
380 Mich. 621 (1968)
158 N.W.2d 483
THEISEN
v.
CITY OF DEARBORN.
Calendar No. 43, Docket No. 51,711.
Supreme Court of Michigan.
Decided May 6, 1968.
*623 James Thomson, for plaintiffs.
Ralph B. Guy, Jr., for defendant.
BRENNAN, J. (dissenting).
Plaintiffs are retired policemen and firemen of the city of Dearborn. Their suit is for payment of retirement benefits alleged to be due.
The Dearborn city charter provides (chap 21, §§ 21.8, 21.28, 21.37):
"Section 21.8. `Average Final Compensation' shall mean the average annual salary or wages paid to a member by the city for service rendered as a policeman or fireman during his last 5 years of service preceding retirement; or if he has less than 5 years service, then the average annual salary or wages paid to him by the city during his total years of service. * * *
"Section 21.28. Upon retirement from service according to the provisions of section 21.27 of this chapter, a member shall receive a service retirement annuity equal to 1/50 of his average final compensation multiplied by his total years of creditable service; provided, however, the service retirement annuity of a member or beneficiary shall not exceed 1/2 his average final compensation, or 7/10 of the annual rate of pay received by a patrolman first-class, or a fireman first-class, whichever amount is the lesser. * * *
"Section 21.37. If hereafter the rate of compensation for the rank, grade, or position on which the annuity, or other benefit, payable to a beneficiary, is based, shall be changed, then the annuity, or other benefit, payable to a beneficiary, shall be adjusted to an amount based upon the changed rate of compensation for the corresponding rank, grade, or position."
The trial court dismissed the action, and the appellate court upheld the dismissal, on the ground that the matter is res judicata. 5 Mich App 607.
*624 The previous case was, like this one, a class action by retired policemen and firemen. The disputed portion of the trial court's opinion in that previous case is as follows (supra p 617):
"`The average final compensation is a figure arrived at by ascertaining what the average salary or wages paid to the member during his last 5 years of service before retirement or if he has less than 5 years then the average annual salary or wages paid to him during his total years of service. The figure arrived at by this process, that is, the average final compensation will determine then the rank, grade, or position of the retiree when he first draws an annuity and that is the rank, grade, or position which is thereafter used in the computation of increases under section 21.37.
"`This, too, must be an individual determination. Whenever the rank, grade, or position is changed under section 21.37, then the retiree or beneficiary is entitled to an adjustment of the annuity in an amount based upon the amount of change in the compensation for that rank, grade, or position in which the retiree was first found in the computation of his average final compensation.'" (Emphasis supplied.)
This holding by the trial court in the previous case is ambiguous. It seems to suggest that, for purpose of adjustment under section 21.37, a retiree will be regarded as holding a fictional grade, rank, or position, for which the rate of compensation is his average final compensation. It is patently impossible that the rate of compensation for a fictional grade, rank, or position will ever be changed, since there are no active officers or fire fighters who hold such fictional rank or receive such rate of compensation.
A judgment which is ambiguous is not res judicata of the issue which is the subject matter of the ambiguity.
*625 The judgment should be reversed and the case remanded. Costs to the appellants.
T.M. KAVANAGH and SOURIS, JJ., concurred with BRENNAN, J.
KELLY, J.
We disagree with our Brother's finding that the "holding by the trial court in the previous case[1] is ambiguous", and we agree with the trial court and the Court of Appeals that the decision in the previous case in regard to the formula determines the question of formula in the present case.
We are remanding to allow plaintiffs' request[2] that discovery proceedings be allowed to determine whether plaintiffs' annuity or other benefits have been properly adjusted by the defendant under the established formula.
Remanded. Costs to abide result.
DETHMERS, C.J., and BLACK, O'HARA, and ADAMS, JJ., concurred with KELLY, J.
NOTES
[1]  Morrison v. City of Dearborn, Wayne Circuit Court No 299-972.
[2]  Paragraphs 12, 13, 14, 15, and 16 of plaintiffs' complaint.
