Jag V6 swapped Dolomite

[Carledo]

It might only be 2" at the axle, but the taper towards the tail carries on to the tail panel itself and is REALLY noticeable as this near perfect rear end shot shows. And you can just see the left front wheel outside the rear one, just to rub it in! The body even tapers visibly over the length of the arch so the rear clearance is less that at the front of the arch. It makes wheel choices a total PITA!



This is running the MGF 6x15 rims with 195/50s and the rear arch lips have been rolled for clearance. But this rear shot makes the car look like a dragster being forced to go round a corner. truthfully, it doesn't FEEL that bad and handling is neutral to oversteer as you'd expect. It's pretty much point-and-squirt. Just LOOKS wrong!

Steve

[Boost All The Dollys]

Some other things I’ve found out now the car off the road and I’ve had time to look things over and think things through:
• The bad handling I was having?
- One of the rear anti roll bar bolts had fallen out so lord knows what that was doing.
• the concerning-ly low ride height?
- rear struts are 1500 spec shocks with Uprated and lowered SPRINT springs. The spring perch height is different for the 1500 shocks, around 16mm or 5/8” lower. So the back end isn’t just 1” lower, it’s 1 5/8” lower. And seeing as the shocks only have around 3-4” of travel, it’s basically on the shock bump stops before anyone gets in!
• near constant oil leak?
- strangely enough, is linked to a near constant clutch leak somewhere. Fluid is escaping but no idea where from and getting to the area where the gearbox and engine meet where the DOT4 is destroying the silicone gasket on the rear of the sump, causing near constant oil leaks no matter how many times I’ve redone the gasket. The clutch leak seems to only be happening when the car is either hot or vibrating (ie running) so difficult to source but I’ll work it out. I think it’s either a bad slave cylinder or bad joint to the slave cylinder as they’re the only things inside the bell housing but hard to tell because everything in there is covered in clutch fluid.

Well, least I’ve got time to find more problems and sort them all out now

TR8 diff is 3.08 but won't fit in Sprint axle case (no idea why, just what I was told) The TR axle case is possible to adapt into a Dolly mounting wise but is 2"+ wider so stretching the arches will be called for.

Steve

After doing some quick maths, even a TR axle with the 3.08 ratio won’t be enough. That on its own will only drop the 70mph rpm down to 3200rpm. Again, not great but better. And I would be out the cost of a fairly expensive axle plus lose the LSD and I wouldn’t be sure the axle would survive.

I’ve been looking into different options and I think the most cost effective option is to change both the final drive AND the gearbox. Drop the final drive down to 3.3 and change the gearbox to a E90 BMW 330i, which is the GS6-37BZ. RX8 gearbox was too long, MX5 gearbox was either too long or hard to come by the right one that could be shortened. I did look at the 2.7 diesel gearbox as it’s the same as in the BMW 335i/330d but bolt pattern is too different and it’s expensive. An even better option would be the box out of a 316/318d (the GS6-17DZ)as it has a Double Overdrive! 6th is a staggering 0.645!! But I don’t know the strength of that box. The 318d only puts out 320nm and there’s almost no information about it online. Maybe I’ll just have to be the pioneer for its use!

Might be a touch harder to find than the diesel variant but is more than strong enough and has both a good overdrive 6th gear at 0.851 and only a marginally more useless 1st gear of 4.35, which the longer final drive will correct towards being better.

The other bonus is that both the BMW box and the Jag box are both Getrag units and look fairly similar so if the length isn’t terribly different, I won’t even need to modify the propshaft!

[Carledo]

It's only a 5 speed, but there's Vauxhall box that might help you. The Omega box I use is from the 2.0/2.2 petrol which is basically the same box as is used on the V6 models of up to 3.2 capacity so plenty strong enough. But there is another variant used on diesel Omegas which have the 2.5 BMW Diesel with a bellhousing to match. I bought one by mistake and it was only about £60! but I took it back cos it wouldn't match my engine (the bellhousing is built in like a Sprint) But it's a lovely box, short, light, strong and with external shift linkage you can shorten easily. Only problem is there's not a lot of ratio choices but 5th is overdriven around 20-25%. It's got a nice concentric hydraulic slave cylinder too. I'll work it out exactly next time I go out in the car, if I check road speed against the satnav at say 3000RPM in 4th gear (1/1) and then at 3000RPM in 5th, I can express the roadspeed difference as a percentage of the 4th gear speed to get a pretty accurate number.

You can get an LSD to go in the TR8 axle too, I plan to do just that, but they aren't cheap.

Steve

[Boost All The Dollys]

Cheers Steve, but think I’ll go with the BMW box as they’re fairly plentiful, reasonably cheap, and strong enough to handle the engine and then some.

And I’ll probably stick with the axle I’ve got but with that 3.3 ratio to save on getting a new lsd and arch flares

[Carledo]

Not sure exactly which axle you are using, Could it be the original 1500 Dolomite axle of 3.89 ratio? If so and you are considering a swap to the rare 3.27 diff, i'd forget it!

The 3.27 is a nice thought, but it's actually really weak, able to take the stress of an 1850 engine (91BHP) only in automatic trans form. It was originally used in the non-overdrive GT6 mkI and plenty got broken by the old inline OHV 2 litre 6, all 98BHP of it! I used to run a GT6 myself and personally broke half a dozen 3.27s, got so fed up I swapped to the more reliable 3.63. Which still gives 23mph/1000rpm in overdrive top (D type overdrive is 25%)

But most folk uprating Dolomites go for the Sprint axle which is a different design from all the lower spec cars and has the tallest gearing at 3.45/1. It's also the strongest of the Dolomite axles, capable of surviving up to around 250bhp on a regular basis. The late, 5 speed TR7 axle (3.63 or 3.45) is a wider version of the Sprint axle and the TR8 axle is a sort of cross between that and the SD1 V8s axle and carries the 3.08. But, AFAIK, the axle case itself is shared by all TR7 and TR8 models except the disastrously undergeared early TR7 4 speed which effectively has a wider Dolomite axle with 3.63 gears and no overdrive. And yes that one is BAD, barely doing 100mph flat out in 4th and screaming it's little nuts off!

Steve

[Boost All The Dollys]

I’m using a Ford Escort “English” axle with the RetroFord upgrade kit with LSD and Uprated halfshaft to take the power. The lowest ratio RetroFord sell is 3.3 which is what I’ll be swapping to

[xvivalve]

I have a pair of standard height rear Springs here with an extra coil in each; no idea what poundage they're uprated to, but they might give you a bit more travel...

[Boost All The Dollys]

I have a pair of standard height rear Springs here with an extra coil in each; no idea what poundage they're uprated to, but they might give you a bit more travel...

Thank you, but I’m ok. I have a set of adjustable rear shocks to go on at some point soon

[Carledo]

I have a pair of standard height rear Springs here with an extra coil in each; no idea what poundage they're uprated to, but they might give you a bit more travel...

Those might be just what I need for the Sprint to go towing with! I've got brand new stock rear springs and shox on it, but it still gets "soggy bottom" when there's some weight in the boot and back seat!

Steve