T5, 4th/5th gear issues - JeepForum.com
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  • 2 Post By torkman1983
  • 2 Post By oldschool74cj5
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post #1 of 14 Old 04-29-2021, 08:11 PM Thread Starter
emiller35
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T5, 4th/5th gear issues

Helping a friend with his project Jeep. Little back story/info itís a 85 CJ7, 258, w/T5 and D300, AMC20 rear end and D35 front.

He recently bought bigger tires (33ís) and had them installed with factory gearing (canít find tag/ stamp on axle and havenít popped the diff cover off to count) but it does have the trac lock. From driving it around the neighborhood and some local trips down the nearest highway to try get some speed/higher gears, we have come to notice the following.

1st gear itís basically useless- very minimal crawl revs high at ~5mph or less
2nd gear decent performance gets and keeps moving normally no noticeable issues
3rd gear same as second no noticeable issues, tops out around 25mph, before rpmís climb

Shift to 4th gear around 25-30mph and 2500-3000rpm and it starts bucking and lurching. Think shifting to 4th at 10mph and then giving it gas. It doesnít stall or die just seems like all engine power and performance has ceased. When you shift back to third you get the high rev but no real speed change.

5th gear same as 4th issues.

So question is, any ideas what the cause is? I was originally thinking gearing due to the 1st gear issues and basic lack of performance, but does this also explain the issues of the higher gears? Transmission issue? Engine runs fine, no issues in lower gears and you can hold any RPM desired in neutral with no issues.

Figured Iíd ask here before telling him to take it into the shop up the road to have them take a stab at it.


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post #2 of 14 Old 04-29-2021, 09:14 PM Thread Starter
emiller35
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Forgot to mention 3Ē suspension lift and 1Ē body lift, no contact from tires to any part of frame/body that might hinder them.


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post #3 of 14 Old 04-29-2021, 10:36 PM
torkman1983
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Just went through my T5. VERY hard to say without pulling it apart, but the case bearing race may have started turning in the case. That might explain high RPMs in 1st (no friction). That would likely cause a leak though. Not sure what could cause that...might actually be a transfer case issue. Have you tried 4H and 4L? Any difference?
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post #4 of 14 Old 04-30-2021, 06:48 AM Thread Starter
emiller35
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We did go through the motions and try 4L and 4H no difference. Does this sound like a tranny issue? Was thinking too low gearing could explain the sluggish 1st gear due to bigger tires, but doesnít explain the issues with 4/5th?


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post #5 of 14 Old 04-30-2021, 08:39 AM
torkman1983
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I have 31s so can’t say. But I have zero issues in 1st. It is a high rpm gear, but I would not be able to start off in 2nd so 1st is needed. But 1st is about a 5 mph gear, I’ll record some data for you today and post it. I think your 4 and 5 may be the problem. If you pull it, I strongly suggest you not put back in a T5. Find a T18. The bell housing is easily modified and with the Novak adapter the total length of trans and transfer are near the same as the T5 setup. This means your driveshafts will both still work with the swap.
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post #6 of 14 Old 04-30-2021, 12:55 PM
katwalk27
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I am running 33s with a T5 and 4.11 rear end. It works very well. Are you 100% sure it is a T5? It sounds a little like a different trans with a granny 1st.
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post #7 of 14 Old 04-30-2021, 02:28 PM Thread Starter
emiller35
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Quote:
Originally Posted by katwalk27 View Post
I am running 33s with a T5 and 4.11 rear end. It works very well. Are you 100% sure it is a T5? It sounds a little like a different trans with a granny 1st.

As positive as one can be. He doesnít have 4.10ish gears, going to pull the cover this weekend and count it up to know what gearing we are dealing with for sure. As if he is running something like 2.73 from the factory we may need to bump it up to see if itís truly the trans


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post #8 of 14 Old 04-30-2021, 03:44 PM
oldschool74cj5
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hello

first you need to know what the gearing in the axle is. the best way is to remove the axle cover and read the numbering on the ring gear. there is a two number coding that will give you the ratio. one number is the ring gear teeth the other is the pinion gear teeth. 4.11 gears are great for a 33 tire with a 5 speed. if you still have close to factory gears it will be a dog in the upper gears because there is too much strain on the driveline.

oldschool
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post #9 of 14 Old 04-30-2021, 03:51 PM Thread Starter
emiller35
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Quote:
Originally Posted by oldschool74cj5 View Post
hello

first you need to know what the gearing in the axle is. the best way is to remove the axle cover and read the numbering on the ring gear. there is a two number coding that will give you the ratio. one number is the ring gear teeth the other is the pinion gear teeth. 4.11 gears are great for a 33 tire with a 5 speed. if you still have close to factory gears it will be a dog in the upper gears because there is too much strain on the driveline.

oldschool

This is my thoughts as well. As stated we will find out this weekend what he has as far as gears.


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post #10 of 14 Old 09-16-2021, 07:14 PM Thread Starter
emiller35
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So finally got a chance to get everything apart and heís got 3.31 gears in it.

Thinking this is going to be the issue with the 33ís heís running.

Given the power train mentioned above what would be the biggest you would advise running?


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post #11 of 14 Old 09-16-2021, 10:09 PM
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My wife once had an 84 with the same setup (I believe you meant a D30 front axle) and was running 3:54's. It was great on the road with fantastic gas mileage, but it didn't see much off road use. So I'm not sure what his use will be.
I have a similar setup in my 82. I put 3:73's in mine but with it's T-4 it would seem to be screaming beyond 55mph. So I swapped in a T-5 and that allowed me to drive at highway speeds without the high revs. and still have power off road.

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post #12 of 14 Old 09-17-2021, 12:04 AM
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Will the Jeep see off road? 4.10's will work well with 33's and a T-5. With that ratio and tires 5th gear will still be useful.
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post #13 of 14 Old 09-17-2021, 01:36 AM
258
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Definitely sounds like a gear ratio issue. I have 32’s with 3:31’s with T5 and I manage but when the time comes to re-gear, I am definitely throwing in 4:11’s. I can cruise at around 65 mph but couldn’t get out of a semi’s way if my life depended on it, lol. Go with 4:11’s!
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post #14 of 14 Old 09-17-2021, 03:17 AM
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Even though I have 4.10 gears, T5 and 32" tires, it's a great combo around were I live due to the hilly terrain. I would think 3.73's and the 33" would be a good choice since you live in Florida where it is relatively flat. The T5, with its overdrive, will come into play when you are on the highway.

I can shift to 5th gear at around 50mph for good fuel economy and seldom go over 65 or 70mph on the highway. It's just to windy for me in an open vehicle with no top driving at highway speeds for anything longer than an hour or two.

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