Transmission swap

[TR7Aaron]

If I wasnted to swap a 5 speed tranny from a 1980 into a 1976 (which currently has a 4 speed) other than the transmissions themselves, what would need to be changed?
Thanks,
Aaron

Relax, all right? My old man is a television repairman, he's got this ultimate set of tools. I can fix it.

[FI Spyder]

Bellhousing, prop shaft, clutch etc. differential is different as is rear brakes. (stronger, bigger). If you can get the transmission see if you can get the whole drive train.

TR7 Spider - 1978 Spifire - 1976 Spitfire - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra

[PeterTR7V8]

On the other hand you don't need to change the diff or the brakes. These parts would still work fine but you would have a diff ratio that was not chosen for the 5 speed not that that would be a problem for anything other than your speedo accuracy. A brake upgrade would be recommended on the assumption that you'd be driving faster with your 5th gear.

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[TR7Aaron]

Well, I have both cars, both complete (more or less). So as a bare minimum I would need to swap the: bellhousing, transmission, clutch & pressure plate, and driveshaft. What about the linkage and hydraulic system for the clutch - the same or would have to be swapped also?
Thanks,
Aaron

Relax, all right? My old man is a television repairman, he's got this ultimate set of tools. I can fix it.

[Workshop Help]

No.

All you need is the complete 5-speed unit with the 4-speed driveshaft stretched to fit. The 3.63/1 rear end ratio is perfect for the internal gearbox ratios of the LT77. The 5-speed speedometer gear can be swapped out with your 4-speed speedo gear. Of course, the interior shifter boot and assorted trim must be swapped out. The clutch slave cylinder is the same.

But, do dismantle and overhaul the LT77 before you pull the 4-speed. We have discussed the why's and wherefore's in the past. Please research those prior conversations.

Mildred Hargis

[V8Wedgehead]

I would also make sure the back plate on the engine is not different for the 4-speed versus the 5-speed. I had a friend about 15 years ago do the same swap and he mentioned something about the rear engine plate for the two transmissions. You will also need to swap speedo cables too. I have seen on some of the early TR7s that the dealers swapped the 4-speed for the 5 that they used an aluminum adaptor from BL to use the 4-speed rear and one of the two driveshafts due to length. Good Luck![;)]

Michael
1980 TR8 FHC/Works Rally Project

"If it is broken then fix it....if it is not then make it faster!"

[TR7Aaron]

Thanks for all the info. I think the 5 speed will be easier to live with until I make the V6/auto switch. I want to be able to drive this car to work occasionally (about 52 miles) and the overdrive on the 5 speed should help cut down on the highway revs a bit.
Thanks again,
Aaron

Relax, all right? My old man is a television repairman, he's got this ultimate set of tools. I can fix it.

[Yoke]

V8Wedge is correct the back plates on the engines from 4 speed to 5 speed are "DIFFERENT" you must grab the 5 speed back plate or be prepared to do some modifications to the 4 speed back plate. Otherwise it's a straight forward swap, especially if you have both cars sitting there like your post stated. Have fun let us know how it goes.[;)]

Can't save them all but I am trying!!!

[Rich in Vancouver]

You may want to consider swapping in the 5-speed's rear end while you are at it. It is considerably beefier than the 4-speed's unit.

1975 TR7 ACL764U

[V8Wedgehead]

I second the motion on the rear end. Your 4 speed rear is 3.73:1 and the 5-Speed 1980 if original is a 3.45:1 . The 4-speed has a 1:1 final gear in 4th. The 1980 5-speed is a .83 or .81:1 so less revs at 70 mph. To do this you will need the 1980 rear, possibly lower control arms, e-brake cable and drive shafft to do the swap. It sounds like a lot of work but it is not.

Michael
1980 TR8 FHC/Works Rally Project

"If it is broken then fix it....if it is not then make it faster!"

[Workshop Help]

Again, No, with a possible maybe.

Our is an Oct 1976, model year 1976, produced for the "Big $4995 sale", car. Our LT77 conversion last year did not need a engine back plate change or any modification. NONE. Perhaps the very early 4-speed cars engine plate was different and I'm not aware. Do note for 1976, the LT77 was an option and then the engine plate would have had to be modified by the factory. However, when your gearboxes are pulled and side by side on the garage floor, examine the bellhousing holes. Are they the same? Are the mounting flanges the same? Does the sun still rise in the north and set in the south? If so, then plug the gearbox in and try it.

The speedo cable. It is interchangeable. Our old two piece cable was replaced on the 4-speed with the 5-speed cable long ago. It fits just fine.

Again, the 4-speed differential is more than adequate in strength and function for our engines. And the 3.63 /1 ratio is ideal for the LT77 ratios. To change to the 5-speed differential and it's 3.90/1 ratio will give you a stump puller where there is no need for a stump puller.

The larger rear brakes issue is pretty much a case of too little and too late. For the brakes to be improved on these cars you need to modify the front brakes as that is where more than 60% of all the braking takes place anyway as there is where the bulk of the cars weight is located.

I am not kidding about overhauling the LT77. It WILL need it. The rear tailshaft ball bearing is the one most exposed to grit and wear. You must remove the rear housing to access it. Do replace it with a high quality bearing that has a shield on one side to keep out the grit from the outside environment. Then crack open the main case and go exploring inside.
Mildred Hargis

[TR7Aaron]

All fantastic info - thank you!
I will be copying and pasting this into my "TR7 files".
I wasn't aware that there would be such little discrepency regarding the final rpms between the two. I'm now wondering if it's going to be worth all this work to reduce the highway rpms only by a couple 100.
Of course, there would be the fun factor of having an extra gear to zoom around in...
Aaron

Relax, all right? My old man is a television repairman, he's got this ultimate set of tools. I can fix it.

[Underdog]

Exellent advise from Mildred again. If you do go inside the LT77, by all means install a new oil pump. They are made of some sort of fiber material and get chewed up with stray metal particles. I've never taken one apart that the pump still looked good. Been discussed before but thought it worth a mention.

72 MGB BRG
80 TR8 Persian Aqua
If women don't find you handsome, they should at least find you handy.

[FI Spyder]

Just a note about rear ends. The 4 speed diff ratio will work fine with drive shaft length mods. Only the late TR7's got 3.45 rear end although I know of an early '80 that has one but I can't be sure it's original. My July 1980 Solihull FI car has a 3.90 (original) and Mildred is right, it's a stump puller. I wish I had a 3.45 as shifting out of 1st happens rather quickly and around 60mph I wish I had a sixth gear (or better yet a different ratio diff).

TR7 Spider - 1978 Spifire - 1976 Spitfire - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra

[Yoke]

Okay this whole discussion on back plates has me frustrated because two years ago I spend three days trying to figure out why my engine was seized after switching engines. It turned out the back plate was wrong [:D] I can prove it. Now I don't know what year the used engine going in came from but it was from a four speed going into a 5 speed. It helps to have a few engines in your garage that you can work with.

Okay the first picture is not the best my apologies but my flash is gone. Anyway side by side 4 speed is sand blasted 5 speed was just taken off an engine.



Again 4 speed back plate sand blasted.



Now the 5 speed back plate.



Now the 4 speed mounting holes for the back of the engine.



Now the 5 speed mounting holes. As you can see the are bevelled/chamfered flush mounted? I hate not knowing the right terminology. Ahhhh counter sunk that's it isn't it?



Now if you were to put the 4 speed backing plate with the bolt heads sticking out with the 5 speed flywheel you will get lock up trust me I did it. Again as Mildred stated this may be an issue with the very early cars, I have no idea but now you know what to look for.

Mildred it's not that I didn't trust what you were saying it's just that I had encountered an issue with different back plates, and it might save someone else some time in the future if they know what to look for.

Other wise like everyone has stated it's a very straight forward swap.

Can't save them all but I am trying!!!