rear diff question

[mrkinsley]

HI! i went through a total rehaul: rebuilt engine, and tranny (automatic) and my mechanic replaced my rear differential "pumpkin" with i believe one from a toyota truck. He visually examined it and counted the same gears and concluded it would work. that was about a year ago. However, i just tried the 4 wheel drive out now and found it doesn't work! He tested it and said the gears in the pumpkin must have been off when he first examined it.
My question is would that cause me to be getting bad gas mileage? (even in 2wd) and what 'pumpkins' are compatible with the 4x4 auto. since i don't see finding one at at the junk yards any time soon

any help will be MUCH appreciated Thank you so much guys

[timsrv]

Hi and welcome to the forum! When you say 4wd doesn't work, please elaborate. If the gear ratio is off (between the front and rear diff's) then it will bind and buck when in 4wd (there will be no question that something is seriously wrong). FWIW, the differentials on automatic 4wd vans have an FDR (Final Drive Ratio) of 43:9 (which works out to 4.778). Did you get any FDR information on the differential that was installed?

When you say you're getting bad gas mileage, what are the numbers? I would consider 18-22 mpg pretty normal for an auto 4wd used in 2wd. Of course there are a whole bunch of variables that can adversely effect mpg (aggressive driving, jack-rabbit starts, wide and/or aggressive tires, a roof rack, low tire pressure, etc). What kind of RPMs are you turning at 60mph? Have you verified the overdrive is engaging? You should count a total of 4 gears (3 shift points). Have you checked TROUBLE CODES yet?

[mrkinsley]

Hi again, and thanks for answering my post. I'm sorry I haven't responded til now but I have been in the middle of a move to a new apartment. Anyway, yup, there was lots of bind and buck when in 4wd, and my mechanic has since figured out that the FDR is off, but he's having a very hard time finding the proper ring and pinion to fit. My question is, would that negatively affect the mileage, (i've been getting about 12- 15 mpg's!!!) and also do you or any one else know where I can get the right ring and pinion? the junk yards NEVER get the 4wd vans, and apparently there's no aftermarket manufacturers either, and the dealer is over $500!! any help would be greatly appreciated, thank you !!!

[timsrv]

If the FDR is making the engine turn high RPMs when cruising then yes, it could have an adverse affect on gas mileage.

What kind of RPMs are you turning at 60mph? Have you verified the overdrive is engaging? You should count a total of 4 gears (3 shift points). Have you checked TROUBLE CODES yet?

Do you have a roof rack, wide or aggressive tires? Do you drive aggressively or enjoy jack-rabbit starts? What's the traffic like there? Do you regularly sit in traffic jams?

You will need a Toyota 7.5" with an FDR (Final Drive Ratio) of 43:9 (which works out to 4.778). I don't have much experience with this area, but I believe the trucks from the same era have the same internals inside the differentials. When you're shopping the salvage yards check the tags. The tags will give axle codes. Your van should say F362. If you find a 4wd or RWD Toyota in the salvage yard that has that same number, then you've found a suitable rear end for parts harvest. Here's an example of the tag and a PDF of how to decipher:



The picture above is from the tag in my 2wd automatic cargo van. Mine has a 7.5" with a 4.300 ratio. The tag sits just below the front of the passenger seat. there's a little flap in the carpet that lets you view. I'm not sure where this tag is on the trucks, but suspect it will be under the hood somewhere. Tim

[Harbilly]

So the guys noticed my rear driveshaft (brand new) can be turned a good 1/2 inch each way causing clunking where the rear axles engage in the dif. Pulled the left axle and there was too much play shoving it in, you know, push and click, click, click, click thump instead of push, click, thump in when re-installing.
Are our ford like rear ends all sloppy or am I needing to get the rear end done? (an old truck rear end or custom or something as I imagine no parts are available).
Thanks all!
Anyone feel fixing the rear end is dumb and I should go to a positive rear end?

[Burntboot]

Can't remember how much play I have back there but I would think that if it isn't overly noisy then I wouldn't kick that dog.
Have heard there is an early supra diff that is posi and will fit but gearing may be an issue.

For what it is worth, brand spanking new units (not rebuilds) are still available from Toyota.
$1200 CDN when I did mine (2 years ago).
BB

[Harbilly]

Good to know but at that price I'd go with a posi insert thing. Yikes!!

[Burntboot]

Posi would definitely be a worthwhile upgrade especially if one spends a lot of time on soft surfaces.
But one does have to relearn how to drive again, they can get away from you pretty fast in wet/slippery conditions.

I looked for a competent shop to rebuild the diff but couldn't find any locally.
I had a window of 1 week to be up and running, so throwing money at it seemed the best course of action, at the time.
If I had the answer of which diff was the perfect match, I may have gone looking, but the yards around here mostly laugh when you say you are looking for parts for anything pre 2000.

BB

[Harbilly]

We have snow on the ground 6 mos of the year. There isn't a lot of pavement but it isn't soft either. I've got 30 years of driving Toyota 4wd under my belt. I may be too old to relearn anything.Posi may be a mistake given my history. I understand the 'one week just fix it thing'.I've been there.More than once.

[Harbilly]

...and so that's a thread I should start. I have the gear rear end chart and I know 7 1/2 2wd truck difs (not reverse cut ifs type) allegedly fit (from the early 90s) but I've never seen a definite statement like: Toyota Xxx truck from 19xx fits 4wd fan 19xxx. Anyone got any direct match story because they did this thing? Or is at as easy as 'any 7 1/2" truck dif'?

[timsrv]

Have you searched the site yet? Here's a thread one thread.......there are others. http://www.toyotavantech.com/forum/s...-diff-question

[Harbilly]

Thanks Tim.
Ya, I've been reading the threads. My plan is starting to look like matching my gear code to the newest truck I can find and then ordering parts for that truck. Toyota isn't helpful with parts listed for the van.
Or making the whole thing my mechanic'a problem. I'm in way over my head here. I just don't want him told 'impossible' when it isn't. So I'm looking fir good info to start him off with.

Can I trust a driveline specialist firm to rebuild the rear end on these? Maybe that's the way to go.

[coronan]

Here is some stuff to drool over.

Identifying Toyota Diffs in the yard:
http://home.4x4wire.com/erik/diffs/


Almost how to's:
http://www.gearinstalls.com/

Some where I came acrost a chart of every axel width known by year, make and model.
Jeep axels might work and then you could have a Dana.

[coronan]

Not the list I'm thinking of but here's a start.
http://www.pirate4x4.com/tech/bible/index.html