The V8 Owners Forum -

Afternoon all.
Ok we are slowly starting the winter rebuild of our car.
Has a 3.9i V8, Lt77 Gbox and ford 7 inch diff (not sure which ratio) defo not lsd tho.

The querie we have is our car was designed and built to have
216/60 14's on the rear but the previous owner fitted 245 section 17inch wheels on the rear, Very wide and very low profile.

The car sticks like absolute glue in the bends due to a mega low center of gravity and quite stiff, but not undriveable suspension. Tis lovely to drive.

The issue we have is that after a day at our owners club meet at the prescot hill climb we did a fair few high throttle lanches which was fun at the time for sure but a bit of a nightmare for the car.

We are quite concerned that the wider wheels that have been fitted are adding extra force to parts of the drivetrain that could be weaker and with no lsd and a standard clutch it maybe only a matter of time b4 something goes ping.

On stripping the gearbox the bearings seem to be on there last legs and think that this could be the cause.

Without an LSD surely more strain is being put on the weaker internals and standard clutch due to the increaded resistance from the tyres. Now how should this be approached??

If we were to uprate the cutch there would be even less slip in this department and even more strain on gearbox and diff. So would a new LSD be the best option to save other parts from collapsing in pain or am i going about this in the wrong way????

Many Thanks All.

Joe

Hi
An LSD will put more load on the drive train not less as it increases rear end grip, true there will be less shock loading when a spinning wheel finds grip, but this is normally because you have taken power off to get the wheel to grip.
You don't say what your car is, but a 3.9 is going to give a good condition LT77 a hard time of it if you have tuned it even a little. I would think you want to rebuild the box first (or replace it with an overhauled R380 even better) then fit an LSD if you want to have one then uprate the clutch. Not all rece cars go quicker with an LSD and if you are going hill climbing this is one place where an open diff can be an advantage as quick precise and predictable steering can be worth more than outright grip.
Mike

How heavy is the marcos, I ran a lt77 for ages without any problem in my cortina, and did many many drag racing starts, and that on a surface that has a adhesive sprayed in it to aid grip,
Probably find the box was worn before you started using it,

Approx 900kgs apparently so all in all a light car. its not used for many launches like the ones at prescot but we would just like it to be reliable if the mood does take us.
Joe

Wider tires will transmit more stress to the rest of the drive train.
Every step of the way to more power will also need steps towards more reliability.
The big question is what to upgrade for how much power, and it sucks to upgrade on part only to have another part break somewhere else.

You are pinching the stress between the wheels and clutch, so the trans, rear end and U joints are what you are looking at for stress and upgrades.
I would not bother attempting to make stock units stronger as it often ends up being patch work.

Here is part of someone else's posting on the LT77 trans.

The LT77 gearbox from the Rover SD1 has a reputation for being weak. The bearings often fail on the shafts on high powered cars.
If you want to use an LT77 it is worth trying to find a 'D' suffix gearbox as fitted to the SD1 Vitesse. This has slightly stronger internals than the earlier 'boxes and is fitted with a higher 5th gear - 0.793 instead of 0.833.


The oil the author said he used was Redline MTL. It is a fully synthetic with friction properties designed especially for gear syncros. This makes the gear changes like a knife through butter and synchro engagement is really good.

I would look for, and swap in a stronger trans, then look for and build at the least an 8" or perhaps even a 9 inch Ford rear to fit the width / application if you are getting serious about power.

The 8" and 9" Ford can be, and have been made to fit almost every application out there including front axles!
Also, they have the removable center section so ratio swaps are a 15 minute job and differential repairs can be done on the work bench, not on your back under the vehicle.

Cheers Quagmire! Looks like a good guide. I just hope I find it when I (eventually) get round to fitting a mega jolt system.