in person to pick out a ring gear or axle. I believe he still has a 4.11 rear with welded spider gears that would make a decent axle for a LSD swap.

Pinion bearings and carrier bearings are probably fine on most used rear ends. But if they aren’t you are looking at a small fortune. The axle bearings are also a fortune ($110+ ea).

It cost me a total of $2000 for my LSD upgrade.

Roll onto the power lightly on the dyno and you’ll probably be fine with stock gears. There are people running V8s on the stock gears on this forum. You’ll eventually break the rear end with sticky tires and harsh throttle application with stock power. As long as your wheels slip before the teeth you will be good:)
I could handle the car being welded..... the autocross part is the killer, especially with how skinny these cars already are....
personally, my thinking is that if I'm going to spend $2000, I can build a new larger and stronger rear end with all the goodies for the same price (including driveshaft) if not slightly cheaper. a lot of info that I'll definitely dig into, Thanks!
 

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Just one other thing to consider with welded rear axle... If the rear wheels have more straightline grip than the fronts have side grip entering a corner, then you ARE going to go straight ahead. YOU ARE! The only way to fight this is to be ready to 'throw' the car sideways into a corner, or somehow break the rears loose

I welded the rear diff on my first Manta rally car and while it worked great for acceleration traction, it was a bear to predict in turns. On a gravel road, your grip front-to-rear varies constantly and all over the map, so you had to throw the car in each corner to be safe. But if you got caught by surprise and the rears had more grip, the it was time to take immediate emergency action! Which was in reality panic for a newbie rally car diver LOL. Ultimately, the welded rear diff was a contributor to the deimse of my 1st Manta rally car against a 2' diameter oak tree in PA.

So I am sure you are saying you won't drive this on gravel? All good but what about on wet surfaces? Rain? Ooops.... same risky problem rears its head.

If you weld the rear, and drive on the street, I strongly advise you to put in 19 mm (3/4") diameter rear wheel cylinders, to get significanlty more rear brake bias. In that way, then the car suddenly wants to drive straight into a corner, then your normal panic reaction of stabbing the brakes will tend to break the rears loose.

But since you are changing the rear axle anyway, I'd just keep it open for now.
 

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Revitalizing this thread to explore axle upgrade options. After reading as much as I can find it seems there are three viable straight axle options for greater than 200hp. The GM or FOrd 7.5" 10 bolt axles or the Toyota axle. I see Heliman installed the Ford 7.5" with L/S...very cool! So what are the current pros and cons for each options? Availability, parts, L/S options, cost?

Thanks!
 

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No upgrades needed

NSFW

Joint Arm Shoulder Leg Stomach
 
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Rear end swap are easy and much cheaper then doing anything with the factory unit. I narrowed Ford 7.5" from a ranger. Factory 4.10 posi, $65 from the bone yard plus new Moser axles $275
 

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Ron,
I've always admired your work and was thinking the exact same option for my next build. Did you make that center link yourself or was that a modified COTS product? Would love to see some more pics of the actual install if you have them.

Mike
 
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