Gswest236 Scott West Seabeck, Washington (28 posts) Registered: 07/14/2021 09:13PM Main British Car: 1974.5 MGBGT V8 Olds 215 Stroked to 266 |
Looking for advice on rear axle ratios with a LT77 5 speed
Ive got a 3.00 axle ratio I知 running now which came with the car ( 74.5 MGBGT V8). It has a PowerTrax LSD installed as well. I知 assuming the builder (deceased) liked some top end and maybe better fuel economy. I知 not concerned about cruising down the interstate as much as feeling the acceleration at take off. So, I知 thinking about swapping he 3.00 gear and pinion out for a 3.73 or similar ratio. The issue might be that the gearing of the LT77 5 speed may make the lower gears spool up too quick. I know I致e seen that this transmission when used by Rover used a 310 gear or something close. Ive looked at the spreadsheet program on here and obviously the change would raise my RPM and highway driving will be noisier; I don稚 really take the car on those roads, mostly on the local mountain roads. The car has a stroked 215 with a few go fast upgrades but not too crazy. Any suggestions or advise would be appreciated.
Edited 1 time(s). Last edit at 09/15/2022 08:32PM by Gswest236. |
minorv8 Jukka Harkola (269 posts) Registered: 04/08/2009 06:50AM Main British Car: Morris Minor Rover V8 |
Re: Looking for advise on rear axle ratios with a LT77 5 speed
British Leyland used this gearbox in several cars. Rover SD1 versions had 2.84:1, 3.08:1, 3.45:1 and 3.9:1 gears, depending on the engine. All V8エs had 3.08:1 ratio and Vitesse V8エs had 2.84:1.
LT77 has a 3.32:1 1st gear ratio and combined with 3.73 may be more or less useless. Good for very low speed crawling, though. Again, more revs all the time and the engine will wear faster. Which rear axle do you have, Ford 8" ? I might consider something around 3.3 - 3.5:1 but that is of course a question of individual preferenses. I used to have LT77 behind a healthy Rover V8 in my Morris Minor. With all the mods the car is around 2100 lbs. (pretty close to a MGB GT) Rear axle is a narrowed TR7 axle with 3.08 gears and Quaife ATB. I have run the car at 1/4 mile and never really liked the ratios for that use. T5 ratios would be better but that is quite an expensive option over here. So, I looked at other options available and chose a ZF 6-speed from a BMW 1-series diesel. Not a direct swap by any means but a local company can mate BMW box to just about any engine with a matching bellhousing. Total cost including the uprated clutch was around 1000 USD. Now, since this box is from a diesel model it has a really useless 5:1 1st gear but 2nd to 6th gear ratios are pretty spot on. Very shooth gear change and will not break behind a Rover V8. I do have a set of 2.84 gears and most likely will fit those. I am close to 60 years of age and (sadly) have to confess that I donエt like high screaming engines anymore:-) |
mgb260 Jim Nichols Sequim,WA (2463 posts) Registered: 02/29/2008 08:29PM Main British Car: 1973 MGB roadster 260 Ford V8 |
Re: Looking for advise on rear axle ratios with a LT77 5 speed
We need to know the make of your rear axle. The ratio sounds like 8" Ford. MGB had 3.91 stock and 3.07 and 3.31 aftermarket ( same ratio's as MGC ), Automatic cars had 3.70 which is too close to 3.91. Have you thought of changing the transmission to a T5 with different ratio's?
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IaTR6 Dennis Costello Central Iowa (192 posts) Registered: 12/29/2007 02:53PM Main British Car: '73 TR 6 '97 Explorer 5.0 |
Re: Looking for advise on rear axle ratios with a LT77 5 speed
I think I've offered my experience before, but I'll throw it out.
I have a Ford 5.0 (302) with some mild modifications. I have a Mustang T5 with the 3.35 1st gear and a Nissan R200 rear with 3.54 ratio. The combination is 11.859, and for me it is a little too low. My TR6 is 2510# without me, and a start from a stop seems to require revving a little high in 1st to keep up with traffic. I would have preferred to have a 2.95 1st gear, giving a total ratio of 10.443. Your 3.0 rear ratio with the 3.32 1st gear in the transmission gives a 9.96 total. Maybe this isn't low enough for your install, as my Ford is a little larger on displacement, but maybe let that be a "wait and see" deal. Dennis |
Gswest236 Scott West Seabeck, Washington (28 posts) Registered: 07/14/2021 09:13PM Main British Car: 1974.5 MGBGT V8 Olds 215 Stroked to 266 |
Re: Looking for advise on rear axle ratios with a LT77 5 speed
Thanks guys. It has a Ford 8 inch rear end. So, It sounds like maybe a 3.55 axle gear ratio might be as high as I should go to keep the revs down. First gear isn稚 that useful as it sits, so that will get worse but I知 willing to compromise for some low end grunt. The car has good power, just not off the line. If the LT77 fails, a T5 would be the replacement. As it is now the 2nd gear synchro is starting to go, but otherwise its fine.
Appreciate the input! |
MGBV8 Carl Floyd Kingsport, TN (4512 posts) Registered: 10/23/2007 11:32PM Main British Car: 1979 MGB Buick 215 |
Re: Looking for advise on rear axle ratios with a LT77 5 speed
Since you 5th gear is either a .79 or .83, I would recommend using no more than a 3.31 - 3.42 rear gear. Your 3.32 1st gear will still be usable & still give you the takeoff acceleration you want.
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Gswest236 Scott West Seabeck, Washington (28 posts) Registered: 07/14/2021 09:13PM Main British Car: 1974.5 MGBGT V8 Olds 215 Stroked to 266 |
Re: Looking for advise on rear axle ratios with a LT77 5 speed
Thanks Carl,
Of course I have no idea which 5th gear I have, but your suggestion is appreciated. I hope the effort of changing out the gears proves worth it. Sometimes its more about the journey than the destination. So, I知 ordering a ring and pinion set. |
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Gswest236 Scott West Seabeck, Washington (28 posts) Registered: 07/14/2021 09:13PM Main British Car: 1974.5 MGBGT V8 Olds 215 Stroked to 266 |
Re: Looking for advise on rear axle ratios with a LT77 5 speed
Getting ready to pull the axles and remove the 3rd member. We got the 3.40 ring and pinion kit (Motive Gear) and the installation kit.
Since I have no experience with a ford 8 inch rear end or any others to be honest, there is a learning curve going on here. First off, all the ford 8 inch pictures i see online don稚 look like my axle to wheel flange. The nut at the end doesn稚 look like the ford wheel flanges I see online. It looks like a MGB flange; 4 lug with a retaining nut. The fords all don稚 have the nut as far as I can see online. Is the axle shaft not a ford?? Or modified maybe. I知 sure someone here knows what this is. Hoping for that guy who knows these axles to school me. |
mgb260 Jim Nichols Sequim,WA (2463 posts) Registered: 02/29/2008 08:29PM Main British Car: 1973 MGB roadster 260 Ford V8 |
Re: Looking for advise on rear axle ratios with a LT77 5 speed
Scott, You may have a Hybrid. Ford 8" with MGB hubs. Glenn Towery used to make those. 8" is banjo type where the center section comes out the front. No separate rear cover. Do you have a picture?
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MGBV8 Carl Floyd Kingsport, TN (4512 posts) Registered: 10/23/2007 11:32PM Main British Car: 1979 MGB Buick 215 |
Re: Looking for advise on rear axle ratios with a LT77 5 speed
First Ford 8 inch/late MGB hybrid that I ran across was Dale Spooner's.
[www.britishv8.org] Jim Stuart also used one. [www.britishv8.org] The MGB vintage racers use a Banjo MGB/Salisbury MGB hybrid. |
Gswest236 Scott West Seabeck, Washington (28 posts) Registered: 07/14/2021 09:13PM Main British Car: 1974.5 MGBGT V8 Olds 215 Stroked to 266 |
Re: Looking for advise on rear axle ratios with a LT77 5 speed
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mgb260 Jim Nichols Sequim,WA (2463 posts) Registered: 02/29/2008 08:29PM Main British Car: 1973 MGB roadster 260 Ford V8 |
Re: Looking for advise on rear axle ratios with a LT77 5 speed
They cut off the flange and splined to fit MGB hub, The housing ends and bearings are MGB also.
Edited 3 time(s). Last edit at 09/15/2022 12:33PM by mgb260. |
mgb260 Jim Nichols Sequim,WA (2463 posts) Registered: 02/29/2008 08:29PM Main British Car: 1973 MGB roadster 260 Ford V8 |
Re: Looking for advise on rear axle ratios with a LT77 5 speed
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Gswest236 Scott West Seabeck, Washington (28 posts) Registered: 07/14/2021 09:13PM Main British Car: 1974.5 MGBGT V8 Olds 215 Stroked to 266 |
Re: Looking for advise on rear axle ratios with a LT77 5 speed
OOPS, I got the install kit for the Ford 8 inch, We値l see if any of it is compatible. The bearings and races probably are fine, but may have to be changed to do the ring and pinion swap. Like I said, learning curve! I値l post some updates as I go. Thanks for the help guys!
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mgb260 Jim Nichols Sequim,WA (2463 posts) Registered: 02/29/2008 08:29PM Main British Car: 1973 MGB roadster 260 Ford V8 |
Re: Looking for advise on rear axle ratios with a LT77 5 speed
You have the right kit for the center section. The outer axle ends are MGB.
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Gswest236 Scott West Seabeck, Washington (28 posts) Registered: 07/14/2021 09:13PM Main British Car: 1974.5 MGBGT V8 Olds 215 Stroked to 266 |
Re: Looking for advice on rear axle ratios with a LT77 5 speed
Awesome, thanks.
Edited 1 time(s). Last edit at 09/15/2022 08:34PM by Gswest236. |
Gswest236 Scott West Seabeck, Washington (28 posts) Registered: 07/14/2021 09:13PM Main British Car: 1974.5 MGBGT V8 Olds 215 Stroked to 266 |
Re: Looking for advise on rear axle ratios with a LT77 5 speed
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Gswest236 Scott West Seabeck, Washington (28 posts) Registered: 07/14/2021 09:13PM Main British Car: 1974.5 MGBGT V8 Olds 215 Stroked to 266 |
Re: Looking for advice on rear axle ratios with a LT77 5 speed
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Spitfire 350 Phil McConnell Perrysburg, OH (Toledo area) (257 posts) Registered: 01/11/2010 09:19PM Main British Car: 74 Spitfire 350Chevy |
Re: Looking for advice on rear axle ratios with a LT77 5 speed
I have always let the professionals do that for me. They have the tools and experience, yes they are expensive, but they have to earn a living too.
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MGBV8 Carl Floyd Kingsport, TN (4512 posts) Registered: 10/23/2007 11:32PM Main British Car: 1979 MGB Buick 215 |
Re: Looking for advice on rear axle ratios with a LT77 5 speed
A twelve bolt Chevy or Ford 8.* is more difficult. An 8 or 9 inch Ford is easier & doable. I would give it a shot myself.
Disclaimer: I had the gears swapped in my 12 bolt Chevy in my 68 Camaro by a Chevy mechanic that did it at his house.... for $100. ;) Been a bunch of years, though. |