Engine and Transmission Tech

A new project for my toy. The plan is to replace the LT77 with something more modern. I fitted the LT77 about 20 years ago. It had unknown mileage and was originally in a TR7. Basically the weakest version of them all. I rebuilt it and it has provided reliable service all these years behind a healthy 4.6 litre engine.

Anyway, updates to follow...

I got a donor bellhousing from UK, a later model automatic version. I only needed the flange so I cut about 3 inches wide rim of the bellhousing. This engine will still run a LT77 box but whilst I had some internals balanced I had the flywheel redrilled for a Sachs clutch bolt pattern. I fitted it on the flywheel to get some measurements for the new gearbox fitment.

I thought that the R380 would be a direct swap & more stout.

I do have a R380 and it both is and is not a direct swap. Yes, the bellhousing fits but the V8 type release bearing carrier did not. At least not with my clutch. The pivot pin boss is taller too. I'll post a pic tomorrow. Also, the ratios are exactly the same as LT77 and I wanted different ratios. Rear support is further back and requires a different crossmember.

The new box is a GS6-37-DZ 6-speed from a BMW diesel. First gear is useless but rest of the gear ratios suit my needs better. Local turbo tuners have put over 500 lb ft thru these boxes and I doubt that my engine will ever produce such numbers. Using a BMW clutch gives a much more options than Rover does.



Edited 1 time(s). Last edit at 10/24/2019 01:45AM by minorv8.

Here is a photo of the R380 front cover plate. Two major points of interest: yellow arrow marks the release bearing arm pivot point. It´s roughly 1/2" taller than LT77. Red arrow shows the general shape of the cover plate. It is also more robust than LT77 one.

Normal SD1 V8 release bearing carrier did not fit between the diaphragm and cover plate (McLeod items). Also the pivot boss+pin height means that you can´t fit the slave cylinder. It won´t reach the bellhousing.

The easy fix is to machine the pivot pin boss down and shorten the release bearing carrier. But this means that it is not a direct swap. How much to machine ? Hard to say but if you take measurements from LT77 one should be close enough.

Borg Warner T5 too hard to get ?

I haven't checked lately but they tend to be pricy. Escpecially if they are WC ones. The bellhousing may prove difficult to source though. And expensive... I only paid 150 $ for this box, including shipping. 100 $ for the bellhousing, again including shipping.

So, here is the end result. Two inch rim of the auto bellhousing, shortened BMW bellhousing and some aluminum sheet to reduce the diameter.

Very nice!

I like seeing these sort of adaptations. Be mindful of your runout both concentrically and radially or at right angles to the driveline. +-0.010" is generally acceptable but the closer you can get it the better. I usually shoot for +-0.001"

Jim

Yes, these conversions are done with a rigid adapter that registers in the gearbox casing. IN the other end, it centers into the main bearing bores. Finally after welding the casing flange is machined at 90 degrees. So, it should be pretty close. How identical the block dimensions are, that is another question :-)



Edited 1 time(s). Last edit at 12/03/2019 12:31AM by minorv8.

I have totally forgotten to report back about my gearbox swap. So, the box is fitted behind a stroked 4.6 engine and it is just SWEET as you can expect from a BMW box. The swap from LT77 was pretty easy, I did have to cut my trans tunnel because of extra bulk of the box. No issue there, some sheet metal work only.

Now, here the real issues began. I had chosen a Sachs 765 clutch (uprated M5) which proved to be too much for my pedal/hydraulics. Internet search revealed that it is not the lightest of clutches... So, when I finally got the clutch to release the pedal was really heavy. Now, going back 25 years I remembered that when doing the hanging pedals I chopped the pedals shorter some 2 inches. My pedal ratio was about 4:1. Easy to figure out what I did last winter... yes, fit new master/booster/pedal assy using BMW parts. Why BMW ? I was running out of space to fit the clutch master cylinder. BMW has that inside the cockpit so problem fixed. Actually not. Clutch hydraulics was a new for me. You see, the master cylinder is plastic and has a quick release connection like late Camaros for example. Finding that was bit of a dilemma but old BMW brake line, AN fitting, some welding and braided hose sorted that out.

Also, the clutch pedal had to be modified and that is also made of plastic. Couple of hours of welding and a steel version was done. So, now the clutch works and the pedal feel is light enough. Like already said, the box is just so sweet. First gear is good for crawling around and if I were 30 years younger good for burning rubber.

Just a what if ? Using the BW 35 or 60 auto bell housing to adapt to various manual transmissions ?
Onward, Art.