New trans or rear end? - JeepForum.com
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post #1 of 19 Old 12-03-2015, 03:03 PM Thread Starter
bpantherone
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New trans or rear end?

I have a 1980 CJ5 with the 304 engine and 4 speed manual transmission. Everything is stock on this one. I know I'm going to have to upgrade the suspension and brake system for better performance and handling...but what is the most effective way to increase the top end speed. I've driven it on the interstate only a few times and prefer to take back roads simply because as I'm trying to keep up with traffic at 65-70 mph..it's struggling and the engine is screaming. Any advice on it is greatly appreciated!!

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post #2 of 19 Old 12-03-2015, 03:15 PM
Newbjeep
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Bigger tires or taller gears Google grimmjeeper gear calculator and put all your specs in and then just change the gearing to what rpm you would like
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post #3 of 19 Old 12-03-2015, 04:24 PM
jeepwhore
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It's a short wheel base tractor that steers, stops and corners like a brick. How much faster do you need to go? I'd start by figuring out what diff gears you have and go from there.

'84 CJ-17: 17" stretch, locked Toy axles, 5.5" lift, FI, AX15, D300 w/twin sticks, boatsides & junk.
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post #4 of 19 Old 12-03-2015, 04:33 PM
skizriz
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The best way I found to increase my top end speed, is to put it on my trailer.
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post #5 of 19 Old 12-03-2015, 04:37 PM
Matt1981CJ7
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The problem with larger tires or numerically lower gears is you will lose take-off and acceleration power.

Remember, you have to do both axles when you swap gears.

An overdrive transmission swap would be cheaper than gears, and it wouldn't affect performance off the line, or during acceleration. If you have the standard SR4 4-speed that was offered in 1980, then a T5 would be a direct swap and give you an overdrive for the highway.

Matt
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post #6 of 19 Old 12-03-2015, 09:53 PM
AntlersCowboy
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Quote:
Originally Posted by Matt1981CJ7 View Post
The problem with larger tires or numerically lower gears is you will lose take-off and acceleration power.

Remember, you have to do both axles when you swap gears.

An overdrive transmission swap would be cheaper than gears, and it wouldn't affect performance off the line, or during acceleration. If you have the standard SR4 4-speed that was offered in 1980, then a T5 would be a direct swap and give you an overdrive for the highway.

Matt
I second that! Regearing is not cheap, even when you do it yourself. Going to numerically smaller gears would gain top end speed, but will shoot you in the foot in 4high. From experience I can tell you that it will wear the clutch a lot faster too.

A Borg Warner T5 will help a lot.

Best of luck!
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post #7 of 19 Old 12-04-2015, 07:27 AM
bob4703
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Matt he has a CJ5 which as I've been told won't take an overdrive transmission. If I'm wrong please tell me which one to use.

My 74 with 3.73 gears, 31s, and 258 will cruise at 65 with no struggle or engine scream. I restrict limited access highway driving to 25 miles or less--never had it on the Interstate. What I have is a dependable engine, rebuilt front suspension, and no lift all of which give me the confidence to cruise at 65.

Ain't nothing wrong with driving the backroads. The scenery is better, the flowers smell better, better food, and friendlier folks to chat with. Never had to use 4Lo on the interstate except to pull a dumb arse out of a snow bank who was only doing 65 when he hit the black ice and slammed on his brakes. They don't have rides like that at the county fair!

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post #8 of 19 Old 12-04-2015, 07:57 AM
Matt1981CJ7
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Originally Posted by bob4703 View Post
Matt he has a CJ5 which as I've been told won't take an overdrive transmission. If I'm wrong please tell me which one to use.
Bob,

If I'm not mistaken, many CJ5s in the '80-'81 came with the SR4 4-speed transmissions.

The T4 and T5 transmissions are the kissing cousins of the SR4. They share the same case length and bolt patterns.

The T5 has overdrive.

Hope this helps,

Matt
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post #9 of 19 Old 12-04-2015, 01:02 PM
bob4703
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Matt
Are they the same length? I've been told they are too long. I had a C10 with a 4.2 diesel that had a 4 speed that 3rd was direct and 4th was OD. I've wondered if that could be adapted to a CJ5. Then I think about it and remember that the transmission was the weak point in that truck. Now that gas is $1.65 a gallon I see less and less need for OD. I might change my mind later.

Bob

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post #10 of 19 Old 12-04-2015, 01:59 PM
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Cj

What R&P gears do you have in now?
How many miles on the engine? Have you done a compression test to confirm the engine in not the issue here?
304's weren't any sort of a 'power-house' either.
Post pictures of the tranny(w'ID numbers)and shift pattern so we can ID it.
LG

Have'n you along, is like loose'n 2 good men
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post #11 of 19 Old 12-04-2015, 02:33 PM
ShiJon
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How many RPM = "screaming"? It's my opinion that peple who never owned a 3 speed get squeamish above 2500rpm because they are/have become used to overdrive. The 304 is [email protected], max torque @ 2500 and red line about 4k.
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post #12 of 19 Old 12-04-2015, 02:53 PM
Matt1981CJ7
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Quote:
Originally Posted by bob4703 View Post
Matt
Are they the same length? I've been told they are too long. I had a C10 with a 4.2 diesel that had a 4 speed that 3rd was direct and 4th was OD. I've wondered if that could be adapted to a CJ5. Then I think about it and remember that the transmission was the weak point in that truck. Now that gas is $1.65 a gallon I see less and less need for OD. I might change my mind later. Bob
Bob the SR4, T4, and T5 all use similar cases, if not exactly the same. I haven't studied them that close.

They all have a total length of 15-1/4".

http://www.novak-adapt.com/knowledge...s/manual/t4-t5

Matt
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post #13 of 19 Old 12-04-2015, 04:09 PM
bob4703
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Matt

Thanks will check them out.

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post #14 of 19 Old 12-04-2015, 08:44 PM
RedNeckCorvette
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Quote:
Originally Posted by bob4703 View Post
Matt
Are they the same length? I've been told they are too long. I had a C10 with a 4.2 diesel that had a 4 speed that 3rd was direct and 4th was OD. I've wondered if that could be adapted to a CJ5. Then I think about it and remember that the transmission was the weak point in that truck. Now that gas is $1.65 a gallon I see less and less need for OD. I might change my mind later.

Bob
Yea like the day after the election and when gas goes back up to four dollars a gallon.
RN
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post #15 of 19 Old 12-05-2015, 08:39 AM
bob4703
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RN everything is relative. I agree gas is going back up, and probably won't wait until after next year's election. Back in the olden days when I reached the legal drinking age of 18 and when you couldn't get liquor by the drink in this state I'd go into what we lovingly called a beer joint and order an ice cold PBR for a quarter. Last week we went out and I had a 24 oz Blue Moon draft for the happy hour price of $3.00. After 50 years of consumption I'm drinking better beer and spending the same amount nightly. The only variable that changed is the amount consumed. When gas price doubles will we cut back on driving? Yes maybe, but brobably not by half.

Now that I think about it an OD transmission would not be cost effective. Drove the Jeep almost daily from early spring to late fall, but only put 1500 miles on the speedometer. Of that only 200-300 miles would have an OD benefited me. I'll save that money to buy beer or replace something that breaks on the CJ5. If I get to the point I need to replace the old speed I'll consider the upgrade.

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