-
Hi Guest!
You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
There are some perks with a member upgrade!**Upgrade Now**
(PS: Subscribers don't see this gawd-aweful banner
Hey - did you know if you click on the title of a thread it will take you to the first unread post since you last visited that thread?
but were afraid to ask: 
STOP!! Never post your email address in open forums. Bots can "harvest" your email! If you must share your email use a Private Message or use the 
smilie in place of the real @
Pretty Please - add it to our Events forum(s) and add to the calendar! >> 
Wedge Tr7, Tr8 or SD1 3.08 rear needed....
- Thread starter tr7andtvr
- Start date
Share this page
3.08 and cheap are not usually found in the same sentence. 3.08, rare, expensive if you can find one are more associated with each other. Good luck. They only came in TR8s and 81 TR7 automatics. SD1s also had a 3.08 pumpkin, but the axle is different. You can remove the SD1 pumpkin and stuff it into a wedge 5 speed rear end, but that isn't all that easy to do. Best bet is to snag a 3.45 out of a 80 convertible TR7 or a 3.90 from a 5 speed coupe or early 79 vert. All that being said, I have 2 spare 3.08 rear ends. I'm 1000 miles from you and then there's always the first part of what I wrote. I just parted out a 76 coupe today and boy those four speed rear ends are flimsy. I swear the driveshaft flexed in my hand when I squeezed it, and those driveshaft bolts were tiny. Those 2.73s are a mythical creature that only came in the SD1 Vitesse models. Rare even in England.
DNK
Great Pumpkin
Offline
SDI, I believe
But Todd might be correct on the number but his sounds funny
From the TR7 site
[FONT=Century Gothic, Verdana, Arial, Helvetica]And then there's the R380 to that...
Anyway, Mildred asked: "to further sort this issue. Does anyone have the 3.08 differential installed?"
Yes, of course - most all the TR8 have the 3.08:1 rear axle ratio. (Some have the 2.84:1 and a small
fraction, mainly cars built for race or rallye use the '7 ratios...)
My TR8 currently have a R380 gearbox (= 0.77:1 5th gear) and the 3.08:1 rear axle ratio.
[The 2.84 with Quaife is currently sitting in the garage again.) Stock alloy rims with 185-70*13 tyres.
The speedo is off by some kph/mph, I think this was a deliberate oem design decision...
OK Mildred, with the above data (and as close as I could keep your wanted 60 mph with a metricated TR8
(the wonders of GPS!) I get roughly 2290 rpm in 5th gear.
Cheers,
/Odd[/FONT]
But Todd might be correct on the number but his sounds funny
From the TR7 site
[FONT=Century Gothic, Verdana, Arial, Helvetica]And then there's the R380 to that...
Anyway, Mildred asked: "to further sort this issue. Does anyone have the 3.08 differential installed?"
Yes, of course - most all the TR8 have the 3.08:1 rear axle ratio. (Some have the 2.84:1 and a small
fraction, mainly cars built for race or rallye use the '7 ratios...)
My TR8 currently have a R380 gearbox (= 0.77:1 5th gear) and the 3.08:1 rear axle ratio.
[The 2.84 with Quaife is currently sitting in the garage again.) Stock alloy rims with 185-70*13 tyres.
The speedo is off by some kph/mph, I think this was a deliberate oem design decision...
OK Mildred, with the above data (and as close as I could keep your wanted 60 mph with a metricated TR8
(the wonders of GPS!) I get roughly 2290 rpm in 5th gear.
Cheers,
/Odd[/FONT]
All TR8s came in 3.08. Nothing else. The five speed rear end also came in 3.45 and 3.90. The 3.27 was a 4 speed rear end used in TR7 automatics up until late 1980 when they finally switched to the 3.08 five speed rear end used in the TR8s. The 3.08 came in the US spec Rover SD1s, so you might be able to find one of them. Problem with that is swapping the R&P isn't that easy because the crush sleeve isn't available. I've reused the old sleeves before and there are tutorials online if you look hard enough for them. If you really want a 3.08, I have a suggestion. Go find a 80s Mustang GT. 3.08 limited slips were fairly common in them and they are only and inch per side wider. They use the same size rear drums and in fact I have redrilled Mustang drums and used them on a TR8 before. Shoes on both are 9"X1.75". The only real difference is the wheel bolt pattern is 4X108 for the Ford and the TR8 is 4X95.25, or 4X4.25" and 4X3.75". If you want to go real crazy, some Mustangs came with a 2.83. Had a non Posi one here over the summer, but I junked it after I stole the rear disc setup for it. Those are going on a 3.08 Posi drum brake rear end I have now ready to go in a TR8 coupe. I'll sell you a real TR8 3.08 rear end for $400, but you need to find a way to get it from here to there, but at least it will be a bolt in and go. Seriously, just go find a Mustang rear end, grind off the mounts, and make new ones, then have a driveshaft made up for it. Redrill the axles to match the TR8 bolt pattern.
I got to wondering why you see reports of different ratios in TR8s, and I think I might have a theory on it. Seems like all the rumors come from England and not on this side of the Atlantic. There were only a handful of true TR8s made for the domestic market. My best guess is that most of the so called TR8s in England were built by specialists like Grinnell or backyard mechanics. They would have sourced gears and in many cases whole rear ends from SD1s which came with 3.08 and in some cases the 2.85. The 2.85 was only on early Vitesse models with an automatic and it was only as an option. Many of the TR8 specials made in England retained the 5 lug rear axles that the SD1 used.
The 3.08 I just grabbed was from an 86 GT. Just saw one from an 89? that looked the same except it was a 3.73. At some point they went to rear discs and 5 lugs. Those are wider. Then they put on ABS sensors and they got even wider. The one I stole the rear disc brakes from was a 95 and it had 5 lugs, so I'll need different rotors, but the calipers and brackets are a bolt on. Narrowing Ford 8.8 rear ends is pretty easy. There is a web site called the ranger station that list just about every stock Ford axle length. If you want to loose 1 inch, chances are there is a stock axle already at the junk yard waiting for you. The other cool thing about Ford rear ends, is even if the one you pick up that has drums, there is a car in the junk yard with basically the same rear end but with discs. So far I have stuffed 8.8s from a turbo Thunderbird, a Lincoln MK VII, a Mustang and a really heavy duty one from an Explorer under TR8s. Playing with the idea of using an aluminum pumpkin independent rear end out of 2000ish full size Ford/Mercury.
Is this the site you are talking about? Do you know what the flange to flange dimension of a TR7 differential is?
From wheel mounting face on the drum to wheel mounting face is about 57 1/4" for both the 4 speed and the 5 speed rear ends. By axles, I was referring to the actual shafts themselves that slide in and out of the axle tubes. If you find a rear end that is too long, you can narrow it and install new shorter axles. Car based rear ends will usually use two axles of the same length. The pin in the center will add an inch to the total length. Truck rear ends usually have one axle longer than the other and that is usually just about a 3" difference. Here is a site that lists all kind of axle lengths. https://www.kabele.com/axleshafts.htm Here is the Ranger station site https://www.therangerstation.com/tech_library/
Out of curiosity, are you building a TR7,8 or SD1? I'm about to start in on an SD1 but it won't likely see time in Chump. Parts are too hard to find and they crash into each other waay too much in Chump. I just skipped a Chump race 30 min from home a couple weeks ago because of all the contact. Actually, the whole team passed. Probably turned out to be the right decision. One of the better BMWs took 5 major hits within an hour and sidelined them for the day. The Sunday driver's meeting was spent having the regional director yelling at everyone for crashing into each other.
A guy who knew me from Lemons who wanted to try Chump sent me an email asking for advise. I told him which cars would body slam if you tried to pass, etc. Here's an exerpt of what he sent after the event. (They were in a Volvo wagon)
"When I was on track, I was suprised by the lack of driver talent. I guess my expectations were high as I thought that all of these ChumpCar guys are more serious than Lemons guys. Maybe I was on track with all the novices but I was easily passing cars that I had no business passing (miatas, 2nd gen RX7's, E30s). I did have trouble with a couple of guys who would throw blocks for no reason (we were in 28th place). That startled me. My Lemons experience has been quite different in that regard. Guys see that you are faster and give you room to get by."
Having said all that, I will be bringing the Jag to a Chump race Laguna Seca in a few weeks. I expect that the Jag will take some shots but it's Laguna so I'll grit my teeth and put up with it. I encourage everyone to try Chump but I have a lot more fun in Lemons. My suggestion would be to bring spares.
Who is a good source for SD1 bits here in the US? I suspect I will need all new brake hydraulics. Woody? Also, there is a caged SD1 in the Cape Fear Pick your Part that I would be happy to pay someone for the suspension bits that are on it.
Here's the Jag going through the corkscrew last year
A guy who knew me from Lemons who wanted to try Chump sent me an email asking for advise. I told him which cars would body slam if you tried to pass, etc. Here's an exerpt of what he sent after the event. (They were in a Volvo wagon)
"When I was on track, I was suprised by the lack of driver talent. I guess my expectations were high as I thought that all of these ChumpCar guys are more serious than Lemons guys. Maybe I was on track with all the novices but I was easily passing cars that I had no business passing (miatas, 2nd gen RX7's, E30s). I did have trouble with a couple of guys who would throw blocks for no reason (we were in 28th place). That startled me. My Lemons experience has been quite different in that regard. Guys see that you are faster and give you room to get by."
Having said all that, I will be bringing the Jag to a Chump race Laguna Seca in a few weeks. I expect that the Jag will take some shots but it's Laguna so I'll grit my teeth and put up with it. I encourage everyone to try Chump but I have a lot more fun in Lemons. My suggestion would be to bring spares.
Who is a good source for SD1 bits here in the US? I suspect I will need all new brake hydraulics. Woody? Also, there is a caged SD1 in the Cape Fear Pick your Part that I would be happy to pay someone for the suspension bits that are on it.
Here's the Jag going through the corkscrew last year
The 2.85 was only in early production automatic Rover V8 SD1 Vitesse models and it was an optional gear. It was only available in Europe. If you find one, it will be very expensive, then you will have to get it here, then you will still have to try and figure out how you will install it in your TR7 five speed rear end housing. No small feat considering some of the parts you will need to pull off this small miracle no longer exist. If you are building a race car, why on earth would you want such a low gear anyway? Your acceleration will be aweful. There is a reason TR7s 5 speeds never came with anything lower than a 3.45, and that reason is there just wasn't enough HP and torque to use that a gear lower than that. TR8s can make the 3.08 work, but many TR8 owners go to the 3.45 for brisker acceleration. I even used a 3.90 on some tracks, but mostly ran the 3.45 in the TR8 race car. Unless you are going for land speed records, you don't want a low gear in a TR7 race car. The 2.85 will be turtle slow. At least you will be able to run the whole track in 3 gears...1st, 2nd, and 3rd. What you need for track racing is a 3.90 or even higher if such a thing exists. Many of the similar powered BMWs run a 4.11 or 4.44.
DNK
Great Pumpkin
Offline
It kinda sounds to me like you think you need different rear end, that you don't really know yet. I would run it for a race and see what you got first. In any case, I can't see where a high 2 or low 3 rear end is going to be much help unless maybe at one of the Rovals (Daytona, Fontana, etc) where you have enough room to get a head of steam going. In my RX7, I went from a 3.90 to 4.11 and I did see the benefits. If I really wanted to cheat and buy expensive aftermarket stuff, I'd probably go to a 4.53. I'm not sure what the Jag has in it but as it stands it's easy to spin 190 treadwear tires off the corners so I'm not sure we'd get much benefit by going to a lower rear end. If this is your first race, I'd concentrate 90% of my efforts on making the thing reliable. Work on speed later. Or practice fueling the car and doing driver swaps. All that time and money you spend on speed parts to gain some time on the track gets thrown away tenfold if you look like a bunch of guys manipulating a football on your pit stop. Look at it this way, let's say your magic axle buys you 5 seconds a lap (suuuper generous assumption). With an avg driving stint of 40 laps, that gains you 3 minutes. You have no idea how fast those 3 minutes go away when you don't know what you are doing during a pit stop. Our stops took 20 minutes when we first started. Our 5 gal fuel jugs originally took about a minute to empty. 3 bucks of fittings from Home Depot racing and 20 minutes of fiddling cut that time to 20 seconds. Make it reliable and make it stop. Make it fast later. I've passed a lot of faster cars that were broken in the pits.